Ventilatory response to erect and supine exercise

Purpose: To test the hypothesis that altering the ventilation-perfusion rat io of the lung by changing the body position from erect to supine would alt er the ventilatory response to exercise as described by the slope of the re lationship between minute ventilation and carbon dioxide production. Method s: Ten normal subjects volunteers (5 female, 5 male: average age 22 yr; ran ge 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 ga s exchange measurements to determine peak oxygen consumption ((V) over dotO (2)) and the slope of the relation between ventilation and carbon dioxide p roduction ((V) over dotE/(V) over dotCO(2) slope). Results: Subjects reache d a higher peak (V) over dotO(2) when erect (mean (SEM))(39.2 (2.4) vs 35.7 (2.0); P < 0.05). Heart rate, ventilation, and (V) over dotO(2) were highe r at each stage in the erect position. The respiratory exchange ratio was t he same in each position at matched workloads and at peak exercise. The (V) over dotE/(V) over dotCO(2) slope was unchanged (27.8 (2.2) erect vs 27.7 (1.9) erect). Conclusion: Cycle exercise in the erect position is associate d with an increase in exercise capacity compared with supine exercise but w ith no associated changes in ventilatory response to carbon dioxide product ion.