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 cardiac cycle  



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Author8 Posts
  #1

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




  #2

D??


  #3

A- diastolic decreased and systolic increases/
i am thinking that due to hypotension sympathetic activity is increased and heart rate is increased as well along with systolic increase.
any further explanation will be appreciated


  #4

The correct answer is D. Under normal conditions, one-third of the cardiac cycle is spent in systole and two-thirds spent in diastole. As heart rate increases dramatically, the time spent in diastole falls precipitously but the time spent in systole falls only slightly.

A large increase in heart rate must produce a decrease in both diastole and systole (compare with choice A).


  #5

yep it is D. Systolic time has decreased but diastolic time has decreased more


  #6

Good question :lol:


  #7

The answer is D....because the diastole is the one usually compensated when it comes to increased heart rate.However the reason why systolic time is decreased is mainly due to the decreased BP....hence the light headedness so it seems that even systole has been affected too


  #8

Malaysian,

The decrease in systolic time is not necessarily because of a drop in BP, it could be the other way around. As heart rate increases, and time in diastole is reduced, you reach a point where EDV is reduced due to the short filling time, this would result in drop in stroke volume and BP. It will also result in a vicious cycle because the response to the low BP is increased Q, which requires greater heart rate, reduced time in diastole, further reduced EDV and stroke volume. Without more information, it is difficult to say which condition came first, low BP or tachycardia.





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