ATYPICAL HEMATOLOGICAL RESPONSE TO COMBINED CALORIE RESTRICTION AND CHRONIC HYPOXIA IN BIOSPHERE 2 CREW: A POSSIBLE LINK TO LATENT FEATURES OF HIBERNATION CAPACITY

Eight humans were isolated for 2 years in Biosphere 2, a sealed airtight habitat with recycled air, food, water, and wastes. A combination of conditions led to selective decline of oxygen (O₂) in the internal atmosphere from 21% to 14%, inducing symptoms of high-altitude sickness but with little or no compensatory increase in red cell production. All crew members exhibited significant decreases in both erythrocyte 2,3-bisphosphoglycerate (2,3-BPG) concentrations and P₅₀ [partial pressure of O₂ for 50% hemoglobin (Hb) saturation] values, changes opposite those expected in adaptation to high-altitude hypoxia. Lower P₅₀ with increased Hb–O₂ affinity induced by low 2,3-BPG is a characteristic of hibernating species and could be advantageous in O₂-impoverished environments. The mechanisms underlying these changes in the Biosphere 2 crew remain obscure but could be related to low-calorie diet (1750–2100 kcal/day). Because the combination of hypoxia and limited caloric intake is also characteristic of hibernation, this unusual response may represent a cross-adaptation phenomenon in which certain features of hibernation capability are expressed in humans.