The effect of posture on the ventilatory response to hypoxia

The ventilatory response to carbon dioxide is known to be uninfluenced by changes in posture. To obtain similar data on the ventilatory response to hypoxia we studied seven subjects in each of two postures, lying and sitting, at a constant PCO2 midway between end-tidal and mixed venous. Minute ventilation was higher in the seated position than supine (p < 0.01) at this isocapnic level, attributable mainly to an increase in tidal volume (p < 0.05). However, there were no statistically significant differences in the ventilatory response, the tidal volume response, or the frequency response to hypoxia between the two postures.