EFFECT OF UPRIGHT AND SUPINE POSTURE ON HYPOXEMIA DURING AIR TRANSPORT

Background: Change in body position can cause hypoxemia at sea level i n patients with lung diseases. Because of concern for the added risk o f hypoxemia during air transport, we investigated the effect of body p osition on arterial oxygen partial pressure (PaO2) in individuals with lung disease under conditions of hypobaric hypoxia. Method: The study groups consisted of 8 patients with chronic obstructive lung disease, 4 patients with interstitial lung disease, and 6 healthy subjects. We obtained samples from radial artery catheters at sea level (SL) and a ltitude (ALT) simulation of 8000 Ft (2438 m) in a hypobaric chamber in supine and upright postures. Results: Altitude exposure did not resul t in a significant change in mean supine minus mean upright PaO2 (dPaO (2)); however, some individuals had large changes at SL. Moreover, the variance for dPaO(2), was significantly smaller at ALT compared to SL with all groups combined (F test, p < 0.05). We found no correlation between dPaO(2) at SL vs. ALT (p = 0.293; r = 0.262; n = 18). At both SL and ALT, dPaCO(2) correlated negatively with dpH. At SL, dPaO(2) di d not correlate with either dPaCO(2) or dpH; at ALT dPaO(2) correlated with dpH (p < 0.05) and correlated negatively with dPaCO(2) (p < 0.01 ). Conclusion: We conclude that significantly less postural variation in PaO2 occurs at moderate ALT compared to SL. In our patients with di ffuse bilateral pulmonary disease, postural change did not contribute significantly to hypoxemia experienced at ALT. We infer that greater v entilatory response to hypoxemia at ALT in either posture may explain this finding.