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Blood Pressure Measurement

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Indirect blood pressure measurement for a systolic or diastolic blood pressure is accomplished by making use of a true Korotkov sound determination. When three or four Korotkov sound signals are found in four successive heart pulses of a body, each of the three or four Korotkov sound signals is determined as a true Korotkov sound signal. A cuff pressure existing when the first true Korotkov sound appears is determined as a systolic blood pressure. Another cuff pressure existing when the last true Korotkov sound signal appears is determined as a diastolic blood pressure. The last true Korotkov sound signal is determined by counting three heart pulses unaccompanied by no Korotkov sound signals following the detection of the last true Korotkov sound appearance. 20

The peak pressure in the arteries during the cardiac cycle is the systolic pressure, and the lowest pressure (at the resting phase of the cardiac cycle) is the diastolic pressure. Typical values for the arterial blood pressure of a resting, healthy adult are approximately 120 mmHg systolic and 80 mmHg diastolic (written as 120/80 mmHg), with large individual variations. 48

If the cause of the increased systemic tension is an arterial fibrosis, sooner or later the heart will become involved in this general condition, and a chronic myocarditis is likely to result. If, on the other hand, there is a continuous low systemic arterial blood pressure, the circulation is always more or less insufficient, nutrition is always imperfect, and the physical ability of the individual is below par. It is evident, therefore, that an abnormally high blood pressure is of serious import, its cause must be studied, and effort must be made to remove as far as possible the cause. On the other hand, a persistently low blood pressure may be of serious import, and always diminishes physical ability. If possible, the cause should be determined, and the condition improved. 31

As the blood is pumped through the vessels a turbulence is heard. These sounds are created by turbulence as the blood begins to flow through the arteries after the blood pressure cuff has temporarily stopped the flow by the pressure exerted as it was inflated. When the sound is first heard, this is the systolic pressure; and when the sound ceases as the turbulence ends, the diastolic pressure is determined. 15

Most often, arterial blood pressure is measured manually using a sphygmomanometer. This is an inflatable (Riva Rocci) cuff placed around the upper arm, at roughly the same vertical height as the heart in a sitting person, attached to a manometer. The cuff is inflated until the artery is completely occluded. Listening with a stethoscope to the brachial artery at the elbow, the examiner slowly releases the pressure in the cuff. When blood flow barely begins again in the artery, a "whooshing" or pounding sound (first Korotkoff sound) is heard. The pressure is noted at which this sound began. This is the systolic blood pressure. The cuff pressure is further released until no sound can be heard (fifth Korotkoff sound). This is the diastolic blood pressure. 48

This requires, at the very least, an inflatable cuff with a pressure gauge (sphygmomanometer). Wind the cuff round the arm (which should be at about heart level) and inflate it to a pressure higher than the expected blood pressure. Then deflate the cuff slowly. With a stethoscope, listen over the brachial artery. When the cuff reaches systolic pressure, a clear tapping sound is heard in time with the heart beat. As the cuff deflates further, the sounds become quieter, but become louder again before disappearing altogether. The point at which the sounds disappear is the diastolic pressure. If you have no stethoscope, the systolic blood pressure can be found by palpating the brachial artery and noting the pressure in the cuff at which it returns. 7

A blood pressure reading is expressed in millimeters of mercury (mmHg) and recorded with two numbers written like a fraction The top number in the reading measures the systolic blood pressure (when the heart is beating); the bottom number represents diastolic blood pressure (when the heart is at rest). When several readings are taken over a few days, your average blood pressure can be determined. 13

The Von Recklinghausen Oscillotonometer is a device which allows both systolic and diastolic blood pressure to be read without a stethoscope. It consists of two overlapping cuffs (one large, one small) a large dial for reading pressure, a bleed valve and a control lever. The large cuff performs the usual function of the sphygmomanometer cuff. The job of the smaller cuff is basically to amplify the pulsations which occur as the larger cuff is deflated, so that instead of listening for the Korotkoff sounds, they are seen as oscillations of the needle on the pressure gauge. The lever simply switches the dial between the two cuffs. 7

The person listens and watches the gauge, then records two measurements. Systolic pressure is the pressure of the blood flow when the heart beats (the pressure when the first sound is heard). Diastolic pressure is the pressure between heartbeats (the pressure when the last sound is heard). Blood pressure is measured in millimetres of mercury, which is abbreviated mm Hg. 44

The sphygmomanometer may be electronic or mercury-based. The mercury-based unit has a manually inflatable cuff attached by tubing to the unit that contains mercury and is calibrated in millimeters of mercury. The electronic unit is similar, but is mercury free and inflates and deflates automatically with the reading displayed digitally. The electronic units are also calibrated to display the measurement in millimeters of mercury. Blood pressure can be measured with either unit, although electronic units are becoming more commonplace in both home care and clinical use. 21

A loud, clear tapping (or snapping) sound is evident, which increases in intensity as the cuff is deflated. As an example, this phase begins at a cuff pressure of 120 millimeters of mercury and ends at a pressure of 106 mm Hg. The beginning of phase 1 is taken as systolic pressure. 40

A cuff of appropriate size is fitted and inflated manually by repeatedly squeezing a rubber bulb until the artery is completely occluded. Listening with the stethoscope to the brachial artery at the elbow, the examiner slowly releases the pressure in the cuff. When blood just starts to flow in the artery, the turbulent flow creates a "whooshing" or pounding (first Korotkoff sound). The pressure at which this sound is first heard is the systolic blood pressure. The cuff pressure is further released until no sound can be heard (fifth Korotkoff sound), at the diastolic arterial pressure. Sometimes, the pressure is palpated (felt by hand) to get an estimate before auscultation. 1

If the blood pressure is monitored with a manual system, a cuff is placed level with the heart and wrapped firmly but not too tightly around the bare arm 1 in (2.5 cm) above the elbow, with any creases in the cuff smoothed out. Leg measurements, require the cuff to be positioned below the groin on the bare leg over the femoral artery. 21

Following the manufacturer’s guidelines (electronic models), the cuff is inflated and then deflated automatically. The reading is displayed and recorded by the user. The results are charted with the systolic pressure first, then by the diastolic pressure in the following manner, xxx/xx (e.g., 120/70). A manual system requires a stethoscope be placed over the artery, the cuff is then inflated until the artery is occluded and no sound is heard through the stethoscope. 21

As the person listens and watches the sphygmomanometer scale, he or she records two measurements. The systolic pressure is the pressure of the blood flow when the heart beats (the pressure when the first sound is heard). The diastolic pressure is the pressure between heartbeats (the pressure when the last sound is heard). Blood pressure is measured in millimeters of mercury, which is abbreviated mm Hg. The harder it is for blood to flow, the higher the numbers will be. 34

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