From Sea Level to Summit
AT 3 A.M. ON A SWELTERING JULY NIGHT, I awake half-parboiled in a clear plastic tent. The tent is set atop my queen-size bed. On the floor, a 70-pound filtration pump siphons 12 liters of oxgyen per minute from the humid night air–then forces the thinned gas gruel inside the tent via a plastic hose.
Feeling headachy and a little nauseated, I fumble through the sweat-soaked sheets for a flashlight, reading glasses, and a pair of high-tech gizmos. According to the first of these–the HandiOxygen sensor–ambient oxygen levels have plummeted by more than 30 percent since I zipped myself in here four hours ago. My western Pennsylvania home is only 770 feet above sea level, but the simulated oxygen level inside the tent is equal to an altitude of 11,885 feet.
I quickly place gizmo No. 2–a SportsStat pulse oximeter–on my index finger. My nocturnal heart is thumping a resting 45 beats per minute, a reassuringly low number for a 54.9-year-old. My blood oxygen saturation, at 83 percent, is low as well–though few medical professionals would find this reading reassuring. Normal, healthy people under normal, healthy conditions boast "sat" levels from 97-100 percent. If I were to arrive at my local hospital with this 83, the ER docs would almost certainly put me in the ICU.
Excellent! The hypoxic crypt is working perfectly!
As Nietzsche once spake from his rarefied mountain cave, "Whatever gaseous deprivation does not destroy me only makes me stronger." Or something along those lines. It's conceivable my grasp of college philosophy has slipped a little after weeks of sleeping nightly in my own oxygen-starved chamber.
For those tackling purely cerebral challenges–acing the S.A.T.'s, for instance, or passing a fourth-grade spelling test–I concede this high-tech contraption may be a less than ideal training tool. If, however, your goal, like mine, is literally loftier–to climb Colorado's highest summit after a lifetime of sea-level habitation–well, that's a different story. For quests of this sort, a few mild semi-hallucinations and magnified levels of whiny hypochondria are small prices to pay to make it to the top.
Over the course of my life, I've hiked–or more accurately, sauntered–over vast tracts–or at least parts–of the low-altitude East. But never in all my years have I aspired to climb so much as a foothill out West. Now, in just two months, I will face the highest peak in the Rocky Mountain range. As BACKPACKER's human guinea pig in a train-for-altitude experiment, I'm using the latest technology to strengthen and pre-acclimatize myself while remaining here in Pittsburgh until the night before my summit attempt.
Chief among these high-tech aids is the hypoxic tent itself. Though invented nearly a century after Nietzsche's time, I suspect he would have approved: Lots of would-be übermensch–mountain-oriented or not–swear by the philosophy of strength through semi-suffocation, also known as sleep high, train low. Lance does (or did) it. Ditto Shaq and Becks. A spokeswoman for Boulder-based Colorado Altitude Training, which manufacturers the $5,795 CAT 150 Tent System I've been using, boasts that her company's roster of clients includes Tour de France cyclists, Ironman triathletes, and NFL wide receivers.
As far as an actual Nietzschian demise goes, tent life is unlikely to cause it. The CAT 150 features airtight zippers and proprietary membranes that allow exhaled CO2 to escape while effectively hampering the infiltration of outside air. Despite this, the spokeswoman has assured me, even in the event of power failure, there's enough air inside the tent to keep me and a bed partner alive for 14 hours.
As if I could coax anyone into joining me inside this turkey-roasting bag. Last week, while dining with a pair of comely swimming teammates, one of them mentioned that her father-in-law owns a cabin in the Laurel Highlands. At 2,200 feet, she said, this is the highest spot in Pennsylvania.
"Actually," I corrected her, "my bed in Sewickley Heights is much higher. Perhaps you two would care to join me?" Sigh. Another lesson for the newbie: The mountaineer's life is nothing if not ascetic. At 3:15 a.m., I switch into a dry T-shirt, turn off the flashlight, and attempt to find my way back to sleep–ménage à un.
The path leading me to this odd station began innocently enough in a Pittsburgh bar. I was trading boasts with a highly competitive triathlete friend, whom, incidentally, I can humiliate in all swimming events.
