Measurement of Systemic Arterial Pressure

Both systolic and diastolic blood pressure are readily measured in human beings with the use of a sphyg-momanometer. An inflatable cuff is wrapped around the upper arm, and a stethoscope is placed in a spot on the arm just below the cuff and beneath which the major artery to the lower arm runs.

The cuff is then inflated with air to a pressure greater than systolic blood pressure (Figure 14-37). The high pressure in the cuff is transmitted through the tissue of the arm and completely compresses the artery under the cuff, thereby preventing blood flow through the artery. The air in the cuff is then slowly released, causing the pressure in the cuff and on the artery to drop. When cuff pressure has fallen to a value just below the systolic pressure, the artery opens slightly and allows blood flow for a brief time at the peak of systole. During this interval, the blood flow through the partially compressed artery occurs at a very high velocity because of the small opening and the large pressure difference across the opening. The high-velocity blood flow is turbulent and, therefore, produces vibrations that can be heard through the stethoscope. Thus, the pressure, measured on the

PART THREE Coordinated Body Functions

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART THREE Coordinated Body Functions

No sound; cuff pressure above systolic pressure; artery completely occluded during cycle

Cuff pressure just below systolic pressure; first sounds heard soft, tapping, and intermittent

Cuff pressure Arterial pressure

Sounds loud, tapping, and intermittent

Low muffled sound lasting continuously

Cuff pressure below diastolic pressure; thus vessel is always open; no turbulence, no sound

Sounds loud, tapping, and intermittent

Low muffled sound lasting continuously

Arterial Pressure And Turbulent Flow

Cuff pressure Arterial pressure

Period of turbulent flow through constricted vessel

Period of turbulent flow through constricted vessel

Time

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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