Isocapnic exercise is

the effects of changes in the level of ventilation on respiratory discomfo 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 used as controls. In 7 subsequent test sessions each lasting 2 min alternating 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 visual feedback system. End-tidal CO2 was regulated automatically at the control level by changing the inspired CO2. Breathing discomfo was measured at the end of each session using a visual analog scale. Isocapnic constraining of ventilation (0.7 times the control) during exercise significantly increased respiratory discomfo (p < 0.05). Increases in ventilation had no significant effect. These results indicate that respiratory discomfo during exercise is exaggerated when the level of ventilation falls below that spontaneously adopted even when chemical drives are held constant. Ref: guyton and hall textbook of medical physiology 12 edition page number: 385,386,387