Extreme Medicine (18 page)

Apart from drowning, this phenomenon of arterial gas embolism is the leading cause of death among divers. This we call barotrauma—literally, the wound of pressure. It is easily avoided. The trick, as with most things in life, is to keep breathing. Breathing in and out during the ascent releases the expanding gas and stops the lungs from overinflating. But panic, followed by a bolt to the surface with your breath held, will kill you.

—

P
RESSURE DOESN'T CHANGE
just the volume of gas within our bodies. It changes the way gases affect our bodies. Air is composed of 21 percent oxygen, 78 percent nitrogen, and a mixture of trace gases. The nitrogen is usually inert, and at sea level pressure, it passes in and out of our lungs without any noticeable effect. But it doesn't remain so innocuous under pressure. Underwater, nitrogen acquires narcotic properties. The higher the pressure, the more intoxicating its effect becomes.

“The narcs,” in divers' parlance, this phenomenon feels almost exactly like being drunk and becomes very noticeable below depths of twenty or thirty meters. While it might sound like fun, it's dangerous in a situation where small mistakes have the potential to be catastrophic. Oxygen, too, becomes less benign at depth. Under pressure it can become toxic—particularly to the lungs and the central nervous system—in the worst cases causing seizures. Again the problems become more severe the deeper you dive. But some of the most severe medical problems associated with diving occur only after you've left the water.

Nitrogen is highly soluble. At sea level, it passes from the lungs into the bloodstream until blood becomes saturated and no more can be taken on board. When we go diving, the increase in pressure temporarily allows more nitrogen to dissolve, supersaturating the body and its tissues. This in part accounts for the narcotic effects seen at depth. But once the diver returns to the surface and normal pressure, this excess nitrogen must come out of solution as gas. This is exactly the same process that we see in the fizzing of a bottle of cola when the cap is twisted off. Surfacing slowly is like releasing the pressure held in the bottle gradually and avoiding the overwhelming surge of bubbles.

We all fizz when we surface from a dive. The trick is to limit the number of bubbles and the rate at which they form. There are two ways of achieving this. Spending less time at depth reduces the amount of additional nitrogen that accumulates. Ascending slowly or stopping on the way up allows the shower of bubbles to be captured in the circulation of the lungs and filtered out of the body. This is the basis for the diving tables that define how long a diver may safely stay at depth and the rate at which one can ascend.

With proficiency and protocol comes an illusion of safety, but the dangers of subjecting your body to extremes of submergence are real and potentially deadly.

—

Q
ALITO IS PART OF
a Pacific Island chain, fringed with the sort of beaches they use to advertise credit cards; it is small enough that you could walk around it in just over an hour. The surrounding waters were crystal clear and warm enough to dive without wet suits. I was part of a coral conservation expedition, based in the Mamanuca island group just a few miles north of Fiji. I had arrived a month or so before Christmas 2003, taking up a less than onerous post as dive medical officer. We were cut off from the rest of the island, living in an abandoned house set back from the beach. For electricity we depended on a diesel generator. Water was delivered by ship and stored in a huge concrete reservoir to the rear.

Weekends aside, we dived most days. For the coral surveys, we swam in teams of four, cataloging the flora and fauna in locations where no one had ever dived before. The dives themselves were conservative; we were forbidden from going deeper than eighteen meters, and we were never under for more than forty-five minutes. There was nothing particularly extreme about any of it. The water was warm and crystal clear.

It was a far cry from the dives I'd done in British coastal waters, where you sometimes had to wear a fleece jacket under your dry suit, were often unable to see your hand in front of your face, and at times had to grapple with ocean swell. Compared to that, the stuff we did on the expedition in the Pacific felt absurdly placid, little more than souped-up snorkeling. And yet the threat was always there.

