VENTILATORY RESPONSES DURING INCREMENTAL EXERCISE IN MEN UNDER HYPEROXIC CONDITIONS

The aim of the present study was to explore the role of the carotid ch emoreceptors in the regulation of breathing during incremental ramp ex ercise. We measured minute ventilation (V-E), Oxygen uptake (V-O2), ca rbon dioxide output (V-CO2), end-tidal P-O2 and P-CO2, (PET(O2), and P ET(CO2)), and heart rate (HR) during incremental exercise in healthy y oung men breathing air and 50% O-2. During incremental exercise (15 W/ min, from 0 to 300 W) V-CO2 in hyperoxia did not differ from the normo xic response, but VE in hyperoxia increased more linearly with an incr easing load in comparison to the curvilinear rise of normoxic VE. The isocapnic buffering of PET(CO2) observed in normoxia at the transition from moderate to heavy work did not appear in hyperoxia until a very heavy work load had been attained. This agrees with the observation th at normoxic VE/V-CO2 that was consistently falling with load and becam e flat near the isocapnic point and then turned upward with a further increase in work load, while VE/V-CO2 in hyperoxia decreased continuou sly during heavy exercise. These results would suggest the delayed ons et of anaerobic metabolism and the depression of VE under hyperoxic co nditions. However, we found that VE and HR increased from a specific w ork rate with a steeper slope during incremental exercise under both n ormoxic and hyperoxic conditions. There was a significant correlation between the work rates at which the inflection points of the VE and HR slopes were observed. These findings suggest that factors unrelated t o peripheral chemoreceptor activity and affecting both the ventilatory and circulatory systems may be responsible for hyperpnea during heavy exercise.