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Biomedical Instrumentation Lab Lab Experiments

Blood Pressure Measurement


To Measure blood pressure using Sphygmomanometer and compare with digital blood pressure meter..

Apparatus Required:

  1. Cuff
  2. Inflator
  3. Power supply
  4. Stethoscope
  5. Sphygmomanometer
  6. Digital Blood pressure meter


Blood Pressure

Blood pressure is a measurement of the force applied to the walls of the arteries as the heart pumps blood through the body. The pressure is determined by the force and amount of blood pumped, and the size and flexibility of the arteries. Blood pressure is continually changing depending on activity, temperature, diet, emotional state, posture, physical state, and medication

The ventricles of heart have two states: systole (contraction) and diastole (relaxation). During diastole blood fills the ventricles and during systole the blood is pushed out of the heart into the arteries. The auricles contract anti-phase to the ventricles and chiefly serve to optimally fill the ventricles with blood. The corresponding pressure related to these states are referred to as systolic pressure and diastolic pressure .The range of systolic pressure can be from 90 mm of Hg to 145mm of Hg with the average being 120 mm of Hg. The diastolic pressure typically varies from 60mm of Hg to 90 mm of Hg and the average being 80 mmofHg.


Mercury SphygmomanometerThis includes a mercury manometer, an upper arm cuff, a hand inflation bulb with a pressure control valve and requires the use of a stethoscope to listen to the Korotkoff sounds. Relies on the ausculatory technique.

bp meter

Digital BP meter (Automated device)

This includes an electronic monitor with a pressure sensor, a digital display and an upper arm cuff. An electrically driven pump raises the pressure in the cuff. Devices may have a user-adjustable set inflation pressure or they will automatically inflate to the appropriate level, about 30 mmHg above the predicted systolic reading. On operation of the start button the device automatically inflates and deflates the cuff and displays the systolic and diastolic values. Pulse rate may so be displayed. Devices may also have a memory facility that stores the last measurement or up to 10 or more previous readings. It is battery powered and uses the ocillometric technique.




  1. The upper arm is wrapped with the cuff belt connected to a mercury pressure gauge and air is pumped with a rubber ball to increase cuff pressure about 30 mmHg higher than the systolic blood pressure to block the artery and stop blood flow downstream.
  2. Then, the cuff pressure is slowly lowered. The artery opens at the instant when the cuff pressure decreases below the systolic blood pressure and blood begins to flow on and off in synchrony with pulses causing the opening and closing of the artery. The sound emitted by the pulses is named Korotkoff's and continues until the cuff pressure decreases below the systolic blood pressure and the artery ceases the opening and closing.
  3. The stethoscope placed closely to the artery downstream of the cuff is used to hear Korotkoff's sound; the blood pressures are measured. Cuff pressure when Korotkoff's sound begins to be heard is defined as the highest blood pressure (Systole) and that when the sound disappears is defined as the lowest pressure(Diastole).


S. No. Patient Name Sphygmomanometer/Systolic (mmHg)/Diastolic (mmHg) Semi Automated/Systolic (mmHg)/Diastolic (mmHg)/Pulse (bpm) Automated/Systolic (mmHg)/Diastolic (mmHg)/Pulse (bpm)
1 X
2 Y
3 Z
4 A

Mean Arterial Pressure (MAP)

M A P = (1/3 X SBP) + (2/3XDBP) OR MAP = DBP + ((SBP-DBP/3))

Pulse pressure (PP) = SBP-DBP

Hyper tension-Above normal BP; Hypo tension-Below normal BP


Thus the blood pressure measurements are done using mercury sphygmomanometer and digital automated device.