In an effort to regain the bragging advantage, he asked me if I'd ever climbed a "14er"–an abbreviation, he explained, used by trekkers to describe mountains 14,000 feet or higher. He claimed to have made it up a good dozen of them.
Climb a 14er? Though I didn't concede this, I'd never so much as ascended a "3er" without automotive assistance. I shook my head dismissively and steered the topic back to swimming, junking his implied challenge as yet another in a long line of insane ideas fueled by beer. But the next morning, to my surprise, I found myself Googling "14er." Somehow, high-altitude trekking had grown more alluring following a good night's sleep. Perhaps it was the chronic pain in my right shoulder–and my doctor's advice to take a break from the water. Perhaps it was Peggy Lee-style "Is that all there is?" ennui setting in: A couple years before, I'd placed fourth in the world in my age group in the 200- and 400-meter freestyle, which put a small bounce in my step–for a while. With each passing year, such accomplishments had begun to seem less like celebratory milestones than mile markers to the sarcophagus.
I was, in short, primed both physically and emotionally to try something new and completely different. A week after first hearing "14er," my quest had an object: Mt. Elbert, 14,443 feet, the highest peak in Colorado. Even the name conjured exotic extremes: K2, Matterhorn, Elbert! In the giddy foremath to reality, I imagined myself at The Explorer's Club, spellbinding my future friends–Messner, Viesturs, and the like–with yarns of Elbert's quixotic treacheries. Rejuvenated by such imaginings, I suggested the idea to my editor at BACKPACKER and soon set myself to the tasks at hand: preparing my lungs, legs, and psyche for the improbable pursuit of a summit.
In contrast to lowland air hogs like me, some creatures are actually at home in rarefied air. In 1975, for instance, a type of vulture known as a Ruppell's griffon was sucked into a jet engine at 37,900 feet, nearly two miles higher than the summit of Everest. Another stratospheric migrant, the bar-headed goose, uses a unique set of re-breathing lung sacks and deeply embedded muscle capillaries to fly 1,000 miles across the Himalaya in a single day. The air on its flight path is so thin that kerosene can't even burn in it.
For certain mammals, like yaks and llamas, natural selection appears to have rewarded genes for exceptional oxygen miserliness. The same process is occurring in select human groups, too: The Andes-dwelling Quechua Indians, who have lived at high elevations for 10,000 years, much prefer glucose over fat–probably because the former requires considerably less oxygen to metabolize. Sharing these beneficial adaptations are the Sherpas of Nepal, who've inhabited the Himalaya for at least 20,000 years. Sherpa breathing capacity and tolerance for high-altitude exercise are legendary: In 2003, a Sherpa named Lhakpa Gelu climbed Mt. Everest from basecamp to summit in 10 hours and 56 minutes, a record that basically relegates the world's highest mountain to essentially the same kind of dayhike I'm attempting on my own puny E.
Not that you need a name like Tenzing or Pemba to excel at mountaineering. In 1978, Peter Habeler and Reinhold Messner became the first humans to climb Everest without supplemental oxygen–an achievement previously considered a physiological impossibility. So incredible was their accomplishment, in fact, that researchers assumed the two must enjoy a freakishly well-tuned hypoxic ventilatory response: As oxygen decreases in the bloodstream, we unconsciously begin inflating our lungs more deeply and more often–an enhanced huffing and puffing that extracts more oxygen from thinner air. "But when Habeler and Messner were measured for this, it turns out they were just normal," says Allen Cymerman, a physiologist at the U.S. Army Research Institute of Environmental Medicine (UARIEM) in Natick, Massachusetts. What Cymerman and other high-altitude researchers have subsequently shown is that hypoxia triggers a host of short-term and long-term changes that together allow us to make the best of a less than ideal situation (see "You, At Altitude").
"Up high, there's a whole cascade of events taking place from the lungs to the blood to the mitochondria in our cells," says Robert B. Schoene, a pulmonary specialist at the University of California San Diego and former president of the Wilderness Medical Society. After years of exercising in low-oxygen conditions, Habeler and Messner appear to have optimized their capacity for high-altitude performance at every step along this physiological cascade.
