Surviving the Extremes: A Doctor's Journey to the Limits of Human Endurance (26 page)

The supple walls of the digestive tract—the esophagus, stomach, and intestines—are also no match for water pressure and quickly collapse. That collapse does not pose a problem, however, because it is not painful, and, unlike breathing, eating and defecating are not normally activities a diver does underwater.

Sinuses, being entirely encased in skull bones, are somewhat resistant to pressure changes, but ears, only partially enclosed by the skull, are much more vulnerable. The middle ear is a chamber containing three tiny bones connected end-to-end to transmit sound waves from the eardrum to nerve sensors that stimulate the brain. Air gets into the chamber through the eustachian tube, a long, delicate channel that brings air up from the throat. With a descent of only 3 feet, outside pressure makes the eardrum bulge inward and causes pain unless more air enters the chamber and provides counterpressure. Adding another foot or so of depth will contract the air space enough to make the soft lining of the Eustachian tube flutter closed. When the tube is blocked, the chamber is sealed. Should the diver ignore the pain and continue downward, the pressure would be relieved within another 10 to 12 feet and the pain would disappear—replaced by a loss of hearing and severe vertigo, as cold seawater floods into the ear through the ruptured eardrum. Humans are able to prevent the dam from bursting by utilizing the Valsalva maneuver, a technique to clear the ears that’s very similar to blowing your nose. A diver with ear pain can increase air pressure in his mouth and throat by blowing against his closed lips while pinching his nostrils—face masks are made with soft rubber covering the nose just so that noses can be pinched from the outside without breaking the watertight seal. The air backs up into the eustachian tube, forcing it open and inflating the middle ear sufficiently to balance the outside pressure. The maneuver is critical at the start of the dive, where pressure changes are most abrupt.

Hovering a few feet below the surface off the rocky shore of an island in the Galapagos, I was pinching my nostrils, waiting for my ears to clear, and wondering why none of the seals zooming down
past me had to squeeze its nose. Not that a seal could anyway. Not since their hands and feet evolved into flippers. Still, seals have ears and lungs, so how do they dive so much more easily than I do? Their trick is to exhale before going into the water and then let their lungs collapse under the increasing pressure. Residual air is forced into the upper airways, and that seems to be enough to maintain ear pressure. As for the collapsed lungs, the seals simply don’t breathe—not a trick that would work for us. It works for them because they can easily hold their breath for over an hour, an adaptation they needed to develop in order to return to the sea, once their ancestors began breathing air. This extraordinary ability evolved through relatively minor changes in their mammalian systems.

Seals have proportionately the same size lungs as humans and use the same oxygen-carrying protein, hemoglobin—except that seals carry a lot more hemoglobin than we do. In addition to having a relatively large volume of blood, seals are able to rapidly inject extra red blood cells into their circulation right before a dive by contracting the spleen, the organ of blood storage. Some other mammals have contractile spleens; initially tantalizing evidence that the ability evolved among South Sea pearl divers, however, has now been largely disproven. Humans and seals do both have myoglobin, a protein stored in muscle that provides an emergency source of oxygen, but again, seals have a lot more of it and use it as an oxygen reservoir. An abundance of hemoglobin and myoglobin lets seals store large quantities of oxygen outside their lungs, giving them a steady supply even when their lungs are shut down. And they use this supply sparingly, because seals have a “mammalian diving reflex” that lowers their heart rate and shunts blood to their brains as soon as they enter the water. Human adults have lost the reflex, but it is still retained in children. It explains how seals can remain motionless on undersea ice shelves waiting patiently for the right fish to pass by, and partly explains how children can “come back to life” after being submerged for over an hour.

Seals and humans both need to maintain the same internal body temperature, yet seals can dive even in Antarctic waters, and enjoy it. They sovled the heat loss problem by developing a layer of blubber around their bodies. Fat has very little blood flow and therefore provides
highly effective insulation. Paradoxically, children tolerate immersion in frigid water far better than adults because cold penetrates them much faster. Their bodies have proportionately more surface area and less distance to their centers. They become “quick-frozen” into a state of drastically lowered metabolism, minimizing their need for oxygen. Activation of the dive reflex followed by quick-freezing explains why all the cold-water survival records for humans are held by children. Adults don’t have either of these advantages but, like seals, many do have thick layers of blubber around them. Though they may have less energy than fit people, they are able to survive immersion longer. So, if you’re going to fall into the sea, try to do it in the tropics, preferably with your clothes on, to retain heat. Get out of the water as fast as possible, and if you’re not a little kid, at least be fat.

