Surviving the Extremes: A Doctor's Journey to the Limits of Human Endurance (28 page)

Even when they have happy endings, stories such as these offer powerful reminders not to skimp on decompression time. Forty minutes after I left the bottom, I was still hanging on the line, looking up at the hull of the research boat, only 10 feet above me. Finally my calculated decompression time, with a safety margin added, was completed.
But I still wasn’t free to just swim up to the boat. There was another invisible barrier between the surface and me, one I had to cross carefully if I wanted to leave the water alive.

From my maximum depth of 126 feet, I was able to ascend 63 feet before the pressure on my lungs was halved (discounting overlying air pressure). From the 10-foot depth where I was now, the pressure would halve with a further ascent of merely 5 feet. But the rapid decrease in pressure as I move toward the surface will mean a reciprocally rapid expansion of the volume of gas in my lungs. That air needs time to be either absorbed or exhaled. If expanding air remains trapped inside the lungs, a pressure change of only 3 or 4 feet is enough for the air to overcome the elastic limit of the alveoli, rupturing the delicate membranes and sending air directly into the pulmonary circulation. From there it usually flows up the carotid arteries in the neck and lodges in the brain, creating the same symptoms as a stroke.

The only safe way to ascend is to exhale continuously and to stay below your smallest bubbles. The bubbles will rise slowly enough to give the excess air in your lungs time to escape. However, a diver running out of air or in a panic may hold his breath and try to get to the surface as quickly as possible. Betrayed by his survival instinct, his lungs will burst as soon as the water gets shallow. The last 10 feet of the undersea world is a treacherous border.

Finally we crossed safely and were able to celebrate our success in true French style—champagne all around. The system had worked, everyone was back on board, and the only bubbles were in the drinking glasses. Had the spring been a little deeper down, we would all still be on the ascent lines—at least those of us who hadn’t succumbed to nitrogen narcosis and been lured away by mermaids. Decompression time increases rapidly with depth, as does the risk of rapture of the deep. Ascent time soon exceeds bottom time, thinking can become cloudy, and you need to save most of your air supply to get back up. The relentless pressure of nitrogen in compressed air creates invisible but very real barriers to penetration of the deep sea.

Given that nitrogen is an inert gas, serving no purpose in the human body and causing real problems under pressure, why not simply take it out of the compressed air? The problem is that it has to be
replaced with something, explained my colleague and dive physiology mentor, Dr. Bernard Gardette of Comex. The world’s foremost underwater engineering and construction company, Comex runs operations in every ocean in the world, but their world headquarters is in Marseille, France, just a few hours by boat from where we were diving. The company’s founder and chairman, Henri Delauze, had lent Pierre Becker his state-of-the-art research vessel and equipment. And he had lent me Dr. Gardette, his chief medical officer.

The answer to the nitrogen problem that had immediately occurred to me was to breathe pure oxygen. I and most other climbers do that routinely high in the Himalayas because it eases breathing in a low-air-pressure environment. The sea, on the other hand, is a high-water-pressure environment, and concentrated oxygen under pressure turns toxic. It is readily metabolized and therefore would not cause the bends, but when absorbed in high doses it irritates nerves and can cause convulsions and sudden loss of consciousness—not a good combination, especially underwater.

No, the oxygen must remain diluted, so nitrogen must be exchanged for some other inert gas—helium, Dr. Gardette informed me. Mixed with oxygen, and called heliox, helium immediately eliminates the problem of narcosis. Since helium is far less soluble in water than nitrogen, the liquid human body can withstand far more pressure before it absorbs the gas. Helium is a very light gas—light enough to float a dirigible—so it remains easy to breathe at depths where all gases become densely compressed. It does have disadvantages, however. Divers get cold breathing helium because it is too light to hold much heat. Also, its decreased density makes vocal cords vibrate faster. Divers on helium talk like chipmunks. It’s not funny—they can’t understand one another and need computerized unscramblers to communicate.