In the run-up to Christmas, we managed to squeeze in a couple of recreational dives. These were the highlight of the expedition—a chance to do some proper exploratory diving. The surveys were great, but being forced to follow compass bearings and record accurate fish and coral species counts on our slates somewhat detracted from the grandeur of the spectacle.

There was a clutch of newly discovered dive sites scattered around our island group that the expedition found and named. We were pretty literal about it. The reef in front of the expedition house was called House; another that was carpeted with sea grass became known as Garden. The site we would dive that day was simply called Magic.

The dive started well enough. We came off the boat as a group of four, split into two buddy pairs, and began moving over the shelf, dropping close to the sandy bottom, drifting slowly along a line of sea fans.

I remember breaking into a broad smile as we settled into position. The reef swarmed with life. It was exploding with color, as beautiful as anything I'd ever seen—“Magic” indeed. There was a gentle current that pushed through alongside the coral shelf, bringing energy into the system: nutrients and foodstuffs. On this the residents of this coral neighborhood feasted. Everything was well fed, from the clownfish and anthias to the barracuda and sharks.

There was no need to swim; the current was doing all the work. I sat, neutrally buoyant, taking it all in. The surface rippling above, with the sunlight playing through it, appeared deceptively close.

We passed by a chunky-looking reef shark, its powerful, diamond-shaped body framed perfectly against the blue. It wasn't on my list of properly dangerous predators. Besides, why would it bother taking us on when there was an endless supply of more predictable prey on the coral wall?

Then the current took us around a corner, and the landscape began to change. I looked down. The reef was fading now, replaced by a sandy surface strewn with more barren-looking dead coral and rock. I was vaguely aware that we'd been picking up speed all along, but things really started moving after we made the turn.

I passed over one of the rocky outcroppings, too quickly for comfort, aware that my pace had suddenly accelerated. I turned to the rest of the dive group behind me and punched the open palm of my left hand with the fist of my right—trying to signal to them that I was worried about the current.

I needn't have bothered; they'd already worked that much out for themselves. All three were below me, hanging off the rock I had just passed, legs and fins fluttering in the current like flags in high wind. The current was growing steadily stronger, threatening to take us beyond the limits of the dive site.

I turned and tried to swim down toward them, descending again at a time when I should have been on my way back to the surface. A handful of meters separated us, and the current couldn't have been flowing at more than a couple of knots, but it felt like running into a gale. I inched forward, trying to reach the relative safety of the rock. I was kicking furiously, my body out at full stretch, heaving great lungfuls of air from my tank, trying to make ground.

I was on the verge of being swept off by the flow and separated from the rest of the group. An earlier expedition had nearly lost a diver this way, pulled away from his buddies by the current. He'd been found many hours later, alone on the surface, more than a mile away, just before nightfall. They were lucky. When they got to him, he'd all but given up hope of rescue.

I was keen to avoid the same fate. But here on this underwater treadmill, kicking as hard as I could, other risks were beginning to creep in. My air supply was falling faster than ever—I had to keep an eye on that. But at the back of my mind, I was aware that all of this frantic thrashing was silently accelerating the changes in my physiology caused by diving, increasing my risk of decompression illness.

—

W
HEN YOU EXERCISE,
your rate and depth of breathing go up. At the same time, the blood flow to your muscles and the capillary network around your lungs increases; your heart pumps harder and faster—chucking out larger volumes of blood—trying to keep up with demand.

I'd gone from sipping around half a liter of air from my tank with each breath to perhaps five times that volume. My heart rate was up too. The five liters of blood ordinarily ejected by my heart every minute had now increased to four or five times that number.

All of this was an effort to step up and meet the demands of this new exertion, helping me to inch closer to that rock. What had started as a sedentary drift had now become a ferocious sprint. But in boosting the output of my heart and the volumes of gas being shifted in and out of my lungs, I was—every second—bringing larger quantities of air into contact with a much greater flow of blood, further saturating my body with nitrogen. The simple fight-or-flight response that I needed to get myself out of immediate danger was adding fizz to the tissues of my body, trading improved performance in this moment for problems that I'd have to deal with later.

