Arterial Pulse



Pulse

When someone 'takes a pulse,' he or she palpates an artery (for example, the radial artery) and feels the expansion of the artery occur in response to the beating of the heart; the pulse rate is thus a measure of the cardiac rate. The expansion of the artery with each pulse occurs as a result of the rise in blood pressure within the artery as the artery receives the volume of blood ejected by a stroke of the left ventricle.

Since the pulse is produced by the rise in pressure from dia-stolic to systolic levels, the difference between these two pressures is known as the pulse pressure. A person with a blood pressure of 120/80 (systolic/diastolic) would therefore have a pulse pressure of 40 mmHg.

Pulse pressure = systolic pressure - diastolic pressure

Pulse As the femoral artery can often be palpated through the skin, it is often used as a catheter access artery. From it, wires and catheters can be directed anywhere in the arterial system for intervention or diagnostics, including the heart, brain, kidneys, arms and legs. Pulse pressure: the difference between diastolic blood pressure (DP) and systolic blood pressure (SP) of the heart cycle (SP - DP) Normally: 30–40 mm Hg; Directly proportional to SV and inversely proportional to arterial compliance. Low/narrow pulse pressure due to ↓ SV (e.g., advanced congestive heart failure, shock, cardiac tamponade. Indirect measurement through oximetry (SpO 2) is a fast, easy, and noninvasive way of measuring blood oxygen saturation without the need for invasive and expensive arterial blood gas sampling. Nonin provides the pulse oximetry tools necessary for accurate and reliable SpO 2 readings.

No sounds

Cuff pressure = 140

Cuff pressure = 120

Systolic pressure = 120 mmHg

Points

Sounds at every systole

Cuff pressure = 100

Last Korotkoff sounds

Cuff pressure = 80

Diastolic pressure = 80 mmHg

Blood pressure = 120/80

■ Figure 14.29 The blood flow and Korotkoff sounds during a blood pressure measurement. When the cuff pressure is above the systolic pressure, the artery is constricted. When the cuff pressure is below the diastolic pressure, the artery is open and flow is laminar. When the cuff pressure is between the diastolic and systolic pressure, blood flow is turbulent and the Korotkoff sounds are heard with each systole.

Cuff pressure

No flow

Arterial Pulses Are A Physical Expression Of

Turbulent flow

Systole

Blood pressure

Diastole

■ Figure 14.30 The indirect, or auscultatory, method of blood pressure measurement. The first Korotkoff sound is heard when the cuff pressure is equal to the systolic blood pressure, and the last sound is heard when the cuff pressure is equal to the diastolic pressure. The dashed line indicates the cuff pressure.

Cardiac Output, Blood Flow, and Blood Pressure

130 120 110 100

Blood flows during systole only (turbulent flow)

14 mmHg

20 mmHg

Snapping sounds

Murmurs

Relative intensity of sounds

5 mmHg

5 mmHg

■ Figure 14.31 The five phases of blood pressure measurement.

Not all phases are heard in all people. The cuff pressure is indicated by the falling dashed line.

At diastole in this example, the aortic pressure equals 80 mmHg. When the left ventricle contracts, the intraventricular pressure rises above 80 mmHg and ejection begins. As a result, the amount of blood in the aorta increases by the amount ejected from the left ventricle (the stroke volume). Due to the increase in volume, there is an increase in blood pressure. The pressure in the brachial artery, where blood pressure measurements are commonly taken, therefore increases to 120 mmHg in this example. The rise in pressure from diastolic to systolic levels (pulse pressure) is thus a reflection of the stroke volume.

Clinical Investigation Clue

Remember that Charlie's pulse was weak.

What is the sequence of effects that caused Charlie's pulse to be weak?

The mean arterial pressure represents the average arterial pressure during the cardiac cycle. This value is significant because it is the difference between this pressure and the venous pressure that drives blood through the capillary beds of organs. The mean arterial pressure is not a simple arithmetic average because the pe riod of diastole is longer than the period of systole. Mean arterial pressure can be approximated by adding one-third of the pulse pressure to the diastolic pressure. For a person with a blood pressure of 120/80, for example, the mean arterial pressure would be approximately 80 + 1/3 (40) = 93 mmHg.

