31.3: Staying in Balance
Lesson
Let's use balanced hangers to help us solve equations.
Exercise \(\PageIndex{1}\): Hanging Around
For diagram A, find:
- One thing that must be true
- One thing that could be true or false
- One thing that cannot possibly be true
For diagram B, find:
- One thing that must be true
- One thing that could be true or false
- One thing that cannot possibly be true
Exercise \(\PageIndex{2}\): Match Equations and Hangers
- Match each hanger to an equation. Complete the equation by writing \(x, y, z,\) or \(w\) in the empty box.
- Find a solution to each equation. Use the hangers to explain what each solution means.
Exercise \(\PageIndex{3}\): Connecting Diagrams to Equations and Solutions
Here are some balanced hangers. Each piece is labeled with its weight.
For each diagram:
- Write an equation.
- Explain how to reason with the diagram to find the weight of a piece with a letter.
- Explain how to reason with the equation to find the weight of a piece with a letter.
Are you ready for more?
When you have the time, visit the site https://solveme.edc.org/Mobiles.html to solve some trickier puzzles that use hanger diagrams like the ones in this lesson. You can even build new ones. (If you want to do this during class, check with your teacher first!)
Summary
A hanger stays balanced when the weights on both sides are equal. We can change the weights and the hanger will stay balanced as long as both sides are changed in the same way. For example, adding 2 pounds to each side of a balanced hanger will keep it balanced. Removing half of the weight from each side will also keep it balanced.
An equation can be compared to a balanced hanger. We can change the equation, but for a true equation to remain true, the same thing must be done to both sides of the equal sign. If we add or subtract the same number on each side, or multiply or divide each side by the same number, the new equation will still be true.
This way of thinking can help us find solutions to equations. Instead of checking different values, we can think about subtracting the same amount from each side or dividing each side by the same number.
Diagram A can be represented by the equation \(3x=11\).
If we break the 11 into 3 equal parts, each part will have the same weight as a block with an \(x\).
Splitting each side of the hanger into 3 equal parts is the same as dividing each side of the equation by 3.
- \(3x\) divided by \(3\) is \(x\).
- \(11\) divided by \(3\) is \(\frac{11}{3}\).
- If \(3x=11\) is true, then \(x=\frac{11}{3}\) is true.
- The solution to \(3x=11\) is \(\frac{11}{3}\).
Diagram B can be represented with the equation \(11=y+5\).
If we remove a weight of 5 from each side of the hanger, it will stay in balance.
Removing 5 from each side of the hanger is the same as subtracting 5 from each side of the equation.
- \(11-5\) is \(6\).
- \(y+5-5\) is \(y\).
- If \(11=y+5\) is true, then \(6=y\) is true.
- The solution to \(11=y+5\) is \(6\).
Glossary Entries
Definition: Coefficient
A coefficient is a number that is multiplied by a variable.
For example, in the expression \(3x+5\), the coefficient of \(x\) is \(3\). In the expression \(y+5\), the coefficient of \(y\) is \(1\), because \(y=1\cdot y\).
Definition: Solution to an Equation
A solution to an equation is a number that can be used in place of the variable to make the equation true.
For example, 7 is the solution to the equation \(m+1=8\), because it is true that \(7+1=8\). The solution to \(m+1=8\) is not \(9\), because \(9+1\neq 8\).
Definition: Variable
A variable is a letter that represents a number. You can choose different numbers for the value of the variable.
For example, in the expression \(10-x\), the variable is \(x\). If the value of \(x\) is 3, then \(10-x=7\), because \(10-3=7\). If the value of \(x\) is \(6\), then \(10-x=4\), because \(10-6=4\).
Practice
Exercise \(\PageIndex{4}\)
Select all the equations that represent the hanger.
- \(x+x+x=1+1+1+1+1+1\)
- \(x\cdot x\cdot x=6\)
- \(3x=6\)
- \(x+3=6\)
- \(x\cdot x\cdot x=1\cdot 1\cdot 1\cdot 1\cdot 1\cdot 1\)
Exercise \(\PageIndex{5}\)
Write an equation to represent each hanger.
Exercise \(\PageIndex{6}\)
- Write an equation to represent the hanger.
- Explain how to reason with the hanger to find the value of \(x\).
- Explain how to reason with the equation to find the value of \(x\).
Exercise \(\PageIndex{7}\)
Andre says that \(x\) is \(7\) because he can move the two 1s with the \(x\) to the other side.
Do you agree with Andre? Explain your reasoning.
Exercise \(\PageIndex{8}\)
Match each equation to one of the diagrams.
- \(12-m=4\)
- \(12=4\cdot m\)
- \(m-4=12\)
- \(\frac{m}{4}=12\)
(From Unit 6.1.1)
Exercise \(\PageIndex{9}\)
The area of a rectangle is 14 square units. It has side lengths \(x\) and \(y\). Given each value for \(x\), find \(y\).
- \(x=2\frac{1}{3}\)
- \(x=4\frac{1}{5}\)
- \(x=\frac{7}{6}\)
(From Unit 4.4.2)
Exercise \(\PageIndex{10}\)
Lin needs to save up $20 for a new game. How much money does she have if she has saved each percentage of her goal. Explain your reasoning.
- 25%
- 75%
- 125%
(From Unit 3.4.2)


18.2: Nursing Care During the First Stage of Labor
By the end of this section, you will be able to:
- Explain the nursing actions during obstetric triage
- Identify the content of the admission history of the laboring person during the first stage of labor
- Perform the admission physical exam on the laboring person during the first stage of labor
- Explain the nursing actions when monitoring a laboring person and fetus during the first stage of labor
- Provide comfort measures to the laboring person during the first stage of labor
Labor places physical and emotional demands on the laboring person and their support persons. The nursing care required during the process of labor and birth is based on the laboring person’s progress, their ability to meet the physical and psychosocial demands of labor and birth, and fetal adaptation. The nurse also follows standards of care, ensuring safety and meeting the needs of both the laboring person and the fetus from admission to the labor and birth unit through the postpartum period.
Labor and Delivery: Part 1
Brianne is a 36-year-old, G1 P0, high school teacher who is being admitted to the Labor and Birth Unit at 39 weeks’ gestation for induction of labor due to gestational diabetes and possible macrosomia. Brianne states she and her partner, Trey, have attended a childbirth education class. Trey has come with Brianne and plans to provide support to Brianne throughout the labor and birth process.
| Past medical history (PMH) |
Medical history:
Social history : Brianne and Trey live in a two-bedroom apartment on the second floor in a building with only a freight elevator. They have a small dog named Candy. Trey works for a construction company and is 40 years old. Neither Candy nor Trey smokes. Trey does drink an occasional beer. Brianne does not drink alcoholic beverages. Prenatal history BP range, 110–128/60–80 Fundal height at 39 weeks, 40 cm Gestational diabetes (diet controlled) No current medications and allergy to penicillin |
| Flowchart |
Height: 5 ft 3 in.
Weight at first prenatal visit: 135 lb Vital signs Admission to Labor and Birth unit BP, 128/74; Temp, 98.2 (F); Pulse, 84; Resp, 18 |
| Lab results |
Initial prenatal labs
A negative, antibody screen negative Rubella nonimmune Negative tests for STIs at initial prenatal visit Urine positive for GBS Genetic and neural tube defect screening labs Screening and diagnostic tests for genetic and neural tube abnormalities negative 28-week prenatal labs 1-hour GCT, 150 3-hour GTT, FBS, and 2-hour glucose levels elevated 36-week prenatal labs Negative tests for STIs at 36 weeks’ gestation |
| Diagnostic tests/imaging results |
Initial prenatal visit
Intrauterine pregnancy Fetal heart rate 154 6 weeks’ gestation 20 weeks’ gestation Ultrasound negative for congenital anomalies and showed fundal placenta Fetal heart rate 148 36 weeks’ gestation Ultrasound indicates EFW 3,150 g (7 lb) Fetal heart rate 148 Vertex presentation Amniotic fluid index, 10 |
| Provider’s orders |
Admit to Labor & Birth Unit for induction of labor
Blood type, Rh, antibody screen CBC Start IVFs of 1,000 LR at 100 mL/hr Pitocin 15 units in 250 mL of LR IVPB, start at 2 milliunits/min and increase 2 milliunits/min every 30 minutes up to 20 milliunits/min to establish labor |
Obstetric Triage
The rapid assessment and prioritization of care based on the specific obstetric and gynecologic needs, or obstetric triage , occurs when a patient at 16 weeks’ gestation, or later, arrives at a hospital for care related to the pregnancy. When the patient presents to the hospital, they will be evaluated by health-care providers who specialize in obstetric care to determine the urgency of the care required. While some patients present for ruling out labor or rupture of membranes, obstetric triage also serves a primary role in evaluating for obstetric emergencies or concerning symptoms throughout a pregnancy. The more common emergencies and symptoms include new onset vaginal bleeding , decreased fetal movement, abdominal pain, swelling, and elevated blood pressure (American College of Obstetricians and Gynecologists [ACOG], 2023a). Other obstetric triage patients may be sent to another unit, such as the emergency department, within the hospital for follow-up evaluation of non–pregnancy-related conditions. If the patient’s situation does not require observation or admission, as in false labor, the patient is discharged with instructions and follow-up with their obstetric care provider (ACOG, 2023a).
When a patient arrives for obstetric triage, the nurse will obtain the presenting symptoms, complete a focused physical assessment, and gather information about the pregnancy. The nurse will also obtain the patient’s vital signs and fetal heart rate (FHR) and contraction patterns to prioritize the patient’s need for care. This information will be entered into the electronic health record (EHR). The nurse will also interview the patient about their current health-care provider for obstetric care. If the patient’s obstetric provider is on staff at the facility, the nurse will notify the health-care provider of the patient’s arrival, presenting symptoms, and other priority information obtained during the triage process. If the patient’s health-care provider is not on staff at the facility or if the patient does not have a preexisting relationship with a provider who has privileges at the facility, the nurse will notify a hospital-based provider (ACOG, 2023b).
