As you have seen, blood pressure is a measure of the pressure of the blood against the walls of a blood vessel. Clinically, blood pressure is usually measured in the brachial (arm) artery, so our discussion will focus on this specific location.

There are two components to blood pressure:

	•	Systolic pressure: The pressure in the artery during the ventricular contraction phase of the heart cycle. The pressure in the vessel is highest at this time.
	•	Diastolic pressure: The pressure in the artery when the ventricles are relaxed. The pressure is at its lowest point, though it does not drop all the way to zero.

Next we will learn how blood pressure is measured.