Change in pulmonary function tests in normal males and females after exposure to 15,000 feet of simulated altitude

Purpose: The primary method of adapting to the stress of altitude is increasing ventilation. We measured pulmonary function tests (PFTs) before and after a normobaric hypoxic exposure to further define the alterations in PFTs after altitude exposure. Methods: Sixteen healthy subjects (8 male, 8 female) ages 18-32 were exposed to 12% oxygen, 88% nitrogen gas mixture (equivalent to 15,000 feet) via a clear plastic hood for 8 hours. The average PaO₂ at sea level was 110 mmHg; at altitude PaO₂ was 45 mmHg. Pulmonary function tests were performed prior to exposure and immediately after exposure. Results: Males FVC(L) FEV1(L) DLCO TLC(L) Pre 5.18 3.98 33.4 7.34 Post 4.92 3.85 32.1 6.22 P value .002 .077 .376 .030 Females FVC(L) FEV1(L) DLCO TLC(L) Pre 3.33 2.75 27.0 4.62 Post 3.27 2.73 26.4 4.72 P value .605 .786 .551 .289 All FVC(L) FEV1(L) DLCO TLC(L) Pre 4.25 3.36 30.2 5.98 Post 4.10 3.29 29.3 5.47 P value .025 .154 .263 .067 Our data show a small but significant decrease in FVC after normobaric hypoxic exposure, without significant change in other pulmonary function tests. Subgroup analysis showed significant decline in FVC and TLC in males that did not occur in females. Conclusions: The majority of prior studies used only male subjects and show small but significant decline in FVC after exposure to altitude. Our combined and male-only data are consistent with prior altitude exposures in both the direction and magnitude of change in PFTs. The lack of effect of altitude in females warrants further investigation. Clinical Implications: Change in lung function caused by altitude could exacerbate altitude-induced hypoxia and may be more significant in males.