NOWRAMP 2002

The Chamber
Written by Mark Heckman, Educator, Waikiki Aquarium/ University of Hawai'i - Manoa

Section 1 - BUBBLES

Much 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.

When 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 depth.

As 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.

If 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 themselves).

For 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.

However, 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.

This 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.

Bubbles 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.

Air 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.

When 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.

Bubble 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.

The 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 treatment.

Most 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.

Once 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.

The 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

Drink your water and stay hydrated, keep that circulation healthy.
Don't push the limits.
Come up slow - slow - slow.

The Chamber is useful, but who really wants to visit.

References: Dr. Robert Overlock, Expedition Dive Medicine Physician

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