Blood Pressure

Blood Pressure is the Pressure against the walls of the blood vessels produced by the discharge of blood into them by contractions of left ventricle. The Blood Pressure is high in arteries, gradually drops in the arterioles and capillaries, and becomes very low in the veins. It is marked gradient of blood pressure that keeps the blood flowing from the arteries through capillaries to the veins. Fluids always flow from areas of high pressure to the areas of lower pressure.

Blood Pressure is generally measured by determining the millimeters of mercury displaced in a pressure gauge called sphygmomanometer. It is expressed as the ratio of systolic pressure over the diastolic pressure. For a healthy restling adult person, the average systolic/ diastolic pressures are 120*/80 mm Hg in arteries near the heart. Pressure drops with increasing distance from the heart. The brachial artery in the arms, a little above the elbow, is used for measuring blood pressure. The systolic pressure shows the force with which the left ventricle pushes blood into the aortic arch. The diastolic pressures indicate the elasticity of blood vessels, and are useful in diagnosing hardening of arteries or strain on their walls.

The difference between systolic pressure and diastolic pressure is known as the pulse pressure. It is about 40mm Hg for a normal person. Pulse pressure may be defined as a variation occurring in an artery during the cardiac cycle.

A persistent rise in BP is called high blood pressure or hypertension.It results from narrowing of arterial lumen and reduces elasticity of arterial walls in old age. It can cause rupturing of capillaries. It is silent killer.

The blood pressure is influenced by many factors, such as force and rate of heart beat, resistance offered by arterioles and capillaries to the flow of blood, viscosity and capillaries to flow of blood, viscosity of blood, and volume of blood pumped out at each beat. An increase in any of these factors can raise the blood pressure. Age also affects blood pressure.

Hypotension: Fall in the arterial blood pressure is called low blood pressure or hypotension. It may result from chronic expansion of arterioles, loss of loss of blood in haemorrhage, or failure of the pumping action of the heart. It may cause fainting.

Many short term mechanisms raise and lower the blood pressure to maintain homoestasis.Rise in blood pressure stimulates basoreceptors in walls of the arteries in the chest and head. In response to stimulation from the baroreceptors, the nervous system, a) widens the small arteries, b) decreases heart rate, c) widens the veins, decreasing the return of blood to the heart. All these factors lower the blood pressure. Rapid fall in blood pressure, as by heavy bleeding, enlist certain hormones that constrict the blood vessels and usually restore the blood pressure to normal within a few minutes.