A lifelong climber himself, Schoene has bronchoscoped elite climbers suffering high-altitude pulmonary edema (HAPE) on 20,320-foot Mt. McKinley and studied acute mountain sickness (AMS) in average people at much more moderate altitudes. Though we're not all cut out for the extremes, Schoene believes most reasonably fit people can do fine at heights like Mt. Elbert's–provided we give ourselves time to acclimatize. Unfortunately, few recreational athletes traveling to altitude from sea level have the luxury of full acclimatization, which can take a month or longer. But going for the gusto too soon can often prove a recipe for misery. In a study published in the Annals of Internal Medicine, researchers looked at 3,158 tourists traveling to ski resorts located from 6,300 to 9,700 feet in the Colorado Rockies. Even at these modest heights, fully 25 percent developed full-blown AMS. And those whose permanent residence was below 3,000 feet proved 3.5 times more likely to get sick than those who lived above 3,000 feet.
The conventional wisdom holds that deadly disorders like HAPE and high-altitude cerebral edema (HACE) only occur at much loftier altitudes. Not true, says Schoene. Early in his medical career, he took a sabbatical at Colorado's Keystone ski resort, elevation 9,400 feet, to study athletic performance and altitude illness. "At the height of ski season, we were averaging five cases of HAPE per week," Schoene recalls. "The victims were almost always people who flew in from either coast and immediately started exercising hard."
Folks, in other words, like me: an alpine rookie with scant time off who must begin his assault on Mt. Elbert as soon after de-planing as we possibly can.
After combing the research literature, it became clear what I had to do: grow myself some cojones–hemoglobin ones, at least–before even departing Pittsburgh. If not, I had no doubt, it would be Mt. Elbert assaulting me.
Sleep high, train low has not always been the operative training mantra. As far back as the 1968 Mexico City Olympics, many endurance athletes believed that the best approach was to move someplace high–the Alps, Albuquerque–where they could live full-time and train in thin air. In the 1990s, however, researchers Ben Levine and Jim Stray-Gundersen revealed a major drawback to this live high, train high approach: Though chronic hypoxia does increase an athlete's red blood cell count, it also makes it impossible to exercise hard enough to get into peak condition.
One of the first high-profile adopters of the altered approach was the U.S. national long-track speed skating team. Three years before the 2002 Olympics, team members moved to Utah. During the days, they trained at Salt Lake City's relatively modest elevation of 4,700 feet, which supplied enough oxygen to train hard. But during the nights, they slept in Park City, a nearby ski area whose 7,000-foot elevation provided sufficient lack of oxygen to stimulate physiological changes. The net effect: The team's six skaters racked up eight medals.
But what if you can't move to Salt Lake, or Boulder, or Chula Vista, or the handful of other sports meccas that offer both high and low altitudes within easy commuting distance of each other? You can train hard and hope for the best (see "How to Reach Your Peak," page 107), or you can move hypoxia to you: Numerous studies have shown that exposure to simulated altitude triggers the same physiological changes enjoyed by those who live at real heights.
What has proven more difficult to demonstrate is whether such changes translate into actual performance boosts. In terms of sports performance at sea level, several studies have found big gains in both aerobic capacity and long-distance running times. Other studies, however, have failed to show any such lift. One possible reason: In some athletes, the oxygen-carrying benefits of increased hematocrit may be offset by the increased "thickness" of their blood. "We know that people who live year-round at 10,000 feet are more predisposed to blood clots and heart problems," says Schoene. "The blood can get sludgy."
What is clear: pre-training helps when you're headed for high altitude. Most researchers agree that the right dose and duration of hypoxia reduces AMS symptoms. In a 2007 study, Natick Institute researcher Stephen Muza concluded that soldiers exposed to a simulated altitude of 14,000 feet for three hours a day for one week had a strong probability of avoiding AMS when deployed to high places. And such pre-inoculation significantly reduced the performance dips seen in unacclimatized soldiers.
