Hypobaric impact on clinical tolerance and 24-h patterns in iron metabolism markers and plasma proteins in men.

Long-distance flights can cause a number of clinical problems due to mild hypoxia resulting from cabin pressurization. Using a chronobiological approach, the aim of this work was to assess the clinical tolerance and biological impact of daytime exposure to hypobaric hypoxia on markers of iron metabolism and plasma proteins. Fourteen healthy, male volunteers, ages 23 to 39 yrs, spent 8.5 h in a hypobaric chamber (from 07:45 to 16:15 h) simulating an altitude of 8000 ft. This was followed by another 8.5-h session 4 wks later simulating conditions at an altitude of 12,000 ft. Biological variables were assayed every 2 h over two 24-h spans (control and hypoxia spans, respectively) per simulated altitude. Whereas most of the subjects tolerated the 8000 ft exposure well, eight subjects (57%) presented clear clinical signs of hypoxic intolerance at 12,000 ft. The 24-h blood iron profile showed a biphasic pattern at both altitude simulations, with a significant (∼40%) increase during hypoxia, followed by a (∼25%) decrease during the first hours of recovery. The iron circadian rhythm showed a significant phase delay during the hypoxic exposure at 8000 ft vs. reference. Mean 24-h ferritin levels decreased at both altitudes, but mainly during the nighttime after the 12,000 ft exposure in accordance with Cosinor analysis. The transferrin and total plasma proteins 24-h profiles did not show significant change. Moreover, significant differences, mainly in iron, ferritin, and transferrin, were found at 12,000 ft according to the clinical tolerance to hypoxia, and significant correlations were found between the mid-range crossing times, i.e., here half-descent times (d-T(50)), for ferritin and total plasma proteins and the reported level of clinical discomfort under hypoxia. This study shows that an 8.5-h exposure to mild hypoxia is able to alter very quickly the 24-h pattern of iron and ferritin. These alterations seem to depend, at least in part, on the clinical tolerance to hypoxia and may help explain the interindividual differences observed in the tolerance to hypoxia.