This study was undertaken to evaluate the postural effect on ventilatory responses during both supine and sitting exercise. Seven healthy men performed two exercise tests utilizing the ramp protocol (20 watts/min) with a cycle ergometer in each position. The results were as follows: The oxygen uptake and the oxygen pulse measured at 180 watts and at anaerobic threshold in the sitting were significantly higher compared with those in the supine position. The average of carbon-dioxide output, minute ventilation and tidal volume at lower exercise intensities showed higher values in the sitting compared with those in the supine position, whereas there were no significant differences for respiratory rate. There was significant difference in the slope of the minute ventilation to carbon-dioxide output plot between sitting and supine position. In conclusion, the higher minute ventilation in the sitting position was mainly performed by higher tidal volume which may counteract the effects of an increase in physiological dead space. The lower slope of the minute ventilation to carbon-dioxide output plot which shows more effective ventilation in the supine position may be due to decreased physiological dead space and higher diffusion capacity.