In my own case, the R&D manager at Colorado Altitude Training suggested I spend at least three weeks in my hypoxic chamber once I cranked it up to peak elevation. After setting it up in July, I spent the first night at 4,700 feet. Over several weeks, I upped the altitude by 500 to 1,000 feet per night until I reached the highest the pump would allow, just shy of 12,000. There I stayed for the rest of the summer.
In my fully oxygenated daytime hours, I set my sights on another critical piece of pre-trip training: resuscitating leg muscles that had become nearly vestigial from decades of swimming as my only exercise. In cardiovascular terms, I'm in pretty good shape for my age. But being fit in the pool is not the same as being fit on dry land. As exercise physiologists have long noted, athletic training is incredibly muscle-specific. Well-exercised muscles adapt in a host of ways–from increasing the size and number of mitochondria to developing extra capillaries. Rarely used muscles, on the other hand, don't need, and hence don't get, this turbo-charge.
The gold standard measure of aerobic fitness is called VO2 max–essentially, the highest volume of oxygen your body can use to do work. Oxygen use is partly dictated by the amount you can breathe in and load into your bloodstream via the lungs. It is, however, much more related to how much oxygen your skeletal muscles can metabolize. Elite marathon runners, swimmers, and other endurance athletes all tend to have high VO2 max levels–especially when measured during the activity they've trained for. A marathoner measured on a rowing ergometer, on the other hand, will not score nearly as high.
In terms of mountain climbing, I was as well-adapted to the task as a manatee. In order to have a chance on Elbert, my climbing muscles–legs in particular–had to be resurrected.
To inaugurate the new regimen, I drove to a local gym where a marathoning friend agreed to give me a graduated treadmill test. This began with a five-minute warm-up at an easy 5-mph pace. The grade then increased from one to three percent, and the speed by 0.3 mph every 90 seconds. After 20:30, I gave up. I was jogging at 7.1 mph, and my heart was beating 171 beats a minute. My saliva felt like Elmer's Glue.
At my friend's suggestion, I began walking gradually longer distances on flat ground. Then I started climbing the stairwells at a gothic skyscraper at the University of Pittsburgh. The first time I attempted to walk up all 43 floors, I nearly collapsed. By the end of the summer, I could make it up and down four times without stopping.
About eight weeks into my program, I tested my progress with a 13-mile hike through the hills and valleys of the Pennsylvania coutryside. With breaks, it took five hours to finish, and I needed a half roll of duct tape for blisters. Still, I'd made the distance without expiring–by far the longest my little legs had ever ferried me at a single stretch. Shortly after Labor Day, I retested myself on the treadmill. This time, I lasted 24 minutes and made it up to 7.7 mph before being forced to stop with a heart rate of 176.
I'd done more land exercise over the course of the summer than the previous 10 summers put together. In mid-September, when my flight finally departed Pittsburgh for Denver, I still wasn't sure I was ready for Elbert. But I did know I was as ready as I'd ever be.
It's 5:25 a.m. on September 18, six days short of my 55th birthday. In a parody of rebirth, I extrude myself through the flaps of a tiny pup tent in Colorado's San Isabel National Forest. My body is shivering and sodden with lung exhaust, which has condensed and rained down upon me in the cold night. The altitude here, 10,280 feet, represents a refreshing descent from Sewickley's higher simulations. On the whole, I'm feeling splendid: There is nary a trace of headache, regurgitative urges, or psychiatric detachment I'd all but accepted as my baseline state back home.
After relieving myself on a lodgepole pine sapling, I use the pulse oximeter to confirm that the apparent bonhomie is no fluke: oxygen saturation a robust 93 percent...heart rate a relaxed 54 beats per minute.
Overhead, dense constellations scatter before the morning sun. The crisp air is redolent of the distant campfires of elk hunters. In this wee morning splendor, I can almost see why people actually enjoy communing with nature and whatnot. What a day! Excitement now trumps all anxiety.
Until, that is, my eyes lock on the crescent moon, which is rising beside a gargantuan pyramidal presence in the gloaming. Suddenly I realize what the colossus is: my magnet and my nemesis, Elbert!
