On maximal oxygen consumption in hypoxic humans

Abstract

The present paper discusses the factors affecting maximal O2 consumption (VO2max) in hypoxia (4300 m above sea level) along the following lines: 1) In acute hypoxia, the fractional limitation to VO2max imposed by circulatory O2 transport (FQ') is 50%, instead of 70% as in normoxia. This is due to the increase in the blood O2 transport coefficient (beta b) as PO2 decreases, as a consequence of the sigmoidal shape of the O2 dissociation curve of hemoglobin. The remaining 50% is assumed to be equally partitioned between tissue O2 transfer (Ft') and mitochondria O2 utilization (Fm'). 2) In chronic hypoxia, FQ' = 0.45, Ft' = 0.20 and Fm' = 0.35, as a consequence of reduced muscle fiber size and muscle mitochondrial density following acclimatization. 3) The relationship between VO2max and PIO2 in both acute and chronic hypoxia reflects the O2 dissociation curve. 4) Acclimatization to chronic hypoxia does not have the function of preserving VO2max.

The decrease of maximal oxygen consumption during hypoxia in man: a mirror image of the oxygen equilibrium curve.

“…The classical non-linear relationship between maximal oxygen consumption (V0, max) and inspired oxygen partial pressure (PI 2) in hypoxia (Cerretelli, 1980;Ward, Milledge & West, 1989;Ferretti, 1990;Cerretelli & Hoppeler, 1996) was established from data obtained on sedentary or nonathletic individuals, who are characterized by relatively low ,2,max values in normoxia. In spite of this, its shape was considered independent of the maximal working capacity or of the maximal normoxic aerobic power of the tested subjects.…”

Energetics of Muscular Exercise

“…From linear regression analysis of the data shown in Fig. 4.3, di Prampero and Ferretti (1990) obtained F Q ¼ 0:70. This means that R Q provides 70 % of the fractional limitation of _ V O 2max : An F Q value equal to 0.70 implies that the respiratory system does not have linear behaviour.…”

“…the volume of V O 2max is imposed by cardiovascular oxygen transport. Modified after di Prampero and Ferretti (1990) oxygen that can be displaced across a gradient of a unit of pressure. In STPD condition, b g is equal to 1.16 ml mmHg −1 and is an invariant constant.…”

“…This means that R Q provides 70 % of the fractional limitation of _ V O 2max : An F Q value equal to 0.70 implies that the respiratory system does not have linear behaviour. In fact, for a linear respiratory system, the ratio of any given R i to R T would be equal to the ratio of the pressure gradient over that R i to the overall pressure gradient, so that: Ferretti 1990). The source of nonlinearity, and thus the source of this discrepancy, was identified in the effects of the oxygen equilibrium curve on b b , as shown in Fig.…”

“…Of Maximal Oxygen Consumption in Hypoxia _ V O 2max decreases in hypoxia, both acute and chronic (see for review Cerretelli 1980;Ferretti 1990;. Conversely, exposure to elevated inspired oxygen pressures leads only to slight, if any, increases in _ V O 2max , the effect being evident only in endurance athletes (Ferretti et al 1997b), who are subject to the Dempsey effect.…”