Health Information
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Blood Pressure

Blood pressure is the term typically used to describe a wave-like pressure against blood vessel walls as blood pulses through systemic arteries in rhythm with the heartbeat. Each time the ventricles of the heart contract, which in the average adult is 60 to 80 times per minute, the blood in the left ventricular chamber is ejected into the arterial system.

This frequent ejection initiates a wave of pulsating blood through the arteries. The peak of the wave represents the maximum pressure exerted on arterial walls with each heartbeat. This is called systolic blood pressure. The trough of the wave represents the minimum pressure on arterial walls. This is called diastolic blood pressure.

Measurement

When this blood pressure wave is measured, it is recorded as systolic blood pressure over diastolic blood pressure. The reading below indicates that the systolic pressure is 120 mmHG (millimeters of mercury) and the diastolic pressure is 80 mmHG.

Blood Pressure     120 / 80

Stethoscope and Sphygmomanometer

Blood pressure is measured with a stethoscope and a sphygmomanometer. The stethoscope (right) is a y-shaped tubing which connects earpieces at one end to a rounded diaphragm or bell at the other. The bell augments the pulsing sounds over the artery.

The sphygmomanometer consists of an inflatable cuff connected by tubing to an air bulb and release screw, and to a manometer or pressure gauge. The mercury sphygmomanometer (left) is an extremely accurate gauge of blood pressure and has been traditionally used in healthcare settings. Thus, blood pressure has been measured in millimeters of mercury (mmHG).

The aneroid sphygmomanometer, such as the one on your right, is highly portable and accurate. It is now widely used and is particularly useful in the homecare setting. *

Procedure

The artery most frequently used to measure blood pressure is the brachial artery which overlies the inner aspect of the elbow. After the inflatable cuff is wrapped and secured on the upper arm, the listener places the bell of the stethoscope over the brachial artery and pumps air into the cuff. As cuff pressure rises, it occludes arterial blood flow. When air is slowly released and cuff pressure falls, the peak pressure within the artery overcomes cuff pressure and blood spurts through the artery.

This first pressure-sound is heard as a sequence of thuds and can be seen on the manometer as the mercury level falls. This is recorded as systolic blood pressure. As air pressure within the cuff continues to fall, the pulsing sounds can still be heard. But when the trough in the wave is reached, the sounds change to become faint or indistinct. This is recorded as diastolic blood pressure.