Written by Mark Heckman, Educator, Waikiki Aquarium/ University
of Hawai'i - Manoa
1 - BUBBLES
of the work done on this trip is done on compressed air.
Air that is packed down and condensed, then delivered to
a similarly pressurized human body. This is not a problem
unless the pressure is released too quickly. Then a bubbling
body can result; not a good thing.
we breathe air, we breathe a mix of gasses. Air is 20 percent
oxygen and 80 percent nitrogen gas. The oxygen is very reactive;
it is used to metabolize (burn) the food we eat. Nitrogen
is basically inert (non-reactive). The nitrogen we breathe
in, we also breathe back out. A human 66 feet down in the
ocean, experiences a pressure three times that of being
at the surface. Air inhaled at that depth and pressure contains
three times the amount of oxygen and three times the amount
of nitrogen. The diver's body becomes saturated or at equilibrium
with the amount of gas that can be held in solution at that
a diver returns to the surface, the pressure drops. As the
pressure drops, the gasses come out of solution. If this
happens slowly, the gasses have time to diffuse out of the
tissues. The oxygen has probably already been used up, but
the nitrogen still has to make its way out of the body.
The nitrogen makes its way from the tissues, to the capillaries
(tiny ends of the blood vessels), into the veins (blood
headed ultimately towards the lungs to release waste gasses),
and out through the lungs to be expelled as we exhale.
the pressure is reduced too quickly, bubbles can form. In
the venous system, these bubbles are generally not a big
issue. If the bubbles are small, the venous circulation
will get them to the lungs to be off-gassed without complications.
Problems arise in tissues that have high nitrogen levels
and limited circulation (hence limited ability to cleanse
instance, nitrogen is highly soluble in fatty tissues. Now
some of our fat definitely has limited circulation, but
much of this body fat is not in critical areas (even if
it does affect our external appearance in ways we do not
always appreciate). Even if small bubbles do arise, they
probably have little effect.
Schwann cells which sheath the nerves contain large amounts
of myelin which is high in fat content. This includes the
white matter of the brain and spinal cord. The brain has
high circulation which assists in high off-gassing before
bubble formation can occur. The spinal cord, on the other
hand, has nearly as high of an amount of myelinated tissue,
but far less circulation. Here is an area where bubble formation
may cause problems. Bubble formation along the spinal column
or other nerve areas may cause pain, paralysis, numbness
or malfunction of various body systems.
is not to say that bubble formation cannot occur in the
brain. If circulation is compromised for any reason, the
results can be less than positive. In fact, if a diver is
dehydrated (causing a higher viscosity of the blood - making
it harder to pump as well as reducing the volume of blood
available for circulation) or has bubble formation along
the spinal column causing system problems leading to shock
(which causes lowered blood pressure and again less circulatory
function), bubble formation within the brain could result.
This diver now has a number of problems.
may also make it into the arterial system (oxygenated blood
coming from the lungs) and thence to the areas of highest
circulation - such as the brain. Some fifteen percent of
the population may have a patent foramen ovale. At birth,
a small flap of tissue between the two main chambers of
the heart closes up. If the closure is not complete or is
reopened by heavy physical activity, blood can spill over
from the venous (waste gas) side to the arterial (oxygenated)
side of the heart. In normal life this is not significant
and would be virtually impossible to notice, but in diving,
if a diver comes up too fast and bubbles form in the venous
system, these can be passed to the arteries and end up in
the brain leading to tissue damage.
embolism is another pathway for bubbles to enter the arterial
system and make their way to the brain. In this case, a
diver breathing compressed air makes the critical mistake
of holding their breath as they ascend. The air in the lungs
expands as pressure decreases upon ascent. The expanded
air has to go somewhere. If it can't get out the mouth or
nose through exhalation, the tiny air sacs of the lungs
(alveolar areas) may blow up like balloons until pinhole
leaks form - leaking gas bubbles to the capillary system,
then to the pulmonary arteries. Here again bubbles are going
into the oxygenated arterial system and will end up in areas
of high circulation - the brain.
a bubble enters the brain via the arterial system, for whatever
reason, circulation is compromised. The capillaries are
only one red blood cell in diameter, and are the point where
resistance is created. A bubble moving through the arterial
tree to the capillaries can get "stuck" or lodged
for some period of time until it clears. The bubble is gas
not liquid. As the heart pumps, the bubble compresses and
expands in its narrow place rather than being forced along.
The blood vessel down current does not get the vital oxygen
it needs and suffers tissue damage. Eventually the bubble
passes through and out into the venous system (and to the
lungs and is off-gassed), but the damage has been done.
The diver may suffer some immediate symptoms while the bubble
is in place and further symptoms down the line as inflammation
of the capillary tissues in the brain results. In other
words, one could have symptoms (similar to a stroke) which
resolve, only to recur later.
formation is often unpredictable. The effects can be mild
to severe, leading to lasting damage. Most symptoms occur
within two hours of a dive, but some may not appear for
twelve hours or more. This gives all divers cause for thought.
Section 2 - TREATMENT
Treatment for bubble formation, no matter what the cause,
is remarkably similar. Crush the bubbles, improve the circulation,
drive the nitrogen out of the tissues, and deal with the
inflammation. It is time for "The CHAMBER". The
Rapture has on board a recompression chamber. If
a diver suspects that they have an embolism or decompression
sickness (bubble formation), they get to go immediately
into the chamber and taken on another "dive" -
a dive not nearly as enjoyable as most.
chamber on the Rapture can simulate a dive to a depth
and corresponding pressure of 165 feet. Chambers at the
Hyperbaric Treatment Center in Hawai`i can simulate depths
of 220 feet. A diver with a diving related problem would
be greeted by Dr. Robert Overlock, our dive medicine physician,
who would examine the diver and if warranted, would begin
likely at this point, the diver would already be breathing
pure oxygen from one of the O2 kits on all of the dive boats.
Pure oxygen has a variety of benefits. First of all, by
breathing O2 instead of air, no further nitrogen loading
is incurred. In fact, the new gas loading equilibrium is
shifted to the O2 side and full nitrogen off-gassing proceeds.
If circulation is impaired, the higher oxygen input will
also enhance tissue and organ survival.
in the chamber, the diver may get an IV inserted to help
add fluids quickly and provide hydration (circulation again
- lower the viscosity and increase blood volume for off-gassing).
The chamber is sealed and the diver and doctor or tender
are "sent down" (pressurized) per a treatment
protocol. The idea is to crush the bubbles.
diver is still on pure oxygen. At the increased pressure,
the oxygen forces the nitrogen out, and as a side benefit,
seems to decrease blood vessel inflammation. Once the diver
is at the pressure limit of the chamber for a designated
interval, the pressure is slowly reduced. The bubbles are
gone; the diver is off-gassed and back to as normal as possible
after a mere six to twenty four hours in a tiny metal tube,
with an IV in their arm and hopefully no lasting damage.
Section 3 Avoiding Recompression
your water and stay hydrated, keep that circulation healthy.
Don't push the limits.
Come up slow - slow - slow.
Chamber is useful, but who really wants to visit.
Dr. Robert Overlock, Expedition Dive Medicine Physician