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Old 12-20-2012
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Vascular Diastolic Blood pressure and compliance

Hi
Does anyone understand why DBP increases when compliance increases?
Thanks in advance
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Old 12-20-2012
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As diastolic B.P shows the volume of blood, so it means when compliance is increasing means it is showing the inc in volume of blood
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Old 12-20-2012
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compliance : how easily a vessel stretch with blood filling.

compliance = change in volume/ change in pressure.
If you are familiar with these kind of formulas. Then u'll see that compliance is directly proportional to change in volume and inversely proportional to change in pressure.

therefore increased compliance means decreased change in pressure ( this is pulse pressure calculated by SP - DP )

if diastolic pressure is increased pulse pressure is decreased.
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Old 12-21-2012
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Quote:
Originally Posted by obinocle View Post
compliance : how easily a vessel stretch with blood filling.

compliance = change in volume/ change in pressure.
If you are familiar with these kind of formulas. Then u'll see that compliance is directly proportional to change in volume and inversely proportional to change in pressure.

therefore increased compliance means decreased change in pressure ( this is pulse pressure calculated by SP - DP )

if diastolic pressure is increased pulse pressure is decreased.
I am aware of the formula and I agree with what you said. However, this ONLY applies to SBP (PP is more dependent on SBP than DBP)
so therefore if you increase your compliance, you decrease you SBP and hence your Pulse pressure (that's why the aorta has more compliance and hence low PP).

The question here is why does DBP increase with increased compliance? So essentially we're saying that the more you stretch a vessel, the more the pressure increases? It would make sense if we go by LaPlace's law: tension is proportional to: rP (radius and pressure), but if this applies to DBP, why not SBP? Afterall, they're both arterial pressures. Also, if you increase compliance, you're technically decreasing TPR because the vessel is now wider, if you decrease TPR you have to also decrease DBP as TPR is a major determinant of DBP.

Do you understand what I'm saying?
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Old 12-21-2012
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Quote:
Originally Posted by dr shamail View Post
As diastolic B.P shows the volume of blood, so it means when compliance is increasing means it is showing the inc in volume of blood
I'm not sure I understand what you're trying to say....
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Old 12-24-2012
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yea i get what you are saying.... and it's a really tricky one... any input guyz???
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Old 12-24-2012
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great explanation above, and i do remember seeing this question somewhere before, probably back in med school in one of our seminars. very tricky imo.
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Old 12-24-2012
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Quote:
Originally Posted by SarahM View Post
I am aware of the formula and I agree with what you said. However, this ONLY applies to SBP (PP is more dependent on SBP than DBP)
so therefore if you increase your compliance, you decrease you SBP and hence your Pulse pressure (that's why the aorta has more compliance and hence low PP).

The question here is why does DBP increase with increased compliance? So essentially we're saying that the more you stretch a vessel, the more the pressure increases? It would make sense if we go by LaPlace's law: tension is proportional to: rP (radius and pressure), but if this applies to DBP, why not SBP? Afterall, they're both arterial pressures. Also, if you increase compliance, you're technically decreasing TPR because the vessel is now wider, if you decrease TPR you have to also decrease DBP as TPR is a major determinant of DBP.

Do you understand what I'm saying?
compliance and elasticity are inversely related and are both properties of vessel wall. DBP depend on arterioles,which compliant vessels whereas SBP is highest pressure in cardiac cycle pressure mostly measured in elasticity arteries like aorta.
Laplace law detail about wall tension which occurs in elasticity arteries as aorta is more prone to develop aneuryms not vein which are compliant vessels.
hope i made my point bit clear as mnot good at explaining as i think u are confusing elasticity and compliance together.
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