The principle of the experiment involves the balancing of air pressure against the pressure of blood in brachial artery, the air pressure being estimated by a mercury or air (aneroid) manometer .
A cloth-covered rubber bag is wrapped around upper arm, and is inflated with air till higher extra-arterial pressure occludes the brachial artery. The pressure in the bag is then gradually reduced and is balanced against intra-arterial pressure. The readings for systolic and diastolic blood pressure are noted and recorded.
sphygmomanometer, stethoscope and chair or couch.
It consists of a mrecury manometer and inflatable cuff. The cuff is called a “Riva Rocci” cuff. The manometer is U shaped tube. One limb being broader than the other. The broader limb is the reservior for mercury and the narrow limb is graduated from O to 300 mm with the smallest division corresponding to a reading of 2 mm.
Cuff consists Of an inflatable rubber bag covered by a non-distensible cotton fabric. The cuff is connected to the manometer and to a hand bulb (rubber pump) by rubber tubing. The cuff can be inflated to any desired pressure with the help of rubber pump and it also permits the reduction in cuff pressure. To overcome tissue resistance the width of cuff should be 20% more than the diameter of the arm. Width of a cuff for adults is 12.5 cm, for children below 8 years is 8 cm, below 5 years is 5 cm and for infants below 1 year is 2.5 cm. Wider cuffs have to be used to record the blood pressure in obese individuals and in the lower limb to overcome tissue resistance. Length of rubber cuff should be 23 cm (It should cover 2/3 of
PROCEDURE of blood presssure measurement:
BP is recorded by two method:
It is possible in experimental animals because it is unsafe. In this method artery cannulated and other end of cannula is connected to mercury manometer. By this method we record end pressure which is slightly higher than lateral pressure measured by indirect methods.
By this method lateral pressure exerted by the column of blood on arteries is recorded. The blood pressure is most commonly measured in brachial artery because it is a convenient place for measuring blood pressure and is approximately at the same level as the heart, so that the pressure is almost equal to the pressure in the aorta.
Subject is asked to sit comfortably in a chair or made to lie down supine on the couch and the arm (branchial artery) is kept at the level the heart to obtain a pressure that is uninfluenced by gravity. The arm is exposed and cuff is tied in such a way that the mid point of the cuff overlies the brachial artery and the lower edge of the cuff is one inch above cubital fossa. Now the BP is recorded by palpatory method first and then by auscultatory method.
The valve on the bulb is closed by turning it clockwise and radial pulse is palpated at the wrist. Rubber bag IS Inflated until the air pressure within it overcomes the arterial pressure and obliterates the arterial luman. This can be confirmed by feeling the radial pulse which will disappear when pressure is raised a little beyond the point, by about 30-40 mmHg and then slowly reduce the pressure in the cuff by turning the valve counter clockwise slightly, to let the air out of the bag, so that the pressure reappearing at a point when pressure in the artery is equal to the pressure of air in the cuff and blood escapes beyond the cuff into the peripheral part of the artery. Manometer reading is taken when radial pulse is first felt at the wrist. It is the index of systolic BP.
Let all the air out of the cuff, allow the subject to rest and then take other readings. Take three readings and calculate the average.
- Pressure recorded is about.6-10 mm Hg less than that recorded by auscuttatory method.
- Only systolic blood pressure can be recorded by this method.
Place the chart piece Of Stethoscope over the arm medial to the tendons of biceps where pulsations of brachial artery are felt.
Then inflate the cuff till the pressure is 3040 mm Hg more than the reading obtained by palpatory method. Now gradually lower the pressure till a sharp light tapping sound (in the rhythm with the heart beat) is heard.
When the pressure in the Cuff Is further lowered, sound undergoes a series of changes in quality and intensity, which were first described by Korotkoff, a Russian Scientist in 1905 and are labeled as Korotkoff sounds.
Phases of the Korotkoff sounds:
There are 5 phases of these sounds.
- Phase I: Sudden appearance of a clear but faint tapping sound growing louder during the succeeding 10 mm Hg fall in pressure.
- phase 2: The sound murmur like quality during the next 15 mm fall in pressure.
- phase 3: The sound change little in quality but becomes clearer and louder during during next 15 mm fall in pressure.
- Phase IV: Muffled quality lasting throughout the next 5-6 mm Hg fall in pressure.
- Phase V: Complete disappearance of the sound.
The appearance of the sound indicates the systolic BP. Disappearance of sound (phase V) indicates diastolic BP. If sound does not disappear muffling of the sound (phase IV) is taken as diastolic BP. It happens in case of hyperdynamic circulation.
Let all the air out of the cuff, allow the subject to rest and then take another reading.
Take three reading to reach the conclusion regarding blood pressure. Calculate mean arterial pressure (MAP) and pulse pressure (PP) from the reading of blood pressure.
- In the suspected hypertensive individuals, cuff pressure should be well above 200 mmHg (or above estimated BP by palpatory method) to avoid auscultatory gap.
- The cuff should not be tied too tight or too loose.
- Arm, with the cuff wrapped around it should be at the leVel of the heart.
- Zero error of sphygmomanometer should be corrected.
- Every Step to measure blood pressure is discussed completely with the subject prior to the procedure.
- The subject should be quiet and comfortable for 5-10 minutes before measurement of BP.
- The inflatable rubber bag along with its tubing should be placed over the inner side of arm.
- The cuff should not be left inflated for long period (more than 2 min), specially in persons suffering from purpura or tetany.
- The muscles of the arm should not be in a state of contraction during determination of blood pressure.
Result Concordant reading:
Systolic BP / Diastolic BP mm Hg.
Normal value Blood pressure:
Average value in adult = 120/80 mm Hg
Systolic BP range = 100 -140 mm Hg
Diastolic BP range = 60-90 mm Hg
Factors Affecting Blood Pressure in Normal Subjects:
- Age: Both systolic and diastolic BP increase with age. Systolic BP increases more than diastolic BP. This is because of loss of elasticity of blood vessel ‘ with age. (It is roughly 100 + age in years).
- Gravity: BP increases in arteries below heart and decrease in arteries above heart.
- Body built: Overweight individuals have higher values.
- sex: In female before menopause blood pressure is lower than male.
- Sleep: BP falls during sleep due to generalised relaxation of blood vessels.
- Exercise: also effect blood pressure.