Training in Normobaric Hypoxia and Its Effects on Acute Mountain Sickness after Rapid Ascent to 4559 m

Abstract

In a randomized, placebo-controlled, double-blind study, we tested a 4-week program in normobaric hypoxia that is commercially offered for the prevention of acute mountain sickness (AMS). Twenty-two male and 18 female healthy subjects [mean age 33 +/- 7 (SD) years] exercised 70 min, 3 x /week for 3 weeks on a bicycle ergometer at workloads of 60% VO2max either in normoxia (normoxia group, NG) or in normobaric hypoxia (hypoxia group, HG), corresponding to altitudes of 2500, 3000, and 3500 m during weeks 1, 2, and 3, respectively. Four passive exposures of 90 min in normoxia (NG) or hypoxia corresponding to 4500 m (HG) followed in week 4. Five days after the last session, subjects ascended within 24 h from sea level to 4559 m (one overnight stay at 3611 m) and stayed there for 24 h. AMS was defined as LL (Lake Louise score) > or =5 and AMS-C > or =0.70. The AMS incidence (70% in NG vs. 60% in HG, p = 0.74), LL scores (7.1 +/- 4.3 vs. 5.9 +/- 3.4, p = 0.34), and AMS-C scores (1.50 +/- 1.22 vs. 0.93 +/- 0.81, p = 0.25) at the study endpoint were not significantly different between the groups. However, the incidence of AMS at 3611 m (6% vs. 47%, p = 0.01) and the functional LL score at 4559 m were lower in HG. SpO2 at 3611 m, heart rate during ascents, and arterial blood gases at 4559 m were not different between groups. We conclude that the tested program does not reduce the incidence of AMS within a rapid ascent to 4559 m, but our data show that it prevents AMS at lower altitudes. Whether such a program would prevent AMS at higher altitudes, but with slower ascent, remains to be tested.

Effect of repeated normobaric hypoxia exposures during sleep on acute mountain sickness, exercise performance, and sleep during exposure to terrestrial altitude

“…In contrast, a significant improvement in Sa O 2 induced over 1 wk of 3-h daily NH treatment exposures was evident only when measured in NH conditions, but not when assessed during HH residence at 4,300 m, and there was also no improvement in TT performance (5). The lack of any retained ventilatory or TT performance benefit during HH residence after NH treatment was considered to be due to a loss of VEacc resulting from the nontreatment time intervals being too long or the NH treatment either not inducing sufficient VEacc or simply not being beneficial during subsequent HH residence (5,27). On the basis of this information, there was an expectation for the Fig.…”

“…This approach also minimized the NH stimulus "down time" between consecutive treatment exposures (22). To that end, treatment involved sleeping for 7.5 h each night for 7 consecutive nights in a room under ambient NH conditions that simulated progressively increasing altitudes ranging from 2,200 to 3,100 m. The total NH treatment duration was therefore 52.5 h, which was nearly twice as long as the minimal total HH treatment duration previously determined to be beneficial during subsequent HH residence (5) and approximately three times longer than the two recent NH treatment-to-HH residence studies described above (5,27). We hypothesized that VEacc induced by NH treatment would be evident, AMS susceptibility would be reduced, and TT exercise performance would be improved compared with a no-treatment control ("sham") group during the first 5 days of residence at a terrestrial elevation of 4,300 m.…”

“…The other study (27), which used 14 -18 h of NH treatment (12-16% O 2 for 70 -90 min/day, 3 days/wk, for 4 wk), along with an overnight stay at 3,611 m, reported no differences in arterial blood gases or AMS compared with no NH treatment during subsequent HH residence at 4,559 m. One interpretation suggested for the lack of effectiveness was a loss of VEacc prior to HH residence (5) that resulted from being at sea level (SL) without NH treatment for much longer than the Յ24 h used during previous successful HH treatment studies (2,4). However, this interpretation is inconsistent with the results of at least one study (17) that reported that VEacc remained evident when assessed under NH ambient conditions 1 mo after the NH treatment ended.…”

“…The only controlled, experimental studies reporting that AMS, exercise performance, and other physiological outcomes were affected favorably relative to no treatment utilized HH treatment prior to HH residence (2)(3)(4)18) or NH treatment prior to NH residence (17,22). Until two other studies were published recently (5,27), no data existed to determine directly whether NH treatment would be more beneficial than no treatment during subsequent HH residence.…”

Acute high-altitude sickness

“…Studies have reported conflicting results regarding intermittent normobaric or hypobaric hypoxic exposures, with some studies showing benefit [107] and others not demonstrating a clear effect [108,109]. One of the challenges in interpreting these discrepant results is that the hypoxic exposure protocols vary significantly between studies with regard to the magnitude and duration of the hypoxic exposures.…”