phuluong2k
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An individual whose CV system was operating at point A, Which is the most likely pertubation if his circulatory system operates at point B.
A. Blood transfusion
B. Exercise
C. Heart failure
D. Hemorrhage
E. Spinal anesthesia
Please give explanation, i always have confusion with this kind of question
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| ssrpk
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well let's see if i can work it out... :roll:
x axis - right atrial pressure (index of preload)
y axis - CO and venous return (index of cardiac performance)
N.B. remember CO nd VR moves in opposite direction
now, as we move along the x axis ,increasing the RAP , VR wud decrease as indicated ; but wht about the CO???
two factors control CO a)preload - via frank starlin mechanism
b)contractlity - via intracelluler Ca homestasis
and they both work independent of each other.
Now, on any given curve if u move along the x - axis(inc. the RAP) CO wud naturally be enhanced via frank starling mech. and this wud tend to keep the VR in control.(atleast initially)
However if u alter the contractlity u will able to get a new curve which wud either increase the CO on any given RAP (in addition to the effect of VR) OR CO wud be decreased relative to previous curves on any given RAP.
Factors increasing contractility : Sympathetic stimulation (short term)
hypertrophy (long term)
Factors decreasing contractility: Heart failure
Now let's consider the choices :idea:
(remember in the graph we hv a new curve representing inc. in contractility )
a)transfusion - tht wud only increase the preload not contractlility, so no
new curve
b)excercise - sure.... sympathetic stimulation
c)heart failure - NO WAY
d)hemorrhage - preload wud be reduced (RAP down the road)
e)spinal anesthesia - here we will get a new curve BUT it will reduce the
contractility coz of sypathectomy
[/b]answer is B)EXERCISE
one more confusing point here is ...y does VR get zero at high RAP
1)CO can't be further enhanced after a certain point.
2)RAP reduces the pressure gradient for blood to return.
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