BLOOD PRESSURE
When blood flows through the blood vessels, it exerts pressure on the walls of the blood vessels. This is referred to as blood pressure. In order to maintain an adequate flow of blood to all parts of the body, a certain level of blood pressure must be maintained. The term "Blood pressure" refers to systemic arterial blood pressure. Systemic arterial blood pressure is the pressure in large arteries such as brachial artery. The pressure in other smaller vessels is lower than the arterial pressure. Blood pressure values are measured and expressed in millimeters of mercury (mm Hg) relative to the atmospheric pressure. Normal blood pressure is regulated by many factors that include the contraction of the heart, the elasticity of arterial walls, blood volume and the resistance offered by blood vessels to the flow of blood.


The systolic pressure is the peak pressure in the arteries during the cardiac cycle. Systole is the active pumping phase of the heart. The diastolic pressure is the lowest pressure at the resting phase of the cardiac cycle. Diastole is the resting phase of the heart between the heart beats. Systolic and diastolic pressures are measured in millimeters of mercury (mm Hg) and expressed as a ratio. The mean arterial pressure and pulse pressure are other important quantities that are important to the physician diagnosing heart disease. Normal blood pressure values for a resting, healthy adult are approximately 120 mm Hg systole and 80 mm Hg diastole (120/80 mm Hg). Blood pressure varies during individuals and even during the normal course of the day in response to emotion, exertion, sleep and other physical and mental changes.

Factors influencing blood pressure:

There are many factors that influence blood pressure. Some of these factors are

A) Rate of pumping

Rate of pumping depends on the heart rate. The higher the heart rate, the higher is the rate of pumping. So the blood pressure increases with increase in the rate of pumping.

B) Volume of blood

Blood pressure increases with increase in the volume of blood. If more blood is present in the body, the rate of blood return to the heart increases, leading to higher blood pressure.

C) Resistance offered by blood vessels

Blood pressure increases with increase in resistance offered by blood vessels. The resistance offered by the blood vessels to the flow of blood depends upon the size as well as on the smoothness of the walls of the blood vessel. The larger the blood vessel, the lower is the blood pressure. With gradual buildup of fatty materials like cholesterol, the smoothness of the blood vessels is reduced. Blood pressure increases with decrease in smoothness of the walls of the blood vessels.

D) Viscosity of blood

Blood pressure increases with increase in viscosity of blood. Viscosity of a fluid is the resistance offered by the fluid to flow. So viscosity of blood is a measure of the resistance offered by blood while flowing through the blood vessels.