Does sitting posture affect breathing patterns and gas exchange compared to supine posture in normal subjects?
Sitting posture increases minute ventilation and lowers arterial PCO2 compared to supine posture in normal subjects, without altering the ventilatory response to CO2.
The effect of sitting and supine posture on breathing patterns and gas exchange during room air breathing and administration of 2 and 4% CO2 was studied in nine normal subjects using a noninvasive canopy system. During air breathing minute ventilation (VE) was 21% (P less than 0.005) higher in the sitting position. Tidal volume (VT) and mean inspiratory flow (VT/TI) were also greater in the sitting position. With the administration of 4% CO2, VE was 13.9 and 20.0 1/min in the supine and seated position, respectively. The relationship between VE and VT was the same in both cases. For any given level of VE, VT/TI was higher in the seated position. No difference in response to CO2 as measured by delta VE/delta PaCO2 and (delta VT/TI)/delta PaCO2 was observed. However, arterial PCO2 was lower both in the resting and stimulated states when sitting.
Weissman et al. (Wed,) studied this question.
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