During the initial interaction with the patient, the nurse will ascertain the patient’s estimated date of delivery (EDD) to determine the gestational age of the fetus. Based on facility-specific policies, those who are less than 20 weeks’ pregnant are often triaged in the emergency department. Medical decisions related to the patient’s complaint and assessment will vary based on the gestational age. In addition, the nurse needs to obtain an obstetric history for the patient, including the number of pregnancies, term and preterm deliveries, abortions, and current living children (Moudi et al., 2020). These initial interview questions are obtained with succinct questioning by the nurse while the initial stages of the physical assessment are being conducted.
Initial vital signs are obtained upon arrival on the unit to detect any abnormal values that require an immediate report to the health-care provider. Elevated blood pressure can be indicative of a serious complication— pre-eclampsia or eclampsia —and require a prompt response by the health-care team. An elevated temperature along with an increased pulse rate can be indicative of infection.
Initial assessment also includes assessment of the fetal heart rate. The type of fetal and uterine monitoring equipment is facility-specific and will vary based on the clinical situation. The nurse will perform Leopold’s maneuvers to determine the fetal position and the placement of any external fetal monitoring equipment. Fetal monitoring, fetal monitoring equipment, and Leopold’s maneuvers are discussed in depth in Chapter 16 Electronic Fetal and Uterine Contraction Monitoring.
Review of Prenatal Record
When a patient arrives for obstetric triage with symptoms of labor, prior to the initial assessment, the nurse will review the prenatal record of the patient to obtain a baseline understanding of the patient’s obstetric and medical history to provide a high level of individualized patient care (Moudi et al., 2020). When the prenatal record is available, the nurse will review the prenatal history, medical and surgical history, and labs to create a plan of care reflective of the findings in the patient’s chart. When a prenatal record is not available, a thorough interview of the patient is necessary to obtain a complete history, and laboratory and diagnostic testing may be performed during their visit. Whether the patient has a prenatal record available or not, it is important to confirm information with the patient and clarify any incomplete information.
Obstetric History
The obstetric history of the patient may have a direct impact on the care provided, requiring a thorough assessment of the history through the patient’s chart and personal interview. The nurse will obtain information on the patient’s history of any previous pregnancies, including the dates, outcomes, type of delivery, and any complications (Tukisi et al., 2022). The nurse will also inquire about any complications with any of the previous pregnancies and the types of deliveries. This information is often found in the prenatal record but should always be verified with the patient. It is important to remember that the patient’s pregnancy history is confidential and should be discussed in private. For more information on the complete assessment of obstetric history, see Chapter 11 Prenatal Care.
Labor and Birth Unit Admission History and Physical Exam
When a patient presents to the labor and birth unit in possible labor or a condition related to pregnancy requiring inpatient care, the nurse first performs an obstetric triage assessment (Moudi et al., 2020). Sometimes, early labor can be challenging to distinguish from false labor or prodromal labor. The nurse will need to use clinical judgment and a combination of the assessment criteria in Table 18.1 to determine whether a patient is in true labor and ready to be admitted for active labor management and delivery (Tukisi et al., 2022).
| Assessment | Data |
|---|---|
| Clinical assessment of contractions |
|
| Cervical examination | A cervical examination is performed to assess the dilation (opening) and effacement (thinning) of the cervix. In true labor, the cervix typically starts to dilate and efface. |
| Assessment of progression | Nurses observe the progression of labor over time. True labor involves a progressive change in contractions, cervical dilation, and effacement. |
| Rupture of membranes (amniotic sac) | The presence of amniotic fluid in or leaking from the vagina can be confirmed through visual inspection or testing. |
| Bloody show | A small amount of bloody discharge or mucus plug is often expelled as the cervix begins to dilate. This is known as a “bloody show” and is a common sign of labor. |
| Patient’s pain and perception | The patient’s description of their pain and discomfort can provide valuable information. Contractions during labor are often more painful and rhythmic compared to Braxton Hicks contractions. True labor contractions also cause cervical change. |
| Assessment of other signs | Nurses assess other signs, such as the urge to push, pressure in the lower back or pelvis, and changes in bowel movements. |
Admission History of the Person in Labor
Once the obstetric triage nurse has received the order from the health-care practitioner (HCP) to admit the laboring person, a more thorough history will be completed per facility protocol. A thorough admission history includes the laboring person ’s medical, surgical, obstetric and gynecologic, and genetic history (Milton, 2024).
Medical History
In reviewing the prenatal history, the nurse will carefully review the list of preexisting conditions and conditions related to the pregnancy that may impact the care of the laboring person and fetus. The nurse will review any pertinent diagnostic tests, including ultrasound results, mainly reviewing the placental placement and fetal positioning or abnormalities. It is important to note any medications that the laboring person is currently taking and document the last time the medication was taken.
A series of laboratory tests are ordered as part of normal prenatal care and should be reviewed by the nurse. The nurse should review the baseline prenatal laboratory tests and any subsequent lab results to identify trends or changes throughout the pregnancy or during the current visit. The nurse will closely assess the laboring person ’s complete blood cell count (CBC), blood typing and antibody screen, rubella titers, hepatitis B and C, human immunodeficiency virus (HIV), and sexually transmitted infection (STI) screenings for abnormal findings that require notification to the provider. Routine prenatal monitoring for gestational diabetes ( GDM ) should be reviewed, and GDM protocol initiated if the laboring person received a diagnosis during pregnancy. A full overview of prenatal care, including lab work, is available in Chapter 11 Prenatal Care.
Surgical History
The surgical history of the laboring person is reviewed by the nurse and should specifically include any past surgical births, surgery to the abdomen or uterus, and any previous cervical procedures that affect the cervix and create scar tissue, such as punch and cone biopsies. The nurse should also inquire about any previous experiences or complications associated with anesthesia.
Obstetric and Gynecologic History
The nurse reviews the obstetric and gynecologic history of the laboring person. The obstetric history includes number of pregnancies, their outcomes, and any complications. The gynecologic history includes any history of cervical or vaginal cytology, gynecologic complications, such as uterine fibroids and cervical cerclage, or past or current STIs that could impact the labor process (Milton, 2024).
In a laboring person with a history of an STI during the current pregnancy, the nurse investigates whether treatment was initiated and completed, whether all sexual partners were concurrently treated, and whether the test of cure was completed with negative results (Milton, 2024). Any STI diagnosed during the pregnancy, its treatment, and verification of the effectiveness of the treatment are reported to the health-care provider and the team assigned to the care of the newborn.
Psychosocial History
During the admission process, the nurse will review and ask questions about the psychosocial history of the laboring person (O’Connor, 2022). The information obtained that is related to the physical environment at home includes housing, transportation restrictions, access to phone, utilities, and appliances. The nurse also assesses the availability of support persons, preparation for labor and birth, and newborn care knowledge. Evaluation of the laboring person’s and newborn’s safety at home as well as the risk for depression are also responsibilities of the nurse. The nurse will enter this information into the EHR.
Genetic History
The nurse also reviews and confirms the genetic history of the laboring person and other biological parent of the fetus from the prenatal record. Prenatal screenings and diagnostics during pregnancy are optional medical tests and procedures performed to monitor the health of both the pregnant person and the developing fetus (ACOG, 2020b). These tests help identify and manage potential risks, ensure a healthy pregnancy, and enable timely interventions when necessary. The information is obtained directly from the laboring person and other biological parent, if present, when prenatal records are not available. Some genetic disorders that affect blood clotting or bleeding increase the risk of morbidity and mortality during labor and should be addressed during the initial admission intake. The medical team will need to be notified of a family history that includes birth defects, newborn screening disorders, or any genetic disorders that could affect the care of the laboring person or fetus (Centers for Disease Control and Prevention [CDC], 2023). These disorders can be inherited from one or both parents or may arise due to spontaneous mutations. Here are some genetic disorders that can impact pregnancy:
- Down Syndrome (Trisomy 21): Down syndrome is a chromosomal disorder caused by an extra copy of chromosome 21. It can lead to intellectual disabilities and physical abnormalities in the affected child. Prenatal screening tests, such as noninvasive prenatal testing (NIPT) and amniocentesis, can detect the presence of an extra chromosome 21.
- Cystic Fibrosis: Cystic fibrosis is a genetic disorder that affects the respiratory and digestive systems. Carriers of the cystic fibrosis gene may pass it on to their children. Prenatal carrier screening can identify couples at risk of having a child with cystic fibrosis.
- Sickle Cell Disease: Sickle cell disease is a genetic blood disorder that can cause anemia, pain episodes, and other complications. It is more common in people of African, Mediterranean, and Middle Eastern descent. Prenatal genetic testing can determine if both parents carry the sickle cell trait, increasing the risk of having an affected child.
- Tay-Sachs Disease : Tay-Sachs is a rare genetic disorder that affects the nervous system. It is more common in people of Ashkenazi Jewish descent. Prenatal carrier screening can identify couples at risk of having a child with Tay-Sachs disease.
- Hemophilia: Hemophilia is a genetic disorder that impairs blood clotting. It primarily affects males, and carriers of the gene can pass it on to their children. Genetic testing can determine the risk of having a child with hemophilia.
- Neural Tube Defects : Conditions like spina bifida and anencephaly are congenital neural tube defects that can have genetic components. Folic acid supplementation and prenatal screening can help mitigate the risk and manage these conditions.
- Congenital Heart Defects : Some congenital heart defects have a genetic basis, and a family history of heart problems can increase the risk of these disorders in offspring. Prenatal ultrasound and genetic testing can help identify these conditions.
