What does blood pressure measure?

Blood pressure specifically measures the pressure exerted by circulating blood upon the walls of blood vessels, particularly arteries. This is crucial for understanding how well blood is being pushed through the circulatory system to deliver necessary oxygen and nutrients to tissues and organs. It is expressed in millimeters of mercury (mmHg) and is typically represented with two numbers: systolic pressure (the pressure during heartbeats) over diastolic pressure (the pressure between heartbeats). This measurement is fundamental in assessing cardiovascular health, detecting conditions such as hypertension, and evaluating the overall function of the heart and blood vessels.

The other options address different physiological concepts that are not directly related to the measurement of blood pressure. For instance, the rate of breathing pertains to respiratory function, the thickness of blood relates to viscosity and can influence blood flow but does not define blood pressure, and the level of oxygen in the blood involves gas exchange and pulmonary function rather than vascular pressure. Understanding blood pressure and its implications requires a clear focus on how it specifically reflects the dynamics of blood flow within the cardiovascular system.