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  #1  
Old 09-07-2011
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Help NBME 1 Concept - Respiratory Physiology

how would a patient with pulmonary fibrosis decrease his work of breathing

Respiratory frequency / tidal volume

a) decrease / decrease
b) decrease / normal
c) decrease / increase
d) increase / decrease

pls help me out
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Old 09-07-2011
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pts wid restrcictive lung disease hav low TV(u can check the the pulm function test graph- which is vry high yield). so option B nd C are out... now also they hav low elastic recoil i.e. they cannot expand their lungs fully i.e they have to breathe more frequently then normal to maintain O2 sats....so answer is D)....
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Old 09-08-2011
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just wanted to clear my concept. i thot to reduce work of breathing he should take slow deep breaths so that he can improve alveolar ventilation and reduce the dead space ventilation
in that case the answer would be decrease in respiratory rate and increase in tidal volume
let me know if i my concept is wrong .my respiratory system is a bit on weaker side./...any idea how i can improve on it
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Old 09-08-2011
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Help pulmonary fibrosis

actually if i think of what i said now...i realize that i m wrong
if a person with with restrictive profile increases his respiratory rate and decreases his tidal volume it would put more stress on his work of breathing since he has difficulty in taking in air

can u answer this also, how would a person with obstructive disease decrese his work of breathing
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Old 09-08-2011
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Some one pls can u tell the answer
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Old 09-08-2011
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In pulmonary fibrosis, compliance of the lungs is reduced. Thus a greater increase in pressure is needed to produce the same increase in volume. In order to avoid doing that, the patient breathes smaller tidal volumes but makes up for it by increasing the RR so that in effect the minute ventilation remains the same and patient gets adequate oxygenation as possible. Hope that helps.
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Old 09-09-2011
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Quote:
Originally Posted by winner21 View Post
actually if i think of what i said now...i realize that i m wrong
if a person with with restrictive profile increases his respiratory rate and decreases his tidal volume it would put more stress on his work of breathing since he has difficulty in taking in air

can u answer this also, how would a person with obstructive disease decrese his work of breathing
so yeah here you are right but i disagree with u with ur previous post..
cuz u know if u inc the work of breathing, means ur lungs into more work. its like aortic stenosis (ur increasing the after load but net fluid going out is less than normal)
and also since ur lungs are working more and net effect is lack of o2 supply and in order to get more o2, lungs work harder and therefore tidal volume is low! cuz if the tidal vol was normal then lungs didn have the need to work hard to obtain more o2!
so the ans is D, hope this helps!
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  #8  
Old 12-20-2011
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Thumbs Up Basic physics guys...

When you get such a question, always enumerate the determinants of that variable [ in this example, first try to know what are the factors that determine the work done ].

Let us try to do that first.

BACKGROUND ::
Work done during normal respiration is during inspiration ( to overcome the elastic recoil of the airways; note that this work is increased in fibrosis as the airways become more elastic ; also note that this work is decreased in obstructive disease like emphysema as the airways recoil is less due to the destruction of the airways ).

Expiration is normally a passive process and you would virtually spend no energy during expiration [although in obstructive diseases as there is a dynamic obstruction caused by the airways during expiration, you would have to spend some energy (so do some work) to overcome the obstruction and push the air outta the lungs ].

So guys, this brings us to the point that, in fibrosis, work done is more during inspiration and in obstructive diseases, work done is more during expiration.

-------------------------------------------------------------------------

Now, let us see what the determinants of the energy spent are.

The chief determinants are [Below are applicable to fibrosis only]

1)The elastic recoil of the lungs ( during inspiration )

2) The rate of respiration.

More the elastic recoil, more the work you do. [ As a simple comparision, get yourselves reminded of the automated doors [swing door] that we have in many places. They would have an elastic joint-pivot behind the door, using which the door automatically shuts off. Remember, when you open such a door, you would have to use more energy than that you use on normal doors which doesn't have such elastic mechanism - like our bathroom doors. ] This has the same mechanism. When the recoil force is more, like in firbosis you would have to do more work.