Mean arterial pressure = diastolic pressure + 1/3 pulse pressure

Arterial Pulse Flow

A rise in total peripheral resistance and cardiac rate increases the diastolic pressure more than it increases the systolic pressure. When the baroreceptor reflex is activated by going from a lying to a standing position, for example, the diastolic pressure usually increases by 5 to 10 mmHg, whereas the systolic pressure either remains unchanged or is slightly reduced (as a result of decreased venous return). People with hypertension (high blood pressure), who usually have elevated total peripheral resistance and cardiac rates, likewise have a greater increase in diastolic than in systolic pressure. Dehydration or blood loss results in decreased cardiac output, and thus also produces a decrease in pulse pressure.

An increase in cardiac output, by contrast, raises the systolic pressure more than it raises the diastolic pressure (although both pressures do rise). This occurs during exercise, for example, when the blood pressure may rise to values as high as 200/100 (yielding a pulse pressure of 100 mmHg).

Test Yourself Before You Continue

1. Describe the relationship between blood pressure and the total cross-sectional area of arteries, arterioles, and capillaries. Describe how arterioles influence blood flow through capillaries and arterial blood pressure.

Explain how the baroreceptor reflex helps to compensate for a fall in blood pressure. Why will a person who is severely dehydrated have a rapid pulse?

Describe how the sounds of Korotkoff are produced and explain how these sounds are used to measure blood pressure. Define pulse pressure and explain the physiological significance of this measurement.

Arterial Pulse Sites

Continue reading here: Hypertension Shock and Congestive Heart Failure

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As the left ventricle ejects blood into the aorta, the aortic pressure increases. The greater the stroke volume, the greater the change in aortic pressure during ejection. The maximal change in aortic pressure during systole (from the time the aortic valve opens until the peak aortic pressure is attained (see Cardiac Cycle) represents the aortic pulse pressure, which is defined as the systolic pressure minus the diastolic pressure. For example, if the systolic pressure is 130 mmHg and the diastolic pressure is 85 mmHg, then the pulse pressure is 45 mmHg.

Arterial Pulse Points

Pulse Pressure = Systolic Pressure − Diastolic Pressure

The rise in aortic pressure from its diastolic to systolic value is determined by the compliance of the aorta as well as the ventricular stroke volume. In the arterial system, the aorta has the highest compliance, due in part to a relatively greater proportion of elastin fibers versus smooth muscle and collagen. This serves the important function of dampening the pulsatile output of the left ventricle, thereby reducing the pulse pressure (systolic minus diastolic arterial pressure). If the aorta were a rigid tube, the pulse pressure would be very high. Because the aorta is compliant, as blood is ejected into the aorta, the walls of the aorta expand to accommodate the increase in blood volume. As the aorta expands, the increase in pressure is determined by the compliance of the aorta at that particular range of volumes. The more compliant the aorta, the smaller the pressure change during ventricular ejection (i.e., smaller pulse pressure) (see figure). Therefore, aortic compliance is a major determinant, along with stroke volume, of the pulse pressure.

Summary:

Arterial Pulse Pressure

  • A highly compliant aorta (i.e., less stiff, normal aorta) has a smaller pulse pressure for a given stroke volume into the aorta than a stiff, low compliant aorta.
  • A larger stroke volume (not shown in the figure) produces a larger pulse pressure at any given compliance.
  • Aortic compliance decreases with age due to structural changes, thereby producing age-dependent increases in pulse pressure.
  • For a given stroke volume, compliance determines pulse pressure and not mean aortic pressure.
  • However, because vessels display dynamic compliance, increasing the rate of ventricular ejection (as occurs with increased ventricular inotropy) will increase the pulse pressure compared to the same volume ejected at a lower rate.

Arterial Pulse Definition

Revised 12/7/16