7.1 Indicators of Physiologic Functioning

Age-Related Variations in Normal Vital Signs

One potential age-related change to vital signs that many people may already be familiar with is high blood pressure, or hypertension. As people grow older, the risk for hypertension increases, as does the risk for other heart problems such as tachycardia (fast heart rate), bradycardia (slow heart rate), or arrhythmia (abnormal heart rhythm). Environmental and lifestyle influences also play a part in the development of diseases like hypertension. Factors such as smoking, drinking, and dietary choices have direct effects on the cardiovascular system and therefore heart rate and blood pressure.

Heart rate is inversely proportional to age; rates are faster at a younger age and get progressively slower as we get older (Ostchega et al., 2011). This can be due to arrhythmias, like tachycardia; comorbidities, like hypertension or atherosclerosis; or may be naturally occurring from the aging process. A resting heart rate of 120 bpm in a newborn is acceptable; however, a resting heart rate this fast is problematic in an adolescent or adult. Knowing these age-related variations is key for the nurse to recognize what heart rate is appropriate for their patient and identify the correct course of action if not appropriate. See Table 7.1 for a general range of normal vital sign measurements across the life span.

While the range of normal temperatures generally stays the same throughout the life span, it does become harder for the body to regulate temperature as it ages. Loss (or gain) of body fat and hormonal changes can affect how comfortably warm or cool the body may feel, resulting in the need to adjust clothing layers or environmental temperature when possible.

Knowing normal age-related variations as well as a patient’s medical history and aspects of their family history can help give the nurse a better understanding of their patients’ vital signs and changes that may occur through the course of their care for them.

When to Assess Vital Signs

In general, healthcare facilities set their own guidelines as to when vital sign should be measured, and these guidelines depend on the acuity of the patients in the facility. Acute care facilities, such as hospitals, usually have a regular schedule of assessing vital signs every four to eight hours, whereas critical care units within the hospital tend to measure vital signs every hour or even every fifteen to thirty minutes depending on patient acuity. Patients who are postsurgical, postprocedure, or clinically unstable will also have their vital signs checked frequently; some of these critical patients will have equipment that provides a constant monitoring of their vital signs to the nurse and medical providers. In contrast, ambulatory facilities, such as clinics and urgent care centers, or outpatient departments, such as physical and occupational therapy, will usually measure vital signs at the start of a patient visit. Assisted living facilities, such as nursing homes, with patients who live there for extended periods of time, may measure vital signs once every twenty-four hours or as necessary.

In addition to assessing vital signs as per facility guidelines, the nurse is empowered to take vital signs when necessary. For instance, if a patient says they are short of breath and they appear pale and sweaty, or complain of a racing heart or a pounding headache, the nurse can recheck the patient’s vital signs on the spot. The information gained from the reported change in patient status and correlated in vital sign measurements is invaluable in deciding the next steps of action and treatment decisions.

In acute care facilities and long-term care centers, such as hospitals and nursing homes, the measurement of vital signs is often delegated to unlicensed assistive personnel, such as nurse’s aides or patient care technicians. Regardless of who takes the vital signs, the registered nurse is ultimately responsible for taking action should there be any issues.

Mechanisms of Heat Transfer

Heat is transferred from areas of higher temperatures to lower temperatures. The body utilizes four types of heat transfer to cool the body when necessary. These mechanisms are evaporation radiation, convection, and conduction (Osilla, 2023). The transfer of heat through dissipation of sweat from the skin, thus cooling the body, is called evaporation. The loss of heat through indirect contact with cooler nearby surfaces or objects, such as when walking outside during the winter without a coat, is called radiation. When cooler air surrounds the body, such as when entering a room with air-conditioning, and the body cools, convection occurs. When skin encounters a cooler object (such as an ice pack), thus lowering its temperature, conduction occurs. On the other hand, shivering and teeth chattering when the body’s temperature is lower than normal is an attempt by the hypothalamus to generate heat.

Factors Affecting Temperature

Sometimes internal or external factors will overrule the body’s homeostatic mechanisms, and the body cannot regulate its temperature enough on its own. This can cause abnormal body temperature. A body temperature greater than 100.4°F (38°C) is called pyrexia, or fever (Cleveland Clinic, 2023). A patient with a fever is considered febrile. When the patient’s body temperature returns to normal after a fever, the patient is considered afebrile, or without fever.

