Letter: Increased hemoglobin-oxygen affinity at extremely high altitudes.

Eaton et al. (1) stated that "increased, rather than decreased, oxygen affinity is an effective mode of short-term adaptation to markedly reduced environmental oxygen pressures" and pointed out the need to reevaluate the idea that "decreased hemoglobin-oxygen affinity is of adaptive value to humans at high altitudes." We fully agree with these authors and wish to call attention to the fact that human natives of high altitudes are unique in having a right shift of the oxygen dissociation curve in their hypoxic environment. Thus, camelids (alpaca, vicunia, llama), rodents (chinchilla, vizcacha), ruminants (yak), and birds (ostrich, huallata) that are native to high altitudes have a higher oxygen affinity than their relatives at sea level (camel, rabbit, ox, and a variety of sea level birds) (2, 3). We have recently shown that the Peruvian high-altitude native increases his hematocrit as a function of both age and altitude (4) and, in collaboration with Sime (5), we have found that this is due to a decrease in ventilatory rate with age. Since the changes observed in the ventilatory function and the hemoglobin-oxygen affinity at high altitude do not seem to be of longterm adaptive value, the physiology of human adaptation to very high altitudes needs to be reevaluated. CARIOS MONGE C. JOSE WHITTEMBURY Biophysical Laboratory, Universidad Peruana Cayetano Heredia, Limna Peru