santaclara
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physiopulmonolgist working on presuure volume relation during inspiration and expiration of lung. he starts from intrapleural pressure -3 mmHg he found that the volume is 1500 ml at rest.during inspiraion he meaured volumes of the lung at different inrapeural pressure of -6, -7, -8, -9, 10..he found that at intrapeural pressure of -8 that is 3000 ml of lung vulme during inspiration. during expiration at same pressure of -8 he will found that lung volume will be
A. 2800 ml
B. 3000 ml
C. 3200 ml
D. 2500 ml
E.29000 ml
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| mani
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A. 2800 ml
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| santaclara
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what is your idea how the answer is"A".
what about"C".
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| hiwa
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3000
the intrapleural pressure is the same, so the volume should be the same.
at this point the the turning point from inspiration to expiration.
If there was any change in the lung volume the pleural pressure should have been different
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| santaclara
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In reply to the query below for a question of explanantion, dear ! you cannot understand it till you read compliance and have a look at the graph lung-volume versus Pressure change during inspiration and expiration.
Compliance is defined as the change in volume by unite change in pressure i.e
compliance C = Delta V/delta P
C= compliance
Delta V = change in volume
Delta P = change in Pressure
And if you have a look on the graph you see that curves of inspiration and expiration form a loop.They are not alike.One is curving right and the other left.
For each given pressue ,volume of lung during inspiration is less as during epiration.But this thing you can only appreciate on the graph.Logic behind is that during inspiration that Airway resistance is less during inspiration while more during epiration (just an idea about it)
So we can conclude if at some particular pressure say -8 mm of H2o lung volume was 3000 ml during inspiration ,then at the same pressure lung volume will be more at the same prssure
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| santaclara
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hey dear this is not my own explanation. i asked some one else and that person replied like this.
can u conclude any idea from this discription pls also explain it.
thanx.
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| mani
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this is how i understand it:
if u loof at the curve of complaince (as in BRS) the path for inspiration and expiration are different and this is called hysterisis. So according to this curve the lung volume is lower at a given intrapleural pressure is lower during expiration than at inspiration
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| hiwa
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all u say is right the INTRAALVEOLAR pressure become negative during inspiration for the air to flow in, BUT the intraalveolar pressure is not used to measure the compliance of the lung, it is the intrapleural pressure change used to measure compliance of the lung, and if u apply the numbers in ur equation it is still 3000
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| santaclara
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u r right.then what do u think what is the answer of above Q?
as where i read that Q the answer is "C".
can u tell me one thing in BRS patho what do u mean by this line
"at high expanding pressure,compliance is lowest.the lungs r least distensible and the curve is flattens."
pls read this on page 131 of BRS.
pls reply.
thanx and good luck.
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| hiwa
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I dont know which curve u talking about.
again look at the equation, if u have high pressure, decreased compliance, the lung must be least distensible(ie least volume change)
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| santaclara
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so hiwa according to u answer should be less then 3000 but i m still thinking that i also post this Q on onther website also and they replied like that during expiration the resistnace is more so volume is more.
i m also still confused dear.
thanx for reply.
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| mani
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santaclara, can u tell from where this question is?? and have they given any explanation?
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| santaclara
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some body post this Q on USMLE.NET.
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