stroke volume question

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Oct 5, 2011
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Stroke volume is the amount of blood ejected by the ventricle in one beat and is determined by ventricular preload, afterload, and contractility. How can stroke volume be decreased?

a) Increase heart rate
b) Increase ventricular contraction
c) Decrease aortic pressure
d) Decrease total peripheral resistance

Guess I'm having a hard time visualizing why A is correct, and why the other options are incorrect.

I know cardiac flow = heart rate x stroke volume.

a) so, (cardiac flow/heart rate) = stroke volume, an increased heart rate would = a lower stroke volume.

b) this would be an increase in stroke volume?

c) this would decrease cardiac flow??? which would mean an increased stroke volume?

d) this would decrease cardiac flow??? would would mean an increased stroke volume?

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Stroke volume is influenced by exercise, contractility (duration and strength), preload, and afterload. The answer choices all stem from one of these factors.

A) Increase heart rate -> lowers stroke volume
*I believe it refers to the resting heart rate. A professional athlete that exercises more should have a lower resting heart rate. Normal heart rate is between 60-100 beats/minute. Marathon runner or someone similar should have 40 or less. A lower resting heart rate means a more efficient heart (more time for the heart to fill with blood) -> increased stroke volume. An increased resting heart rate gives you the opposite, hence this is the correct answer.

B) Increase ventricular contraction -> increased stroke volume
*This is more straightforward; a longer/stronger contraction should give you more blood ejected -> increased stroke volume

C) Decrease aortic pressure -> increased stroke volume
*Greater aortic pressure due to narrowing of aorta means the left ventricle has to overcome more pressure than usual, which means more blood left in the left ventricle. Having less aortic pressure has the opposite effect; the left ventricle has to overcome less pressure than usual, so it can eject more blood, hence increasing stroke volume.

D) Decrease peripheral resistance -> increased stroke volume
*People with hypertension -> elevated blood pressure due to increased total peripheral resistance; heart has to work harder to pump blood, more blood left in the heart than usual. Lower total peripheral resistance has the opposite effect

This is good study material as I didn't know either/had to look it up to understand. Hope this helps.