Factors that affect temperature include the following:

• Age. Studies have shown that older adults tend to have lower baseline body temperatures. This can be due to natural age-related changes in the body, such as loss of insulating muscle mass and/or body fat.
• Environment. Changes in the environment can affect a patient’s temperature, especially if they are older and cannot thermoregulate as well anymore due to reduced muscle mass and body fat.
• Hormones. Recent research has shown that the hormonal changes that accompany menopause can cause a reduction of core body temperature (Neff et al., 2016). The decreased levels of estrogen in the body cause the hypothalamus to become more sensitive to minor changes in body temperature. When the hypothalamus “thinks” the body is too warm, it sends messages to thermoregulate, which is why menopausal women often shiver after a hot flash.
• Disease states. The body’s immune system response is frequently responsible for increases in core body temperature. Research has shown that the systemic inflammation often accompanying a fever is an evolutionary response to infection (Evans et al., 2015). A fever is a sign the body is out of its homeostatic balance and that the normal methods of thermoregulation are unable to return the body to its afebrile state. The resulting inflammation is the body’s attempt to fight what is likely an invading pathogen, and this process raises the body’s core temperature. From an evolutionary perspective, a fever also indicates a person should let their body heal and regain homeostasis. When we run a fever, often our instinct is to rest or sleep.

Of course, these factors are not definitive. Body temperature provides information at a specific moment, and the nurse should consider all factors when assessing a patient. The nurse should always look at the whole patient, think critically, and avoid jumping to conclusions based on temperature alone.

Physiology of the Pulse

During a normal heartbeat, blood flows from the right atrium into the right ventricle, then is pushed out to the lungs’ vasculature where it is oxygenated by the pulmonary system. The newly oxygenated blood returns to the heart via the left atrium. It progresses into the left ventricle and from there is pushed out to the rest of the body. When the heart is relaxed, it allows blood to fill into it, and when it contracts, it pushes blood into the next chamber from the atrium to the ventricles, and from the ventricles out into the arteries. The right ventricle pushes blood into the pulmonary artery and toward the lungs to be oxygenated, and the left ventricle pushes blood into the aorta that then distributes it throughout the rest of the body.

Pulse refers to the pressure wave that expands and recoils arteries when the left ventricle of the heart contracts. It is palpated at many points throughout the body. The most common locations to assess pulses as part of vital sign measurement include radial, brachial, carotid, and apical areas (Figure 7.14).

Factors Affecting Pulse

There are factors that can affect a patient’s pulse. These factors can affect the pulse rhythm, pulse rate, pulse force, and pulse equality. It is important to include these characteristics in the assessment documentation.

A normal pulse has a regular rhythm, meaning the frequency of the pulsation felt by your fingers is an even tempo with equal intervals between pulsations. For example, if you compare the palpation of pulses to listening to music, it follows a constant beat at the same tempo that does not speed up or slow down. Some cardiovascular conditions, such as atrial fibrillation, cause an irregular heart rhythm.

The pulse force is the strength of the pulsation felt on palpation. Pulse force can range from absent to bounding. The volume of blood, the heart’s functioning, and the arteries’ elastic properties affect a person’s pulse force. Pulse force is documented using a four-point scale:

• 3+: full, bounding
• 2+: normal/strong
• 1+: weak, diminished, thready
• 0: absent/nonpalpable

A comparison of the pulse forces on both sides of the body is referred to as pulse equality. For example, a nurse often palpates the radial pulse on a patient’s right and left wrists at the same time and compares if the pulse forces are equal. However, the carotid pulses should never be palpated at the same time because this can decrease blood flow to the brain. Pulse equality provides data about medical conditions such as peripheral vascular disease and arterial obstruction.

Factors Affecting Respiratory Status

Many factors can affect the quality, rhythm, and rate of respirations. The quality of a patient’s respirations can be affected by acid-base imbalances, low oxygen levels, carbon dioxide levels, or damage to any component of the respiratory system. The following are common factors that can affect respiratory status:

• Age. Lungs become less elastic with age, decreasing respiratory strength and room in the lungs for gas exchange. This can increase the work of breathing and prevent a person from having a strong, productive cough for airway clearance.
• Activity level. Physical activity and exercise make the lungs more adept at expanding and recoiling. A person who exercises frequently or regularly meditates and does deep breathing develops lungs that constantly stretch and contract. Their lungs are conditioned to this frequent expansion and contraction and become more efficient. Conversely, a person who is mostly sedentary does not have lungs that are conditioned to take the deep breaths required with strenuous physical activity, which is why a sedentary person is out of breath after strenuous physical activity.
• Disease states. Diseases that specifically affect the lungs include chronic obstructive pulmonary disease (COPD), asthma, pneumonia, and COVID-19, among others. The course and severity of these diseases varies greatly from person to person. Because of this, it is always important to consider how a patient’s current or past medical histories can affect respiratory function.
• Environment. Factors in a person’s surroundings can affect their respiratory status. For example, visiting places at high altitudes, such as Colorado or Peru, can affect respiratory function due to the thinner atmosphere and less available oxygen. This can negatively affect a person’s oxygenation status and respirations, as the body attempts to maintain homeostasis. Pollution is another environmental factor that can negatively affect a person’s oxygenation and respirations. Some jobs with poor air quality (mining, factories, military, construction) can also have deleterious harmful effects on the lungs, which can affect a person’s respiratory status.
• Lifestyle. Damaging lifestyles and behaviors such as smoking or vaping introduce harmful toxins and pollutants into the lungs that have been proven to negatively affect a person’s respiratory health. Multiple research studies have ascertained that smoking and vaping cause significant health risks due to the chemicals brought into the body, such as acetaldehyde, formaldehyde, and acrolein (American Lung Association, 2023).
• Emotions. Pain, anxiety, excitement, fear, and other emotions can affect a person’s respiratory status. A heightened emotional state can cause a person to hyperventilate or breathe rapidly or deeply. Hyperventilation causes low levels of CO₂ in the blood and can make a person feel lightheaded, dizzy, short of breath, or even faint. This is not uncommon and often resolves once the person begins to breathe normally.