Humans are mammals with the same basic organ systems as seals, but without all the fine-tuning that seals have undergone, the final difference in underwater adaptation is dramatic. Nevertheless, free divers do the best they can with what they’ve got. With rigorous training, some can hold their breath for over three minutes and make round-trips to depths of over 250 feet. The most demanding part of the training involves mental discipline and body control; it amounts to underwater yoga. The pioneer practitioner of the hybrid sport was Jacques Mayol, who became a French national hero when he established the free deep-diving record at age sixty-four. Jacques and I often swam together. As I splashed vigorously along, trying to keep up with him, he would glide ahead to the shore and smoothly transform himself into a land animal by continuing his exercise sitting with his legs crossed, placing his hands on his knees, and closing his eyes. He was “rejoining the water,” he used to tell me. Jacques said he felt his ancestral aquatic origins within him and thought that, like the dolphins, humans could return to the seas. He often said he was more suited to life in the water than to life on land, and I believed him. His sensitive soul made him at one with sea creatures, but it was less suitable for people. Years later, perhaps out of the water too long, Jacques committed suicide.

His spiritual heir is Francisco Ferreras, better known as “Pipin,” a Cuban living in Miami, where he and his French wife, Audrey Mestre,
were routinely breaking all the free-diving records. Like Mayol, they were able to reach incredible depths by riding a weighted sled down a steel cable, then inflating a balloon to rocket them back to the surface. Doctors had once predicted that human lungs would be incapable of withstanding pressures over five atmospheres, which corresponds to a depth of 160 feet. Beyond that, they said, the lungs would be the size of potatoes, squeezed so tightly that their tissue fluid would seep out like water wrung from a sponge. In January 2000, Pipin set a new record of 531½ feet. The doctors need to recheck their numbers. Perhaps adult humans do retain some vestige of the mammalian dive reflex—what Jacques Mayol meant when he said that while free diving he could feel his acquatic origins.

Breath-hold diving remains very dangerous, however. Even if the human body can withstand the pressure, sometimes technology cannot. Mestre, a twenty-eight-year-old marine physiologist, already held the women’s depth record but set out, with her husband’s help, to break his record as well. On the morning of October 12, 2002, the weather was stormy off the coast of the Dominican Republic, but by early afternoon the sea had calmed enough to proceed with the highly publicized dive. Surrounded by boatloads of filmmakers, reporters, and spectators, Audrey Mestre slipped into a meditative trance, detaching herself from the crew on her catamaran who were checking last-minute details. Pipin himself tested the air tank that would be used to inflate the lift bag. He didn’t use a pressure gauge but cracked open the valve and heard the reassuring high-pressure hiss. Audrey donned her yellow and black wet suit and slid into the water, which was still slightly choppy from the morning storm. She mounted the metal sled—a vertical tube with two crossbars. Attached to the sled were the compressed air tank, lift bag, and a camera with newly added stabilizer wings. Through the vertical tube ran a vinyl-coated cable, held taut by a concrete weight far below. Cables on previous dives had been weighted with lead.

Audrey grasped the top bar of the sled with both hands and folded her knees around the bottom bar so that her fins pointed up. She wore no mask. She took rhythmic breaths until she was ready, then slowly and deeply inhaled the one breath she would carry down with her.
She gave a quick nod to release the catch, launching the weighted sled downward. Audrey then plummeted to the world record depth of 561 feet in one minute and forty-two seconds. Waiting there was safety scuba diver Pascal Bernabe, who watched as Audrey uncoupled the ascent portion of the sled and opened the compressed air tank that would fill the lift bag. It didn’t fill. Audrey tried a second time. It didn’t fill. Thirty seconds had elapsed. Pascal placed his regulator under the bag and pressed the purge valve to force air into it. It was enough to get the sled to rise—but too slowly. Pascal got below the sled and started pushing it up. It repeatedly caught against the cable and several times almost stopped. Audrey remained calm, but she had already been holding her breath over three minutes. The pair moved up to 394 feet before Audrey collapsed onto Pascal like a falling leaf. He continued to swim upward with her until he was met by Pipin, who had donned scuba gear and dived in as soon as he realized she had been down too long. In a grim relay, Pascal passed to Pipin his unconscious wife. They reached the surface far too late for Audrey. It had been eight minutes and thirty-eight seconds since she took what proved to be her last breath.