It is important to note that advances in genetic testing and prenatal screening have improved the ability to detect and manage many of these genetic disorders during pregnancy. Genetic counseling and testing are recommended for couples with a family history of genetic disorders or other risk factors to assess the likelihood of having an affected child and to make informed decisions about prenatal care and interventions (CDC, 2023).
Physical Exam of the Person in Labor
Performing a physical examination during labor is a critical aspect of obstetric care, allowing the close monitoring of the progression of labor and the well-being of both the birthing person and the fetus. This hands-on assessment involves a systematic evaluation of various physical parameters and vital signs to ensure a safe and healthy labor and delivery process (Milton, 2024).
General Survey
The nurse will conduct a general survey of the laboring person upon admission. The nurse will observe the laboring person’s appearance and behavior. Deviations from the expected findings should be documented, and further action may be required.
Heart, Lungs, and Extremities
Upon admission, the laboring person’s heart, lungs, and extremities should be evaluated. The nurse should auscultate for heart and lung sounds and report any abnormal findings to the provider. The nurse should visually inspect the extremities for edema, bearing in mind that dependent edema can be a normal finding related to increased fluid volume during pregnancy. Generalized edema of the face, hands, and feet may be indicative of preeclampsia if accompanied by physical symptoms of preeclampsia (Rana et al., 2020). If the laboring person presents with any signs of preeclampsia, including headache and visual disturbances, the nurse should perform an assessment of the laboring person’s deep tendon reflexes (DTRs) and clonus. Any abnormal findings should be immediately reported to the provider.
Obstetric Exam
An obstetric examination , a medical assessment by a health-care provider to evaluate and monitor the health and progress of the pregnant person and their developing fetus throughout pregnancy, will be completed upon admission of the laboring person to the facility. The exam is relatively consistent for term and preterm labor, except where noted (Milton, 2024). The nurse will establish the fetal heart rate and contraction pattern through auscultation and palpation or external fetal monitoring. The status of the membranes will be assessed to determine whether the membranes are intact or ruptured. The assessment may include the laboring person’s report of a gush or leaking of fluid before arrival, visual inspection of the vagina for pooling, or laboratory testing of the fluid for ferning or pH. The nurse should document the time of the rupture of membranes and identify the color of the fluid through visual inspection or patient report and assess for any odor associated with the fluid. Amniotic fluid is expected to be clear. Green or yellow color is associated with meconium-stained fluid. Bloody fluid is associated with placenta previa or abruption.
The nurse will then conduct a vaginal examination to determine cervical dilation, effacement, cervical position, station, and presenting part and position of the fetus. The vaginal exam may be deferred in the preterm laboring person to allow for additional testing, including fetal fibronectin testing. Additionally, the nurse should defer the vaginal examination in laboring persons with vaginal bleeding, a documented placenta previa, or other factors where a vaginal examination may result in complications. Before performing the vaginal examination, the nurse must consider the following complications that may arise from performing the examination.
- Infection: Frequent vaginal examinations can introduce bacteria into the birth canal, potentially increasing the risk of infection, especially if strict aseptic technique is not followed. This can lead to conditions like urinary tract infection s or chorioamnionitis (infection of the fetal membranes).
- Ruptured Membranes: Overly forceful or poorly timed vaginal examinations can cause unintended premature rupture of membranes (PROM) or artificial rupture of membranes (AROM), which may increase the risk of infection and potentially lead to complications for both the laboring person and the fetus.
- Discomfort and Pain: Vaginal examinations can be uncomfortable and painful for the laboring person, causing anxiety and distress. Repeated examinations may exacerbate this discomfort.
- Cervical Edema and Bleeding: Frequent or aggressive cervical checks can cause irritation, swelling (cervical edema), and bleeding, potentially leading to cervical injury or hematoma formation.
Performing a Sterile Vaginal Exam
Explain the procedure to the patient and obtain consent using a trauma-informed approach/language with all patients.
Drape a sheet to maintain the patient’s privacy during the exam.
Don a sterile glove on your dominant hand.
Lubricate the index and middle fingers of your dominant hand.
Inform the patient you will be inserting two fingers into the vagina, and they will feel pressure.
After inserting your fingers into the vagina, locate the cervix.
Check the cervix for the following:
- Cervical Dilation: Estimate the distance between one side of the cervix and the other, documented in centimeters (see Figure 15.3).
- Cervical effacement: Estimate the length of the cervix. A cervix is 0 percent effaced when it is 2 cm long and 100 percent effaced when it is paper thin. Estimate the percentage between 2 cm and paper thin.
- Cervical position: A cervix that “points” toward the patient’s back is in a posterior position, whereas an anterior position is oriented toward the vaginal introitus. If the cervix is located somewhere between the two, it is in the midposition.
Check the presenting part for the following:
- Presentation: Assess the part of the fetus that is presenting in the maternal pelvis: cephalic (vertex), breech (frank).
- Station: Determine the level of the presenting part in relation to the ischial spines of the pelvis.
- Fetal Position: Palpate the relationship of the presenting fetal part (skull if cephalic and sacrum if breech) in relation to the maternal pelvis).
Monitoring the Physical Response during the First Stage of Labor
The assessment of the patient in labor includes obtaining regular maternal vital signs and monitoring the fetal heart rate as outlined in (Table 18.2). Hospital policies are created to reflect the guidelines for fetal monitoring and vital signs, based on the recommendations of professional organizations. These policies dictate the minimum frequency of vital signs, contraction patterns and labor progress, pain, and emotional response checks to be performed by the nurse (Milton, 2024). The nurse should use discretion based on the laboring person’s situation and may complete the assessment more frequently than the minimal policy standard.
| Assessment Data | Early Phase of Labor | Active Phase of Labor |
|---|---|---|
| Vital signs | Every 1 hour | Every 1 hour |
| Contraction pattern | Intermittently every 15–60 minutes or continuously based on low- or high-risk labor status, and documented at the same interval as FHR (refer to Chapter 16 Electronic Fetal and Uterine Contraction Monitoring for both intermittent and continuous monitoring) | Intermittently every 15 minutes or continuously based on low- or high-risk labor status, and documented at the same interval as FHR (refer to Chapter 16 Electronic Fetal and Uterine Contraction Monitoring for both intermittent and continuous monitoring) |
| FHR pattern | See Table 18.3 | See Table 18.3 |
| Labor progress | As indicated based on significant changes in patient behavior, uterine contraction pattern, or abnormalities in the FHR | As indicated based on the patient’s presentation, the feeling of pressure, significant changes in patient behavior, uterine contraction pattern, or abnormalities in the FHR |
| Pain | Hourly or as needed | Hourly or as needed |
| Emotional response | Continuous | Continuous |
Monitoring the Fetal Response to the First Stage of Labor
The Association of Women’s Health, Obstetric and Neonatal Nurses [AWHONN] (2018) recommends fetal heart rate monitoring of uncomplicated pregnancies be reviewed every 15 to 30 minutes during the first stage of labor when electronic monitoring is in place (Table 18.3). When intermittent auscultation is in place, fetal monitoring in the early phase of labor is at the recommendation of the health-care provider and every 15 to 30 minutes in the active phase. See Chapter 16 Electronic Fetal and Uterine Contraction Monitoring for more information on fetal heart rate during labor. In patients who present with or develop complications during labor, the recommendation is for a review of the heart rate every 15 minutes during the first stage of labor. Laboring persons with risk factors should be monitored continuously, allowing for prompt intrauterine resuscitation or delivery.
| FHR Assessment Data |
Early Phase of Labor
(cervix < 4 cm dilated) |
Early Phase of Labor
(cervix 4–5 cm dilated) |
Active Phase of Labor
(cervix ≥ 6 cm dilated) |
|---|---|---|---|
|
FHR baseline
FHR variability Periodic changes |
Frequency at the discretion of the midwife or physician |
Low risk without
oxytocin
: every 30 minutes
With risk factors or oxytocin: every 15 minutes |
Low risk without oxytocin: every 30 minutes
With risk factors or oxytocin: every 15 minutes |
Monitoring for Complications of the First Stage of Labor
Consistent monitoring for complications begins during the first stage of labor and continues through the succeeding stages of labor and into the postpartum period. During the first stage of labor, the most common complications are related to periodic fetal heart rate changes and labor progress that deviates from normal. The nurse will regularly assess the fetal heart rate, contraction pattern, and labor progress, and watch for any signs of complications during the first stage of labor (Milton, 2024).
Monitoring of the fetus during the first stage of labor will depend on the phase of labor and hospital policy or provider order. The nurse may auscultate the fetal heart rate intermittently or apply external fetal monitors for continuous monitoring. If the nurse detects any abnormalities in the fetal heart rate during auscultation or continuous fetal monitoring, the nurse will perform interventions and notify the provider immediately. Complications and nursing actions are covered in more detail in Chapter 19 Complications of Labor and Birth.
Nursing Interventions during the First Stage of Labor
During the first stage of labor, the nurse will support and educate the laboring person and their partner on comfort measure s, mobility, pain relief, and emotional support. These needs will be constant during labor, but the role of the nurse will change as the labor progresses.
Encouraging Position Changes of the Person in Labor
Whenever possible, the nurse should encourage the laboring person to change positions and ambulate during the first stage of labor. The nurse should educate the laboring person on the benefits of position change and ambulation and demonstrate how the partner can assist during the labor process (see Figure 15.11). The laboring person should be advised that lying flat on their back can result in hypotension related to the compression of the vena cava. Walking and upright positions have been shown to decrease the duration of the first stage of labor. Compared to semirecumbent or supine positions, upright positions during labor often result in shorter labors, fewer interventions, and decreased pain for laboring persons. In addition, upright positions allow gravity to assist in bringing the fetus down. No matter the position, frequent position changes create slight movement in the pelvic bones and help the fetus find the best fit into the pelvis (Ondeck, 2019).
