Why is diastolic pressure typically lower than systolic pressure?

• A. Because diastolic pressure is produced during relaxation
• B. Because diastolic pressure is always lower than systolic
• C. Because the heart spends more time in diastole
• D. Because systolic pressure reflects ventricular ejection while diastolic is relaxation; the difference is the pulse pressure

Answer: (D)

The key idea is how arterial pressure changes with the heart’s pumping action. Systolic pressure is the peak pressure that occurs when the ventricles contract and eject blood into the aorta and large arteries. Diastolic pressure is the lower pressure that remains while the heart is relaxed and the arteries continue to contain blood, helped by the elastic recoil of the arterial walls and ongoing peripheral resistance. Because the heart actively drives blood into the arteries during systole, the pressure there is much higher than during diastole when there’s no active ejection. The difference between these two pressures is pulse pressure, which grows with larger stroke volume or stiffer arteries. So the statement that systolic pressure reflects ventricular ejection while diastolic pressure reflects relaxation, and that their difference is the pulse pressure, captures the mechanism behind why diastolic pressure is typically lower.