ARTERIAL BLOOD PRESSURE ESTIMATION
AIM
To determine the arterial pressure of the given subject at rest and to note the variations with change in posture and after exercise.
APPARATUS:
Sphygmomanometer, Stethoscope.
The Sphygmomanometer consists of a cuff which is an inflatable rubber bag covered with cloth. The cuff is connected to a mercury manometer through a rubber tube. By using a hand pump provided with a valve, the cuff can be inflated or deflated. When the cuff is inflated the pressure in the mercury manometer will rise. The mercury manometer is a glass tube which is graduated from 0-300 and each division corresponds to 2 mm of Hg pressure difference. It is connected to a mercury reservoir. Ideally the width of the cuff should be about 20% more than the diameter of the limb from which blood pressure is recorded. For an average adult the cuff used is about 18 cm long and 10 cm wide.
The stethoscope is an instrument used to auscultate different sounds in the body and it consists of two ear pieces and a chest piece connected by rubber tubings. The chest piece has a bell and a diaphragm, and can select either bell or diaphragm by rotating the chest piece in either direction. The bell is being used for low pitched sounds and the diphragm is for high pitched sounds.
PROCEDURE:
The blood pressure is determined using the sphygmomanometer. A rough assessment of the systolic presssure is made by the palpatory method. Then a more accurate assessment is made by the auscultatory method.
Palpatory method:
Apply the cuff of the sphygmomanometer around the arm of the subject, an inch above the elbow joint, leaving the cubital fossa exposed. Feel for the radial pulse at the wrist. Inflate the cuff till the radial pulse disappears. Raise the pressure still further by 20 to 30 mm of Hg. Then slowly release the pressure and note the reading in the manometer when the pulse reappears. This gives an idea about the systolic pressure.
Disadvantages:
1. The value obtained is about 5 to 10mm of Hg lower than the actual systolic pressure.
2. The diastolic pressure cannot be measured using this method.
Ausculatatory method:
Feel for the brachial pulse in the cubital fossa. Apply the diaphragm of the stethoscope firmly over this point. First determine the systolic pressure by palpatory method. Inflate the cuff about 40mm of Hg above this level. Slowly deflate the cuff. Due to the turbulent flow of blood through the partly collapsed artery, a series of sounds are heard. To begin with, the sound is sharp tapping which becomes louder, then gets muffled and finally diappears. The pressure at which sounds appear is taken as systolic pressure and the pressure at which they completely disappear is taken as the diastolic pressure. The value is expressed as systolic pressure over diastolic pressure.
Eg: 120/80 mm of Hg.
First check the blood pressure in the recumbent posture and then in the erect posture. Then determine the blood pressure after doing moderate exercise.
Discussion:
Blood pressure is defined as the lateral pressure exerted by the column of blood on the walls of the containing vessel. The maximum pressure exerted during systole is the systolic pressure and the minimum pressure exerted during a cardiac cycle and which exists throughout the cycle is the diastolic pressure. The normal systolic pressure in the healthy young adult ranges from 100 to 140 mm of Hg and the distolic pressure ranged from 60 to 90mm of Hg. The difference between systolic and diastolic pressure is called pulse pressure. Normal value ranges between 30 and 60mm of Hg. The mean arterial blood pressure is the average pressure throughout the cardiac cycle. As the duration of systole is shorter than diastole the mean arterial pressure is taken as diastolic pressure plus 1/3 pluse pressure.
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