can anyone explain the effect of standing and lying down on preload? and the mechanism also..........
while lying down , gravitation force is equally implied on the whole body. so no change in blood supply by that ( well, due to equal distribution of blood this way , we prescribe lying down all the time with simple pre-renal azotemia = increased clearance ).
but when we stand up, gravitation comes to play , pulls the blood in leg , veins are reallllly compliant and holds a big amount of that. so, there is an artificial volume shortage in the body . carotid receptor senses that and fires less/actaivated less and sympathetic system is activated.increases TPR , so BP increased and body has a normal perfusion restored,again.
so,upon standing pre load decreases.but it becomes normal overtime with good autonomic circuitry.
if this total circuit is deficit somewhere, orthostatic hypotension occurs.or you can call it autonomic dysfunction.
all that being said, i know i am not wrong but also this is like a very distant memory of mine.so, plz the entire wisedom cumulated in this forum, CORRECT ME!!!