USMLE Forums banner
1 - 4 of 4 Posts

·
Registered
Joined
·
62 Posts
Discussion Starter · #1 ·
can anyone explain the effect of standing and lying down on preload? and the mechanism also..........
 

·
Registered
Joined
·
121 Posts
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!!!
 

·
Registered
Joined
·
121 Posts
But how does preload increase with squatting ? what is the pathophysiology ?
Hi Zamzam,
Actually here I was talking about normal condition. But you are referring to TOF , a congenital disease where pulmonary valve stenosis is present as well as a VSD(plus 2 more). Blood needs more pressure to go to the pul artery than in aorta(opposite of what normally happens). Sometimes , depending on the severity of stenosis, blood doesn't go to the pul artery at all, resulting in a very severe "artificial" hypovolemic stage. This can be end up in brain hypoxia and even death. It is called "tet spell". Older kids can guess the situation, so they squat. That simply increases the total peripheral resistance and blood pressure builds up in aorta>LV>through VSD , RV> more pressure to pass through the pulmonary stenosis = symptoms relieved.

I hope I made myself clear.good luck.
 
1 - 4 of 4 Posts
Top