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  #1  
Old 05-14-2015
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Default Q. confusing terminologies in lung mechanics

Can anybody pls help to clear my doubts.

While doing respiratory physiology, I came across these terminologies :
1. Intrapleural pressure
2.Chestwall transmural pressure
3. Intrathoracic pressure
4. Airway pressure.
5.Alveolar transmural pressure

My questions are:

1.In kaplan there is no such use of "transmural" pressure but U-world use it as mentioned above. Is there any difference between : alveolar pressure and alveolar transmural pressure , AND, between chestwall pressure and chestwall transmural pressure?

2. what is the difference between chest wall transmural pressure, airway pressure and intrathoracic pressure?

3.what exactly is this airway pressure? I have read about Continuous positive airway pressure but not simply "airway pressure" before and in kaplan too there is no such mention of airway pressure in lung mechanics.

4. During inspiration, intrapleural pressure, alveolar pressure, chest wall pressure & airway pressure all decreases (and increases during expiration) by virtue of the boyles law, is that right ? Pls correct me if I am wrong.

Thanks.
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Old 05-14-2015
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No reply, no explanation from anyone!!!!!!
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Old 05-15-2015
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Quote:
Originally Posted by Aumsai View Post
Can anybody pls help to clear my doubts.

While doing respiratory physiology, I came across these terminologies :
1. Intrapleural pressure
2.Chestwall transmural pressure
3. Intrathoracic pressure
4. Airway pressure.
5.Alveolar transmural pressure

My questions are:

1.In kaplan there is no such use of "transmural" pressure but U-world use it as mentioned above. Is there any difference between : alveolar pressure and alveolar transmural pressure , AND, between chestwall pressure and chestwall transmural pressure?

2. what is the difference between chest wall transmural pressure, airway pressure and intrathoracic pressure?

3.what exactly is this airway pressure? I have read about Continuous positive airway pressure but not simply "airway pressure" before and in kaplan too there is no such mention of airway pressure in lung mechanics.

4. During inspiration, intrapleural pressure, alveolar pressure, chest wall pressure & airway pressure all decreases (and increases during expiration) by virtue of the boyles law, is that right ? Pls correct me if I am wrong.

Thanks.

Transmural refers to 'pressure across'
For example, consider a hypothetical tube. The outside pressure might be -2. Inside the tube, pressure is +2. Trains mural pressure GRADIENT is the difference of pressures across the tube. Since they cancel out, it's zero.

Airway pressure, as the name suggests, is the pressure inside the air conducting system.

Intra thoracic pressure is pressure inside the thoracic cavity.
The lungs, being elastic(balloon) have a tendency to collapse.
The CHEST wall, on the other hand, is like a broken umbrella. It's nature is to expand.

Think of the set up - like, the lungs stuck to the chest wall with Velcro.

During inspiration, diaphragm goes down, chest goes out. This forces the lungs to expand, making the alveoli bigger (by stretching). Air obviously is not going to stretch, so it gets negative, and drags air from the atmosphere into the lungs.

The opposite happens in expiration, chest recoils, squeezes the lungs, and high pressure air exits.

Intra thoracic- pressure inside the chest, as the name suggests. It's always negative, and gets more neg- when you inspire! Can go from -5 to -13. This keeps the alveoli pulled open. So inspiration is made easy. Expiration is a passive process so it's anyway easy.

Remember, it's harder to inflate the first puff of a balloon than the mid. Then gets bars again at max stretch!! Surfactants n -be ITP helps in this.

Hope this helps
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  #4  
Old 05-15-2015
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Quote:
Originally Posted by Aumsai View Post
Can anybody pls help to clear my doubts.

While doing respiratory physiology, I came across these terminologies :
1. Intrapleural pressure
2.Chestwall transmural pressure
3. Intrathoracic pressure
4. Airway pressure.
5.Alveolar transmural pressure
Ok I didnt wanted to answer at first because the question you are having I have them too and I found a simple way out of all these in BRS Physio which I am gonna share first and then I will try to answer your questions:

Just remember two pressure to avoid confusion,they are:
Alverolar pressure: pressure of air inside the alveolus (Zero at FRC)
Intra-pleural pressure: pressure of air inside the pleura (-3cmH20 at FRC)

Now comes the fact of adding the term "-trans" to all these to confuse us!

