The influence of P(a)O2, pH and S(a)O2 on maximal oxygen uptake

Abstract

Influence of arterial oxygen pressure (P(a)O2) and pH on haemoglobin saturation (S(a)O2) and in turn on O2 uptake (VO2) was evaluated during ergometer rowing (156, 276 and 376 W; VO(2max) 5.0 L min-1; n = 11). During low intensity exercise, neither pH nor S(a)O2 were affected significantly. In response to the higher work intensities, ventilations (V(E)) of 129 ± 10 and 155 ± 8 L min-1 enhanced the end tidal PO2 (P(ET)O2) to the same extent (117 ± 2 mmHg), but P(a)O2 became reduced (from 102 ± 2 to 78 ± 2 and 81 ± 3 mmHg, respectively). As pH decreased during maximal exercise (7.14 ± 0.02 vs. 7.30 ± 0.02), S(a)O2 also became lower (92.9 ± 0.7 vs. 95.1 + 0.1%) and arterial O2 content (C(a)O2) was 202 ± 3 mt L-1. An inspired O2 fraction (F(I)O2) of 0.30 (n = 8) did not affect V(E), but increased P(ET)O2 and P(aO)2 to 175 ± 4 and 164 ± 5 mmHg and the P(ET)O2-P(a)O2 difference was reduced (21 ± 4 vs. 36 ± 4 mmHg). pH did not change when compared with normoxia and S(a)O2 remained within 1% of the level at rest in hyperoxia (99 ± 0.1%). Thus, C(a)O2 and VO(2max) increased to 212 ± 3 mL L-1 and 5.7 ± 0.2 L min-1, respectively. The reduced P(a)O2 became of importance for S(a)O2 when a low pH inhibited the affinity of O22 to haemoglobin. An increased F(I)O2 reduced the gradient over the alveolar-arterial membrane, maintained haemoglobin saturation despite the reduction in pH and resulted in increases of the arterial oxygen content and uptake.