A stupid question but it's really confusing. How does vasodilation improve perfusion as we're told but at the same time decrease blood pressure? Aren't those two things mutually contradictory? If blood pressure decreases then perfusion would also deteriorate?
not a stupid question at all. when we talk about vasoconstriction and BP we are taking about systemic resistance, eg. the combined effect of all the blood vessels constricting through out the body. when we talk about vasodilation and perfusion we are often referring to the smaller blood vessels supplying local tissues. The smaller blood vessels, direly supplying the tissue, need to be dilated enough to allow blood to flow. At the same time, larger vessels may be constricting increasing BP. Hope that's helpful, its a complicated question that's hard to answer in brief.... Dan
I don’t understand how you say if the heart beats too fast there will be no time to fill it in adequate amounts so the blood ejected will be lower thus cardiac output will be lower but then you say that if we increase heart rate, cardiac output will increase?? Doesn’t one contradict the other?
there is a diminishing return to increased heart rate. Up to a point an increased HR will increase output, and therefore BP. However if HR increases too much then filling time (preload) begins to be adversely effected and BP will be reduced. The heart has to be going pretty fast before BP starts to reduce. Hope that makes sense.
