EXTENT OF EXPIRATORY FLOW LIMITATION INFLUENCES THE INCREASE IN MAXIMAL EXERCISE VENTILATION IN HYPOXIA

Increasing ventilation ((V) over dot(E)) during hypoxic exercise may h elp to defend arterial O-2 saturation (Sa(O2)) and (V) over dot(O2max) , however, many athletes experience limitations to ventilatory flow an d are not able to increase (V) over dot(E) at high workrates. Five of 19 highly trained endurance athletes screened had < 5% of their tidal flow-volume loop during maximal exercise meet the boundary set by thei r maximal resting flow-volume loop. These five athletes were grouped a s non-flow limited and compared to the five athletes who demonstrated the greatest percent of tidal volume flow limitation (56 +/- 11%) duri ng maximal exercise (flow limited). Each athlete completed two increme ntal treadmill tests to exhaustion: normoxia and hypoxia (FIO2 = 0.187 ). Non-flow limited athletes increased (V) over dot(E) at (V) over dot (O2max) from normoxia to hypoxia (140.9 +/- 13.4 vs. 154.7 +/- 11.9 L/ min, P < 0.05), while how limited athletes did not (159.5 +/- 9.4 vs. 162.3 +/- 6.0 L/min). The decline in Sa(O2) at (V) over dot(O2max) fro m normoxia to hypoxia was not significantly different between groups. We conclude that athletes with little or no expiratory flow limitation are able to increase ire during maximal exercise in mild hypoxia, com pared to athletes with significantly higher degrees of mechanical limi tation. However this 'mechanical ventilatory reserve' does not appear to influence the ability to defend Sa(O2) or (V) over dot(O2max) durin g maximal exercise in mild hypoxia. (C) 1998 Elsevier Science B.V. All rights reserved.