THE VENTILATORY RESPONSE TO MODERATE HYPOCAPNIC EXERCISE IN HUMAN-BEINGS

We examined the exercise hyperpnoea during hypocapnia which, by necess ity, was brought about by voluntary hyperventilation (VHV). At cessati on of VHV, ventilation (Vover dotE) decays gradually exhibiting a phen omenon known as the afterdischarge (AD; Eldridge, Med. Sci. Sports Exe rc. 26:319-327, 1994). A new technique was employed to overcome the po tentially contaminating influence of the AD upon the exercise hyperpno ea. Ventilatory parameters were measured in eight subjects during hype roxic cycle ergometry at 3 intensities. The pure Vover dotE response t o 'hypocapnic' exercise was obtained by subtracting the resting recove ry following VHV from the response during 'hypocapnic' exercise (Vover dotE(sub)). Vover dotE(sub) increased abruptly at exercise onset at a ll work rates (phase 1) and remained at this level until PET(CO2) achi eved a threshold; thereafter, it rose further (phase 2) towards a seco nd plateau. The phase 1 increase in Vover dotE(sub) is consistent with neurally mediated control. The apparent link between PET(CO2), and ph ase 2 suggests the involvement of a second, humorally mediated mechani sm.