INFLUENCE OF BODY POSITION ON PRESSURE AND AIR-FLOW GENERATION DURINGHYPOXIA AND HYPERCAPNIA IN MAN

1. Inspiratory oesophageal pressure and ventilatory responses to hyper oxic, progressive hypercapnic rebreathing (HCVR) and isocapnic, progre ssive hypoxic rebreathing (HVR) were studied in five normal males in b oth supine and upright seated positions. 2. No significant differences were found in the ventilatory response to hypercapnia between the sup ine and upright position. The slopes of the relationship between minut e ventilation (V(I)) and the increase of end tidal P(CO2) (DELTAP(ET, CO2)) were 3.27 +/- 0.23 and 2.76 +/- 0.24 1 min-1 mmHg-1 supine and u pright, respectively. However, the change in oesophageal pressure from the end expiratory level observed during quiet breathing to that at p eak inspiration (DELTAP(oes, I)) in relationship to DELTAP(ET, CO2) wa s greater supine than upright (1-23 +/- 0.07 versus 0.79 +/- 0.11 cmH2 O mmHg-1, P < 0.01). 3. In contrast, during hypoxia-stimulated breathi ng the slope of the minute ventilation versus oxyhaemoglobin saturatio n curve (V(I)-S(a, O2)) was flatter supine than upright (1.00 +/- 0.03 versus 1-75 +/- 0.05 l min-1 (percentage fall in S(a, O2))-1, P < 0.0 001), but DELTAP(oes, I) in relation to S(a,O2) during hypoxic rebreat hing was similar supine and upright (0.38 +/- 0.03 versus 0.40 +/- 0.0 4 cmH2O (percentage fall in S(a, O2))-1, respectively). 4. It is concl uded that body position does not affect the ventilatory response to pr ogressive hyperoxic hypercapnia but does affect the relationship betwe en DELTAP(oes, I) and DELTAP(ET, CO2). In contrast, body position affe cts the ventilatory response to isocapnic progressive hypoxia, but doe s not affect the relationship between DELTAP(oes, I) and S(a, O2).