Adrian Fogarty wrote:
> Surely increasing the EDV will produce a tachycardia to increase the
> cardiac output. That's what happens in exercise; there is an increased
> venous return resulting in raised EDV which produces tachycardia.
> Similarly, in a vasovagal collapse, we used this technique to restore
> EDV and thereby increase the cardiac output. So what I'm saying is,
> how does "decreasing the heart rate" "maintain the cardiac output" as
> you're suggesting?
Your physiology is probably much better than mine, but in exercise your
oxygen requirements are greater, so both your stroke volume and heart
rate increase to imporve cardiac output. Theoretically in someone at
rest , if you passive leg raise then you autotransfuse increasing venous
return, stroke volume increases, cardiac output does not need to go up,
therefore heart rate would fall. The effect must all be down to those