Changing Our Spots

Getting ourselves accustomed to extreme differences in altitude or climate is no walk in the woods.

Field & Stream Online Editors

A quarter century ago i stood on the lip of Washington's Mount St. Helens, 9,677 feet above sea level, with my hands on my knees and my head splitting with pain. During the last 1,000 feet of the climb, I'd had to labor for breath, feeling the ground veer under my feet as my focus dissolved. Overcome with nausea and vertigo, I unceremoniously leaned over the precipice and puked into the long-dormant volcano.

By the time St. Helens returned the favor two years later, vomiting fire and ash thousands of feet into the air, I had moved from an apartment on Puget Sound to the Rocky Mountains. The elk I shot on the 13th day of a late-October muzzleloader season fell dead in 2 feet of snow on the upper slopes of Tin Cup Creek, in Idaho's Centennial Mountains, at about 9,400 feet. Clear-headed, and as fit as I would ever be, I packed an 80-pound quarter 3 miles down to the road, hung it at camp, then hiked back in for another.

How could the pathetic specimen who stumbled up St. Helens in 1978 transform into the surefooted hunter who packed elk quarters down from a similar elevation only two years later? In a word, acclimatization, which is the body's adaptation to extreme changes in environment, including high altitude, tropical heat, and Arctic cold.

In Washington, I drove from sea level to 6,000 feet, then climbed to the summit of St. Helens in a few hours. Having no time to adapt, my body exhibited the classic symptoms of acute mountain sickness-throbbing headache, lassitude, shortness of breath, and nausea. By contrast, my home in the Rockies was a mile above sea level, and I had hunted at lung-searing elevations for two weeks before dropping the elk.

Spending time at high altitudes, the body adjusts to the decreased oxygen in the air by increasing the depth and rate of breathing, which helps remove carbon dioxide from the bloodstream. In addition, changes in kidney function make the blood more alkaline, enabling it to transfer more oxygen to the muscles. The resting heart rate increases. Red blood cell production does, too, which helps in heavy lifting. Because of those changes, I was stronger on the Montana trip than out-of-towners could be in the same way that the Denver Broncos are stronger football players than their East Coast opponents. Having John Elway at quarterback never hurt, but the reason the Broncos could come from behind in the fourth quarter at Mile High Stadium was because the lowland gorillas just ran out of steam.

Take It Slow
Some of the changes that occur during acclimatization, such as in the rate and depth of one's breathing, begin on the first days of being at high altitude. Efficient transfer of oxygen to the muscles occurs gradually during the first week. The aerobic power of the cardiorespiratory system is still improving after 14 days. Peak performance at high hunting altitudes takes several more weeks. Does this mean that a hunter who has never climbed higher than the observation deck of the Empire State Building should cancel his sheep hunt in British Columbia's Athabasca Mountains? Not at all. He can't expect to climb as effortlessly as his guide, but by allowing his body a few days to acclimatize, he ought to be able to keep his lunch out of the lichens.

The key to acclimatization is gradual exposure. If you are traveling from sea level, spend at least two days at 5,000 to 6,000 feet before going higher. Don't climb more than 2,000 feet a day, and after each 2,000-foot gain in elevation, spend a rest day in camp before moving on. Much elk and mule deer hunting, and many pack trips to alpine lakes, takes place at elevations from 7,000 to 9,500 feet, altitudes where acute mountain sickness (AMS) affects one in two people who don't take the time to acclimatize. If time restrictions prevent you from doing it gradually, ask your doctor about acetazolamide (Diamox), which increases blood oxygen content, promottes restful sleep, and will help prevent many symptoms of altitude sickness.

Other tips for acclimatization: Drink plenty of water, eat your pasta (a high-carbohydrate diet can reduce symptoms of AMS by one-third), and avoid alcohol. For reasons not entirely known, acclimatization progresses more rapidly if you sleep at a lower elevation than you climb.

Aspirin, acetaminophen, and ibuprofen will help relieve headaches, and most symptoms of mild altitude sickness will fade in a couple of days. However, if symptoms do not disappear, or if you notice a companion staggering, acting irrationally, or refusing to eat or drink, immediately return to a lower elevation. And keep a close eye on children, who are more susceptible to altitude sickness than adults. Two potentially fatal forms of altitude sickness-high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE)-can also fell fit men and women at Western hunting altitudes. Drowsiness, shortness of breath, fatigue, and dry cough are early signs of HAPE, which is caused by an accumulation of fluid in the lungs; later warning signs include blue lips, a high resting heart rate (above 90 beats per minute), and a cough with white (later pink) phlegm. HACE, caused by pressure on the brain, manifests itself in symptoms associated with AMS-headache, difficulty speaking, hallucinations. HACE victims often cannot pass the "drunk test" of placing one foot in front of the other and walking a straight line. Any of these symptoms warrants immediate descent and medical attention.

Too Darn Hot?
When your body is subjected to intense heat, the strain produces symptoms not unlike those that occur at altitude: headache, shortness of breath, dizziness, nausea, and vomiting. Others include rapid pulse, weakness, and flushing of the neck and face. Children and the elderly are particularly susceptible. If you suspect someone is succumbing to a heat illness, get them out of the sun and have them drink water. In severe cases, remove their clothes, sponge the body with a wet cloth, then fan vigorously to promote evaporative cooling. If possible, apply cold packs to the armpits, groin, and behind the neck.

Acclimatized individuals fare much better than their counterparts in hot weather, primarily because they sweat more and the evaporation cools them. They also begin to sweat at a lower core body temperature and more uniformly over larger skin surfaces. Their resting heart rate is lower, yet the heart pumps more blood. And their skin and rectal temperatures remain slightly lower during exercise than those of people who are not acclimatized.

The catch for a Minnesota fisherman traveling to Key West for tarpon, say, is that acclimatization takes 10 days for adults and up to two weeks for children. Also, men sweat more readily than women and may have an easier time acclimatizing to tropical conditions (the converse is true in the desert).

There is good news. Strenuous aerobic exercise in the moderate temperature of a health club or, preferably, outdoors under the sun can improve your sweating response and lower your exercise heart rate significantly. Ideally, you should exercise an hour a day for at least 10 days before heading south. If you can't find a warm place to exercise, pile on extra layers of clothing. The more you sweat at home, the better you'll feel when you step onto the casting platform of a backcountry skiff.