Deep-Six Underwater Systems, Inc.
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Table of Contents

1 Pressure and Gases
2 The Face Mask
3 The Snorkel
4 The Fins
5 Weight Systems
6 The Knife
7 The Wetsuit
8 Pressure and Water
9 The Ear and Pressure
10 The Sinus and Pressure
11 The Stomach/Intestine and Pressure
12 The Lung and Pressure
13 Barotrauma caused by External Air Spaces
14 The Buoyancy Compesation Device (BCD)
15 The Scuba Cylinder
16 The Scuba Cylinder Valve
17 The Regulator
18 Density and the Diver
19 The 4 Gas Laws
20 Hand Signals
21 Carbon Monoxide Poisoning
22 Hyperventilation
23 Nitrogen Narcosis
24 Diver's Flags
25 Sound Underwater
26 Color Underwater
27 Decompression Sickness
28 Breathing Oxygen
29 Deep Diving
30 Thermoclines
31 Thunderstorms
32 Underwater Life
33 Open Water Dives
34 The Final Examination
35 The Environment
36 Advanced Course

12 - The Lung and Pressure

     Of all the barotrauma discussed, this is the most serious. Lung squeeze and over-expansion can lead to a diver's death. And, if not death, damage to the lungs can lead to serious disabilities. It is most important to heed Boyle's law and never allow a pressure difference to occur between the inside of the lungs and the outside, especially on the ascent!  

LUNG SQUEEZE: Your lungs are designed to go from one size to another as you breathe in and out. The lungs never completely empty. In fact, if they did totally deflate they might not be able to reinflate because the small surfaces might stick together. That is a collapsed lung.  The minimum size the lungs become when one exhales all the air they can is called the residual volume. If you compressed the chest and forced air to leave the lungs until they were smaller than the residual volume it could cause serious barotrauma. There could be lung rupture due to rib penetration. There might be a fluid build-up in the lungs leading to pneumonia. There could be a total lung collapse possibly resulting in death.

      Taking a full breath and skin diving to 33' would cause the lungs to be 1/2 of their original size. At 66' they would be 1/3, and at 99' they would be 1/4. If your lungs' residual volume was between 1/3 and 1/4 serious damage might result from this breath-hold dive to 99'. Most people do not hold their breath and dive that deep so this is not usually considered a serious problem. The few divers that do dive that deep holding their breath have trained for years to do it and have a changed lung capacity.

LUNG OVER-EXPANSION: If you were to take a balloon from the surface to 33' it would be 1/2 the size. If you let it go to the surface it would return to its full size. That is what happens to a skin diver's lungs as they go up and down in the water. If you took a balloon down to 33' and blew it up, tied it closed, and then let it go to the surface it would explode. Scuba divers take air into their lungs. If they don't let it out on the way up awful things can happen. Never hold your breath while scuba diving. Don't dive with asthma or pneumonia unless a doctor says it is OK! The practical application of Boyle's law can kill!

     It's not nice to dwell on the negative aspects of scuba diving. Since this is a very serious matter, it is important to spell out the gory details of what can happen to person that holds their breath as they ascend after inhaling underwater. Please make sure to read the words following the gore in order to get a true perspective of the entire issue!

     Following the course from the mouth to the lungs the airways get smaller and smaller. It looks similar to a tree that is upside down. The trunk is the trachea. Put your hand on your Adam's Apple and feel the size of the "trunk." From the trachea there is a branch that travels into each lung. Those 2 branches are known as the bronchi. Just as with a tree, the airways keep decreasing in size until the end of each "twig" is reached. At the end there are alveoli, billions of them. The ends are microscopic but the way it looks resembles broccoli. Each alveolus is very tiny and fragile.

     The following is a model of the airways in the lungs:

     At the end of each branch are the microscopic alveoli. Each alveolus is surrounded with a small blood vessel called a capillary. They are also microscopic. So, the lungs contain both air and blood vessels.

     The following top diagram diagram shows the mixture of the air and the blood vessels in each lung. The bottom diagram shows what a bunch of alveoli look like. Again, they are similar to broccoli.

     If diver takes a breath from a scuba then heads toward the surface without exhaling the lungs will overinflate. Each alveolus overinflates. Air breaks the thin walls of the alveoli and is forced directly into the blood capillaries. Now we have air bubbles in the blood stream which travel out of the lung and back to the heart. They may grow larger as the divers ascends. They may join together becoming larger as well. The bubbles than move out of the heart to the body and some to the brain. In the brain the bubbles travel until they can go no further because the blood vessels get too small. The bubbles are trapped. Clots may form around them. In any case, the blood stops flowing at that point and brain cells get starved for oxygen. If the brain cells start dying certain functions are lost. The diver has caused a stroke! This can happen in as little as 4' of water!