Nonetheless, heliox has pushed the undersea frontier down below 800 feet. Deeper than that, divers become prone to a bizarre new malady: high-pressure nervous syndrome, in which divers become giddy and shaky, apparently due to helium’s finally being absorbed, or perhaps due to sheer pressure. Ironically, when nitrogen is added back into the divers’ breathing mixture, its narcotic effect calms them. Even helium gets heavy at these enormous depths, particularly when combined
with nitrogen. To get humans deeper, Dr. Gardette and others have been experimenting with hydrogen, a gas that weighs only half as much as helium but is highly explosive. Handling it requires extreme precaution, as I saw when I toured the Comex facility, replete with gas sensors, huge ventilation ducts, and No Smoking signs everywhere. But hydrogen is now routinely handled as fuel in space exploration; certainly it can also be used safely as a breathing gas to explore the ocean depths.

We may never know how much deeper hydrogen might take us, however. Human penetration to ever greater depths has been stopped by a barrier perhaps more formidable than anything that would have been encountered in that hostile environment—marketplace economics. With the advent of unmanned deep-sea submersibles that can descend thousands of feet with TV cameras and robot arms, it has become easier and cheaper to let a robot do the job. The need to send humans to those extreme depths has become obsolete.

Nonetheless they are still very much needed at “moderate” depths, especially for work involving offshore oil rigs and pipelines. People all over the world live and labor in oceans at depths of 1,000 feet or more. They are blue-collar workers—welders, mechanics, electricians—who go to their jobs in diving bells, stay a month or so, and then return to the surface after a weeklong commute. To be sure, these people are also highly trained divers, specializing in the art and science of saturation diving.

Using standard dive technique below about 165 feet, bottom time becomes so short and decompression time so long that the sea becomes an impractical place to get any work done. Commercial divers need a better way to get to work, and they need the time to get their jobs done right without having to watch the clock to see how much gas they’re absorbing. Fortunately, there’s a limit to how much gas a liquid can absorb. Human bodies become maximally saturated after about twenty-four hours at any given depth. After that, no matter how much longer you stay, you don’t absorb any more gas. That means your decompression “obligation” doesn’t increase. Once you’re down that long, you may as well stay awhile.

A thick glass porthole was all that separated me from the saturation
diver I met at sea. I was breathing fresh salt air. He was breathing heliox, and his body was under 600 feet of pressure. He smiled, said,
“Bonjour”
then turned back to his card game with his dive buddy. They were in the hull of a ship inside a hyperbaric chamber, a thick metal canister containing a living room, bedroom, bathroom, and a lock-in/lock-out chamber that overlooked the moon pool—a hole in the bottom of the ship. When they started the job, they entered the chamber at atmospheric pressure. The chamber was then gradually pressurized until it equaled the depth of their intended work site. The two divers donned their elaborate gear with the help of a bellman, a combination diving bell operator, troubleshooter, and valet. All three passed through a hatch into the diving bell, which is hermetically clamped to the lock-out chamber and hangs above the moon pool. The diving bell was lowered deep into the dark cold sea, tethered by a cable that contains compressed gas hoses, electrical power and telecommunications wires, and tubes to circulate hot water. When it reached the designated depth, the pressure inside and outside the bell was equal. The door at the bottom opened outward easily. The divers swam out to their workplace, each tethered to the bell by a second cable, a lifeline that provided breathing gas, light, heat, two-way communication, and biomonitoring. The bellman stayed behind in the bell, monitoring the support systems and keeping a watchful eye on his two charges. He continually adjusted the length of their umbilical cords to allow the divers to move freely yet without slack, which might entangle them. As an extra measure of security, each diver carried a bailout bottle with a small supply of breathing gas in case his lifeline was accidentally cut or in case he became entrapped and had to cut it himself. The extra minutes would give the diver enough time to return to the bell—his only possible refuge.

Emergencies are, surprisingly, very rare. With meticulous preparation and intense supervision of their habitat, commercial deep-sea divers have far fewer accidents than do even the most careful shallow-water divers. They must, however, remain completely enclosed in their environment; rapid depressurization due to a break in any of the seals in their system would immediately inflict the bends. A doctor has access to them through the lock-in hatch of the hyperbaric chamber,
but for a major medical problem, or a fire or other emergency, the divers cannot get out quickly. Evacuation means transferring them to a portable capsule that can be loaded onto, and hermetically linked to, a helicopter equipped with a hyperbaric chamber. Then they have to be offloaded, still under pressure, to the medical recompression facility for treatment.

