As you ascend into Earth's atmosphere, the air thins, providing less oxygen and humidity to support your body's metabolic processes and potentially causing unpleasant physical symptoms. High elevation is a relative term -- if you live at sea level, skiing at a mere 3,000 to 4,000 feet may make a difference, whereas someone who lives in mile-high Denver may have to go much higher to notice an effect. Acute Mountain Sickness, or altitude sickness, is notoriously random -- it affects about half of those who ascend above 8,000 feet, according to the authors of "Mountaineering: The Freedom of the Hills," but there's no way to predict whom it will strike.
Physical Symptoms
You may notice shortness of breath, increased heart rate and light-headedness at higher elevations, even if you have no other symptoms of AMS and particularly during strenuous activities such as skiing. Because thinner air carries less oxygen, your cardiopulmonary system is less able to deliver oxygen to your muscles to support athletic performance. Expect to feel a little "out of shape" and take it easy during your first few days at altitude. Your body will begin to adapt by producing additional red blood cells to compensate for the oxygen shortage. Other common symptoms of AMS include headache, nausea, insomnia, poor appetite, coughing and muscle cramps.
Mental Symptoms
As your brain is forced to function on less oxygen, it may be less reliable than usual. You may find yourself irritable, unusually forgetful or prone to slight cognitive errors such as misstating directions or mixing up words. The effect may increase the higher you ascend. Poor sleep or dehydration -- also common at high elevation due to low humidity -- can exacerbate the mental fog. You may also experience deficiencies in your physical coordination. On the mountain, it's wise to remind yourself that your judgment and athletic performance may be compromised for the first few days at altitude; avoid taking unnecessary risks such as skiing runs that may be above your skill level or trying new tricks in the terrain park.
Prevention
The best way to prevent symptoms of AMS is to ascend gradually -- ideally by sleeping at no higher than 1,000 additional feet per day if your destination is above 10,000 feet. Most skiers probably don't have the luxury of patience of such a gentle ascent, however. You can ask your doctor for a prescription for acetazolamide, which can lessen the symptoms of AMS; take it for several days prior to your ascent and for your first 48 hours at altitude. Drink plenty of fluids; your kidneys work harder at altitude which, along with the typically drier air, can lead to dehydration and exacerbate headaches and muscle cramping. Avoid alcohol and caffeine.
Treatment
You can reverse simple AMS by returning to a lower elevation. If this is impossible, use rest, over-the-counter pain relievers and ample fluids to treat the condition as appropriate. Symptoms usually begin to abate after 48 hours. Keep in mind, however, that AMS can progress to much more dangerous high-altitude pulmonary edema and high-altitude cerebral edema at elevations above 10,000 feet. Victims of HAPE and HACE become very ill, suffering severe headache, vomiting, abnormal heart rhythms, disorientation and blue lips and nails. Descend and seek medical help immediately if you or a companion displays symptoms of HAPE or HACE; both can be deadly, and patients may require treatment in a hyperbaric chamber.