The position and station of the fetus during labor can impact the progress of labor and the comfort of the laboring person. Table 18.4 lists specific position changes recommended based on fetal position and station (Dhekra et al., 2020; Garbelli & Lira, 2021).
| Goal | Fetal Position | Recommended Laboring Person Positions |
|---|---|---|
| Changing fetal position during labor | Occiput anterior (OA): This is the most favorable position for labor. |
Encourage the laboring person to try the following position changes to facilitate labor progress (Garbelli & Lira, 2021):
|
| Occiput posterior (OP): The fetus’s head is facing the laboring person’s front. |
Labor can be more challenging, and position changes can help:
|
|
| Occiput transverse or asynclitic: When the fetus’s head is not well aligned with the pelvis, these positions can lead to prolonged labor. |
Recommended position changes include (Garbelli & Lira, 2021):
|
|
| Changing fetal station during labor | High station (above 0 station) |
When the fetus’s head is high in the pelvis, position changes can help engage the head in the pelvis and encourage descent (Dhekra et al., 2020):
|
| Low station (below 0 station) |
If the fetus’s head is low but not progressing, these position changes can help facilitate descent (Dhekra et al., 2020):
|
|
| Changing fetal position at the pelvic outlet |
When the fetus’s head is at the outlet (crowning), position changes focus on guiding the head through the birth canal (Huang et al., 2019):
|
Remember that every labor is unique, and the effectiveness of position changes may vary from person to person. Continuous communication with the laboring person, monitoring the baby’s heart rate, and working collaboratively with the health-care team are essential for safe and effective labor progress in different fetal positions and stations.
Encouraging Breathing and Relaxation of the Person in Labor
The nurse should encourage the laboring person to try to relax and breathe during the first stage of labor. Breathing techniques distract from pain, help in the relaxation of muscles in the pelvis to allow descent of the fetus, and maintain blood oxygen levels for the laboring person and fetus (Heim & Makuch, 2023). Pain management is discussed in detail in Chapter 17 Pain Management During Labor and Birth.
Providing Emotional Support to the Person in Labor
The onset of labor can be a time of excitement and anxiety for new parents. The nurse can provide emotional support to the laboring person and partner by answering questions that they may have. The nurse can ease the laboring person’s anxiety by explaining the expected progression of labor and creating a plan of care with the laboring person and the partner. The nurse should ask the laboring person how they envision their labor and how their wishes can be accommodated while discussing any potential barriers to their desired birth plan. Throughout the labor and delivery, the nurse should discuss any changes with the laboring person and their partner and continually explain what is happening.
Providing Measures for Pain Relief to the Person in Labor
Pain management during the first stage of labor varies based on the patient’s preferences. The nurse is an integral part of the laboring person’s pain management plan. Some laboring persons may opt for nonpharmacologic pain management strategies in which the nurse will provide support with positioning, room ambiance, and management of staff and visitors (Heim & Makuch, 2023). When a laboring person desires analgesia, the nurse may provide options for the laboring person, obtain an order from the provider, administer the medication, and monitor the laboring person following administration. Many facilities offer epidural anesthesia for persons in labor. The nurse will assist the laboring person in proper positioning and will support and monitor the laboring person following the initiation of the epidural. For a more detailed comparison of pain management options, benefits, and risks, refer to Chapter 17 Pain Management During Labor and Birth.
Assisting with Amniotomy
The nurse’s role during an amniotomy , known as breaking of water or artificial rupture of membranes (AROM), is to assist the laboring person and the health-care provider. The nurse’s duties take place before, during, and after the procedure.
Assisting during an Amniotomy
Informed Consent: The nurse witnesses that the procedure, as well as the reasons for the amniotomy, potential benefits, risks, and alternatives, has been explained to the patient.
Preparation: The nurse ensures that all necessary supplies and equipment are readily available. Such items include sterile gloves, a sterile amniotomy hook or instrument, sterile drapes, and a waterproof pad or absorbent materials to manage amniotic fluid.
Positioning: The patient is positioned comfortably in bed, typically in the lithotomy position (lying on the back with knees bent and feet in stirrups) or another position that allows easy access to the perineal area.
Assisting the Provider: The nurse assists the health-care provider (usually an obstetrician or midwife) during a vaginal examination in which the provider evaluates the cervix’s position, dilation, and effacement.
Performing the Amniotomy: The health-care provider uses a sterile amniotomy hook or instrument to puncture a small opening in the amniotic sac, causing the slow release of amniotic fluid. The nurse may assist by holding the drape or offering support to the patient during the procedure.
Assessing Amniotic Fluid: After the amniotomy, the nurse monitors the characteristics of the amniotic fluid, including color, odor, and the presence of meconium (fetal stool). Any abnormal findings are reported to the health-care provider.
Monitoring Contractions and Fetal Heart Rate: The nurse closely monitors the patient’s uterine contractions and fetal heart rate patterns before and after the amniotomy. Changes in these patterns may indicate the need for further intervention or adjustments in labor management.
Comfort and Emotional Support: Throughout the procedure and in the postamniotomy period, the nurse provides emotional support to the patient, addressing any concerns or questions.
Documentation: Accurate and detailed documentation of the procedure, including the date, time, provider’s name, amniotic fluid characteristics, and maternal and fetal assessments, is essential in the patient’s medical record.
Postamniotomy Care: The nurse continues to monitor the patient’s progress, ensuring they remain comfortable and well hydrated. Frequent assessments of vital signs, contractions, and fetal well-being are maintained.
Education during the First Stage of Labor
The nurse should be a continual resource for educating the patient during labor. The laboring person should be encouraged to ask questions to clarify any information presented by the nurse or health-care team (Milton, 2024). To ease the stress of labor, the nurse should always explain what is happening to the laboring person and their partner and immediately notify them of changes or concerns about the plan of care.
When the nurse applies the external fetal monitoring equipment or auscultates the fetal heart rate, the nurse should educate the laboring person and their partner on the importance of and reason for fetal monitoring during labor (AWHONN, 2018). The nurse can give a brief description of what the health-care team is looking for on the fetal monitor and assure the laboring person that the monitoring is being continually watched so that the health-care team will respond immediately when necessary.
Upon admission, the nurse should discuss the process of labor and birth. The laboring person and their partner should understand the first stage of labor begins with early dilation and ends at full dilation and effacement. The nurse should educate the laboring person on what pain management options are available during the first stage, the value of position changes and rest and relaxation, and the importance of being hydrated during labor. The laboring person should be educated on the differences in pain medication and pushing during the second stage, complete dilation to delivery, when and how pushing will occur, and the team members who will be present for the delivery (Milton, 2024).
Nursing care plays a crucial role in decreasing the cesarean birth rate by promoting and supporting safe and healthy vaginal births. Table 18.5 lists ways in which nursing care can contribute to reducing the cesarean birth rate, with references to evidence-based practices and guidelines.
| Nursing Care | Nursing Intervention | Specific Details of the Intervention |
|---|---|---|
| Labor support and education | Continuous labor support | Nurses will provide continuous emotional support, comfort measures, and encouragement to laboring persons (ACOG, 2019). |
| Frequent position changes and movement | Encourage mobility | Nurses can encourage laboring persons to change positions frequently, such as walking, swaying, or using a birthing ball. ACOG recommends movement and position changes during labor to reduce the risk of cesarean births (ACOG, 2024). |
| Pain management and comfort measures | Nonpharmacologic pain relief | Nurses can offer nonpharmacologic pain relief methods, including relaxation techniques, massage, warm compresses, and hydrotherapy, to help manage pain and discomfort during labor. Effective pain management can reduce the need for epidurals and other interventions associated with cesarean births. |
| Monitoring fetal well-being | Intermittent auscultation and continuous fetal monitoring | Nurses can use intermittent auscultation or continuous electronic fetal monitoring (EFM) to assess fetal well-being during labor. Appropriate and judicious use of EFM can help detect and address fetal distress promptly, potentially avoiding unnecessary cesarean births (AWHONN, 2018). |
| Labor progress assessment | Regular cervical examinations | Nurses can perform cervical examinations at appropriate intervals to assess labor progress. However, they should avoid unnecessary or frequent cervical checks, as they can increase the risk of infection and interventions (ACOG, 2021). |
| Supporting physiologic birth | Promotion of physiologic birth | Nurses can advocate for and support physiologic birth, including spontaneous labor onset and the avoidance of unnecessary interventions. ACOG emphasizes the importance of supporting low-intervention births when appropriate (ACOG, 2019). |
By implementing evidence-based nursing care practices and promoting physiologic birth, nurses can contribute to reducing the cesarean birth rate and ensuring safe and positive birthing experiences for laboring persons.
Adoption
A patient may present for delivery with a legal adoption plan or may decide upon arrival to place their newborn up for adoption. The decision to place a newborn for adoption is a personal one, and the patient may change their mind multiple times during the labor and birth. The nurse should support the patient through decisions and emotional changes during their stay. When a patient presents with a prearranged adoption plan, the nurse should discuss the plan with the patient and any intended parents who are present. It is important to have a clear understanding ahead of time of whether adopting parents will be present in the room/hospital at the time of delivery, whether the patient wants to see or hold the newborn, skin-to-skin, whether any of that should be offered after delivery according to patient desire, and so forth. If a patient does not have a prearranged legal plan or decides during their stay to surrender the newborn, legal arrangements can be initiated. The nurse should consult a social worker to provide resources to the patient and arrange for postdelivery care of the newborn.


11.5: E- Dynamics of Hamilton’s Equations
In this appendix we give a brief introduction to some of the characteristics and results associated with Hamiltonian differential equations (or, Hamilton’s equations or Hamiltonian vector fields). The Hamiltonian formulation of Newton’s equations reveals a great deal of structure about dynamics and it also gives rise to a large amount of deep mathematics that is the focus of much contemporary research. .
