LUNG-FUNCTION DURING MODERATE HYPOBARIC HYPOXIA IN NORMAL SUBJECTS AND PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Background: We sought to describe changes in spirometric variables and lung volume subdivisions in healthy subjects and patients with chroni c obstructive pulmonary disease (COPD) during moderate acute hypobaric hypoxia as occurs during air travel. We further questioned whether ch anges in lung function may associate with reduced maximum ventilation or worsened arterial blood gases. Methods: Ambulatory patients with CO PD and healthy adults comprised the study populations (n = 27). We obt ained baseline measurements of spirometry lung volumes and arterial bl ood gases from each subject at sea level and repeated measurements dur ing altitude exposure to 8000 ft (2438 m) above sea level in a man-rat ed hypobaric chamber. Results: Six COPD patients and three healthy sub jects had declines in FVC during altitude exposure greater than the 95 % confidence interval (CI) for expected within day variability (p < 0. 05). Average forced vital capacity (FVC) declined by 0.123 +/- 0.254 L (mean +/- SD; 95% CI = -0.255, -0.020; p < 0.05) for all subjects com bined. The magnitude of decline in FVC did not differ between groups ( p > 0.05) and correlated with increasing residual volume (r = -0.455; <0.05). Change in maximum voluntary ventilation (MVV) in the COPD pati ents equaled -1.244 +/- 4.797 L . min(-1) (95% CI = -3.71, 1.22; p = 0 .301). Decline in maximum voluntary ventilation (MVV) in the COPD pati ents correlated with decreased FVC (r = 0.630) and increased RV (r = - 0.546; p < 0.05). Changes in spirometric variables for patients and co ntrols did not explain significant variability in the arterial blood g as variables PaO2, PaCo2 or pH at altitude. Conclusions: We observed a decline in forced vital capacity in some COPD patients and normal sub jects greater than expected for within day variability. Spirometric ch anges correlated with changes in reduced maximum voluntary ventilation in the patients but not with changes in resting arterial blood gases.