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
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
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
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.