We can calculate a heart rate maximum for humans using the equation 220-years of age. However, is there a systemic vascular resistance maximum for humans in either absolute or percentage?
I don't believe so. Since SVR is defined as (MAP - CVP)/CO, if CO tends to zero, SVR will tend to infinity.
Yes, but one cannot simply have an infinite SVR. There should be some upper limit as too how much vasoconstriction can occur in the peripheral vasculature. If SVR increases exponentially, blood flow will be reduced to practically zero. Since SVR is calculated mostly indirectly via CO, yes, it would be possible to have an "infinite" SVR, but that is simply not physiologically possible. I will have to perform some research on the subject to gain some more insight. Thanks for your feedback.
I think that SVR can not be considered as a final determinant. The resistances in transport arterial segment and in resistive segment are defined by different mechanisms. So the approach to SVR analysis should be specified by particular circulatory pool.
Good point Alexandre. Based on %CO to different organ systems, one could determine the SVR for a specific organ system, this is where impedance measurements would come in handy. The total SVR is the sum or average of organ system SVR's, which would be based on the current oxygen demand of that organ system. During physical activity, SVR in the skeletal muscle decreases, due to high 02 demand, whilst gastrointestinal SVR increases, for example. The total SVR would not reflect this distribution then. In this light, I guess I would have to rephrase my question, in asking if there is an organ specific SVR maximum?
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