I reached them, finally, still breathing uncontrollably hard, paying back the oxygen debt. I scrambled to look at my air gauge. I had a little less than a quarter of a tank remaining.

We still had to work out what to do. Bryn, the most experienced diver among the four of us, scribbled some words on a slate while we held on to him. “Near Wilkes Passage!!!” he wrote. I shrugged at him, unsure of what that meant. He scribbled some more. “Shipping lane.”

We had to stick together and get to the surface and hope that we hadn't drifted too far from our boat. We aborted the dive, ascending into the pounding flow, sticking close to one another, stopping the ascent as we reached the five-meter depth, hoping that this would be enough to help release the nitrogen that we'd stored up in our bodies.

I imagined the frothing of my blood. The nitrogen would be rushing out of solution now, possibly overwhelming the capillaries of my lungs. Usually the three-minute stop at five meters was just an added precaution, something you did to make sure that you were absolutely covered. But I wondered this time if it would be enough. We stayed as long as we could at five meters. We had the luxury of no more than a few extra minutes. My air was nearly finished, and the current was still carrying us.

I had time enough to think about where we were. Our shallow excursion of a few meters into warm, clear water suddenly looked far less benign. At the surface, we'd have to hope that the dive boat could find us. It was already late afternoon, and the sun would set fast.

Then there was the decompression. Even if I felt OK, it would probably be more than twenty-four hours before I knew whether I'd managed to deal with the additional burden of nitrogen. The symptoms of decompression illness—the numbness, the tingling, the pains in your chest, the difficulty with breathing, the creeping disabilities—all of that could evolve at pretty much any time while the fizzing in my bloodstream continued.

Nothing in my knowledge of dive medicine was particularly reassuring. We had stuck well within the limits of the dive tables, but about half of all episodes of decompression illness happen to people diving within recommended limits. I had just compounded the issue by exercising for a couple of minutes at top whack, loading my tissues and blood with far more nitrogen than I would have on any ordinary dive.

The nagging uncertainties that come with diving are easier to dismiss when you're within close reach of a recompression chamber. But out here it would take the best part of a day to get to the mainland and into a place with that kind of equipment. That journey could safely happen only during daylight.

There was no fallback position here, nowhere to go if I really was sick. My body had started changing the instant I'd entered the water, adapting to the new environment, yielding to the pressure and the changes that this inflicted. It suddenly seemed ridiculous to have carted a bag full of diving gear out into the middle of nowhere just to scratch the surface of the ocean.

The gadgetry that allowed me to descend a few meters beneath the water left me naked above it and far from help. When we broke the surface, I had never before been so happy to spit my regulator out and breathe ordinary air.

After a mercifully brief search, the dive boat found us. We drove back to Qalito, arriving just before sunset, happy—for once—to be out of the water. I spent the evening in my bed on the beach, reading my dive medicine textbook by the light of a headlamp. Having pushed the most sublime edge of the envelope that supports human life—using a twenty-first-century sports kit I'd bought in a dive shop in London—I was left underneath that palm tree in darkness hoping that the envelope didn't push back, little better equipped than a physician from the 1900s. I was hopeful that this time I'd get away with it, but in that moment it seemed like tremendous folly.

—

H
UMAN LIFE IS SUPPORTED IN ONLY
the narrowest margin around our planet; the water that covers fully four fifths of its surface doesn't support the immersed explorer. I'm not just talking about the absence of breathable oxygen. Taking air with us into the deep doesn't allow us to extend our stay indefinitely. We change as we dive, adapting to the new environment, but the water column also changes us, as do the gases that we take into our lungs. We're not supposed to stray from sea level. At least that's what our physiology tries to tell us. We're hopeless in the water without support—not much better even with our own oxygen. We should stay on dry land, somewhere warm. We are tropical animals, after all.