vallmo
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A decrease in HR (while stroke volume and peripheral resistance remain constant will cause increase in:
a. arterial diastolic pressure
b.arterial systolic pressure
c.cardiac output
d arterial pulse pressure
e. mean arterial pressure
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| mani
Forum Guru
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a. arterial diastolic pressure ?
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| Renegade
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Why, if peripheral resistance remains constant :?:
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| vallmo
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The right answer=d: (explanation given
The arterial pulse pressure increases when the heart rate decreases but the stroke volume and peripheral resistence remain constant.
A constant stroke volume coupled with a decreased heart rate produces a decrease in cardiac output. The reduced flow, in tandem with the constant peripheral resistance, means that the mean arterial pressure must decline. The fact that the pulse pressure increases is obtained from an analysis based on the vascular elastic modulus:
E =V *P/dV
(E=elastic modulus, v= arterial volume(which is determined by the arterial pressure), p=pulse pressure, dV= arterial uptake)
When cardiac output is reduced, arterial pressure, and therefore arterial volume decrease. The arterial uptake remains constant because it is primarily related to stroke volume. To maintain the elastic modulus, which varies nly as a function of age, as a constant, the pulse pressure must increase to counteract the decreased arterial volume
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| luckiest
Forum Senior
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Why is the elastic annulus have to remain constant? Does TPR have to increase to keep BP constant .I mean BP VS elastic annulus what is more important to keep it normal? :?
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| vrach
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Dude!!! you totally lost me on that explination. It's too hi-fi for me. The way I understood it (Kaplan style) is: if you are decreasing the heart rate, like you said, the cardiac output and mean arterial pressure would decrease, if the SV and TPR are kept constant.
A decrease in heart rate is due to an increase in the diastoli. This means that there is more time available for the arteries to empty. So the diastolic presseure will decrease and thus increase the pulse pressure. There should be no change in the systolic pressure since the after load, which is TPR hasen't changed. Since Diastolic pressure is the major component of MAP, it will have to decrease.
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| vallmo
Forum Junior
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Well, its too high level for me also :oops: , that is the exact answer the book had for the q.
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