Question

How are systolic and diastolic blood pressures measured with a sphygmomanometer?

Answer 1

blood pressure refers to the lateral force exerted by the blood as it presses against and attempts to stretch the walls of blood vessels. The blood pressure is not steady throughout the cardiac cycle but fluctuating i.e. it is pulsatile. It rises and falls, reaching its maximum during systole of the heart, when it is called systolic blood pressure. Falling to its minimum during diastole of the heart when it is called diastolic blood pressure.

Principle: a sufficient length of a single artery is selected in the arm (brachial artery), or in the thigh (femoral artery). The artery is first compressed by inflating a rubber bag(connected to a manometer) placed around the arm (or thigh) to stop the blood flow through the occluded section of the artery. The pressure is then slowly released and the flow of blood through the obstructed segment of the artery is studied by listening to the sounds produced in the part of the artery just below the obstructed segment- auscultatory method.

1. Place the cuff over the upper arm and record the BP by palpatory method. make the subject set or lie supine and allow 5 minutes for mental and physical relaxation. Place the cuff around the upper arm, with the centre of the bag lying over the brachial artery keeping its lower edge about 3 cm above the elbow. Wrap the cloth covering around the arm so as to cover the rubber bag completely and to prevented bulging out from under the wrapping on inflation. The cuff should neither be too tight nor very loose. Palpate the radial artery at the wrist and feel it's pulsations with the tips of your fingers. Keeping your fingers on the pulse, hold the air bulb in the palm of your other hand and tighten the leak valve screw with your thumb and fingers. Inflate the cuff slowly until the pulsations disappear, note the reading then raise the pressure another 30-40 mmHg. Open the leak valve and control it so that the pressure gradually falls in the steps of 2-3mmHg. Note the reading when the pulse just reappears. The pressure at which the pulse is first felt is the SYSTOLIC BLOOD PRESSURE.
2. Locate the bifurcation of brachial artery (it divides into radial and ulnar branches) in the cubital space just medial to the tendon of the biceps which can be easily palpated in a semi flexed elbow as a thick hard elongated structure.
3. Please the chest piece of the stethoscope on this point and keep it in position with your fingers and a thumb of your left hand (if you are right handed).
4. Inflate the cuff rapidly by compressing and releasing the air pump alternatively (sounds may be heard as a Mercury column goes up). Raise the pressure to 40-50 mmHg above the systolic level as determined by the palpatory method.
5. Lower the pressure gradually until a clear sharp tapping sound is heard. Continue to lower the pressure and try to note a change in the character of the sounds. These sounds are called Korotkoff's sounds and show the following phases:

Phase I: This phase starts with a clear sharp tap when a jet of blood is able to cross the previously obstructed artery. As the pressure is lowered, the sounds continue as sharp and clear taps. The level at which the first sound (clear, sharp or faint) is heard, is taken as the systolic blood pressure.

Phase II: The sounds become murmurish and remain so during next 10-15mmHg fall in pressure when they again become clear and banging.

Phase III: It starts with clear, knocking or banging sounds that continue for the next 12 to 14 mmHg pressure, when they suddenly become muffled.

Phase IV: The transition from phase III to phase IV is usually very sudden. The sounds remain muffled, dull, faint and indistinct until they disappear. The muffling of sounds and their disappearance occurs nearly at the same time, there being a difference of 4-5 mmHg.

Phase V: This phase begins when the Korotkoff's sounds disappear completely. If you reduce the pressure slowly, you will not that total silence continues right up to the zero level. Criteria for Diastolic blood pressure: is the muffling of sounds and disappearance of sounds.

6. Take three readings with the auscultatory method and repeat 3 readings on the other arm.

Blood pressure is expressed as Systolic/1st Diastolic/2nd diastolic. 1st diastolic means muffling of sounds and 2nd diastolic means disappearance of sounds. eg 120/80/72.