title: Oxygen transport in blood at high altitude: role of the hemoglobin-oxygen affinity and impact of the phenomena related to hemoglobin allosterism and red cell function.
abstract: Altitude hypoxia is a major challenge to the blood O2 transport system, and adjustments of the blood-O2 affinity might contribute significantly to hypoxia adaptation. In principle, lowering the blood-O2 affinity is advantageous because it lowers the circulatory load required to assure adequate tissue oxygenation up to a threshold corresponding to about 5,000 m altitude, whereas at higher altitudes an increased blood-O2 affinity appears more advantageous. However, the rather contradictory experimental evidence raises the question whether other factors superimpose on the apparent changes of the blood-O2 affinity. The most important of these are as follows: (1) absolute temperature and temperature gradients within the body; (2) the intracapillary Bohr effect; (3) the red cell population heterogeneity in terms of O2 affinity; (4) control of altitude alkalosis; (5) the possible role of hemoglobin as a carrier of the vasodilator nitric oxide; (6) the effect of varied red cell transit times through the capillaries.
mesh_terms: D000494:Allosteric Regulation; D000531:Altitude; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000502:physiology; D004058:Diffusion; D004905:Erythrocyte Aging / Q000502:physiology; D004912:Erythrocytes / Q000378:metabolism / Q000502:physiology*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000503:physiopathology; D008958:Models, Molecular; D009569:Nitric Oxide / Q000378:metabolism / Q000502:physiology; D010100:Oxygen / Q000097:blood* / Q000378:metabolism; D010313:Partial Pressure; D011485:Protein Binding / Q000502:physiology; D013696:Temperature
chemical_list: D006454:Hemoglobins; D002245:Carbon Dioxide; D009569:Nitric Oxide; D010100:Oxygen