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Old 10-28-2011
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Question Nitrates and myocardial oxygen consumption

FA 2011 Page 281 said Nitrates will decrease myocardial oxygen consumption.
Can anybody explain why??
cuz Nitrates will increase contractility and HR (via reflex response), I thought it would increase oxygen consumption.
Thx for help!!
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Old 10-28-2011
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Originally Posted by ZoeZ View Post
FA 2011 Page 281 said Nitrates will decrease myocardial oxygen consumption.
Can anybody explain why??
cuz Nitrates will increase contractility and HR (via reflex response), I thought it would increase oxygen consumption.
Thx for help!!

Nitrates are prodrugs of nitric oxide

Will produce Venodilatation: that means less blood coming back to the heart( remember veins are the major reservoirs of blood in the body)

So Venodilatation-> less preload-> less cardiac work -> less oxygen requirment.

So as veins are very compliant, they can act as major blood pools, and prevent more blood coming in to the heart, so the heart works less.

One thing you said was correct. Considering all this may lower the B/P one should think of reflex tachycardia.
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Old 10-31-2011
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Thx, LatinGeorge~!
Yes, as you said, nitrates will decrease the preload, but the myocardial oxygen consumption is related with heart rate, contractility, afterload, and preload.

In the case of nitrates, preload decrease, afterload decrease, but both heart rate and contractility increase. however the total effect is still decreased cardiac oxygen consumption.

so it means in thie case the net effect of afterload and preload outweighs the effect of heart rate and contractility?
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Old 10-31-2011
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Originally Posted by LatinGeorge View Post
Nitrates are prodrugs of nitric oxide

Will produce Venodilatation: that means less blood coming back to the heart( remember veins are the major reservoirs of blood in the body)

So Venodilatation-> less preload-> less cardiac work -> less oxygen requirment.

So as veins are very compliant, they can act as major blood pools, and prevent more blood coming in to the heart, so the heart works less.

One thing you said was correct. Considering all this may lower the B/P one should think of reflex tachycardia.
thanks a lot for explanation
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