Measurement of blood pressure in humans

physiology of blood pressure -short seminar

1. Blood Pressure Measurement in Humans Dr.Praveen Nagula

2. Direct measurement of pressure Needles or catheters are introduced into peripheral arteries of patients and arterial blood pressure is measured directly by means of strain guages .

3. Indirect measurement In the vast majority of cases, however, the blood pressure is estimated indirectly by means of a sphygmomanometer.

4. BP apparatus Inextensible cuff containing an inflatable bag. The cuff is wrapped around the extremity (usually the arm, occasionally the thigh) so that the inflatable bag lies between the cuff and the skin, directly over the artery to be compressed. The artery is occluded by inflating the bag, by means of a rubber squeeze bulb, to a pressure in excess of arterial systolic pressure. The pressure in the bag is measured by means of a mercury manometer or an aneroid manometer. Pressure is released from the bag at a rate of 2 or 3 mm Hg per heartbeat by means of a needle valve in the inflating bulb.

5. Palpatory method When blood pressure readings are taken from the arm, the systolic pressure may be estimated by palpating the radial artery at the wrist ( palpatory method). When pressure in the bag exceeds the systolic level, no pulse will be perceived. As the pressure falls just below the systolic level, a spurt of blood will pass through the brachial artery under the cuff during the peak of systole and a slight pulse will be felt at the wrist.

6. Auscultatory method More sensitive More precise method for measuring systolic pressure Permits the estimation of the diastolic level as well. The physician listens with a stethoscope applied to the skin of the antecubital space over the brachial artery. While the pressure in the bag exceeds the systolic pressure, the brachial artery is occluded and no sounds are heard. When the inflation falls just below the systolic pressure , the small spurt of blood escapes through the cuff and a slight tapping sound is heard. This represents the systolic pressure.

7. Korotkoff sounds It usually corresponds closely with the systolic pressure when it is measured directly and exceeds by a few mm Hg the pressure estimated by the palpatory method (because the auscultatory method is more sensitive than the palpatory method). As inflation pressure continues to fall more blood escapes under the cuff per beat and the sounds (called Korotkoff sounds) are hears as louder thuds. As the inflation pressure approached the diastolic level, the Korotkoff sounds become muffled. As they fall just below the diastolic level , the sounds disappear, this indicates the diastolic pressure.

8. Physiology of Korotkoff sounds The origin of the Korotkoff sounds is related to the spurt of blood passing under the cuff and meeting a static column of blood; the impact and turbulence generate vibrations, some of which are in the audible range of frequencies . Once the inflation pressure is less than the diastolic pressure,flow is continuous in the brachial artery and sounds are no longer audible.

9. Auscultatory Gap

10. Cardiovascular Physiology , 4 th edition Robert M. Berne, Matthew N. Levy