Cardiac Output and Blood Pressure

[sunshine02]

Does blood pressure influence cardiac output at all?

I know that blood pressure influences stroke volume, but then a decrease/increase in blood pressure also affects the sympathetic nervous system so that heart rate is increased/decreased, so wouldn't the cardiac output remain constant?

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[thehundredthone]

Actually it is cardiac output that influences blood pressure. The answer to your second question is no, because cardiac output is dependent on stroke volume and heart rate. The aortic/pulmonary arterial pressure during systole (which generates afterload) can affect stroke volume but we don't usually refer to it as blood pressure.

It depends on whether you're looking at the isolated dynamics or the physiology. In the lab, increasing cardiac output through stroke volume will increase blood pressure in the absence of feedback mechanisms. In physiology, the end point of regulation is blood pressure (and tissue perfusion), so the systems will compensate to maintain the desired blood pressure by adjusting either the cardiac output (through heart rate/stroke volume) or the total peripheral resistance.

Remember that cardiovascular feedback circuits sense changes in pressure and perfusion/O2 content, and not cardiac output.