The number of people travelling to the high altitude regions, especially South America, Nepal, and India, has risen enormously in the past 10 years. Without special climbing ability these trekkers can be exposed to altitudes they will not have encountered in their home countries.
In India tourists traveling towards remote areas of Leh and Laddakh region of Jammu and Kashmir state complain of breathlessness and fatigue.
The concentration of oxygen at sea level is about 21% and the barometric pressure averages 760 mmHg. As altitude increases, the concentration remains the same but the number of oxygen molecules per breath is reduced. At 12,000 feet (3,658 meters) the barometric pressure is only 483 mmHg, so there are roughly 40% fewer oxygen molecules per breath. In order to properly oxygenate the body, your breathing rate (even while at rest) has to increase. This extra ventilation increases the oxygen content in the blood, but not to sea level concentrations. Since the amount of oxygen required for activity is the same, the body must adjust to having less oxygen. In addition, for reasons not entirely understood, high altitude and lower air pressure causes fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain. Continuing to higher altitudes without proper acclimatization can lead to potentially serious, even life-threatening illnesses.
What are the symptoms?
Symptoms usually begin within 48 hours of arriving at high altitude. The higher the altitude, the greater the effects. People can notice effects when they go to an altitude of 7,000 to 8,000 feet. If you have heart disease (such as heart failure) or lung disease (such as emphysema), you may have symptoms at lower altitudes. Symptoms include headaches, breathlessness, fatigue, nausea or vomiting, inability to sleep swelling of the face, hands and feet.
Both heart rate and breathing rate increase as the body tries to send more oxygen to its tissues. At very high altitudes, body fluid can leak into the brain (called brain or cerebral edema) or into the lungs (pulmonary edema). Both these conditions can be serious or even life-threatening.
You can do two important things to prevent high-altitude illness:
L. Jordan, March 2009. Scientific American, India. pp.19