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> illness symptoms run the gamut from headaches to waking up dead. The > Andean natives *may* have genetic differences allowing greater > tolerance for hypoxic conditions. Just some more interesting facts on hypoxia at altitude... If a man were placed at 19 000 m (63 000 ft) altitude, his lungs would be filled with water vapour, and no air or oxygen could enter his lungs (because at the body temp of man, the water vapour pressure is 47 mm Hg (6.28 kPa)). During acclimitization to altitude there is a change in the reponses of the respiratory centre and an adjustment of the bicarbonate concentration in the blood that permits the normal maintenance of acid-base balance and a normal blood pH at a lower P CO2. As these changes progress, the increase lung ventilation can be maintained with less difficulty. The diffusion capacity of lowland antives remains unchanged at high altitudes. Highland natives, however, have larger lung volumes, and thus have greater pulmonary difusing capacity. The difference results from an increased growth of the lungs during childhood. Similar changes have been documented in young rats exposed to low pressure during growth. Thus the difference in diffusing capacity is related to a lifetime acclimitization. Acclimitization also affects the transport of oxygen in the blood. In humans the number of red blood cells is increased from about 5 million per cubic mm to as many as 8 million at altitudes above 4000 m. This change is found in both permanent residents and acclimitized lowland natives when they live at high altitudes. Animals native to high altitudes have blood with a higher oxygen affinity and this facilitates the uptake of oxygen in the lung. However, man at altitude has a _decrease_ in the oxygen affinity of the blood. This slightly facilitates the delivery of oxygen to the tissues. Also, it has been found that number of capiilaries per unit volume may be increased (decreasing the diffusion distance), and the is increased myoglobin in the muscles (increasing the rate of diffusion). So I would hesitate to say the the Andean natives necessarily have a _genetic_ difference, rather they are acclimitized from birth. Cheers Bridget Elliott /\ /\ Department of Zoology / /\\ @@ //\ \ University of Port Elizabeth ///\ \\ (())) //\\ \ Box 1600 ////\\ ((***))//\\ \ Port Elizabeth // \ ((())/ \\ South Africa / \ 6000 fax : +27-41 - 504 2317 voice : +27-41 - 504 2424 e-mail:ZLBBLE@ZO*.UP*.AC*.ZA*
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