Our purpose here is not to derive Hamilton’s equations from Newton’s equations. Discussions of that can be found in many textbooks on mechanics (although it is often considered ‘’advanced mechanics”). For example, a classical exposition of this topic can be found in the classic book of Landau, and more modern expositions can be found in Abraham and Marsden and Arnold. Rather, our approach is to start with Hamilton’s equations and to understand some simple aspects and consequences of the special structure associated with Hamilton’s equations. Towards this end, our starting point will be Hamilton’s equations. Keeping with the simple approach throughout these lectures, our discussion of Hamilton’s equations will be for two dimensional systems.
We begin with a scalar valued function defined on \(\mathbb{R}^2\)
\[H = H(q, p), (q, p) \in \mathbb{R}^2. \label{E.1}\]
This function is referred to as the Hamiltonian. From the Hamiltonian, Hamilton’s equations take the following form:
\(\dot{q} = \frac{\partial H}{\partial p} (q, p)\),
\[\dot{p} = \frac{\partial H}{\partial q}(q, p), (q, p) \in \mathbb{R}^2. \label{E.2}\]
The form of Hamilton’s equations implies that the Hamiltonian is constant on trajectories. This can be seen from the following calculation:
\(\frac{dH}{dt} = \frac{\partial H}{\partial q} \dot{q} +\frac{\partial H}{\partial p} \dot{p}\)
\[= \frac{\partial H}{\partial q} \frac{\partial H}{\partial p} - \frac{\partial H}{\partial p} \frac{\partial H}{\partial q} = 0. \label{E.3}\]
Furthermore, this calculation implies that the level sets of the Hamiltonian are invariant manifolds. We denote the level set of the Hamiltonian as:
\[H_{E} = \{(q, p) \in \mathbb{R}^2 | H(q, p) = E\} \label{E.4}\]
In general, the level set is a curve (or possibly an equilibrium point). Hence, in the two dimensional case, the trajectories of Hamilton’s equations are given by the level sets of the Hamiltonian.
The Jacobian of the Hamiltonian vector field (E.2), denoted J, is given by:
\[J(p, q) = \begin{pmatrix} {\frac{\partial^{2}H}{\partial q \partial p}}&{\frac{\partial^{2}H}{\partial p^2}}\\ {-\frac{\partial^{2}H}{\partial q^2}}&{-\frac{\partial^{2}H}{\partial p \partial q}} \end{pmatrix}, \label{E.5}\]
at an arbitrary point \((q, p) \in \mathbb{R}^2\). Note that the trace of J(q, p), denoted trJ(q, p), is zero. This implies that the eigenvalues of J(q, p), denoted by \(\lambda_{1, 2}\), are given by:
\[\lambda_{1, 2} = \pm \sqrt{-det J(q, p)}, \label{E.6}\]
where detJ(q, p) denotes the determinant of J(q, p). Therefore, if \((q_{0}, p_{0})\) is an equilibrium point of (E.1) and \(detJ(q_{0}, p_{0}) = 0\), then the equilibrium point is a center for \(detJ(q_{0}, p_{0}) > 0\) and a saddle for \(detJ(q_{0}, p_{0}) < 0\).
Next we describe some examples of two dimensional, linear autonomous Hamiltonian vector fields.
Example \(\PageIndex{41}\) (The Hamiltonian Saddle )
We consider the Hamiltonian:
\[H(q, p) = \frac{\lambda}{2} (p^{2}-q^{2}) = \frac{\lambda}{2} (p-q)(p+q), (q, p) \in \mathbb{R}^2, \label{E.7}\]
with \(\lambda > 0\). From this Hamiltonian, we derive Hamilton’s equations:
\(\dot{q} = \frac{\partial H}{\partial p} (q, p) = \lambda p\),
\[\dot{p} = \frac{\partial H}{\partial p} (q, p) = \lambda q, \label{E.8}\]
or in matrix form:
\[\begin{pmatrix} {\dot{q}}\\ {\dot{p}} \end{pmatrix} = \begin{pmatrix} {0}&{\lambda}\\ {\lambda}&{0} \end{pmatrix} \begin{pmatrix} {q}\\ {p} \end{pmatrix}. \label{E.9}\]
The origin is a fixed point, and the eigenvalues associated with the linearization are given by \(\pm \lambda\). Hence, the origin is a saddle point.The value of the Hamiltonian at the origin is zero. We also see from (E.7) that the Hamiltonian is zero on the lines \(p - q = 0\) and p + q = 0. These are the unstable and stable manifolds of the origin, respectively. The phase portrait is illustrated in Fig. E.1.
The flow generated by this vector field is given in Chapter 2, Problem Set 2, problem 6.
Example \(\PageIndex{42}\) (The Hamiltonian Center)
We consider the Hamiltonian:
\[H(q, p) = \frac{\omega}{2} (p^{2}+q^{2}), (q, p) \in \mathbb{R}^2, \label{E.10}\]
with \(\omega > 0\). From this Hamiltonian, we derive Hamilton’s equations:
\(\dot{q} = \frac{\partial H}{\partial p} (q, p) = \omega p\),
\[\dot{p} = \frac{\partial H}{\partial p} (q, p) = -\omega q, \label{E.11}\]
or in matrix form:
\[\begin{pmatrix} {\dot{q}}\\ {\dot{p}} \end{pmatrix} = \begin{pmatrix} {0}&{\omega}\\ {-\omega}&{0} \end{pmatrix} \begin{pmatrix} {q}\\ {p} \end{pmatrix}. \label{E.12}\]
The level sets of the Hamiltonian are circles, and are illustrated in Fig. E.2.
The flow generated by this vector field is given in Chapter 2, Problem Set 2, problem 5.
We will now consider two examples of bifurcation of equilibria in two dimensional Hamiltonian systems. Bifurcation associated with one zero eigenvalue (as we studied in Chapter 8) is not possible since, following (E.6), if there is one zero eigenvalue the other eigenvalue must also be zero. We will consider examples of the Hamiltonian saddle-node and Hamiltonian pitchfork bifurcations. Discussions of the Hamiltonian versions of these bifurcations can also be found in Golubitsky et al.
Example \(\PageIndex{43}\) (Hamiltonian saddle-node bifurcation)
We consider the Hamiltonian:
\[H(q, p) = \frac{p^2}{2} - \lambda q+\frac{q^{3}}{3}), (q, p) \in \mathbb{R}^2, \label{E.13}\]
where \(\lambda\) is considered to be a parameter that can be varied. From this Hamiltonian, we derive Hamilton’s equations:
\(\dot{q} = \frac{\partial H}{\partial p} (q, p) = p\),
\[\dot{p} = -\frac{\partial H}{\partial p} (q, p) = \lambda - q^2, \label{E.14}\]
The fixed points for (E.14) are:
\[(q, p) = (\pm \sqrt{\lambda}, 0), \label{E.15}\]
from which it follows that there are no fixed points for \(\lambda < 0\), one fixed point for \(\lambda = 0\), and two fixed points for \(\lambda > 0\). This is the scenario for a saddle-node bifurcation.
Next we examine stability of the fixed points. The Jacobian of (E.14) is given by:
\[\begin{pmatrix} {0}&{1}\\ {-2q}&{0} \end{pmatrix}. \label{E.16}\]
The eigenvalues of this matrix are:
\(\lambda_{1, 2} = \pm \sqrt{-2q}\).
Hence \((q, p) = (-\sqrt{\lambda}, 0)\) is a saddle, \((q, p) = (\sqrt{\lambda}, 0)\) is a center, and (q, p) = (0, 0) has two zero eigenvalues. The phase portraits are shown in Fig. E.3.
Example \(\PageIndex{44}\) (Hamiltonian pitchfork bifurcation)
We consider the Hamiltonian:
\[H(q, p) = \frac{p^2}{2} - \lambda \frac{q^2}{2}+\frac{q^{4}}{4}), (q, p) \in \mathbb{R}^2, \label{E.17}\]
where \(\lambda\) is considered to be a parameter that can be varied. From this Hamiltonian, we derive Hamilton’s equations:
\(\dot{q} = \frac{\partial H}{\partial p} (q, p) = p\),
\[\dot{p} = -\frac{\partial H}{\partial p} (q, p) = \lambda q - q^3, \label{E.18}\]
The fixed points for (E.18) are:
\[(q, p) = (0, 0), (\pm p\lambda, 0), \label{E.19}\]
from which it follows that there is one fixed point for \(\lambda < 0\), one fixed point for \(\lambda = 0\), and three fixed points for \(\lambda > 0\). This is the scenario for a pitchfork bifurcation.
Next we examine stability of the fixed points. The Jacobian of (E.18) is given by:
\[\begin{pmatrix} {0}&{1}\\ {\lambda-3q^2}&{0} \end{pmatrix}. \label{E.20}\]
The eigenvalues of this matrix are:
\(\lambda_{1,2} = \pm \sqrt{\lambda-3q^2}\).
Hence (q, p) = (0, 0) is a center for \(\lambda < 0\), a saddle for \(\lambda > 0\) and has two zero eigenvalues for \(\lambda = 0\). The fixed points \((q, p) = (p\lambda, 0)\) are centers for \(\lambda > 0\). The phase portraits are shown in Fig. E.4.
We remark that, with a bit of thought, it should be clear that in two dimensions there is no analog of the Hopf bifurcation for Hamiltonian vector fields similar to to the situation we analyzed earlier in the non-Hamiltonian context. There is a situation that is referred to as the Hamiltonian Hopf bifurcation, but this notion requires at least four dimensions, see Van Der Meer.
