Blood pressure is the force exerted by your heart, against the resistance created by the arteries, to keep blood flowing through your body. Your blood pressure is high (hypertension) when the force is excessive.

Blood pressure is the pressure exerted by the blood on the walls of the arteries. Your heart functions as a muscular pump that contracts rhythmically and squirts blood into your arteries. From there your blood flows to your entire body through a circulatory system of smaller vessels. In this way oxygen is delivered to all the living tissue in your body. The resistance offered by these arteries and the smaller arterioles is very significant. Constriction of the muscle in the artery wall causes it to narrow, which increases the resistance and hence the pressure within. This can be compared to taking a garden hose and reducing the opening at the nozzle. Pressure in a hose can of course also be raised by increasing the amount of water flowing from the tap. Similarly, the amount of circulating blood, and the strength of the heart muscle contractions, can also influence blood pressure.

If your blood pressure is too high, your heart must work much harder to maintain adequate blood flow to your body.

Terminology

If your blood pressure is recorded as, for example 120/80, the first number is the systolic pressure, and the second number the diastolic pressure. It is measured in millimetres of mercury. 120/80mm also happens to be the optimal blood pressure.

Systolic pressure is the pressure generated by each heartbeat. This occurs during the contraction of the heart muscle, which is called a systole. Diastolic blood pressure is the pressure between the heartbeats when the heart is resting. Systolic pressure is obviously always higher than diastolic blood pressure. Pulse pressure is the difference between the two readings.

If any of these are significantly elevated, it increases the risk for heart disease, stroke or kidney damage.

Essential to life

Blood pressure is essential to life. In fact, when a person dies of so-called “shock”, it usually implies events that cause a fatal drop in blood pressure. This leads to inadequate perfusion of vital organs like the brain and kidneys. Starved from their life-giving source of oxygen, these organs cannot function anymore.