A patient develops sinus tachycardia at 150 per minute with a shortened diastolic filling period. Compared with the same patient at rest, which pattern best describes the arterial pressures?

• A Diastolic pressure falls markedly because of reduced diastolic run-off time
• B Diastolic pressure tends to rise because less time is available for run-off into the periphery between beats ✓
• C Systolic pressure rises because of increased peripheral resistance alone
• D Both systolic and diastolic pressures fall equally

Explanation

Mean arterial pressure equals cardiac output times total peripheral resistance. With faster rates, each diastole is shorter, so there is less time for blood to drain from the elastic arteries into arterioles before the next systole. Residual volume in the large arteries therefore rises and diastolic pressure increases. Systolic pressure may fall slightly because of reduced stroke volume from poor ventricular filling, narrowing the pulse pressure. Reduced resistance would lower, not raise, systolic pressure.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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