I was confused about a similar question so I emailed feedback. I actually really recommend this- they respond within a few days if you tell try to them they are wrong. To answer your second question more specifically I think FA 2016 does a poor job by distinguishing sympathetic effect with exercise effect. The graphs are trying to show things in isolation- for instance graph 1 is showing the effect of change in inotropy. It is NOT showing the effect of catecholamines on the CV curves- but it is giving the example that catecholamines can influence inotropy and a change in inotropy is shown in the graph.
Increased sympathetic activity via activation of a1 receptors will cause venoconstriction which will increase venous return (less blood in the compliant/unstressed veins) -> increased RA pressure-> increased preload which will manifest as a shift to the right of the venous function curve with an increased mean systemic pressure. But sympathetic activation of b1 receptors should also increase CO independently of preload (ie increased contractility) causing an upward shift of the CO curve. FA even says this in curve 1 giving the example of catecholamines increasing contractility.
However I think pure sympathetic stimulation can be differentiated from exercise since sympathetics will generally increase TPR through vasoconstriction of splanchnic arterioles whereas exercise will decrease TPR via b2 activation/local metabolites causing vasodilation in arterioles supplying skeletal muscle capillary beds.
ME:
Hi- I don't see how the venous curve would rotate upward- increase in blood volume should not decrease resistance (Costanzo Physiology pg 162). And if resistance does in fact decrease there should be a corresponding increase in cardiac output due to decreased afterload.
Question ID: aOL1999
the good folks over at KAPLAN:
Hello,
Thank you for contacting MedFeedback. As you say, increasing blood volume would have no direct effect on systemic vascular resistance and negligible effect on resistance to flow through the venous system.
The clockwise rotation of the vascular function curve indicates that sympathetic activity has decreased and that systemic vascular resistance has fallen as a consequence (vasodilation). This is not mentioned in the explanation. In practice, there would be a concomitant rotation of the cardiac vascular function curve through reduced myocardial drive, but this is not shown in the graph. We will edit the explanation to clarify.
Best wishes,
MedFeedback
