Acclimatization Near Home? Early Respiratory Changes After Short-Term Intermittent Exposure to Simulated Altitude

Objective With the ultimate goal of finding a straightforward protocol for acclimatization at simulated altitude, we evaluated the early effects of repeated short-term exposure to hypobaric hypoxia on the respiratory response to exercise in hypoxia. Methods Nine subjects were exposed to a simulated altitude of 5000 m for 2 hours a day for 14 days. Arterial oxygen saturation (SaO 2 ), expired volume per minute ( V ˙ E ), respiratory rate, tidal volume ( V ˙ T ), and heart rate were measured during rest and during exercise (cycloergometer, at 30% of maximum oxygen consumption at sea level), both in normoxia and at 5000 m of simulated altitude on the first and 15th days. On the same days, blood samples were obtained for hematological tests. Results During exercise in hypoxia, Sao 2 rose from 65 to 71% (P = .02), and V ˙ E rose from 55.5 to 67.6 L·min −1 (P = .02) due to an increase in V ˙ T from 2 to 2.6 L (P = .003). No significant differences were found in any of the variables studied at rest either in normoxia or in hypoxia or in exercise in normoxia after the exposure program. In the second week, changes in packed cell volume and blood hemoglobin concentration were nonsignificant. Conclusions After short-term intermittent exposure to hypobaric hypoxia, subjects increased their ventilatory response and Sao 2 during exercise at simulated altitude. These changes may be interpreted as acclimatization to altitude. The monitoring of ventilatory response and Sao 2 during moderate exercise in hypobaric hypoxia may be used to detect the first stages of acclimatization to altitude.