Rate :: You do more work when you open that door 100 times than when you open it once, right???
Same here, when you increase the rate of respiration, you would have to overcome that resistance repeatedly, and so you have to do more work.

Hence, according to the above determinants, we can conclude that


Work done during respiration = Elastic recoil x REspiratory rate.

Alright, now that you know this. Let us now take a step forward. Imagine you have 2 people one who is very lean and one who is very fat. You are asked to open the door to let them come in. So, for the lean guy ( whose width is say 40cms ) to pass through the door, you would have to open it, let us say 1/4rd (so that it creates a space of 40cms. Imagine that the door if fully open would create a space whose width is 160cms]. Now for the fat guy ( width is 80cms ) you would have to keep the door 1/2 open, right?

In your lungs, the only guy that goes is the AIR. So the more air you take in(tidal volume), the more wide you have to keep the airways, the more work you have to do to do against the recoil [more air = like the fat guy; less air = lean guy]

Now can we make a new formula??

Work done = (tidal volume) x elastic recoil x respiratory rate.

So, as the elastic recoil is same in a given patient and because the given variables in the questions are the TV and RR.

We can see that work done = tidal volume x respiratory rate.

It should be clear by now that, decreasing both the tidal volume and respiratory rate would decrease the total work done. Hope it helped....
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  #9  
Old 12-20-2011
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Thumbs Up Basic physics guys...

Guys, Please note that the above given explanation is wrong. Please go through this. I am sorry for the trouble caused.

When you get such a question, always enumerate the determinants of that variable [ in this example, first try to know what are the factors that determine the work done ].

Let us try to do that first.

BACKGROUND ::
Work done during normal respiration is during inspiration ( to overcome the elastic recoil of the airways; note that this work is increased in fibrosis as the airways become more elastic ; also note that this work is decreased in obstructive disease like emphysema as the airways recoil is less due to the destruction of the airways ).

Expiration is normally a passive process and you would virtually spend no energy during expiration [although in obstructive diseases as there is a dynamic obstruction caused by the airways during expiration, you would have to spend some energy (so do some work) to overcome the obstruction and push the air outta the lungs ].

So guys, this brings us to the point that, in fibrosis, work done is more during inspiration and in obstructive diseases, work done is more during expiration.

-------------------------------------------------------------------------

Now, let us see what the determinants of the energy spent are.

The chief determinants are [Below are applicable to fibrosis only]

1)The elastic recoil of the lungs ( during inspiration )

2) The rate of respiration.

More the elastic recoil, more the work you do. [ As a simple comparision, get yourselves reminded of the automated doors [swing door] that we have in many places. They would have an elastic joint-pivot behind the door, using which the door automatically shuts off. Remember, when you open such a door, you would have to use more energy than that you use on normal doors which doesn't have such elastic mechanism - like our bathroom doors. ] This has the same mechanism. When the recoil force is more, like in firbosis you would have to do more work.

Rate :: You do more work when you open that door 100 times than when you open it once, right???
Same here, when you increase the rate of respiration, you would have to overcome that resistance repeatedly, and so you have to do more work.

Hence, according to the above determinants, we can conclude that


Work done during respiration = Elastic recoil x REspiratory rate.

Alright, now that you know this. Let us now take a step forward. Imagine you have 2 people one who is very lean and one who is very fat. You are asked to open the door to let them come in. So, for the lean guy ( whose width is say 40cms ) to pass through the door, you would have to open it, let us say 1/4rd (so that it creates a space of 40cms. Imagine that the door if fully open would create a space whose width is 160cms]. Now for the fat guy ( width is 80cms ) you would have to keep the door 1/2 open, right? Now, the more you open the door, the more you have to work against the resistance of the door.

In your lungs, the only guy that goes is the AIR. So the more air you take in(tidal volume), the more wide you have to keep the airways, the more work you have to do to do against the recoil [more air = like the fat guy; less air = lean guy].

So the elastic recoil of the lung is proportional to the tidal volume.

