Problems on the High Peaks

As altitude increases, barometric pressure falls logarithmically.  In fact, mountaineers depend on barometric pressure to accurately gauge their altitude. The altimeter references the pressure level of their surroundings and then calculates altitude according to standard atmosphere laws. Standard barometric pressure at sea level is 760 mmHg.  Ascending to 5000 meters causes barometric pressure to fall to half its sea-level value.  At altitudes above 6000 m, altitude illness often occurs. Low barometric pressure (hypobaria) in the alveoli, small sacs that vastly increase surface area available for gas exchange in the human lung.  This reduced pressure can alter the forces governing transcapillary fluid flux resulting in the life-threatening conditions of High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE).  For a further explanation of these conditions, see the section on Altitude Illness.

courtesy of Dr. J. Bindon, University of Alabama

Hypoxia

The main problem climbers face at altitude is the condition of hypoxia, the reduction of oxygen supply to tissues despite adequate perfusion of the tissues by blood.  Diminished barometric pressure reduces the partial pressure of oxygen in the alveoli causing oxygen to diffuse from air to the blood at a slower rate than under sea-level conditions.  At 18000 ft., blood only reaches 71% oxygen saturation. The oxidation of food materials as a major source of energy, a constant supply of oxygen is essential to human respiration. Without sufficient oxygen, muscles lose power and mental processes slow.  At extreme altitudes, hypoxia can cause ataxia, lethargy, or unconsciousness as core organs are starved of their energy supply.

courtesy of Dr. J. Bindon, University of Alabama