Mild Hypobaric Hypoxia Effects on Murine Skeletal Muscle Morphology and Macrophages and Well-Being.

BACKGROUND: In the last 10 yr, the number of ultra-haul flights-defined as flights greater than 12 h of flying time-has increased. While the medical complications of these flights are well-known, the underlying cellular effects are less clear. The primary objective of this study was to test the effects of extended mild hypobaric hypoxia on overall well-being and skeletal muscle morphology and macrophage populations. METHODS: A total of 22 male C57BL/6 mice were assigned to a normobaric (NB) or hypobaric (HB) chamber for 14-17 h. Overall mouse well-being and the general morphology and resident macrophage number in hindlimb muscles were compared between the two pressure conditions. RESULTS: During mild hypobaric hypoxia, the mice behaved normally and no changes were observed in general muscle morphology. Regarding resident macrophages, the mean antigen area of CD206 in the hindlimb muscles, lateral gastrocnemius (LG, 33.8 +/- 2.0 vs. 35.3 +/- 1.6), medial gastrocnemius (MG, 32.4 +/- 1.6 vs. 32.6 +/- 1.5), and quadriceps femoris (QF, 36.3 +/- 1.2 vs. 34.3 +/- 1.1) were similar between NB and HB conditions, and the number of CD68-positive cells in the LG and QF were similar between the two conditions. Significantly fewer CD206-positive cells were counted in the LG muscle under the HB condition. CONCLUSION: Our findings indicate that extended exposure to mild hypobaric hypoxia, similar to that of an ultra-long-haul flight, does not adversely affect healthy skeletal muscle.