3rd variety of pressure to remember is:
Trans-pulmonary pressure = Alveolar pressure - Intrapleural Pressure = 0 - (-3) = +3cm of H20(water) at FRC

Trans-pulmonary pressure means the tendency of air to travel from the alveoli into the pleura but obviously those two aint connected so basically suggests the pressure difference in the lung

Now coming to your questions:

Quote:
1.In kaplan there is no such use of "transmural" pressure but U-world use it as mentioned above. Is there any difference between : alveolar pressure and alveolar transmural pressure , AND, between chestwall pressure and chestwall transmural pressure?
Ans: Transmural pressure is the difference in pressure between two sides of a wall or equivalent separator.For lung physiology it is Transpulmonary pressure.

I dont know if chestwall transmural pressure = Transpulmonary pressure but from what I suspect chestwall pressure = - Intra-pleural pressure

and whenever we are adding the term -trans we basically try to point at a difference between two pressures.

Quote:
2. what is the difference between chest wall transmural pressure, airway pressure and intrathoracic pressure?
Ans: Airway pressure means the pressure in the airways obviously. Think of it like this, the airways are connected to the atmosphere via the nostrils so during FRC airway pressure = atmospheric pressure

Now coming to intrathoracic pressure, again it is the pressure inside the thorax, think of it like this,we consider the upper part of our body above the diaphragm as thorax so when we expire the diaphragm moves up thus decreasing the volume of the space called "thorax" we know a decrease in volume means increase in pressure, so when we are talking about intrathoracic pressure we are considering thorax as a space and then considering the change in volume and pressure.

Quote:
3.what exactly is this airway pressure? I have read about Continuous positive airway pressure but not simply "airway pressure" before and in kaplan too there is no such mention of airway pressure in lung mechanics.
Ans: I mentioned that the airways are connected to the atmosphere and so normally atm pressure = airway pressure (air in trachea and other resp tree exerting pressure), now in many diseases in artificial respirators we give positive airway pressure that is pressure greater than the atm pressure in the airways so that the partial pressure of oxygen will increase since the pressure itself is increasing making it easier for oxygen to diffuse into blood.

Quote:
4. During inspiration, intrapleural pressure, alveolar pressure, chest wall pressure & airway pressure all decreases (and increases during expiration) by virtue of the boyles law, is that right ? Pls correct me if I am wrong.
Ans: You are correct but I wont comment on the exact values of the -trans pressures because,

Trans-pulmonary pressure = Alveolar pressure - Intrapleural Pressure

So a greater decrease in intrapleral pressure than decrease of alveolar pressure might actually increase trans-pulmonary pressure.

Basically just know on expiration, Alveolar pressure and Intrapleural Pressure both individually decreases dont worry about the -trans ones


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  #5  
Old 05-15-2015
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Thanks Gokulramani for your nice explanation with superb examples like "elastic balloon", "broken umbrella" etc. Remembering this way gives theory a life force.

And, many thanks to cleverfox for addressing all my individual questions. You are awesome always.
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Old 05-16-2015
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Hey Cleverfox

You mentioned that intrapleural pr. at FRC is -3cm H2O. But, in U-world it's mentioned that at FRC it is -5cm H2O.Pls double check it.

Thanks.
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Quote:
Originally Posted by Aumsai View Post
Hey Cleverfox

You mentioned that intrapleural pr. at FRC is -3cm H2O. But, in U-world it's mentioned that at FRC it is -5cm H2O.Pls double check it.

Thanks.
Yeah I checked brs says -3cm h20 but indian authors and uworld says -5cm of h20 so stick with "-5"
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Old 05-16-2015
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Ok, thanks.
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