Factors Affecting Oxygen Saturation

Oxygenation is affected by many factors that are interconnected with other vital signs; thus, anything that affects one of the other vital signs can also affect oxygen saturation. Lung diseases such as COPD and asthma will affect oxygen saturation; pain and anxiety can affect it as well. If heart rate or respirations are abnormal, oxygen saturation may be affected as well.

Cold limbs, poor circulation from peripheral vascular disease, and certain blood disorders, such as sickle cell disease, can give a falsely low reading. A patient can also have a falsely low oxygen saturation reading if the oxygen probe is incorrectly placed or there is fingernail polish on the finger being used.

Physiology of Blood Pressure

When systemic arterial blood pressure is measured, it is recorded as a ratio of two numbers expressed as systolic pressure over diastolic blood pressure (e.g., 120/80, which is a normal adult blood pressure). The systolic blood pressure is the higher value (typically around 120 mmHg) and reflects the arterial pressure resulting from the ejection of blood during ventricular contraction, or systole. The diastolic blood pressure is the lower value (usually about 80 mmHg) and represents the arterial pressure of blood during ventricular relaxation, or diastole (Figure 7.4). Because of the physiology of the heart, the systolic pressure will never be lower than the diastolic pressure.

Figure 7.4 The combination of cardiac muscle contraction and relaxation results in (a) systolic and (b) diastolic blood pressure, which is the metric healthcare providers use called blood pressure. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

The difference between the systolic pressure and the diastolic pressure is the pulse pressure. For example, an individual with a systolic pressure of 120 mm Hg and a diastolic pressure of 80 mm Hg would have a pulse pressure of 40 mm Hg. Generally, a pulse pressure should be at least 25 percent of the systolic pressure.

The mean arterial pressure (MAP) represents the “average” pressure of blood in the arteries, that is, the average force driving blood into vessels that serve the tissues. A mean is a statistical concept (also known as an average) and is calculated by taking the sum of the values divided by the number of values. Although MAP can be complicated to measure directly and calculate accurately, it can be approximated by adding the diastolic pressure to one-third of the pulse pressure, or systolic pressure minus the diastolic pressure. See this calculation:

Normally, MAP falls within the range of 70 to 110 mm Hg. If the value falls below 60 mm Hg for an extended time, blood pressure will not be high enough to ensure circulation to and through the tissues, which results in ischemia, or insufficient blood flow.

Factors Affecting Blood Pressure

There are many factors that affect a person’s blood pressure, and the mechanics of these factors as they relate to blood pressure and the heart are discussed in Chapter 19 Oxygenation and Perfusion. This discussion focuses on the various internal and external factors that can affect blood pressure readings:

• Emotional states. Heightened emotions such as anger, sadness, fear, and anxiety can increase a person’s heart rate, which will accordingly increase their blood pressure. In situations such as this, relieving the emotional distress can often alleviate the high blood pressure.
• Disease states. Obesity, high cholesterol, coronary artery disease, and diabetes all affect the cardiovascular system and therefore will also affect blood pressure readings. Sometimes, chronic kidney disease or lupus can alter blood pressure and perfusion.
• Social and dietary habits. Smoking, excessive alcohol, caffeine, and sodium consumption can all increase the risk of hypertension.
• Medications. Patients who have heart arrhythmias, such as persistent tachycardia, at baseline can be put on a medication called a beta blocker, which slows their heart rate; this will also affect their blood pressure.

A low pulse pressure may occur, for example, in patients with a low stroke volume, which may be seen in congestive heart failure, stenosis of the aortic valve, or significant blood loss following trauma. In contrast, a high or wide pulse pressure is common in healthy people following strenuous exercise, when their resting pulse pressure of 30 to 40 mm Hg may increase temporarily to 100 mm Hg as stroke volume increases. A persistently high pulse pressure at or above 100 mm Hg may indicate excessive resistance in the arteries and can be caused by a variety of disorders. Chronic high resting pulse pressures can degrade the heart, brain, and kidneys and warrant medical treatment.

A condition called hypoxia, inadequate oxygenation of tissues, commonly accompanies ischemia. The term hypoxemia refers to low levels of oxygen in systemic arterial blood. Neurons are especially sensitive to hypoxia and may die or be damaged if blood flow and oxygen supplies are not quickly restored.