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28 Jan 2022
updated 19 Nov 2022
gi.alaska.edu/alaska-science-forum/breathing-through-hollow-reed-unlikely-escape-gimmick

Breathing Through Hollow Reed is Unlikely Escape Gimmick

June 25, 1984 / Larry Gedney

How many times have you watched the scene? Gary Cooper comes bounding through the woods with a dozen screeching, tomahawk-waving Indians in close pursuit. He stops in a swamp, breaks off a hollow reed and submerges himself, breathing through the stem while the "savages" rush past, oblivious to his presence. Many movie escapes have been engineered in this manner, and it makes me wonder if any Hollywood actor or director has actually tried the technique.

I did, once as a boy, and the results were both unexpected and disappointing. To begin with, my "swamp" was a nice, clear swimming pool, and my "reed" was a two-foot length of garden hose so that there was no mud or other gunk to interfere with the experiment After insuring that the hose had no water in it and that the end was open to the air, I pulled myself down the ladder to a depth of two feet and attempted to take a breath. I couldn't, no matter how hard I tried to inhale, and I was eventually forced to conclude that Gary Cooper knew something that I didn't.

The reason, I later discovered, was that the weight of the water pressing on my chest was greater than my breathing muscles were designed to overcome. Human chest muscles and the diaphragm function both to expand the lungs during inhalation and to force the air out during exhalation. The muscles used in exhaling are much stronger than those designed to inhale (this is easily demonstrated by placing your palm over your mouth and comparing the pressures you can generate by sucking in and blowing out).

At sea level, every portion of our bodies is subjected to an air pressure of 14.7 pounds per square inch--a considerable load, but one which we are not even conscious of because the pressure within our bodies is maintained at the same level as the air pressure around us.

This pressure of 14.7 pounds per square inch is the same as that existing at the interface of the air and the water at the swimming pool's surface. However, once we submerge ourselves in the pool, pressure from the surrounding water increases at the rate of an additional 0.433 pounds per square inch for every foot which we descend, although the air pressure in the hose remains the same as at the surface. This means that, at a depth of two feet, the confining pressure on the rib cage (assuming about two square feet of surface area for an average chest) totals about 250 pounds! Accordingly, inhaling would be roughly equivalent to trying to take a deep breath with a sumo wrestler sitting on your chest. It can only be surmised that Gary Cooper must have used a very short reed and very shallow water for this trick.

Most diving apparatus employs some means by which to equalize pressures inside and outside some sort of hull, whether this "hull" be that of a submarine or a human body. Both positive and negative exterior pressures pose risks to the frail human structure.

Assume that a body is being maintained at normal atmospheric pressure. If equivalent exterior pressure is suddenly removed (such as might happen during an accident in deep space or in a high-flying airplane) the pressurized body would want to expand to fill the void, with all sorts of nasty results. Among other things, "depressurization" causes gasses that have been dissolved in the blood to expand and form bubbles, resulting in the dreaded "bends." To make matters worse, submariners during WWII learned that, while a small air supply called the "Momsen lung" could sustain them for a while at depths, upon releasing it and bobbing to the surface, they must expel air from their lungs as fast as possible in order that they not explode as the confining water pressure lessened and the lungs expanded.

But the need to combat higher surrounding pressures, rather than lower, probably represents the situation with which we are more familiar. The old deep-sea diving suit with all its hoses and tubes, the submarine and the more modern diving bells all represent equipment designed to withstand high exterior pressures by the expedient of raising internal pressures to match those being exerted on the outside. Even scuba-diving gear performs this function by utilizing the body itself as the vessel, and providing it with air under a pressure equalized to that of the water around it.

In practice, scuba diving gear actually provides the body with air under pressure slightly above that of the surrounding water, making it necessary for the diver to exert slightly more effort to exhale than to inhale. This obviates the problem encountered by Gary Cooper in trying to inhale through the reed while submerged.