The effects of changes in functional residual capacity with posture on mouth occlusion pressure and ventilatory pattern.

Abstract

The inspiratory pressure developed in the mouth after 0.1 sec of occlusion at functional residual capacity and the maximal rate of increase of this pressure within 0.2 sec after occlusion were measured at rest and during CO2 stimulation in the seated and supine postures assumed by 6 healthy normal subjects. Minute ventilation and respiratory frequency per min, and the pattern of ventilation of individual breaths in terms of inspired volume, inspiratory time, and the mean inspiratory flow rate were measured for the 2 postures. The resting mixed venous Pco2, the respiratory exchange ratio, and the functional residual capacity for the 2 postures were also measured. There was a significant decrease in functional residual capacity in the supine posture in comparison with the sitting position in all subjects (mean decrease 0.799 liters, P < 0.01), but there was no systematic change in the resting values of inspiratory pressure after 0.1 sec, in the maximum rate of increase of inspiratory pressure within 0.2 sec...