Pleural pressure and Guyton?
The latest edition of Guyton states in chapter 37 on page 472 that: "The normal pleural pressure at the launch of inspiration is about -5 centimeters of water, which is the amount of suction required to hold the lungs open to their resting level"
-5 cm H20 = -3.68 mm Hg
In the subsequent chapter, 38, on pages 489-491 it states:
" Because the normal collapse tendency of the lungs is going on for -4 mm Hg, the pleural fluid must always be at least as negative as -4 mm Hg to maintain the lungs expanded. Actual measurements have shown that the pressure is usually about -7 mm Hg.
As you can see there is a chief inconsistency. On one hand, in Chp. 37 a pressure of -3.86 mm Hg is seen at the formation of inspiration and as the inspiration progresses it drops to 7.5 cm H20 (-5.5 mm Hg).
On the other hand, in Chp. 38 a pressure of -7 mm Hg is required just to hold on to the lungs expanded.
So my question is :Which one is it? -3.86 mm Hg ( -5 cm H20) or -7 mmHg. What pleural pressure is required to keep the lungs expanded.
You will note that a pressure of -3.86 mm Hg would, according to chp 38 (which give a pressure of -7 mm Hg) collapse the lung, and would not permit the initiation of inspiration. Even the -7.5 cm H20 pressure, which is -5.5 mm Hg, that is stated to be seen during the course of inspiration would not meet your requirements to even keep the lung expanded, if the -7 mm Hg pressure is to be believed.
Thoughts and ideas, if you will...
Answers:
Thumbs up to Peter H.
And as a former student of Arthur Guyton, I enjoy to add: picky, picky!
I only know a little physiology.
The main subject matter is the negative pressure required to keep the lung from collapse. Getting a reading on these types of things is an experimental challange. Its not something that a medical doctor is going to do on a daily font with his/her patients.
It is the concept that is important.
Relax. I agree it looks untidy, but the authors of the separate chapters hold probably used figures from different references based on different populations. In respectively case it is only an average value which is reported, and it would not surprise me if the span for the population as a whole was the mean +/- a few mmHg.
Actually, you enjoy slightly misread the second chapter, where it says that the normal collapse proclivity is about -4 mm Hg (a figure which is almost identical to the -3.68 mm of the first chapter). The -7 mm Hg is more than sufficient to counteract this, and -5.5 would be more than sufficinet too. Source(s): BSc surrounded by physiology
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-5 cm H20 = -3.68 mm Hg
In the subsequent chapter, 38, on pages 489-491 it states:
" Because the normal collapse tendency of the lungs is going on for -4 mm Hg, the pleural fluid must always be at least as negative as -4 mm Hg to maintain the lungs expanded. Actual measurements have shown that the pressure is usually about -7 mm Hg.
As you can see there is a chief inconsistency. On one hand, in Chp. 37 a pressure of -3.86 mm Hg is seen at the formation of inspiration and as the inspiration progresses it drops to 7.5 cm H20 (-5.5 mm Hg).
On the other hand, in Chp. 38 a pressure of -7 mm Hg is required just to hold on to the lungs expanded.
So my question is :Which one is it? -3.86 mm Hg ( -5 cm H20) or -7 mmHg. What pleural pressure is required to keep the lungs expanded.
You will note that a pressure of -3.86 mm Hg would, according to chp 38 (which give a pressure of -7 mm Hg) collapse the lung, and would not permit the initiation of inspiration. Even the -7.5 cm H20 pressure, which is -5.5 mm Hg, that is stated to be seen during the course of inspiration would not meet your requirements to even keep the lung expanded, if the -7 mm Hg pressure is to be believed.
Thoughts and ideas, if you will...
Answers:
Thumbs up to Peter H.
And as a former student of Arthur Guyton, I enjoy to add: picky, picky!
I only know a little physiology.
The main subject matter is the negative pressure required to keep the lung from collapse. Getting a reading on these types of things is an experimental challange. Its not something that a medical doctor is going to do on a daily font with his/her patients.
It is the concept that is important.
Relax. I agree it looks untidy, but the authors of the separate chapters hold probably used figures from different references based on different populations. In respectively case it is only an average value which is reported, and it would not surprise me if the span for the population as a whole was the mean +/- a few mmHg.
Actually, you enjoy slightly misread the second chapter, where it says that the normal collapse proclivity is about -4 mm Hg (a figure which is almost identical to the -3.68 mm of the first chapter). The -7 mm Hg is more than sufficient to counteract this, and -5.5 would be more than sufficinet too. Source(s): BSc surrounded by physiology
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