EFFECTS OF CHANGES IN VENTILATION ON RESPIRATORY DISCOMFORT DURING ISOCAPNIC EXERCISE

We studied the effects of changes in the level of ventilation on respi ratory discomfort during isocapnic exercise. Six subjects exercised at 60 W on a cycle ergometer. They initially breathed 2.5% CO2 in oxygen for 75 breaths. Ventilatory parameters of the last 10 breaths were us ed as controls. In 7 subsequent test sessions each lasting 2 min alter nating with 2 min free breathing periods, subjects tried to achieve a target ventilation ranging from 0.7 to 1.3 times the control with a vi sual feedback system. End-tidal CO2 was regulated automatically at the control level by changing the inspired CO2. Breathing discomfort was measured at the end of each session using a visual analog scale. Isoca pnic constraining of ventilation (0.7 times the control) during exerci se significantly increased respiratory discomfort (p < 0.05). Increase s in ventilation had no significant effect. These results indicate tha t respiratory discomfort during exercise is exaggerated when the level of ventilation falls below that spontaneously adopted even when chemi cal drives are held constant.