VENTILATORY CHEMOREFLEXES AT REST FOLLOWING A BRIEF PERIOD OF HEAVY EXERCISE IN MAN

1. Ventilatory chemoreflex responses have been studied at rest during the recovery from a brief period of heavy exercise. 2. Six young, heal thy male subjects each undertook four experimental studies. Ln each st udy measurements were made at rest during recovery from an exhaustive 1-2 min sprint on a bicycle ergometer with a workload of 400 W. Three levels of end-tidal O-2 pressure (P-O2) were employed. Continuous vent ilatory measurements were made during euoxia (end-tidal P-O2, 100 Torr ), hypoxia (end-tidal P-O2, 50 Torr) and hyperoxia (end-tidal P-O2, 30 0 Torr). Arterialized venous blood samples were drawn during each of t he measurement periods for the estimation of arterial pH. In two of th e studies, end-tidal CO2 pressure (P-CO2) was maintained throughout at 1-2 Torr above the eucapnic level that existed prior to exercise (iso capnic post-exercise protocol, IPE). In the other two studies, end-tid al P-CO2 was allowed to vary (poikilocapnic post-exercise protocol, PP E). Data from a previously published study on the same subjects involv ing an infusion of hydrochloric acid were used to provide control data with a varying level of metabolic acidosis, but with no prior exercis e. 3. Ventilation-pH slopes in the IPE protocol were no different from control. Ventilation-pH slopes in the PPE protocol were significantly loT;ver than in the IPE and control protocols (P < 0.05, ANOVA). This difference may be due to the progressive change in end-tidal P-CO2 in the PPE protocol compared with the constant end-tidal P-CO2 in the IP E and control protocols. 4. An arterial pH value of 7.35 was attained 30.4 +/- 2.7 min (mean +/- S.E.M.) after the end of exercise in the IP E protocol and 17.1 +/- 1.4 min after the end of exercise in the PPE p rotocol. 5. Hypoxic sensitivities at an arterial pH of 7.35 were not s ignificantly different between the PPE, PPE and control protocols (ANO VA). 6. Euoxic ventilation at an arterial pH of 7.35 was significantly greater than control for the IPE protocol (P < 0.001, Student's paire d t test) and no different from control for the PPE protocol. 7. The r esults suggest that 30 min after heavy exercise, ventilation remains s timulated by processes other than the post-exercise metabolic acidosis , and that changes in peripheral chemoreflex sensitivity to hypoxia an d acid are not implicated in this.