Lung overexpansion

[tbone1004]

both of those have your epiglottis open for most of it. Violent coughing fits I imagine would cause some temporary issues, but nothing long lasting. Your body has some pretty impressive self preservation tricks and while I'm sure your diaphragm is strong enough to cause an injury, I doubt the average person would have enough control over their body to be able to force it to do that....

 

[drrich2]

both of those have your epiglottis open for most of it.

True. Even so, for the air to be forcefully expelled, it has to be under significant positive pressure. Witness how far one can inadvertently blast something across a room.

Similarly, kids holding their breaths may puff out their cheeks and are obviously holding against some pressure. Not much, granted, but TS&M's mention of a roughly 2 PSI difference being problematic, at least in rare cases, got me wondering what pressure differences happen all around us every day.

Richard.

 

[TSandM]

Yes, medical pressure measurements are done in torr, not psi.

When we put patients on a ventilator, we are very vigilant to monitor the pressure it is taking to give them the volume of breath we wish to deliver. Certain conditions can cause the lungs to become stiff and resistant to inflation, thus raising the required pressures. We know if the pressure gets high enough, we run serious risk of popping a lung. Of course, these lungs are by definition less compliant than the normal, which may actually make them MORE resistant to barotrauma.

The bottom line is that lungs are pretty fragile balloons, and don't tolerate much inflation pressure. They're designed to be inflated by being surrounded by a relative, mild vacuum, and not to hold positive pressure at all.

I did a brief search and found one paper about pressures generated by forceful coughing. The highest they recorded was about 4 psi. The paper had only a handful of subjects, and the peak pressures were obviously very brief. This is not entirely equivalent to the prolonged and steadily increasing pressure created by surfacing from depth with a closed glottis.

 

[socc]

I suppose most people do not know how to close their glottis and still push more air in the lungs while they are fully inflated. I mean if I get a full breath I do not know how to force more air in than that. So I suppose generally whatever hard you try you cannot inflate your lungs more that they take simply because most people do not know how or cannot control their body in such a way.

 

[dumpsterDiver]

Ever blow up a balloon? An everyday example of generating pressure in the lungs which exceeds the ambient.

 

[socc]

Ever blow up a balloon? An everyday example of generating pressure in the lungs which exceeds the ambient.

Yeah sure but there you have a resistance from the latex of the balloon thats why - you put that pressure on the balloon to inflate not in your lungs (your lungs just generate that pressure). When your lungs are full and you cannot suck more air than that, then there is no way unless you use some technique like packing as you mentioned before, to push more air in the lungs than full capacity. I suppose you need to know a technique as well as put some force in order to fill something that is already full. If you see what I mean.

I am just trying to understand how easy can someone cause an overexpansion injury to his lungs by just trying very hard to take the biggest deep breath that he/she possibly can. People that just taking as much as deep breaths as they possibly can, I suppose they cannot hurt themselves because they just do not know the way to push more air in their lungs that they can take, whatever they try. Am I assuming this right ?

 

[TSandM]

Socc, the way air is drawn into the lungs is that the diaphragm (bottom limit of the chest cavity) and ribcage (side limits) expand. The lung is not actually attached to any of those things -- it sits within what's called the pleural space, and as the pressure in that space drops from the expansion of the walls, the pressure is less than the atmospheric pressure in the lungs, and air travels down into the lungs and allows them to expand. Therefore, no matter how hard you try to inhale, so long as you are INHALING, the pressure in the lungs will never exceed atmospheric. As long as you are inhaling, the glottis is open (by definition, because otherwise you could not inhale) so pressure equalizes between the lung and the outside air.

If you CLOSE the glottis, the lung becomes essentially a balloon with a knot in the stem. It is an elastic structure containing air and unable to vent any of it. At this point, if you, for example, bear down hard as one does in a Valsalva, you increase your intraabdominal and intrathoracic pressure. The pressure in the lung goes up with that muscle activity. Per the article I found, it looks as though the maximal amount most people can achieve is no more than 4 psi -- which sounds trivial, but remember that there are 760 torr in 14.5 psi, so a pound per square inch is a lot more than a cm of water.

The lung is not designed as a pressure vessel. It does have some support from the chest wall and diaphragm, but not enough to protect it against pressure that is significantly greater than atmospheric, particularly if prolonged. We have known for ages that bad hand-bagging of non-breathing patients can blow a lung; stacking of breaths in people with outflow obstruction can do the same thing. This is why we monitor peak and average airway pressures while running a ventilator, where the patient cannot tell us how their breathing feels.

The precise mechanism of air embolism, posited as being blowing air out of the lungs into the bloodstream, has seemed quite dubious to me since I first learned about it, and precisely how and where it occurs is still unclear to me. But the phenomenon of blowing a hole in the lung is very familiar, very possible, but cannot occur with an open glottis, not ever.

 

[Subcooled]

To put it simply: Could something bad happen if you sneeze while keeping the mouth and nose forcibly closed (e.g. for social reasons in a cinema)? Yes? Is this even more likely if you have suffered damage in your lungs as a result of some infection, blow, surgery, ...? Yes? Both lungs and ears adversely affected? Yes?

 

[dberry]

Great explanation - thanks. Related to the "blowing up a balloon question", though, I've always wondered about that strong-man stunt of inflating a medicine bottle until it explodes. Consider the last breath to add air into the engorged bottle... he contracts his diaphragm and rib cage to generate pressure, opens the glottis and unplugs the bottle with tongue/lips/teeth. That would seem to need heck of a lot of pressure**. I guess part of the training/trick is reducing the pleural space as he forces the air out. That, and never, ever releasing muscle tension while open to the inflated bottle!

**The catch, I suppose, is really knowing the bursting pressure of the medicine bottle. Like others have said, even a small fraction of 14.7 psi is a lot of force over even a few square inches, and it only takes a small rip to start a catastrophic failure ("burst"). Maybe it doesn't take that many torr over 1atm?

Challenge: anyone with a pressure rig with gauge willing to sacrifice a medicine bottle in the name of science?
-Don

 

[DocVikingo]

(1) Could something bad happen if you sneeze while keeping the mouth and nose forcibly closed (e.g. for social reasons in a cinema)? (2) Is this even more likely if you have suffered damage in your lungs as a result of some infection, blow, surgery, ...?

Hi Subcooled,

(1) Yes.

(2) Yes, although it depends on the nature of the injury.

Regards,

DocVikingo



---------- Post added February 10th, 2015 at 04:56 AM ----------

The catch, I suppose, is really knowing the bursting pressure of the medicine bottle. Like others have said, even a small fraction of 14.7 psi is a lot of force over even a few square inches, and it only takes a small rip to start a catastrophic failure ("burst"). Maybe it doesn't take that many torr over 1atm?

Hi dberry,

To review, 1 atm=760 torr/14.7 psi.

It takes a surprisingly small pressure differential between the inside and the outside of the lung to cause an overexpansion injury. The tissue surrounding alveoli can rupture with only a 77.6 torr/1.5 psi rise in internal pressure.

Regards,

DocVikingo