In the gathering light, it's clear the mountain has donned unseasonable raiments. From treeline to summit, the peak is cloaked in shades of white–a mix of slush, crust, powdery fluff, and ice crystals. From steamy Pittsburgh yesterday, the promise of icy wisps seemed almost refreshing in a beer commercial kind of way. Now that I am actually here, I'm reminded once again that distance is the greatest cosmetic.
By 8:30, with breakfast wolfed and gear packed, I make my way to Elbert's official trailhead, elevation 10,367 feet. From this vantage, the peak is concealed by a forest of pines. Left unhidden is its immediate neighbor–the aptly named Mt. Massive–which soars to heights seemingly unscalable by hominids like me.
At 8:53 a.m., my oxygen/heart rate readings are an acceptable 89/72. I take one final cleansing breath and launch off into the woods. If distance swimming has taught me anything, it's to avoid flooding yourself with lactic acid in the first 45 seconds of an all-day swim. Taking pains to pace accordingly, I ford a small stream without falling in; negotiate several rocky switchbacks steep enough to trigger sweating and the delayering of garments; and somehow manage to stave off total exhaustion–until 9:13 a.m.
The entirety of the vertical ascent in these first 20 minutes: 400 feet, or about one gothic cathedral climb. Despite such modest advance, my ox sat has dropped to 81, and my heart is jack-hammering 132 times a minute. After a restorative rest, my readings stabilize at 86/102. Once again, I soldier onwards and upwards, reaching 11,000 feet by 9:34 a.m.
Continuing with baby steps up the ever-steepening slopes, I plod across an avalanche-scoured meadow strewn with boulders and felled trunks. After one last stand of pines, I finally reach treeline at 10:37 a.m. and celebrate with brunch. There are no elk to join me, but an odd chipmunk-squirrel chimera seems fascinated by my baggie of gorp. I layer back up and start the final 2,400 vertical feet.
The steeper the slope, the babier my steps become. Within another 10 minutes, sun-melting slush has turned into ice, then an inch of snow, then six. The path is barely visible, crisscrossing through outcroppings of windswept rock. By 12,500 feet, the air has grown noticeably thin. Perhaps it is hypoxia, but with each grueling switchback, I expect to see prayer flags and empty canisters of oxygen.
By the time I hit 13,000, the snow is a foot deep, deeper still in the frequent drifts. Twice I've had to guess which way the official trail goes; twice I suspect I've guessed wrong. The internet experts had all promised Elbert would be a "walkup" for 14er novitiates. I realize too late they meant a snow-free Elbert, an Elbert in the salad days of summer.
This is, alas, no salad day. I take refuge behind a boulder, my legs quivering, my diaphragm sucking in breaths as fast as it can. Readings now: 79/148. Inside my summer boots and cotton socks, snow has wedged itself around my toes, temporarily melted there while warm blood still circulated–and now refrozen with the closing of my arterioles.
I have developed, in other words, cold feet–that vanguard of self-pity and defeatism. For the first time today, I seriously mull the possibility of turning back. But then I take a look at the surrounding panorama, which is nothing short of spectacular. To the right and far below, at the base of a green valley dappled with wildflowers, sit a couple tjörns (better known to non-ancient-Norse laymen as "ponds"). A dozen miles in the distance, the town of Leadville–North America's highest incorporated municipality–resembles a craft shop miniature of Whoville. Faced with such beauty, I'm rejuvenated. Soon, my oxygen is back in the upper 80s, my heart rate has settled under 110, and I've regained my will to summit. I'm just about to re-start when I see five young Marines descending toward me, the middle guy green-faced. "It's bad up there," says one. "There's a demoralizing series of false summits before you even see the real one."
They wish me luck and resume their speedy march towards less nauseating air. I resume my own slog in the opposite direction. In minutes, the snow drifts are so deep I have to posthole each excruciating step.
By 11:30, I'm forced to a standstill at 13,280 feet, my legs knee-deep in snow and burning with lactate. It's not the snow, however, that makes me stop: Rather, it's a boulder the size of an industrial refrigerator. There's no way to walk or even crawl around it. My only choices: retreat back and choose a better route, or try to lift my bulk over it. I doubt I have the strength for the latter, but I know I'm too tired to descend and reclimb. I decide the only hope is to go for it.