What caused the tragic end of Audrey Mestre? The final report concluded that there were many contributing factors. The lift bag did not inflate adequately, possibly due to the compressed air tank not being totally filled. The ascent was slowed because the concrete weight at the bottom was not heavy enough to keep the line taut and vertical, and also because the new stabilizer wings on the camera were pushing sideways against the cable, acting like a brake. The interruptions when the sled actually stopped may have been due to intermittent slack in the ascent line created by ocean swells left over from the morning storm. Audrey’s cause of death was listed as accidental drowning. But she wasn’t 561 feet under the sea by accident. She had ridden there on the edge of technology—a technology that placed her body at the extreme limit of survival, and then proved too frail to bring her back.

Breath-hold diving tests human limits, but it’s no way to explore a vast, unknown environment, which is why I was in full scuba gear as I descended along an anchor line 126 feet to the sea floor, 1 mile off the coast of Monaco. That there could be unknown territory so
close to the bustling, glamorous city of Monte Carlo gives some idea of how little of the sea has been explored. Less than 1 percent of the world’s ocean bottom has even been seen. The focus of attention of the team I was diving with on that day was an 8-by-2-foot crack running along the base of a submerged limestone cliff. Out of that crack, fresh water gushed into the salty sea at a rate of well over 100 gallons a second. Local fishermen have known of the existence of the underwater mineral spring for centuries. From the surface its location was obvious even to me as we approached the site in our research vessel. A patch of smooth surface water about 10 feet in diameter suddenly interrupted the regular pattern of waves. A crewman lowered an empty bottle, brought it up filled, and handed it to me to drink: cool fresh water.

I had been invited here to be a medical consultant for NympheaWater, a French undersea research and engineering company about to test the feasibility of capturing that fresh water before it became diluted by the sea, and then providing it as a renewable source of municipal drinking water—in this case to Ventimiglia, a thirsty city in northern Italy. Once they perfect the technology, the company has contracts to set up similar systems in arid countries such as Israel, Morocco, Saudi Arabia, and Qatar, underwater springs being plentiful throughout the Mediterranean basin and Persian Gulf. Company president Pierre Becker got the idea while working on another project off the coast of Greece. At a cove near Port d’ltea, he saw shepherds lead their goats a few yards into the sea to quench their thirst. Pierre realized these springs were hidden treasures and he became an underwater prospector. He talks to local fishermen everywhere, studies geologic maps, then uses infrared cameras mounted in ultralight aircraft to search the seas for the telltale water-temperature differences that reveal likely sites.

Underground springs are common in limestone cliffs. When water infiltrates and reacts with calcium in the limestone, the acid solution that is formed cuts channels and carves spaces deep within the rock. Rainwater falls into the channels to form rivers and collects in the hollow spaces to form lakes. The network continues its downward flow, emptying out at the base of the cliff. During the last ice age, as water became locked in glaciers, the underground rivers and lakes
dried up, becoming tunnels and caves. Then, about twenty-one thousand years ago, the climate started to warm up again. Melting glaciers resupplied water to underground rivers and raised the level of the Mediterranean Sea by 600 feet. The outlets of the rivers became submerged. Once the pressure of overlying seawater rises enough to overcome the force of a river, the flow backs up and the tunnel floods with seawater. Should the river flow remain strong enough, however, it will continue to empty into the sea. Being less mineral-laden than salt water, it floats to the surface, where it has long been tempting seafarers, whether on oceanographic research vessels or ancient wooden cargo ships. Three thousand years before Pierre Becker, Phoenician sailors covered undersea mineral springs with bronze bells and brought the water to the surface through leather tubes covered with tar for waterproofing. The NympheaWater project is simply an updated version of their extraction system.