Sw. Knutson et al., EFFECT OF UPRIGHT AND SUPINE POSTURE ON HYPOXEMIA DURING AIR TRANSPORT, Aviation, space, and environmental medicine, 67(1), 1996, pp. 14-18
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.