Stalling for time, I take inventory of my symptoms. Chief among these is a bone-deep weariness. It's official: I've now set a new personal best for physical exhaustion, eclipsing the old mark established seven years earlier during an ill-fated blowgun monkey hunt in the Amazon. But when I attempt to inventory more subtle excuses for whining, I'm surprised to find a dearth of usual suspects. Conspicuously missing are headache, nausea, or any related hangoverlike symptoms so common in unacclimatized climbers and/or the hypochondriac fraternity.
Clearly, I can't credit a surfeit of oxygen here. My pulse oximeter readings: 72/152, the stuff of death beds. Perhaps my parents did adopt me from a Sherpa couple back in 1952. More likely, a summer of hypoxic discomfort in the CAT tent in Pittsburgh is what's helping me overcome the misery: a kind of pre-suffering on the installment plan. Whatever the cause, I just don't seem to need much air any more. I feel like a 6'1" anaerobic bacterium.
Muscle exhaustion, of both the leg and cardiac variety, is another story. My hands are now too cold and tired to write, so I use a digital tape recorder to document my increasingly erratic stream of consciousness. In between lung gasps, I record: Must keep reminding myself...the Atlantic sea whelk...is not used to...these conditions...My slimy molluscal feet...must necessarily move...at a literal snail's pace...with plenty of rest...No headache yet...but must not let down guard prematurely...the metaphor itself may...indicate early signs...of HACE...HAPE a threat too....Must keep checking self...for pink and frothy...sputum.
After three minutes of rhythmic pressure breathing through pursed lips, my oxygen saturation finally climbs back to the low 80s. I grab a crook on the boulder, wedge my right foot into a high cranny, inflate my lungs, and give it all I've got. Halfway through the hoist, I can feel my legs quivering. The alleged musculature, trained all summer in the art of a baby-stepping Everest Shuffle, is not prepared for heavy lifting.
Midway through my attempted heave, my right quad muscles stall out completely. My upper extremities are poised on the cusp of total failure. Throughout my entire musculoskeletal system, a cacophony of nerves fire frantic messages of surrender to my brain: Give it up! they harp. You are no summiteer. You're not even a false summiteer. Time to descend to low country for rest and relaxation! Soon enough, you'll be lying even lower!
As I hover in midair, it occurs to me that I don't want to give up. Sometimes trying is not enough. Either I finish today's assault on E–or leave knowing, for the duration and for certain, that it is E who has finished me. Who knows where a second wind comes from? Perhaps it is the result of summit fever; or a baser drive to avoid humiliation; or a middle-age guy's first genuine intimation of mortality. Regardless, my physiology suddenly rallies–from pulmonary gas exchange to mitochondrial energy production, the whole cascade upticks in concert with my will. Ever so slowly, the twitching bulk–that is to say, me–resumes its upward trajectory. With one final push, I make it over the boulder's top and collapse in the snow.
Ten minutes later, after I've finally caught my breath, the rest of the climb proceeds with surprising ease. The trail to E's first false summit is swept free of snow and nearly level. With each false summit thereafter, my confidence only grows. At one point, giddy, I take out my tape recorder and sing, Julie Andrews-style, "The hills are alive!" Alas, my attempted falsetto, unreachable in the cold, comes out as a manly bass. Treble was I ere I saw Elbert, I croak into the recorder, feeling in some small way Napoleonic on the brink of conquest.
After rounding a final switchback, it's there: the last, indisputable peak of E. You are a summiteer! I tell the recorder. Not just a false summiteer! A real one!
The wind, gusting at 40 mph, drowns out the boast, but I'm confident I'll remember it even without voice notes. I haven't felt this exhilarated in years. If I can make it back down the mountain, there's a 50-50 chance I'll return someday to climb an even more challenging 14er. Then again, I could just buy a Segway and never have to take another step under my own power.