Now can we make a new formula??

Work done = (tidal volume) x respiratory rate.

It should be clear by now that, decreasing both the tidal volume and respiratory rate would decrease the total work done. Hope it helped....
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  #10  
Old 12-20-2011
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i dont get it
like he decreases both but then he will die
if it is just to answer how u decrease work ,u can just shoot him and he will stop breathing and work is zero
i think the question is like how a pt with fibrosis can decrease work without dying or turning blue so i would choose decrease/increase..
im not sure but that what would i choose
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Quote:
Originally Posted by dr.muhamad View Post
i dont get it
like he decreases both but then he will die
if it is just to answer how u decrease work ,u can just shoot him and he will stop breathing and work is zero
i think the question is like how a pt with fibrosis can decrease work without dying or turning blue so i would choose decrease/increase..
im not sure but that what would i choose

Dear Dr. Muahmad, decrease of both RR and TV doesn't necessarily mean that we are making the patient cyanotic and allow him to die. Remember even if you decrease the respiratory rate by 1% and TV by 1%, you are decreasing both and I don't believe that a patient would die just because you reduced the respiratory rate and TV by 1%. Imagine that the patients respiratory previously was some 40, and now if he reduces it to 38 and if he reduces his tidal volume to 420 ( from the previous 430 ), do you think the patient would die???

NO, He wouldn't. Although, there might be a proportional decrease in Sp02 and Pa02, I do not believe that he would die and this can be done to reduce the work of breathing.

Hope this helps.
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Old 12-20-2011
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Originally Posted by docchitra View Post
Dear Dr. Muahmad, decrease of both RR and TV doesn't necessarily mean that we are making the patient cyanotic and allow him to die. Remember even if you decrease the respiratory rate by 1% and TV by 1%, you are decreasing both and I don't believe that a patient would die just because you reduced the respiratory rate and TV by 1%. Imagine that the patients respiratory previously was some 40, and now if he reduces it to 38 and if he reduces his tidal volume to 420 ( from the previous 430 ), do you think the patient would die???

NO, He wouldn't. Although, there might be a proportional decrease in Sp02 and Pa02, I do not believe that he would die and this can be done to reduce the work of breathing.

Hope this helps.
yea i got this thanks but what i meant is that they should say something in the stem of the question to direct you to that ,,i mean like in general fibrosis of the lung make the patient hyperventilate coz he needs O2 so he is not doing an extra work just for fun
so what i meant is like u want to keep him ventilating with the same amount of O2 but still decreasing the work so it would be decrease/increase
i am with you that decrease both (maybe just1%) would decrease the work and it is right concept but clinically why would you do that??
i guess the stem of the question should mention that you want to decrease the work but still having the same amount of O2
so you can pick the answer you like then
i hope you get what i meant
btw your explanation above is great
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Old 12-21-2011
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Quote:
Originally Posted by dr.muhamad View Post
yea i got this thanks but what i meant is that they should say something in the stem of the question to direct you to that ,,i mean like in general fibrosis of the lung make the patient hyperventilate coz he needs O2 so he is not doing an extra work just for fun
so what i meant is like u want to keep him ventilating with the same amount of O2 but still decreasing the work so it would be decrease/increase
i am with you that decrease both (maybe just1%) would decrease the work and it is right concept but clinically why would you do that??
i guess the stem of the question should mention that you want to decrease the work but still having the same amount of O2
so you can pick the answer you like then
i hope you get what i meant
btw your explanation above is great
I completely understand, what you are trying to tell me. But, physiology is more of physics and experiments. The question basically is trying to know if you know the basics of energy consumption in the lungs. Questions in physiology can be at times experimental, although in many cases you would also have to consider the compensatory mechanisms of the normal body. Consider this as an experiment where you are doing this to decrease the energy levels of the patient. And moreover, even by doing both of these (dec RR, dec TV ), you can supplement oxygen {% grater than 21%, i.e, room air) to the patient that compensates for the decrease of TV. I hope you know what I mean.
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