Surviving the Extremes: A Doctor's Journey to the Limits of Human Endurance (22 page)

Prosperi suddenly had a great deal in common with other desert animals. Thirst and hunger are powerful motivators, and the Italian policeman’s survival instinct was activated. He climbed up under the roof, grabbed two sleeping bats, and twisted their heads off. After sucking his prey dry, he ate them raw. Two days in the desert had turned a marathon runner into an opportunistic predator.

At dawn of the fourth day of Prosperi’s time in the wilderness, a plane flew over the shrine. It did not spot the Italian flag he had taken from his pack and hung on a pole outside nor the SOS he had traced in the sand. By noon the sun had baked his disappointment into despair. He became suicidal, slashing his wrist with his survival knife. But his dehydrated blood was so thick it oozed and soon clotted. As the sun set, the air cooled his brain, sharpening his conscious will and with it, his instinct for survival. He could see mountains along the horizon. Remembering that the finish line was located at the foot of a mountain range, he set out to reach them.

Trying to outwit his adversary, Prosperi walked in the early morning, before the sun could muster its full power. He shielded himself against a cliff, within a cave, or beneath a tree in the afternoon, then resumed his march in the evening. At night he dug a pit in the sand to keep warm. His survival thus far had been a unique combination of primal animal behavior mixed with the props of civilization he still carried. He slaked his thirst by chewing on towelettes and by licking the morning dew off hollows in rocks. In a dried-up riverbed, or wadi, he dug up some grass and sucked the still-wet roots. He drank his own urine but saved some of it to boil a packet of freeze-dried food on his portable burner. He ate beetles and plants, and one mouse, which he killed using a slingshot made from a stick and a bungee cord.
Every day he was progressing steadily east toward the mountains—except they were the wrong mountains.

On the fifth day, Prosperi spotted water dead ahead. He moved toward it hopefully but with tempered enthusiasm, aware that it might not be real. Sure enough, the water always seemed to evaporate just before he got to it, and he was never quite able to get his feet wet. It wasn’t his brain that was playing tricks on him, though, it was the desert atmosphere. A mirage, unlike a hallucination, is an optical phenomenon that exists outside the brain. It can be photographed. A ray of light will bend as it crosses the boundary between two transparent mediums of different densities. Imagine a pencil as a beam of light, and picture how it looks from the side in a half-filled glass of water. This is how a lens bends and focuses light, and why fish underwater are closer than they appear to be (ask Steve Callahan). The same phenomenon occurs when a large layer of air wrapped over the desert surface (or a small pocket of air hovering over a hot asphalt road) is superheated, expanding drastically and becoming far less dense than the air layer above it. The radical difference in densities bends the incoming light rays so severely that they are nearly parallel to the ground by the time they reach the observer—that is, the desert wanderer staggering over the sand. The image projected into his forward-looking eyes actually originates from the light overhead. Brains interpret light rays as if they were traveling a straight path, so the patch of sky above is seen as a pool of water in the sand ahead.

Not until the eighth day did Prosperi stumble into a wadi that contained a real puddle. By this time his mouth and throat were so swollen that he could not swallow; he vomited his first drink. Only by taking a small sip every few minutes could he keep the water down, so he lay alongside the puddle all day and night, periodically licking at the muddy liquid. He set off again the next morning. A day later, he came across fresh goat droppings, then small human footprints, then finally the eight-year-old Tuareg girl who was making the footprints and tending the goats. The girl screamed at the sight of the desiccated carcass shambling toward her and ran off across the dune. Soon she reappeared with her grandmother, who led the poor stranger to their encampment.

Prosperi had crossed into Algeria. He was taken first by camel, then by truck, to an Algerian military hospital, where doctors reported that the desert wanderer had lost 33 pounds and that 16 liters (4 gallons) of intravenous fluid were needed to replace his water loss. His kidneys were barely functioning, his liver was damaged, and he was unable to digest food. His eyes had sunk back inside their sockets, and his skin was dry and wrinkled. He looked like a tortoise. But he would survive.

Military doctors in Morocco said that never before now had they seen anyone survive in the Sahara without water for more than four days. Maybe they still hadn’t. Prosperi received a hero’s welcome when he returned to Italy, but his tale was soon challenged by doctors, who argued that his story was physiologically impossible. They postulated that he must have been taken in, if only temporarily, by some desert nomad, then, somewhat restored, reentered civilization with a dramatic story to tell.