I'm mulling such options when suddenly something flaps toward me from the horizon. It's a solitary raven, black as night, bobbing through the turbulence like an untethered prayer flag. It swoops overhead and gives me a quick, curious look. It almost seems he's quothing something about my future as a mountaineer, but I can't make out the sound over the noise of the wind.
Then, as if having reached some tentative conclusion, the raven turns its head and banks its wings to the left. In an instant, it glides into the vast cleavage separating Mt. Elbert from Mt. Massive and the limitless peaks beyond. I follow the flight as long as I can. Somewhere by the Continental Divide, which looks unimaginably vast from here at the top of the world, I lose track of the raven altogether.
Beautiful bird, the raven, and so dark: I'm sure I'll see another soon enough. For now, I envy the ease of his descent as my breaths come deep and quick in preparation for my own long way down.
A National Magazine Award winner for his health reporting, Jim Thornton often takes unorthodox approaches to his subjects–like the time he laid down with dead cows in the Chihuhuan Desert to see if vultures would land on him.
You, At Altitude
The highter you go, the more your body has to adapt. Here's what happens–from the inside out.
No matter where you travel on Earth, the concentration of oxygen in the air remains a steady 21 percent. At sea level, the weight of the atmosphere compresses lots of oxygen molecules into any given volume. The higher you climb, however, the less overhanging atmosphere there is to do this compaction. The result: Air becomes increasingly less dense. Atop Mt. Elbert, the absolute number of oxygen molecules per lungful is 59 percent the number at sea level. On Everest, it's a skimpy 33 percent. But even though the human body clearly hates being deprived of its favorite gas, we've evolved ways to cope.
Rapid-fire breathing brings more oxygen into your system, but it also causes you to blow off CO2 faster than normal. This lowers CO2 levels in the bloodstream–which, over time, can leave you feeling light-headed and actually decrease ventilation, upping the odds of altitude illness.
Reduced blood flow through the retinas can cause visual disturbances, from changes in color perception to reduced sensitivity to light and dark.
Performance on cognitive tests–pattern recognition, short-term memory, and the like–initially declines, but rebounds within a week or so as the body becomes acclimatized. Edema in the brain can cause side effects that progress from severe headache and loss of coordination to impaired judgment and eventually coma.
A warning sign of deterioration: subtle slurring of speech, with the pronunciation of the letters P, T, and K shortening so they're indistinguishable from B, D, and G–an effect that has also been found in patients suffering from Parkinson's.
The heart contracts more often, more forcefully, to increase total blood flow. Your lungs and cardiovascular system begin processing greater volumes of thin air in order to extract the same absolute amount of oxygen.
Blood pressure rises, especially on the right side of the heart, which supplies blood via the pulmonary artery to the lungs. This enhances gas exchange–but if the pressure gets too high, the smaller tributary vessels interlacing the alveoli can begin to leak like soaker-style garden hoses, leading to fluid buildup and HAPE.
As blood-oxygen saturation drops, sensors called carotid bodies, along with central receptors in the brain stem, detect the threatening condition and sound an alarm.
Blood pressure rises, especially on the right side of the heart, which supplies blood via the pulmonary artery to the lungs. This enhances gas exchange–but if the pressure gets too high, the smaller tributary vessels interlacing the alveoli can begin to leak like soaker-style garden hoses, leading to fluid buildup and HAPE.
The enhanced ventilatory response inflates additional lung sacks–or alveoli–deep inside and opens extra pulmonary capillaries you normally don't need to use.
Blood distribution patterns shift throughout the body: More blood is routed from the periphery and shunted to vital organs–the same basic process seen in hypothermia.
Hemoglobin carries oxygen in the blood, and a similar protein, myoglobin, delivers oxygen within muscle cells themselves. One study suggests myglobin levels slowly increase the longer you spend at altitude–though it may take weeks or months.
Increased hematocrit–a measure of red cell count and size–bumps up oxygen-carrying capacity, but it also makes blood thicker, harder to pump, and more prone to the clotting problems that can trigger heart attacks.
EPO signals your bone marrow to start making new red cells, a process that can take up to a month. Because of this, people who live at high altitude tend to have significantly higher hematocrits.
