BLOOD PRESSURE

Blood pressure is the force exerted by the blood on the inner walls of the blood vessels. It is different in the different blood vessels.

Arterial blood pressure depends on the volume of blood in the arteries and the elasticity of the arterial walls and on the rate of the heart beat. The pressure is greatest in the large arteries leaving the heart, and gradually falls in the arterioles. It is lower in the capillaries and still lower in the veins.

 Systolic Pressure: When the ventricles of the heart contract the arterial blood pressure is the highest. It is called systolic pressure.

Diastolic Pressure: When the ventricles of the heart relax, the arterial blood pressure is the lowest. It is called diastolic pressure.

Measuring Blood Pressure: The instrument used for measuring blood pressure is called sphygmomanometer. The instrument consists of an inflatable cuff, a rubber bulb and a column of mercury. The hollow cuff is wrapped around the upper arm and inflated to a pressure above the systolic pressure (the tightened cuff closes the arteries in the upper arm and prevents blood from flowing into the lower arm). A stethoscope is placed over the artery just below the cuff, and the pressure in the cuff is slowly released until the arterial pressure is greater than the pressure of the cuff.

At that point, a recognizable sound can be heard through the stethoscope. This sound signals the high-velocity release of blood, and the figure on the mercury column at which it occurs represents the systolic blood pressure.

When the cuff pressure is lowered further, a louder sound is heard, and then the sound gradually becomes softer. When the sound stops altogether, the diastolic blood pressure is noted on the column.

The absence of sound indicates a free flowing gush of blood through the open artery. The blood leaving the ventricles and entering the aorta and the pulmonary artery is under considerable pressure, where it normally reaches to 140mm of the mercury.

Variations in Blood Flow: The flow of blood also varies according to the conditions such as exercises, after eating and when the body is hot or cold. It also varies according to the need of the organs. Steady flow of blood is maintained to heart and brain.