Determination of human blood pressure

When the blood flows through the blood vessels it exerts lateral pressure on the wall of the blood 

vessels and this pressure is called as blood pressure. Blood is pumped by the heart into blood vessels 

through arteries and capillaries to distribute various substance to the cell. Heart contracts and then relaxes with the help of cardiac muscles. Contraction 

phase is called a systole and relaxation phase is known as diastole which constitutes cardiac cycle 

Pumping of heart maintains sufficient pressure for the flow of blood through the blood 

vessels. Blood pressure also provides the driving force of exchange at fine capillary beds and thus assuring regular nutrient exchange to the tissues, cells. Blood pressure helps in urine formation,proper working of lymphatic, immune 

and blood vascular systems. Stress and diseases cause changes in blood pressure. Blood pressure is 

measured by an instrument called as sphygmomanometer .

Apparatus consists of a 

graduated column in millimeter (mm) in a hollow glass-tube attached to Mercury tank, a rubber-cuff  connected by a tube to a rubber bulb for pumping air and a stethoscope.

Blood pressure in man is  measured by brachial artery of the arm which supplies blood to the arm. Since the blood in pumped  by heart in a rhythmic cycle hence blood pressure is highest during systole (contraction) and lowest 

at diastole (relaxation). Systolic pressure is called as upper limit which is 120 to 135 mm Hg.

B.P. of a healthy human is 120/80 mm Hg. 

Regular exercises helps in maintaining normal level of B.P. Emotions, excitement, diseases, 

food, body posture and constriction of blood vessels increase or decrease in blood pressure.

Procedure : Fo

(1) Person whose blood pressure is to be measured may be seated on chair by the side of a doctors table.

(2) Stretch the left hand on the table with palm upwards. Ask the person to close the palm.

(3) Wrap the rubber cuff around the arm above the elbow over the brachial artery.

(4) Feel the pulse above the elbow and insert the chest (diaphragm) of the stethoscope just above the

pulse place under rubber cuff.

(5) Attach rubber-cuff to a compressible rubber-bulb through tube. Hold the rubber bulb in your right hand.

(6) Compress the rubber bulb very gently and gradually to exert air pressure against outside brachial artery.

(7) Keep on gradually pumping the air until the air pressure exceeds the blood pressure within the brachial artery or in other words starts compressing the brachial artery. At such point no pulse is

heard through the chest of the stethoscope kept at the brachial artery 

(8) Now very slowly release the air pressure in the cuff around the arm to decrease the pressure until

it is approximately equal to blood pressure in the brachial artery. At this juncture small gush of blood

comes out in the artery. The sudden flow of blood is marked by a sound 'dup'. The pressure at this point is systolic pressure.This is followedby increasing louder sound ,by the flow of blood in the arteries. After sometimes the sound disappears

with a last sound like 'lup' and then no sound appears.The pressure at this time is diastolic pressure.The

person observing blood pressure must be very trained to detect  the 'dup' and 'lup' sound for correct

measurement of the blood pressure.

(9) The blood in the arteries of normal adult exerts a pressure equal to that required to raise a column of mercury approximately 120 mm high in a glass tube during systole of ventricles and 80 mm during diastole of ventricles. Pulse pressure (PP) is the difference between SBP and DBF i.e., 120-180 = 40. 

(10) After taking blood pressure unwrap the cuff and close the B.P. apparatus.