In Hamiltonian systems a natural bifurcation parameter is the value of the level set of the Hamiltonian, or the "energy". From this point of view perhaps a more natural candidate for a Hopf bifurcation in a Hamiltonian system is described by the Lyapunov subcenter theorem, see Kelley. The setting for this theorem also requires at least four dimensions, but the associated phenomena occur quite often in applications.


10.2A: Occurrence of a Disease
- Recognize the steps taken by epidemiologists when investigating disease outbreaks
Outbreak is a term used in epidemiology to describe an occurrence of disease greater than would otherwise be expected at a particular time and place. It may affect a small and localized group or impact thousands of people across an entire continent. Two linked cases of a rare infectious disease may be sufficient to constitute an outbreak. Outbreaks may also refer to endemics that affect a particular place or group, epidemics that affect a region in a country or a group of countries, and pandemics that describe global disease outbreaks.
The epidemiology profession has developed a number of widely accepted steps when investigating disease outbreaks. As described by the Centers for Disease Control and Prevention, these include the following:
- Verify the diagnosis related to the outbreak.
- Identify the existence of the outbreak (if the group of ill persons is normal for the time of year, geographic area, etc. ).
- Create a case definition to define who/what is included as a case.
- Map the spread of the outbreak.
- Develop a hypothesis (if there appears to be a cause for the outbreak).
- Study hypothesis (collect data and perform analysis).
- Refine hypothesis and carry out further study.
- Develop and implement control and prevention systems.
- Release findings to greater communities.
There are several outbreak patterns that can be useful in identifying the transmission method or source and predicting the future rate of infection.
- Common source – All victims acquire the infection from the same source (e.g. a contaminated water supply).
- Continuous source – Common source outbreak where the exposure occurs over multiple incubation periods.
- Point source – Common source outbreak where the exposure occurs in less than one incubation period.
- Propagated – Transmission occurs from person to person.
Each has a distinctive epidemic curve, or histogram of case infections and deaths.
Outbreaks can also be:
- Behavioral risk related (e.g. sexually transmitted diseases, increased risk due to malnutrition)
- Zoonotic – The infectious agent is endemic to an animal population.
Key Points
- Outbreaks may also refer to endemics that affect a particular place or group, epidemics that affect a region in a country or a group of countries, or pandemics that describe global disease outbreaks.
- The epidemiology profession has developed a number of widely accepted steps to investigate a disease occurrence.
- Outbreak patterns, which can be useful in identifying the transmission method or source, and predicting the future rate of infection include common source, continuous source, point source, and propagated source.
- Outbreaks can be behavioral risk related (e.g., sexually transmitted diseases, increased risk due to malnutrition) or zoonotic (e.g. the infectious agent is endemic to an animal population ).
Key Terms
- outbreak : A term used in epidemiology to describe an occurrence of disease greater than would otherwise be expected at a particular time and place.
- epidemic : A widespread disease that affects many individuals in a population.
- pandemic : A disease that hits a wide geographical area and affects a large proportion of the population.


7: C7) Conservation of Angular Momentum II
In the previous chapter, we dealt with objects having real size for the first time, and we learned how to calculate the angular momentum for extended objects as \(\vec{L}=I\vec{\omega}\). In this chapter, we have to acknowledge that if extended objects can have angular momenta, singular points can also (!), if we use a point other then their location as the reference. This sounds very counter-intutive, so let's first make sure we understand why that must be - essentially, objects are made up of points, and we believe angular momentum should be additive (two objects with angular momentum \(L_1\) and \(L_2\) have total angular momentum \(L_1+L_2\)...sounds like something we want, right?). If that's true, then when you think about an extended object as a collection of points, each of those points should have individual angular momenta \(L_i\) so that we can add them all to get the total \(L=\sum_i L_i\).
Of course, those individual points themselves are not spinning, they are moving around the axis of the object (see the leftmost figure below). But how do we determine the angular momenta of these individual points? The answer is to use a cross-product:
\[\vec{L}=\vec{r} \times \vec{p}.\]
In this formula, the \(\vec{r}\) is the position of the point and \(\vec{p}\) is the momentum. We will go into this equation in some detail in the rest of the chapter, but the important thing to notice now is that it is a vector, so it has magnitude and direction. The magnitude can be found with the formula
\[|L|=|r||p|\sin\phi,\]
where \(\phi\) is the angle between \(\vec{r}\) and \(\vec{p}\). The direction of any cross product \(\vec{u}\times \vec{v}\) can be found with the right hand rule . The right hand rule (see second figure to the right) says:
- Point (the fingers on your right hand!) in the direction of the first vector in \(\vec{u}\times \vec{v}\).
- Curl your fingers into the second vector in \(\vec{u}\times \vec{v}\) (you may need to flip you hand around...)
- Your thumb is now pointing in the direction of \(\vec{u}\times \vec{v}\).
"This" right hand rule is actually related to the "first" right hand rule we learned in the last chapter for the direction of \(\vec{L}=I\vec{\omega}\), but the one presented here works for any cross product, whereas the other one is just for the angular momentum of an object. The figure below (three images on the right) illustrates a few examples of these directions - check that you can get the right answers!
(images from Open Stax!)


14.3: Environmental Health Assessment
By the end of this section, you should be able to:
- Discuss the methods of measuring pollutants in the environment.
- Explain the steps in the risk assessment and risk-management processes.
- Assess the environmental health of individuals, homes, and communities.
Environmental assessment is the process of identifying, evaluating, and mitigating environmental risks to human health. It involves measuring pollutants, determining and managing risks, and conducting individual, home, and community assessments.
Measuring Pollutants
Measuring pollutants is essential for assessing and managing environmental and public health risks (Figure 14.4) (Manisalidis et al., 2020). Accurate measurement helps identify sources of pollution, monitor trends, and guide regulatory action. While environmental scientists are responsible for measuring pollutants, the C/PHN’s role is to ensure that measurements are taken, the results are communicated to the public, and any issues of concern are followed up on. The first step in measuring pollutants involves collecting samples. Different collection methods are used depending on the type of pollutant and the medium in which it is present (air, water, soil, etc.). Sampling may involve placing sensors, samplers, or collection devices in the target environment. Once samples are collected, various analytical techniques such as spectroscopy are deployed to determine the concentration of specific pollutants. For air pollutants, monitoring stations are set up in various locations to measure the concentration of gases and particulate matter. Instruments like gas analyzers, particle counters, and meteorological sensors help assess the levels of pollutants such as carbon monoxide, sulfur dioxide, nitrogen oxides, ozone, and particulate matter. Water pollutants are measured with optical sensors, ion-selective electrodes, and spectroscopy to determine the presence and concentration of contaminants like heavy metals and chemicals. Soil is assessed using chemical and spectral analysis, with samples collected from different depths to understand the distribution of pollutants in the land.
Pollutants may also be measured indirectly through remote sensing techniques such as satellite imagery and aerial photography, which can be used to monitor larger areas and track pollution trends over time. These methods are also very useful for gauging changes in land use, deforestation , erosion , climate change , and other environmental factors that can contribute to pollution. Finally, climate modeling is used to predict and assess the impact of climate change, such as an increase in extreme weather that may lead to an increase in heat-related mortality.
In addition to providing data to assess and monitor the health of a population, measurements of hazardous agents play a significant role in protecting the community by supplying evidence for developing and enforcing environmental regulations.
Determining Risk and Risk Management
The EPA uses a four-step risk assessment to evaluate potential pollution and hazards, evaluate the likelihood of exposure-related health threats, and develop standards (EPA, 2023k). The first step, Hazard Identification , aims to identify potential negative outcomes that may result due to exposure to a specific agent. While multiple data points are involved in this analysis, the emphasis is on toxicokinetics , or the study of how chemicals are absorbed, metabolized, and eliminated, and toxicodynamics , which examines the impact of chemicals on the body and health.
The second step, Dose Response , aims to identify the ways that the amount of exposure (dose) relates to the probability and severity of negative health effects (response). The third step, Exposure Assessment, involves quantifying the extent, frequency, and length of human contact to an environmental agent or predicting the potential impact of future contact. Finally, Risk Characterization, the fourth step, aims to synthesize information from the first three steps to provide an overall understanding of the characteristics and occurrence of risks as well as indicate where uncertainties remain.
When the available evidence is uncertain or incomplete, a guiding concept is the precautionary principle , which directs decision makers to be proactive in safeguarding the environment and public health rather than waiting for conclusive evidence of harm. This principle shifts the burden of proof, or responsibility, to those advocating for a particular action, such as building a new power plant, to demonstrate that it will not cause harm to the environment or community. The principle can also lead to taking action to prevent harm, such as the decisions made by various governments at the start of the COVID-19 pandemic to institute public health measures such as mask wearing, lockdowns, and travel restrictions, among others. Since little was known about this novel coronavirus, early action without scientific certainty was deemed necessary to protect the health of the public. This is an example of the precautionary principle in action.
Environmental Health Assessments
The link between human health and the environment underscores the need for systematic evaluations, which play a critical role in understanding population health. This section examines how environmental assessments inform nurses about the impact of the environment on the health of communities as well as individuals.
Individual Assessment
Individual environmental health assessments are essential tools for identifying, preventing, and educating individuals about environmental health concerns. These assessments aim to identify hazards, understand health implications, and mitigate risks. Individual environmental health assessments encompass a broad range of potential environmental exposures, including indoor agents, outdoor air pollution, water sources, exposure to pesticides or industrial waste, and the presence of radiation sources like radon. Factors such as the home and school or work environments, recreational activities, lifestyle, and personal health history are all considered. These assessments empower individuals to make informed decisions and assist nurses with individualizing care, creating action plans, and providing education, referrals, advocacy and follow-up.