     The same thing could happen, usually to a lesser degree, if you have asthma, pneumonia, or smoke. If there is mucous in your lungs it might allow air to enter the alveolus easily but not leave on the ascent. In the areas of the lungs that could have these reverse blocks air could be forced into the blood stream. That is why it is important to have a doctor say you can dive with asthma, or if you smoke heavily.

     Any plug in the blood stream is called an "embolus."  The air bubble that might be in the brain is an "embolus." Since it came to the brain in an artery, and since it is made out of gas, the entire problem is called, "Arterial gas embolism", or "AGE" for short.

     In the meantime, the excess pressure in the lungs from holding your breath while ascending could also cause the lung to rupture. This can lead to bleeding which could flood the lungs and make breathing difficult. Also, air might get trapped outside the lung in the chest cavity. If that air expands upon ascent and cannot find its way back into the lung, the lung could collapse and the heart could be pushed to the side. This is a miserable condition. Breathe normally.

     Now for the good news! With the exception of the fluid-in-the-lung cases, arterial gas embolism does not occur without warning. Take a deep breath. Now add more air to your lungs. Fill them up as much as you can. That is what a diver would feel like just prior to lung damage. It's uncomfortable and you can feel it. If you are traveling rapidly to the surface, and you are near the surface where the pressure changes are most rapid, if your lungs are full it would take as little as four (4') feet of water to incur damage. But if you are rational, and not in the state of panic, you would get a full-chest feeling prior to this occurring. So, while you are enjoying the scuba experience it is important to stay relaxed and breathe normally.

     We do not want to pass over the word "panic" too lightly. Panic is a condition that causes one to be temporarily mentally ill. It is caused by a powerful chemical called adrenaline secreted by the adrenal glands located above the kidneys. When a severe stress is applied to an animal they will react to it in a variety of ways. Sometimes the reaction is swift and without thought. Thinking you are going to drown could cause you to "claw" your way to the surface, instinctively hold your breath, IGNORE the warning signals, and be unaware of anything that is going on around you. It is easy to say, "Don't panic, stay calm!" When a problem arises are you really going to be able to maintain your composure?

     First aid for a diver with lung injuries consists of the immediate administration of pure oxygen at no less than 15 liters per minute. If the diver is not breathing the oxygen should be injected into the mouth during the CPR process. This is so vital it's almost nuts to dive without an emergency supply of oxygen at the dive site. Oxygen not only keeps cells alive, but it helps to reduce bubble size as will be explained in the the chapter on decompression sickness.

     At the same time first aid is being administered, it is important to notify the nearest rescue squad so the patient can be transported to the nearest hospital. The hospital should be told about the suspected condition of the patient, and the doctor-in-charge should be told to call the Divers Alert Network (DAN) at 919-684-8111 or 919-684-4DAN. (They accept collect calls in emergencies.) A DAN doctor, an expert in underwater medical problems, is available 24 hours per day to provide advice to the emergency room doctor.

     If a diver encounters arterial gas embolism (AGE) they most likely will be rushed to the nearest recompression chamber that is operational. There are recompression chambers all over the world. Some of them are not operational at all times. The DAN doctor will be able to provide the latest information on chambers in the area of the accident that could be used for immediate treatment. (They do not provide this to the general public, but will provide medical personnel chamber information.) Once the diver is in the chamber the air pressure is increased. This, according to Boyle's law, will reduce the size of the arterial gas embolism bubbles. The patient will also breathe pure oxygen for prescribed periods of time while in the chamber. Hopefully, the AGE bubbles will leave the brain before too much damage has been done. The pressure is then reduced gradually to allow the diver to return to one atmosphere.

     The cost of the above might be more than $30,000! The money goes for payment to the rescue squad and hospital, transportation to the chamber (oftentimes via low-flying aircraft to keep the bubbles from growing),  the recompression chamber use, and the personnel operating the chamber.  It's a very expensive venture because one held their breath and ascended.      

     One last point: In the rare instance where an unconscious diver is brought to the surface there is no need to worry about whether the diver is exhaling or not. Unconscious divers do not hold their breath so the chances of lung damage and AGE are slim. As the diver was brought to the surface the expanding air in the lungs would escape from the mouth without doing damage to the lung tissue.

Copyright Information about this text, DIVING WITH DEEP-SIX is as follows: Copyright 1996 - 2007 by George D. Campbell, III; President. All Rights Reserved. This file may be posted on Electronic Bulletin Boards for download, but may not be modified, printed for distribution, or used for any commercial purpose without the author's written permission. is using this material with the permission of Deep Six. The full version is available at:
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