To examine the effect of altitude on expiratory flow rates, we measured maximal expiratory flow volume curves at sea level in Brussels (1x) and at different altitudes during the ascent of mount Shisapangma in the Himalaya : in Chengdu at 600 m, Lhasa at 3683 m (2x), Xegar at 4340 m and Base camp at 5000 m.
Our data were collected from then mountaineers (9 men and one women, mean age 32.8 years).A portable Microspiro HI-298 dry spirometer was used. Test results were compared using Repeated Measures Analysis of Variance, and multiple comparison was done with Bonferroni-t-test. Differences between paired measurements were considered significant at p < 0.05.
See also table 1. FVC decreased with increasing altitude. The change was significant above 3683 m compared to sea level values. FEV1 did not significantly change with altitude. PEF (above 3683 m), FEF75% (above 4340 m), FEF50% (above 4340 m) increased significantly when mounting to 5000 m compared to sea level values. For FEF50% the increase was less pronounced than for the other parameters. FEF25 % did not change significantly with altitude. After a nine days stay at high altitude, when returning from 5000 m to 3683 m FVC, FEV1, PEF, FEF75 %, FEF50 % and FEF25 % did return to values recorded earlier at that altitude.
These data suggest that the drop in FVC, without change in FEV1, during ascent to high altitude, is due to restrictive pulmonary changes. The rise in PEF, FEF75 %, FEF50 % can be explained by the breathing of gas of decreased density at high altitude. The decrease after returning to 3683 m, the less pronounced increase for FEF 50 % and the absence of changes in FEF25 % favour this hypothesis.
Real life spirometry done during the ascent to high altitude confirm the observations done in simulation chambers.
Table 1Sea levelChengduLhasaXegarBase campFVC101.2±7.096.9±8.396.0±9.193.9±7.591.1±8.0FEV196.0±6.893.9±7.595.8±7.195.5±7.994.0±8.7PEF77.3±1076.1±1791.7±15.394.2±13.996.6±12.8FEF7576.9±15.275.8±15.784.6±15.092.6±22.693.5±21.9FEF5073.3±19.874.0±16.781.5±22.585.0±2686.7±30FEF2572.7±23.669.0±24.275.6±28.982.5±4079.4±37.8
Values are expressed as mean (of % predicted) ± SD
Marc Meysman, None.