What Happens When You Dive Too Deep?

[fog37]

TL;DR Summary

Breathing in human beings...

Hello,

Human breath the following way: air at ambient pressure is pushed into the lungs during the inhaling phase because the air pressure inside the lungs is lower than ambient pressure: $p_{inside}<p_{outside}$. During the exhaling phase, the air pressure inside the lungs becomes instead slightly larger: $p_{inside} >p_{outside}$. Is that correct? I think so.

What kind of pressure differences are we talking about? Is the pressure difference larger or smaller during the exhale phase?

I am trying to better understand what happens when the diaphragm contracts: the diaphragm contracts, move downward ,expands laterally becoming less thick but large, causing the thoracic cavity to expand and move slightly upward...I guess the diaphragm is connected to the lower part of the thoracic cavity that is why the thoracic cavity responds when the diaphragm, which is a muscle, contract.

I have been thinking about how deep underwater someone can go with a snorkeling tube and that caused these thoughts...

Thank you for any input in advance...

 

[russ_watters]

What kind of pressure differences are we talking about? Is the pressure difference larger or smaller during the exhale phase?

This is easily googlable:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1501025/

 

[berkeman]

Summary: Breathing in human beings...

I have been thinking about how deep underwater someone can go with a snorkeling tube and that caused these thoughts...

Having tried that as a kid in our backyard pool using a short garden hose, the answer is about a meter. At about 1m depth, I could barely get a partial breath in.

 

[gleem]

From the Google reference above the max inspirational pressure produced by a male was about 100 cm-H20 or about 0.1 atmospheres. As Berkeman noted he only got to about 1 meter depth before he had difficulty breathing atmospheric air. The diaphragm could not produce enough force to cause the lungs to expand against the high external pressure of the water once the pressure of the air in the lungs was less than the water pressure against the chest. That is also why scuba divers need pressurized tanks.

 

[berkeman]

the max inspirational pressure produced by a male was about 100 cm-H20 or about 0.1 atmospheres. As Berkeman noted he only got to about 1 meter depth

Yeah, maybe I over-estimated that one meter depth...

 

[BillTre]

Its not just the diaphragm that can cause inhalation.
Expansion of the ribs can also increase the volume of the chest causing the same thing.

In addition, there is also the intrinsic elastic properties of the lungs which tends to make it smaller, favoring exhalation.

There is also (or maybe its part of the preceeding item) the surface tension of the alveoli (little air bags at the end of the air tubes in the lung which exchange gas with the blood). These are small spherical bags with the air tube attached. Their surface tension tends to collapse them. The body produces a surfacant to reduce the surface tension and deep breaths produce a greater release of it in the lungs.

 

[fog37]

Thank you everyone.

This discussion made me think about this device called iron lung: individuals who lost the ability to contract their diaphragm can use the "iron lung", which is essentially a large respirator. I think the inside of the iron lung, where the thoracic cavity is, have a pressure (partial vacuum) lower than the external atmospheric pressure. That causes the thoracic cavity to expand, which in turn causes the lungs, inside the cavity, to automatically expand, which causes the lungs' internal pressure to become lower than the ambient external pressure and inhalation to happen... Is that the iron lung correct principle of operation?

 

[BillTre]

Is that the iron lung correct principle of operation?

Yes.

 

[gleem]

, which is essentially a large respirator.

More correctly an iron lung was an early version of a ventilator. A respirator as commonly used today is protective device to prevent the inhalation of hazardous materials.

 

[fog37]

From the Google reference above the max inspirational pressure produced by a male was about 100 cm-H20 or about 0.1 atmospheres. As Berkeman noted he only got to about 1 meter depth before he had difficulty breathing atmospheric air. The diaphragm could not produce enough force to cause the lungs to expand against the high external pressure of the water once the pressure of the air in the lungs was less than the water pressure against the chest. That is also why scuba divers need pressurized tanks.

So a pressurized tank forces air into the lungs and this air is at a pressure that is the same as the water pressure in the water surrounding the diver...is that how it works? As the diver goes deeper, the tank should provide air at a progressively higher pressure...What about the exhaling phase? Does the exhaled air go into the water?

 

[gleem]

Yes but an interesting problem is that the high pressure forces more "air" into the blood stream resulting in less time that can be spent at greater depths.

 

[jim mcnamara]

Deep diving may create Decompression Sickness (bends) since divers using mixed gases ( O₂ with N₂ for example) have dissolved gases other than O₂ in the blood plasma. Bubbles of the gases form blood when the diver ascends, causing pain and sometimes very serious tissue damage. Embolisms (clots) result from exposure to gas bubbles, for example.
https://www.ncbi.nlm.nih.gov/pubmed/21215883