Introduction to Blood Pressure

Blood pressure is the force that blood exerts on the inner walls of blood vessels. It is expressed with two numbers: the systolic pressure, which occurs when the heart ventricles contract, and the diastolic pressure, which occurs during ventricular relaxation. The pressure is highest in the arteries and lowest in the veins. A typical normal reading is around 120 / 80 mmHg, with 120 mmHg representing the systolic value and 80 mmHg the diastolic value. When blood pressure is elevated, a higher pulse rate is often observed.

Factors Influencing Blood Pressure

Cardiac output—the speed and strength of each heartbeat—directly affects blood pressure. If the heart is enlarged, has blockages, or has suffered damage, it may increase its output to compensate, which can raise blood pressure. Blood viscosity, which reflects how thick the blood is, also plays a role. Vasoconstriction (narrowing of vessels) and vasodilation (widening of vessels) change blood viscosity; thicker blood requires the heart to work harder to push it through the circulatory system.

Mechanisms & Explanations

The systolic number represents ventricular contraction, while the diastolic number represents ventricular relaxation. Elevated blood pressure can result when the heart must exert more force because of conditions such as an enlarged heart, blockages, or damage, leading to higher cardiac output to maintain circulation. Vasoconstriction and vasodilation influence blood viscosity; thicker blood increases the force the heart must generate to move blood through the vessels.

Hard Facts & Numbers

• Normal blood pressure range: 120 / 80 mmHg.
• Normal systolic pressure: 120 mmHg.
• Normal diastolic pressure: 80 mmHg.