title: Insensitivity of VO2max to hemoglobin-P50 as sea level and altitude.
abstract: O2 uptake in the lungs, and therefore arterial oxygenation, is favored by a low Hb-P50 but this inhibits tissue O2 extraction, raising the question of optimal P50 during maximal exercise when VO2 is limited by O2 supply. Using a model of the lungs and muscles connected by the circulation so that O2 transport is simultaneously considered in both sites, sensitivity of VO2max to P50 was determined at three altitudes: PB = 760, 464 and 253 Torr, encompassing sea level and Mt. Everest. At Pb = 760 Torr, VO2max peaked at P50 = 30 Torr, was 99.4% (of that at 30) at normal P50 (26.8) and exceeded 95% (of that at P50 = 30) over the P50 range from 24 to 43 Torr. Optimal P50 at PB = 464 Torr was 25 Torr, VO2max at P50 = 26.8 was reduced only 0.1% and exceeded 95% over the P50 range from 19 to 41 Torr. At Pb = 253, optimal P50 was 20 Torr, VO2max at P50 = 26.8 was reduced only 0.4% and exceeded 95% over the wide P50 range from 15 to 47 Torr. While this analysis shows that technically, optimal P50 falls with altitude, VO2max is insensitive to P50 over a range that widens with altitude, so that P50 changes over a realistic interval would not measurably affect VO2max.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, USA.
authors.forename: P D
authors.initials: PD
authors.lastname: Wagner
mesh_terms: D001274:Atmospheric Pressure; D015444:Exercise / Q000502:physiology; D006454:Hemoglobins / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012119:Respiration
chemical_list: D006454:Hemoglobins; C036602:hemoglobin P