In 2005, a team of nurses devised a framework, termed I PREPARE , as a tool for conducting individual environmental health assessments and developing a plan of action. I PREPARE is a mnemonic; each letter stands for a specific step in the assessment (Paranzino et al., 2005) as shown in Table 14.3. The Case Reflection that follows walks through an example of a nurse using I PREPARE to perform an individual environmental health assessment.
| Explanation | Examples of Nursing Actions | |
|---|---|---|
| I | Investigate potential exposures: This step involves asking questions to uncover potential sources of exposure to environmental hazards. | Ask if a client has ever felt sick after handling chemicals or toxic substances. |
| P | Present work: Inquire about the person’s current occupation and any potential workplace hazards. | Ask the client to describe their current job, the industry they work in, and any hazardous substances that they handle. |
| R | Residence: Assess potential residential exposures. | Ask about the age and type of dwelling, their water source, and indoor hazards such as mold or mildew. |
| E | Environmental concerns: Encourage clients to discuss environmental concerns in their neighborhood. | Ask if they live near landfills, farms, or factories. |
| P | Past work: Inquire about past occupations or exposures that may have exposed the client to hazardous materials in the past. | Ask if they have ever worked on a farm or in a factory or used solvents or other chemicals. |
| A | Activities: Assess the client’s activities that may have exposed them to environmental hazards. | Ask about hobbies, outdoor recreation, smoking, and diet. |
| R | Referrals and Resources: Provide information about relevant resources, referrals, or organizations that can help the individual address their environmental health concerns. | Provide information on government sites, such as the CDC, Agency for Toxic Substances & Disease Registry, or the Occupational Safety & Health Administration. |
| E | Educate: Share information about the client’s potential environmental health risks and provide guidance on how to prevent or reduce exposure to protect their health. | If they may have been exposed to lead in their drinking water, provide information about testing and mitigation from local, state, and federal resources. |
Read the scenario, and then respond to the questions that follow.
Kyra, a 35-year-old client, presents to the county clinic after experiencing persistent symptoms, including coughing, sneezing, and hoarseness, for several months. She’s concerned that her symptoms might be related to the apartment she recently moved into. After reviewing her health history, Nurse Kyle uses the I PREPARE framework to perform an individual environmental health assessment.
I—Investigate Potential Exposures: Kyle asks Kyra if she has had any known exposure to pollutants at home, at work, or in the community. He asks if her symptoms improve or worsen when she is at home, at work, or outside. Kyra notes while she isn’t sure what she’s being exposed to, she usually feels worse in the morning.
P—Present Work: Kyle asks about Kyra’s work environment. Kyra is a graphic designer who works 3 days a week in a well-ventilated office building downtown and works from home the remaining 2 days.
R—Residence: Kyle investigates potential exposures by asking about the age and upkeep of the apartment building, such as whether it’s properly ventilated, if there have been any water leaks or mold issues, and if there are any pets or smokers in the home. She lives with her cat Mittens in an interior apartment on the first floor of an older building without air conditioning, but she does have a window in her kitchen. Kyra notes that the basement is used for utilities, such as laundry, and is poorly lit, unventilated, and damp.
E—Environmental Concerns: Kyle asks about industries, farms, and waste sites near Kyra’s home or workplace. She states that there has been ongoing construction adjacent to her building that often creates a layer of dust and construction debris in the immediate surroundings.
P—Past Work: As a junior designer, Kyra worked for a small business in an old industrial warehouse. She doesn’t know much about the history but states that they were not allowed to drink from the building’s faucets and were directed to use the water cooler.
A—Activities: Kyra enjoys gardening on her small balcony but finds it increasingly challenging due to her symptoms, which she says worsen when the nearby construction is underway.
R—Referrals and Resources: As a nurse working in a community clinic, Kyle is well prepared to offer referrals and local resources. After confirming Kyra’s insurance, he provides contact information for an allergy center covered by her plan and refers her for allergy testing.
E—Educate: Kyle works with Kyra to educate her about indoor and outdoor air quality, potential allergens, and actions she can take to make her environment and lifestyle healthier for now and the future.
- If you were Nurse Kyle, what additional questions would you ask Kyra to further investigate her symptoms and potential sources of exposure?
- From an environmental health perspective, what are some possible indoor environmental hazards that could be linked to Kyra’s health issues? What about outdoors? How can these be mitigated?
- Given Kyra’s past work history in the warehouse and the directive to avoid tap water, what are some potential concerns in the warehouse space?
- How might Kyra’s gardening activity on her patio interact with the nearby construction? How might Kyra’s activities be adapted to minimize her exposure to allergens and irritants?
- What education should Nurse Kyle provide? What role does education play in preventing environmental health concerns such as Kyra’s? How might this knowledge empower her to take proactive steps to improve her environment and overall health?
Home Assessment
What constitutes an environmentally healthy home? According to the National Center for Health Housing , a healthy home is dry, clean, safe, ventilated, pest and contaminant free, regularly maintained, and has a comfortable temperature (National Center for Healthy Housing, 2023). Home health assessments are critical for promoting health equity by addressing disparities in housing quality. For example, programs to improve home indoor air quality are proven to reduce the incidence of asthma among BIPOC children and children residing in substandard housing (Martin et al., 2021). Furthermore, this intervention can improve the health of older adults with respiratory diseases.
Some individuals are more vulnerable to the effects of an environmentally unhealthy or unsafe home. Children, whose bodies and systems are still developing, are particularly prone to negative impacts from exposure to contaminants. Older adults, who may have preexisting health conditions, may have weaker immune systems, and may spend more time indoors, can be more susceptible to respiratory and other disorders. Pregnant people can be exposed to indoor pollutants that affect fetal development, such as secondhand smoke. Individuals with chronic conditions, such as immune or respiratory disorders, are at a higher risk of exacerbations. Individuals with limited mobility due to disability, age, or aging may spend more time indoors and have difficulty relocating to a safer environment. Table 14.4 presents some examples of possible hazards inside the home.
| Type of Hazard | Potential Negative Health Effects |
|---|---|
| Biological Hazards | |
| Mold and fungi |
|
| Rodents (rats, mice) |
|
| Dust mites and cockroaches |
|
| Toxic Gases | |
| Radon |
|
| Carbon monoxide |
|
| Tobacco smoke |
|
| Toxic Substances | |
| Asbestos |
|
| Lead |
|
| Pesticides |
|
Due to the disproportionate impact of the home environment on children, it’s especially important for nurses to incorporate home environmental assessments when caring for the pediatric population. The Pediatric Environmental Home Assessment is an excellent tool for assessing the pediatric home environment, with a section for nursing observations. The National Center for Healthy Housing provides numerous interventions and resources focused on safe and healthy housing for all, especially the millions of Americans living in substandard housing. The passage of the Inflation Reduction Act in 2023 included substantial funding to improve efficiency and resilience in affordable housing and significant funding for research, development, and implementation (Goodwin & Jacobs, 2022).
Community Assessment
Community health assessments provide information about the potential, and real, environmental risks faced by individuals living, working, or recreating in a particular community. The assessment should include environmental health risks using online tools to identify potential exposures and types and levels of pollution using Envirofacts . While this data is critical, it is only part of the community assessment . Nurses can conduct a windshield survey to visually identify potential environmental risks, such as the location of industries, hazardous waste, dumps, major thoroughfares, pests, the use of pesticides, air quality, and housing conditions (see Creating a Healthy Community and Appendix A). In addition to observing environmental risks, a windshield survey should note areas that promote health in the community, such as parks, open spaces, gardens, and outdoor recreational areas. The University of Maryland School of Nursing and Environmental Health Center has developed the following Environmental Health Community Assessment tool focused on environmental health.
This scenario continues to follow Mr. Harper from earlier in this chapter. Read the scenario, and then respond to the questions that follow.
While assessing Mr. Harper’s home environment, Nurse Regis discovers that the house is adjacent to a mound of mining waste, raising concerns about the possible inhalation of particulate matter. Moreover, after hearing rumors that the community’s water supply might be contaminated, Mr. Harper now uses water hauled by his neighbor from a nearby stream. Mr. Harper points out the stream to Nurse Regis, who notes that rocks are tinged with red, a sign of acid mine drainage. Upon further assessment, Nurse Regis finds that Mr. Harper’s skin is reddened, dry, and itchy. When asked about the rash, Mr. Harper becomes irritable, stating he isn’t sure when the rash began and is more upset that he’s recently been having difficulty remembering things and easily becomes confused.
The nurse collaborates with a social worker from the county’s department of aging to arrange for an aide to assist Mr. Harper twice weekly, helping to keep his home dry and free of dust and bringing him a supply of bottled water to use until the community’s water is verified as safe.
- What further assessments should the nurse conduct given the suspicion of hazardous exposures?
- How should the nurse address Mr. Harper’s exposure to heavy metals in his daily life?
- As a public health nurse, what immediate actions would you take for Mr. Harper and his community? What resources would you use?


21.2.2: Chapter 2
Review Questions
1.
d.
Arsenic is heavy metal and will not clear by boiling, so purchasing water is the best choice.
2.
a.
Water does not contain any energy and is calorie free.
3.
b.
The Mediterranean diet is high in complex carbohydrates (fruits, vegetables, beans, legumes, nuts, and seeds) as well as fish, seafood, and poultry and includes moderate amounts of dairy products.
4.
a.
The individual who is lactose intolerant should consume lactose-free dairy products.
5.
d.
Omega-3 fatty acids play a role in heart health and are found in salmon, eggs, soybeans, flaxseed, and canola oil.
6.
d.
The client who is well hydrated will have pale or light-colored urine.
7.
c.
Soy is the only complete protein listed. Oats, barley, and wheat are incomplete proteins and do not include all essential amino acids.
8.
c.
Pasta with a plain red sauce is the lowest-fat item on the list and contains less than 3 g of fat per serving.
9.
a.
During exercise, circulating glucose is the first source of energy used. When this energy source is depleted, glycogen stored in skeletal muscle is used, followed by fat.
