PULMONARY VENTILATORY FUNCTION DECREASES IN PROPORTION TO INCREASING ALTITUDE

The objective of this study was to examine how pulmonary ventilatory f unction, including response to bronchodilation, is related to altitude during high-altitude trekking. This cohort experiment consisted of mu ltiple spirometric tests before and after bronchodilation in participa nts at baseline (1624 m) and at different altitudes (3404-4896 m) duri ng a 2-week trek. The setting was in the Himalayas. Eleven men (ages 2 2-68 years) and eight women (ages 19-42 years) participated. Intervent ions were at altitudes of 1624 m to 5265 m; albuteral was administered via Rotahaler((R)). Forced vital capacity (FVC) decreased by an avera ge of 3.8% [95% confidence interval (Ci) 1.6 to 6.0] per 1000-m altitu de increment, Forced expiratory volume in 1 second (FEV1.0) decreased 3.7% (95% CI 1.9 to 5.5) per each 1000-m altitude increment. Maximal m idexpiratory flow rate (FEF25-75%) decreased by 3.6% (95% CI 0.9 to 6. 3) per each 1000-m altitude increment. Small, postalbuterol now increa ses were present al baseline and at altitude. Ventilatory function ret urned quickly toward baseline upon descent. One trekker developed coug h, dyspnea at rest, extreme weakness, rales, tachycardia, and oxygen d esaturation to 71%, His ventilatory measurements did not differ signif icantly (p > 0.32) from the group means. We concluded that changes in some pulmonary ventilatory parameters (FVC, FEV1.0, and FEF25-75%) wer e proportional to the magnitude of altitude during a high-altitude tre k. These were tolerated well and do nor seem to relate to acute mounta in sickness, A bronchodilator effect was not increased at altitude.