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#1
12-20-2012
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Diastolic Blood pressure and compliance

Hi
Does anyone understand why DBP increases when compliance increases?
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#2
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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#3
12-20-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 304 Threads: 48 Thanked 291 Times in 106 Posts Reputation: 301

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.

#4
12-21-2012
 USMLE Forums Addict Steps History: Not yet Posts: 164 Threads: 35 Thanked 147 Times in 47 Posts Reputation: 157

Quote:
 Originally Posted by obinocle 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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#5
12-21-2012
 USMLE Forums Addict Steps History: Not yet Posts: 164 Threads: 35 Thanked 147 Times in 47 Posts Reputation: 157

Quote:
 Originally Posted by dr shamail 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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 The above post was thanked by: cooooh (03-07-2014)
#6
12-24-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 304 Threads: 48 Thanked 291 Times in 106 Posts Reputation: 301

yea i get what you are saying.... and it's a really tricky one... any input guyz???
#7
12-24-2012
 USMLE Forums Guru Steps History: Not yet Posts: 315 Threads: 115 Thanked 161 Times in 85 Posts Reputation: 171

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.
#8
12-24-2012
 USMLE Forums Scout Steps History: Step 1 Only Posts: 65 Threads: 8 Thanked 16 Times in 11 Posts Reputation: 26

Quote:
 Originally Posted by SarahM 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.

 Tags Cardiovascular-, Physiology-

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