10.
b.
The client with stage 3 chronic kidney disease should consume no more than 0.6 g/kg of body weight daily. Therefore,
of protein daily.


11.8.2: Recycling and Composting
In 2018, the United States generated 292.4 million tons of MSW, and recycled or composted 94 million tons of it - amounting to about 32.1% of the total. While some other methods were also used to recover energy or create animal feed, over ½ of all waste still ended up in a landfill. While this may not seem like progress, the amount of MSW discarded in landfills has remained relatively constant since 1990 - in spite of population growth - while other methods like recycling and composting have grown (EPA, 2023a). While metals (like steel and aluminum), glass and paper products (including cardboard), are relatively easy to recycle, plastics are much less commonly recycled. Approximately 9% of the world’s plastic containers, bottles, bags and other materials are recycled; 50% end up in landfills, another 20% are mismanaged (burned or dumped, potentially ending up in lakes and rivers), and 0.5% end up in the ocean (Ritchie et al., 2023). See Fig. \(\PageIndex{1}\) below.
Plastic pollution is particularly hazardous because of the characteristics of plastic that make it so desirable. Plastic is durable, and doesn’t break down easily. It may take a plastic water bottle floating in the ocean nearly 450 years to decompose (Harris, 2023), broken down by UV rays into smaller and smaller pieces called microplastics. The Great Pacific Garbage Patch is really a misnomer because it’s not an island or “patch” of trash floating in the Pacific Ocean: much of the plastic pollution is microplastics, swirling around the ocean currents like a plastic soup (Evers, 2024). These microplastics can get into our food and water sources, be ingested by birds and fish, and make their way up the food chain into human tissues. Microplastics have been found in the human gastrointestinal tract and in placental tissue (Ragusa et al., 2021). We may even be breathing in microplastics in the air, which can get into lungs and eventually the bloodstream. Exposure to microplastics and the chemicals that make them could have profound effects on human health, particularly in the immune system response to plastic toxins, chronic inflammation, and a myriad of other subsequent health problems (Prata et al., 2020). The best way to manage plastic waste is not to rely on recycling, but to produce less of it in the first place.
Composting is another way to manage biodegradable waste such as food waste. In the U.S., it is estimated that 30-40% of the food supply ends up as waste - much of that at the retail or consumer level (USDA, n.d.). Food waste may include inedible food scraps such as eggshells or fruit rinds, but it also includes food that could have been consumed but perhaps was spoiled or uneaten. Not only does the food wasted cost energy to grow and transport, it also produces methane gas while decomposing in a landfill - contributing to GHG production and climate change. Food waste can be reduced at the retail and consumer levels by only producing and purchasing what is needed, donating leftover food and preventing spoilage. Composting is also a much better use of food waste, as it produces usable fertilizer for agricultural and landscaping purposes (EPA, 2015). While backyard composting can support a home garden, industrial or large-scale composting has much greater potential for managing food waste, yard waste, sludge and other agricultural or industrial wastes. Bacteria and fungi feed off of the waste products, creating heat which destroys undesirable microbes and weed seeds, and turns the solids into excellent fertilizer for plants. When those raw materials are chipped up into smaller pieces, combined in appropriate ratios, and well-aerated, the composting process can be completed more quickly and produce high-quality soil amendment (Sherman, 2020). As of 2022, California requires that organics be disposed of separately to recyclables and MSW in order to be composted or used to generate biofuel (CalRecycle, 2024).


4.21: Investing Time in the Research Process
Discuss the steps in the research process
This page discusses a general research process, one that is useful in a variety of organizations to support report writing. We borrow the process largely from social science, where the focus is answering a question or gaining insight about human affairs. The general research process is usually as follows:
- Determine a problem and define a question to answer.
- Find general background about your problem/question.
- Develop a research strategy to address any data, information or knowledge gaps. These gaps may be referred to as “sub-questions.”
- Conduct research.
- Collect, read, evaluate and write what you have learned.
- Cite the information you have found so that others will be able to follow your research trail.
Consider Martha’s case as a study or illustration of the above process. Martha is a junior analyst with The Human Fund, a business in Chicago specializing in selling local handicraft goods made by homeless families. The Human Fund supplies raw materials such as yarn, cloth, leather or other items, training homeless participants in their use and then providing a safe place to make clothing, bags, and other items. The organization has experienced fairly consistent growth in their three years of operation and has received excellent local press for its help to the city.
Martha’s boss directs her to study whether their work is benefiting families in the downtown area because the company’s leadership is considering whether to put more resources into that neighborhood. Martha considers her assignment and does the following:
- She determines her research question: “Is The Human Fund’s work helping homeless families in downtown Chicago?” Martha also considers that the business report’s central goal is not necessarily answering ONLY whether their organization is benefiting downtown Chicago already, but also whether The Human Fund should do more in downtown Chicago. She decides to proceed with her research question but tells herself to write up the report later in a way that will help the executives make their decision about whether to expand operations downtown.
- She sets aside about 10–20 hours for general online reading/fact-finding, primarily from major newspapers and social services websites. During her general background reading, she collects various facts, figures and other data. Most of this data is quantifiable data, or data that has numbers associated with it. For example, she learns that various charities and the Chicago city government estimate that around 2,000 people are homeless downtown. There is some mention of The Human Fund in downtown-oriented press, but there’s nothing that shows their specific impact. She identifies various gaps in her data and determines she will need to do further research outside the office.
-
Her largest gap in data is hearing from the downtown homeless themselves. She could not find sources that discussed the downtown homeless experience or had any quotes or other qualitative (non-numeric) data. She decides to visit with several families downtown over the course of a week. She plans to talk to as many families as she can. To frame her interaction, she develops three sub-questions:
- Do you know about The Human Fund and its mission?
-
Have you sold goods through The Human Fund?
- If yes, has the The Human Fund helped you?
- Are you still working with us (The Human Fund)?
- Would you like to sell goods through the Human Fund?
Martha’s technique is a structured interview or survey. She has structured questions that will yield a fairly straightforward and closed (yes/no) type answer. While interviewing, she can make a note of how many people she talks to, how many answer a certain way, and based on other data she found in her general reading—particularly the total number of estimated homeless in downtown Chicago—she can gain an understanding of The Human Fund’s current impact, and possible expansion.
-
Martha visits with several homeless families downtown, and determines the following:
- 25 percent of her respondents (74 families asked over a week) know about the Human Fund.
-
Of the 19 families that have heard of the Human Fund, 10 have made and sold goods with The Human Fund.
- Of the 10 families that have made and sold goods through the Human Fund, 9 said they benefited from the help.
- Of the 9 that said they benefited from the help, all 9 families plan to continue the interaction.
- Of the 55 families she polled who had not heard of The Human Fund, 25, or 45 percent, expressed an interest in learning more.
- Martha begins writing up her report. In the report, she clearly outlines her research question, the background reading, the gaps in data she found in the background reading, the field research and sub-questions, and the data gathered from the fieldwork.
- Martha is careful to cite all of her work. For her background reading, she hyperlinks to various newspapers or other sources, and for her fieldwork, she gives general data on whom she talked to (e.g., “family of four, sleeping on the streets off of Lake Shore Drive, dad’s name is George).
The above process is one possible way to conduct research. It reflects the general approach to social science inquiry, which seeks to answer a specific (as specific as possible) question about a human circumstance. In Martha’s case, she will now need to develop a report that quickly and concisely details what she found. Most importantly, Martha needs to consider what type of informed recommendation she should make to her boss.


2.6: Regional Topography and Biodiversity
The previous examples have shown how global factors can influence biodiversity, but it is important to note that regional factors on a smaller spatial scale than the entire globe can also strongly influence biodiversity. In this section, we will consider regional impacts of topography , the physical structure of the landscape, including mountains, valleys, etc. Consider, for example, the complex topography that results from California’s numerous mountain ranges (Fig 2.6.1). Air masses moving across the California landscape must rise to go over these mountain ranges. As they rise, the air masses cool, expand, and drop much of their moisture as rainfall on the ‘front’ or windward side of the mountain range. When the air masses fall on the ‘back’ or leeward side of the mountain range, they are dry and so rainfall in this area is minimal. This process is called the rainshadow effect because the leeward side of the mountain ranges are ‘shadowed’ from receiving rainfall by the windward side of the range. Which side of a mountain range is the windward or leeward side depends on which direction the air masses are moving.
In Northern California, air masses generally come from the Pacific Ocean and move east over the landscape (Fig 2.6.2). These air masses first rise over the coast ranges and deposit some rainfall on the western sides of these mountains. The central valley is in the rainshadow of the coast ranges and so receives less rainfall. The air masses then rise over the Sierra Nevada mountains, which are much taller than the coast ranges, and so the air masses deposit their remaining moisture on the western side of these mountains. Consequently, the great basin of Nevada is in the rainshadow of the Sierra Nevadas and is a desert, receiving very minimal rainfall. This pattern can be clearly seen in maps of the average annual precipitation of northern California (Fig 2.6.2)
The rainshadow effect influences biodiversity due to the influence it exerts on climate on the windward and leeward sides of mountains. The pattern of precipitation and elevation across a topographically complex landscape like northern California leads to differences in the plant and animal communities that inhabit these areas. For example, the western windward side of the coast ranges are famous for their redwood forests, while the eastern leeward sides are primarily oak forest. Similarly, the western windward side of the Sierra Nevadas are primarily mixed pine and fir forest, while the eastern leeward side contains a mix of juniper and pine woodlands, sagebrush scrub, and alkaline scrub systems as the landscape transitions to the desert flats of western Nevada. In both cases, the plant communities on the leeward side are more drought adapted than the communities on the windward side. The central valley between the coast ranges and Sierra Nevadas was historically grassland, though much of it has now been converted to agricultural and urban landscapes.