Exactly how long a human being can survive without water is not known. Gathering such data would mean engaging in atrocity. The Nazis, notoriously, carried out just such experiments but never published the results of their criminal activity. Egyptian soldiers in the Sinai during the 1967 war with Israel received 3 liters of water per day, but the army still suffered numerous heat-related fatalities. Israelis, who were required to drink 10 liters a day, reported no cases of heat deterioration at all. So unquestioned is the need for large amounts of water that developing heat illness in the Israeli Army is punishable by court-martial.

Could Prosperi have survived what he said he did? A loss of greater than one-fifth of one’s body water is usually fatal; he had lost one-third of his. Nine days with virtually no water far exceeds the known limits of the human body. As awesome a machine as the human body is, under extreme environmental stress can it kick into overdrive and become even more awesome?

For humans, the desert can be thought of as a pathogen like a virus or bacteria—a natural substance that causes disease. To some extent, therefore, humans can be “vaccinated” against the desert. Vaccines work because they expose the body to an inoculated pathogen
in a weakened form, causing the body to undergo protective biochemical changes that create immunity if the pathogen should ever strike in full force. It is possible that Prosperi survived because his first four days of controlled marathon running exposed him to the desert in a weakened form and the stress served like an inoculation, one that the hotel-sheltered Hughes family never had the opportunity to acquire. Given time, the human body, ever adaptable, can be stimulated to make some defensive changes in response to any extreme environment. Fending off the heat load is the first priority in responding to the pathogen of the desert. Over the course of several days, sweating becomes easier, beginning soon after the body has begun to exercise and occurring at a lower outside temperature; this serves to keep the body’s engine cool before it even starts to overheat. The volume of sweat also increases. To prevent wholesale loss of its precious minerals and salts, the body withdraws them from the sweat, which no longer stains or even smells bad, having become nearly pure water.

This increased sweating response requires water, and lots of it. To conserve that precious commodity, the hypothalamus begins periodic activation of the sweat glands within each patch of skin. Sweating becomes cyclical. Three hundred thousand sweat glands, all with their valves wide open at the same time would cause the skin’s surface to flood, and water that drips off the body before it evaporates is a complete waste. To give each released droplet the time and space to evaporate, adjacent valves open and close sequentially, so that the body obtains maximum cooling from each drop of water it sacrifices.

Sweating more effectively and efficiently after several days of desert conditioning, Prosperi’s skin would be cooler than that of the average wanderer suddenly cast into the desert after a week of hotel air-conditioning. He could maintain body temperature with less surface blood flow, and by now he would have more total blood flowing. Even before he became water-deprived, his hypothalamus had responded to the prolonged heat exposure by sending hormones to the kidneys, signaling them to extract even more water from the urine and recycle it to the blood. Concentrated urine and efficient sweating meant that more blood was available for Prosperi’s vital organs, helping him avoid stomach cramps, muscle fatigue, and fainting.

The brain is the vital organ most important to protect. An unconscious human is defenseless. The brain must be kept cool (figuratively as well as physiologically) and, conveniently, it is located close to the face, an area with a rich blood and sweat gland supply and thus well suited to dissipate heat. Normally, blood from the brain flows outward to the face. When the brain temperature gets too high, however, the direction can be reversed, and face-cooled blood will flow inward, a priority circuit that gives the brain precious, additional cooling. The evidence for preferential brain cooling in humans is controversial, but it is a well-established phenomenon in many desert mammals. Under stress and breathing hard to escape a hyena, an antelope will send the moist, air-cooled blood from its nose directly back to its brain, allowing the rest of its body to overheat while keeping its vital command center cool. It makes sense that humans like Prosperi, functioning under stress, could invoke the same physiology.

Stress signals a danger to survival. Whether the peril is actual or just imagined, whether you’re lost in the desert and short of water or trapped in traffic and late for an appointment, the body releases the same stress hormones. Adrenaline will make your heart beat faster and start you sweating. Cortisol and catecholamines will mobilize glucagon stores from the liver and muscles and convert them rapidly to glucose, the body’s sugar fuel, for a quick infusion of energy. That energy burst can get you over the next sand dune or make you yell and slam the car horn.