Within minutes of hypoxia, your kidneys begin releasing erythropoitin (EPO), which stimulates blood production. They also react to plummeting blood CO2 levels in a complicated cascade that triggers increased urination–which removes liquid from your blood, concentrating red blood cells. Good news: more oxygen uptake. Bad news: Your blood is "sludgier" and requires more power to pump.
Diaphragm and ribs
Nerves relay the emergency alert to your diaphragm and ribcage intercostal muscles, causing you to breathe more deeply and more often–something called enhanced ventilatory response.
The Kili Cure
The same attractions that make 19,341-foot Mt. Kilimanjaro a life-list peak (highest mountain in Africa, nontechnical hike) make it a haven for altitude sickness (plenty high, easy to rush). Here, experienced guides share their secrets for getting everyone to the top.
Slow down "I'm amazed at the number of people who start out like a gunshot cougar," says Peter Whittaker, owner of Rainier Mountaineering, Inc. and a 13-time Kili vet. Guideline: If you're too breathless to gab, you're going way too fast.
Take breaks "It's important to take a break every hour for five or 10 minutes," says Todd Burleson, president of Alpine Ascents. "It might take a half hour longer to make camp on a 6-hour day, but those are the people who make the summit."
Breathe In thin air, you need to learn pressure breathing: Inhale deeply, purse your lips, and slowly blow out as if you're inflating a balloon. "The back pressure in your lungs helps push oxygen from the alveoli into the bloodstream," says Whittaker.
Rest You can even conserve energy while walking: Use the rest step. As you walk up a steep grade, straighten your lower leg, "locking" at the knee. Your upper leg is bent, letting you rest your weight on your bones, not muscles. Pause for a few beats between steps.
Hydrate High-altitude trekkers lose moisture to the sweat of exertion, the "insensible perspiration" of water vapor exhaled through hyperventilation, and increased urination triggered by blood turned alkaline by hypoxia. Translation: "Drink 4 to 5 liters a day," says Burleson.
Eat often "We have a saying that lunch starts after breakfast and finishes right before dinner," says Whittaker. A sustained endurance climb requires serious fuel.
Sleep well Besides the obvious (warm bag, level tent site), ask your doctor about a temporary supply of Ambien, says guide Gavin Attwood. This sleep aid can also prevent Cheyne Stokes respirations–an apnea-like breathing pattern common at very high altitude.
Allow extra time "We build in an extra rest day at 14,000 feet," says Darsie Culbeck, director of Alaska Mountain Guides, "because in our experience its lets an extra 10% of our clients summit."
How to Reach Your Peak
Short of bivouacing in a hypoxic tent, no known lowland training will accelerate the complex physiological systems involved in acclimatization. But with these tips, you can still improve your chances of summiting.
Take steps "Be as specific as possible in your physical conditioning," says Allen Cymerman, physiologist at the U.S. Army Research Institute of Environmental Medicine. That means using a step mill, stairclimber, elliptical–or real stairs or hills. Adds Todd Burleson, president of Alpine Ascents, "Work up gradually to training with a heavy pack and boots–even indoors."
Up load By the time you're two weeks from your climb date, you should be able to ascend 3,500 feet in about three hours–carrying the weight you'll be hauling on summit day. Start training with a light pack, then add 5 to 6 pounds a week.
Go long "You don't want to arrive at your climb never having hiked for 8 hours before," says Peter Whittaker, owner of Rainier Mountaineering, Inc. Schedule weekend days to build up to a distance and time as close to your summit plan as possible.
Give it a rest "Taking breaks is an important aspect of mountain climbing," says Burleson, who suggests kicking off your training regimen with three days of exercise and four days of rest. After a few weeks, add another workout, and eventually get yourself up to five days on and two days off.
Ease off The last thing you want to do is show up on summit day already wiped–or overtrained. A good rule of thumb? Get into peak shape about two to three weeks before your climb, then gradually reduce your effort–called tapering–until the big trip.
Arrive early Though complete acclimatization can take months, the lion's share of the benefits occur within several days of your arrival at altitude. Plan to include a few easy days up high before your final push.