Human llamas: adaptation to altitude in subjects with high hemoglobin oxygen affinity.

A C T To assess the adaptive value of the right-shift ofthe oxyhemoglobin dissociation curve (de- creased affinity for oxygen) observed in humans upon altitude exposure, the short-term physiologic responses to altitude-induced hypoxia were evaluated in two sub- jects with a high oxygen affinity hemoglobin (Hb Andrew-Minneapolis) and in two of their normal sib- lings. In striking contrast to normal subjects, at moderately high altitude (3,100 m) the high affinity subjects manifested: (a) lesser increments in resting heart rate; (b) minimal increases in plasma and urinary erythropoietin; (c) no decrement in maximal oxygen consumption; and (d) no thrombocytopenia. There was no difference between subject pairs in 2,3-diphosphoglycerate response to altitude exposure. These results tend to contradict the belief that a decrease in hemo- globin oxygen affinity is of adaptive value to humans at moderate altitudes. Rather, they support the hypothesis that, despite disadvantages at low altitude, a left-shifted oxyhemoglobin dissociation curve may confer a degree of preadaptation to altitude.