PURPOSE: To test the hypothesis that altering the ventilation-perfusion ratio of the lung by changing the body position from erect to supine would alter the ventilatory response to exercise as described by the slope of the relationship between minute ventilation and carbon dioxide production. METHODS: Ten normal subjects volunteers (5 female, 5 male: average age 22 yr; range 19-25 yr; height (SD) 173.5 (3.8) cm; weight 68.0 (3.3) kg) performed in random order erect and supine incremental cycle exercise with metabolic gas exchange measurements to determine peak oxygen consumption (VO2) and the slope of the relation between ventilation and carbon dioxide production (VE/VCO2 slope). RESULTS: Subjects reached a higher peak VO2 when erect (mean (SEM))(39.2 (2.4) vs 35.7 (2.0); P < 0.05). Heart rate, ventilation, and VO2 were higher at each stage in the erect position. The respiratory exchange ratio was the same in each position at matched workloads and at peak exercise. The VE/VCO2 slope was unchanged (27.8 (2.2) erect vs 27.7 (1.9) erect). CONCLUSION: Cycle exercise in the erect position is associated with an increase in exercise capacity compared with supine exercise but with no associated changes in ventilatory response to carbon dioxide production.
PURPOSE: To test the hypothesis that altering the ventilation-perfusion ratio of the lung by changing the body position from erect to supine would alter the ventilatory response to exercise as described by the slope of the relationship between minute ventilation and carbon dioxide production. METHODS: Ten normal subjects volunteers (5 female, 5 male: average age 22 yr; range 19-25 yr; height (SD) 173.5 (3.8) cm; weight 68.0 (3.3) kg) performed in random order erect and supine incremental cycle exercise with metabolic gas exchange measurements to determine peak oxygen consumption (VO2) and the slope of the relation between ventilation and carbon dioxide production (VE/VCO2 slope). RESULTS: Subjects reached a higher peak VO2 when erect (mean (SEM))(39.2 (2.4) vs 35.7 (2.0); P < 0.05). Heart rate, ventilation, and VO2 were higher at each stage in the erect position. The respiratory exchange ratio was the same in each position at matched workloads and at peak exercise. The VE/VCO2 slope was unchanged (27.8 (2.2) erect vs 27.7 (1.9) erect). CONCLUSION: Cycle exercise in the erect position is associated with an increase in exercise capacity compared with supine exercise but with no associated changes in ventilatory response to carbon dioxide production.