Ventilation studied with circulatory occlusion during two intensities of exercise

Our purpose was to study the possible role of a pulmonary chemoreceptor in the control of ventilation during exercise. Respiratory gas exchange was measured breath-by-breath at two intensities of exercise with circulatory occlusion of the legs. Eight male subjects exercised on a cycle ergometer at 49 and 98 W for 12 min; circulation to the legs was occluded by thigh cuffs (26.7 kPa) for two min after six min of unoccluded exercise. PETCO₂ and \(\dot V_{{\text{O}}_{\text{2}} }\) decreased and PETO₂ increased significantly during occlusion at both workloads. Occlusion elicited marked hyperventilation, as evidenced by sharp increases in \(\dot V_{\text{E}} ,{\text{ }}\dot V_{\text{E}} /\dot V_{{\text{CO}}_{\text{2}} }\) , and \(\dot V_{\text{E}} /\dot V_{{\text{O}}_{\text{2}} }\) . A sudden sharp increase in PETCO₂ was seen 12.3±0.5 and 6.5±1.2 s after cuff release in all subjects during exercise at 49 and 98 W, respectively. At 49 W a post-occlusion inflection in \(\dot V_{\text{E}}\) was seen in 7 subjects 21.1±5.8 s after the PETCO₂ inflection. Three subjects showed an inflection in \(\dot V_{\text{E}}\) at 98 W 23.3±7.5 s after the PETCO₂ inflection. There were significant increases in PETCO₂, \(\dot V_{{\text{O}}_{\text{2}} } ,\dot V_{{\text{CO}}_{\text{2}} }\) and \(\dot V_{\text{E}}\) after cuff release. \(\dot V_{\text{E}}\) mirrored \(\dot V_{{\text{CO}}_{\text{2}} }\) better than \(\dot V_{{\text{O}}_{\text{2}} }\) , post occlusion. On the basis of a significant lag time between inflections in PETCO₂ and \(\dot V_{\text{E}}\) following cuff release, it is concluded that the influences of a pulmonary CO₂ receptor were not seen.