What does blood pressure measure?

Blood pressure specifically measures the pressure exerted by circulating blood on the walls of blood vessels, particularly arteries. This measurement reflects how hard the blood is pushing against the vessel walls as the heart pumps it throughout the body. It is typically expressed in millimeters of mercury (mmHg) with two values: systolic pressure (the pressure during heartbeats) and diastolic pressure (the pressure when the heart rests between beats). Understanding blood pressure is crucial because it provides insight into cardiovascular health, indicating how well the heart and blood vessels are functioning together to maintain adequate blood flow to tissues and organs.

The other options detail different aspects of the circulatory system but do not specifically pertain to the definition of blood pressure. The flow rate refers to the speed of blood movement, volume pertains to how much blood is contained in the circulatory system, and oxygen levels relate to the amount of oxygen carried by the blood, none of which define the pressure blood exerts on vessel walls. Understanding these distinctions is key for accurate comprehension of cardiovascular health metrics.