Altitude tolerance of general aviation pilots with normal or partially impaired spirometric function.

The altitude tolerance of 10 spirometrically impaired (SI) general aviation pilots with an average forced midexpiratory flow (FEF25--75%) value of 65.1% was compared to that of 10 spirometrically normal (SN) pilots. Cardiorespiratory parameters assessed at ground level (GL) and at 8,000- and 12,500-ft altitudes were blood pressure, pulmonary ventilation, oxyhemoglobin saturation, temporal artery flow velocity, heart rate, and single-lead electrocardiogram. Although altitude exposure quantitatively displaced the SI group more than the SN group, the differences were not statistically significant at the probability level of 0.05. Unifocal premature ventricular contractions were present at GL in three of the pilots and showed no further changes at altitude. Therefore, the mean FEF25--75%, values of 65% of predicted normal for the SI group becomes a reasonable option as an objective screening norm for acceptable tolerance to general aviation altitudes in the ambient-air-breathing range.