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Climb Higher

With the right preparation–and a little help from a half-dozen friends, two exotic techno-gadgets, and one very sweaty hypoxic chamber–can a sea-level-dwelling rookie climb the highest peak in Colorado?

From Sea Level to Summit | You, At Altitude | The Kili Cure | How to Reach Your Peak

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.

Breathing
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.

Eyes
Reduced blood flow through the retinas can cause visual disturbances, from changes in color perception to reduced sensitivity to light and dark.

Brain
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.

Speech
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.

Heart
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.

Pulmonary artery
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.

Neck
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.

Pulmonary artery
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.

Lung sacks
The enhanced ventilatory response inflates additional lung sacks–or alveoli–deep inside and opens extra pulmonary capillaries you normally don’t need to use.

Circulation
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.

Muscles
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.

Blood
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.

Bone marrow
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.

Kidneys
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.

From Sea Level to Summit | You, At Altitude | The Kili Cure | How to Reach Your Peak

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