Blood Vessels

Blood Pressure

Systolic blood pressure is the pressure against the vessel walls during ventricular contraction, and diastolic blood pressure is the pressure exerted on the vessel walls during relaxation of the ventricles.
The force that blood exerts against vessel walls is blood pressure. A sphygmomanometer is the device typically used to measure blood pressure, specifically systemic arterial blood pressure at the arm's brachial artery, which is near the heart. A blood pressure measurement records two pressures, systolic and diastolic. Systolic blood pressure is the pressure blood exerts against vessel walls during ventricular contraction. It is the peak arterial blood pressure during ventricular systole, when blood is forced from ventricles into the aorta and pulmonary artery. Diastolic blood pressure is the pressure blood exerts on vessel walls during ventricular relaxation. It is the lowest arterial blood pressure between heartbeats. Arterial blood pressure is recorded as a ratio of systolic/diastolic pressures, in units of mmHg. A typical healthy blood pressure in a young adult includes a systolic blood pressure of 120 mmHg and a diastolic blood pressure of 75 mmHg, recorded as 120/75. Hypertension is high blood pressure, which is defined as any chronically occurring systolic pressure above 130 mmHg or diastolic pressure above 80 mmHg. These measures represent early-stage hypertension in adults. Blood pressure is maintained by arterial flexibility, arteries' capacity to distend and recoil with the pumping of blood during the cardiac cycle. Blood pressure thus tends to increase with age, as arteries become more rigid.

Measuring Blood Pressure

Blood pressure measurements monitor pressure in the brachial artery in a ratio of systolic/diastolic pressure. Arterial pressures are much higher than capillary pressures, which are higher than venous pressures. The mean arterial pressure refers to the average pressure in the arteries during a single cardiac cycle, which includes all of the events that take place when a heart beats.