• Choose a category
• All
• Classic-Fiction

By Root 1632 0

heart beat following the alternating expansion and recoil of arteries during each cardiac cycle (Marieb and Hoehn 2010). A pulse can be palpated in any artery that lies close to the surface of the body. The radial artery at the wrist is easily accessible and therefore the radial pulse is frequently used, but there are several other clinically important arterial pulse points, such as the carotid, femoral and brachial plexus (Marieb and Hoehn 2010) (see Figure 12.3).

Figure 12.3 Pulse points.

Reproduced from Tortora and Derrickson (2009).

Anatomy and physiology

In health, the arterial pulse is one of the measurements used to assess the effects of activity, postural changes and emotions on the heart rate. In ill health, the pulse can be used to assess the effects of disease, treatments and response to therapy. Each time the heart beats, it pushes blood through the arteries. The pumping action of the heart causes the walls of the arteries to expand and distend, causing a wavelike sensation which can then be felt as the pulse (Marieb and Hoehn 2010). The pulse is measured by lightly compressing the artery against firm tissue and by counting the number of beats in a minute.

The pulse is palpated to note the following:

rate

rhythm

amplitude.

Rate

The normal pulse rate varies in different client groups as agerelated changes affect the pulse rate (Weber and Kelley 2003). The approximate range is illustrated in Table 12.1.

Table 12.1 Normal pulse rates per minute at various ages

Age Approximate range

1 week–3 months 100–160

3 months–2 years 80–150

2–10 years 70–110

10 years–adult 55–90

The pulse may vary depending on the posture of an individual. For example, the pulse of a healthy man may be around 66 beats per minute when he is lying down; this increases to 70 beats per minute when sitting up and 80 beats per minute when he suddenly stands (Marieb and Hoehn 2010).

The rate of the pulse of an individual with a healthy heart tends to be relatively constant. However, when blood volume drops suddenly or when the heart has been weakened by disease, the stroke volume declines and cardiac output is maintained only by increasing the rate of heart beat.

Cardiac output (CO) is the amount of blood pumped out by each ventricle in 1 minute. It is the product of heart rate (HR) and stroke volume (SV). Stroke volume is defined as the volume of blood pumped out by one ventricle with each beat. Using normal resting values for heart rate (75 beats/minute) and stroke volume (70 mL/beat), the average adult cardiac output can be calculated:

The heart rate and hence pulse rate are influenced by various factors acting through neural, chemical and physically induced homoeostatic mechanisms (see Figure 12.4 for factors that increase cardiac output).

Figure 12.4 Factors that increase cardiac output.

Reproduced from Tortora and Derrickson (2009).

Neural changes in heart rate are caused by the activation of the sympathetic nervous system which increases heart rate, while parasympathetic activation decreases heart rate (Patton and Thiobodeau 2009).

Chemical regulation of the heart is affected by hormones (adrenaline and thyroxine) and electrolytes (sodium, potassium and calcium) (Patton and Thiobodeau 2009). High or low levels of electrolytes, particularly potassium, magnesium and calcium, can cause an alteration in the heart’s rhythm and rate.

Other factors that influence heart rate are age, sex, exercise and body temperature (Marieb and Hoehn 2010).

Tachycardia

This is an abnormally fast heart rate, over 100 beats per minute in adults. It may result from an elevated body temperature, stress, certain drugs or heart disease (Marieb and Hoehn 2010). Persistent tachycardia is considered pathological because tachycardia occasionally promotes fibrillation (Marieb and Hoehn 2010).

Bradycardia

This is a heart rate slower than 60 beats per minute (Marieb and Hoehn 2010). It may be the result of a low body temperature, certain drugs or parasympathetic nervous system activation. It is also found in fit athletes when physical and