Other reactions to stress are more specific and far more subtle. In response to too much heat, the body changes at the molecular level. All proteins and all cells have a three-dimensional folded shape that unravels at high temperature. If the heat to which they are exposed rises only gradually, however, once the temperature reaches 105°F, the cells in any organ will produce a new class of substances called
chaperone,
or
heat-shock proteins,
which bind to normal proteins to prevent them from deforming. They can even fold damaged proteins back to their original shapes. Chaperone proteins require about one hour to form and allow the body to withstand an extra 4°F of heat.

Heat shocking is not the only way to create these proteins, nor is heat protection their only function. Chaperone proteins are more accurately
thought of as all-purpose stress proteins, because they develop after any intensely stressful “insult” and, once formed, will defend against any other stress. Chaperone protein levels rise in response to cold, starvation, sleep deprivation, toxins, and even vigorous exercise, which may be the biochemical basis for why a vigorous physical workout relieves mental stress, and why subjecting military recruits to physical hardships during basic training makes them tougher soldiers. Chaperone proteins are produced just as easily by psychological stresses, such as isolation or fear. Consequently, there is a biochemical way in which confronting fear can sometimes strengthen the body enough to enable it to prevail over the harshest environments.

In his struggle to stay alive, Prosperi was making use of all these defenses and more. A week of heat exposure had already pushed his body into full survival mode, but not many desert wanderers are also marathon runners, and that gave him some additional advantages. Desert survival depends not only upon maximizing heat loss but also upon minimizing heat production. Prosperi had a fine-tuned, highly efficient body that could produce a lot of work while generating only a little heat. Endurance training strengthens the heart so that less pumping is needed to maintain blood flow. This eases the work of breathing. Endurance training also enhances the liver’s ability to convert stored energy (glycogen) to fuel (glucose). A marathoner’s muscles cover distances more easily. The total energy saved dramatically reduces heat buildup, since the heart, lungs, liver, and muscles are the four biggest furnaces in the body. Endurance athletes have a preponderance of type I “slow-twitch” muscles, which contract smoothly and steadily and thus conserve energy. Nonathletes (and more especially, athletes in sports that require fast, powerful moves such as weight lifting) have a higher percentage of type II “fast-twitch” muscles, which burn fuel far more extravagantly.

The marathoner’s strong heart and extensive network of blood vessels make it easier for blood to flow to the surface for cooling and to reach the deep organs for nourishment. Circulation is also aided by muscular activity in the legs that pumps blood up from the veins, which explains why it is so much more uncomfortable to stand in the heat than to walk, and why a punishment for soldiers during World
War II was to make them stand in the sun until they passed out. An athlete’s ability to keep moving greatly favors heat dissipation by creating wind over the skin. The “cooling down” period that runners need before they can actually stop after a race helps ensure that air flow continues until enough of their body heat has been lost by convection. Even when not moving, a marathoner has passive heat loss advantages; he has very little fat insulation and is usually slightly built—a shape that translates as a high surface area in proportion to body mass. Thinly insulated exposed surfaces will undergo rapid heat loss by conduction and radiation.

Endurance athletes have still one more card to play. For years, their steady, prolonged exercise program has put unrelenting upward pressure on the maintenance of their body temperature. Whether the heat load is generated by muscular activity or by solar radiation, the adaptation required to sustain it remains the same. In addition to the constant buildup of heat-shock proteins, the bodies of athletes undergo a long-term change in the enzymes that control the rates of biochemical reactions. Genes are activated that alter the shape and amino acid content of metabolic enzymes, making them more resistant to heating and thus better able to maintain proper reaction rates in the face of elevated temperatures. Small molecular changes can produce dramatic effects. For example, heat-tolerant bacteria called hyperthermophiles contain many proteins similar to those found in humans, yet with only a few amino acid changes they are able to survive in boiling water. A 10°F rise in body temperature is usually fatal to humans, yet experienced marathon runners develop a heat tolerance that enables them to perform quite well during competitions in which their body temperatures rise by over 8°F. In that way, runners have become like camels. During the day, a camel’s body temperature can rise 12°F. The animal “stores” the heat until nighttime, when it will be passively dissipated by the cool air. Avoiding the need to sweat or to increase blood flow to the skin saves water and energy, reducing heat production. A conditioned marathon runner employs the same tactic, bringing him one step closer to becoming a denizen of the desert.