However, very few saturation divers leave the work site that way. Statistically the profession is no more dangerous than the same blue-collar occupations are on land. When the day’s work is finished, the divers swim back to the bell, take the elevator ride to the surface, and enter the hyperbaric chamber, where they shower, rest, relax, and remain under high pressure, awaiting their next shift. Going to work at the frontier of the most hostile environment on earth becomes a daily routine. After following the same schedule for several weeks, they stop diving, so they can ready themselves for some R&R. Though only a few feet away from everyone else, they are separated by hundreds of pounds of seawater pressure that has to be reduced very gradually. It’s a long, slow, boring trip back to their native habitat. Depending on the depth at which the divers have been working, they may need seven to ten or more days of decompression before they can breathe fresh sea air.

For a large operation, teams of these saturation divers are “stored” onboard ship at various pressures so that they can be injected into the sea to work simultaneously on parts of the project located at different depths. It’s easy to imagine each group of pressurized divers as an artificially created sea species with a habitat limited to a narrow depth range. In a cross section of the ocean, they would be stacked one below the other, sharing their designated layer of water with the deep-dwelling fish that are confined to the same narrow zone by their millennia-old adaptations.

Most fish have swim bladders, a space within their bodies that controls buoyancy. When a fish secretes gas into the space, it expands and the fish rises. When the fish absorbs the gas back into its blood, the bladder contracts and the fish sinks. It’s an effortless way to move vertically through the water. Bladders have limited capacity, however; they have been preset by evolution to function within a depth range
specific to each species. Saturation divers have evolved their own version of a swim bladder: the buoyancy-compensation vest—a jacket that can be inflated with air from the scuba tank or deflated by bleeding air out through the regulator.

In the sea, deeper is darker. Many deep-dwelling fish have grotesquely enlarged eyes, and many are bioluminescent, creating their own light using chemical reactions similar to those of fireflies. Humans don’t have huge eyes, and their lenses are adapted to focus light rays traveling through air. Because water bends light enough to change the angle at which it hits the lens, underwater images appear blurry to us. To see clearly in the water, humans need to enclose air in front of their eyes by means of a face mask. The mask not only refocuses the image, it intensifies and enlarges it, since light traveling through dense water into thin air is refracted in the same way it would be were it to pass through a magnifying glass. Images appear closer, bigger, and brighter. When there is no light at all, a diver will bring along head-lamps and flashlights. He might also carry a light stick, a clear plastic tube containing two liquids separated by a delicate partition. When that partition is broken—which the diver can do by snapping the tube—the liquids mix to create a bioluminescent glow.

There are some adaptations a human cannot mimic. Every living cell of every living creature is enclosed and protected by a cell membrane, a somewhat flexible covering of protein and lipids. In humans, the lipid is a saturated oil that, like butter, will solidify at cold temperatures and deform under pressure. The cell membranes of deep-sea fish are made of unsaturated oils that, like olive oil, remain liquid at low temperatures and can therefore withstand the cold and high pressure of the sea much better.

The most fundamental difference between deep-sea fish and humans, however, is also the subtlest. Ongoing biochemical processes in living organisms create constant changes in the three-dimensional shapes of proteins and in the total volume of molecules produced by chemical reactions. When they are placed under intense pressure, proteins are not able to unfold, and expansive reactions are constrained. Deep-sea fish have undergone evolutionary modifications in their protein design and in their metabolism to allow protein unfolding and
energy production to occur without any increase in volume. In humans at the same depths, those chemical reactions would be smothered by the surrounding pressure.

Deep-sea fish are so exquisitely adapted to their extreme environment that they are unable to survive when brought too near the surface, where they are exposed to the unhealthy conditions of light, warmth, and low pressure. They won’t get the bends, since their gills have been extracting only oxygen from the water they breathe. Their liquid-oil cell membranes begin to ooze, however, responding to the lack of any containing pressure. Some fish literally fall apart as their chemistry goes haywire. Others explode when their swim bladders overexpand and burst, like the lungs of a diver who ascends while holding his breath. Actually, very little is known about these denizens of the deep. They are extraordinarily difficult to collect, and they self-destruct before they can be studied.