What is the difference between systolic and diastolic blood pressure?

• A. Pressure during heart contraction
• B. Pressure during heart relaxation
• C. Mean arterial pressure
• D. Venous pressure

Answer: (A)

Systolic and diastolic blood pressure describe arterial pressure at different times in the heartbeat. Systolic pressure is the peak pressure in the arteries when the heart contracts and pushes blood out into the circulation. Diastolic pressure is the lower pressure in the arteries when the heart is relaxed and filling between beats. The higher systolic value comes from the forceful ejection of blood during ventricle contraction, while the diastolic value reflects the pressure when the heart is at rest. A typical reading shows systolic as the first number and diastolic as the second, e.g., around 120/80 mmHg. Mean arterial pressure is a separate measure that estimates the average pressure in the arteries over the whole cycle, not the difference between the two; it depends on both systolic and diastolic pressures. Venous pressure refers to the pressure in the veins and is not what systolic versus diastolic describe.