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Old 10-15-2010
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Heart Cardiac Cycle Adjustments!

A 54-year-old male is seen in clinic with complaints of palpitations and light-headedness. Physical examination is remarkable for a heart rate of greater than 200 beats per minute and a blood pressure of 75/40 mm Hg. What adjustments have probably occurred in the cardiac cycle?

A. Diastolic time has decreased and systolic time has increased
B. Diastolic time has decreased but systolic time has decreased more
C. Systolic time has decreased and diastolic time has increased
D. Systolic time has decreased but diastolic time has decreased more
E. Systolic time has decreased but diastolic time has not changed

Please answer with reasoning written.
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Haisook (10-15-2010)

Old 10-15-2010
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D. Systolic time has decreased but diastolic time has decreased more

Tachycardia will decrease both systole and diastole times, but because the diastole constitutes two thirds of the cardiac cycle, the decrease will be more pronounced. Systole time is already small, being one third of the cycle, so further reduction of time would not make a large difference, not as much as that of the diastole.
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Old 10-15-2010
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Post confounding reason

My answer is D as well...with rapid heart rates there is not enough time to relax and fill the ventricles. Systole would be decreased as well but since it is the contract and eject phase it is not as reduced as diastolic phase. Not 100% sure though!
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