PlanHab: Hypoxia counteracts the erythropoietin suppression, but seems to exaggerate the plasma volume reduction induced by 3 weeks of bed rest

Abstract

The study examined the distinct and synergistic effects of hypoxia and bed rest on the erythropoietin (EPO) concentration and relative changes in plasma volume (PV). Eleven healthy male lowlanders underwent three 21‐day confinement periods, in a counterbalanced order: (1) normoxic bed rest (NBR; PIO 2: 133.1 ± 0.3 mmHg); (2) hypoxic bed rest (HBR; PIO 2: 90.0 ± 0.4 mmHg, ambient simulated altitude of ~4000 m); and (3) hypoxic ambulation (HAMB; PIO 2: 90.0 ± 0.4 mmHg). Blood samples were collected before, during (days 2, 5, 14, and 21) and 2 days after each confinement to determine EPO concentration. Qualitative differences in PV changes were also estimated by changes in hematocrit and hemoglobin concentration along with concomitant changes in plasma renin concentration. NBR caused an initial reduction in EPO by ~39% (P = 0.04). By contrast, HBR enhanced EPO (P = 0.001), but the increase was less than that induced by HAMB (P < 0.01). All three confinements caused a significant reduction in PV (P < 0.05), with a substantially greater drop in HBR than in the other conditions (P < 0.001). Thus, present results suggest that hypoxia prevents the EPO suppression, whereas it seems to exaggerate the PV reduction induced by bed rest.

PlanHab*: hypoxia does not worsen the impairment of skeletal muscle oxidative function induced by bed rest alone

“…In the present study, the respiratory impairment observed in H-AMB at the fibre level did not translate into a functional impairment in vivo during small muscle mass exercise, as also observed in the study by Calbet et al 2009. It can be hypothesized that this observation, together with the absence of further functional impairments following H-BR, compared to N-BR, could be attributed, at least in part, to the increased blood [Hb] occurring in hypoxia (Keramidas et al 2016b).…”

“…Such a stimulus is sufficiently severe to induce a down‐regulation of the oxidative processes inside the skeletal muscle (Horscroft & Murray, ) and a significant erythropoietin response, as indeed demonstrated by Keramidas et al . () in the same subjects of the present study.…”

“…It can be hypothesized that this observation, together with the absence of further functional impairments following H‐BR, compared to N‐BR, could be attributed, at least in part, to the increased blood [Hb] occurring in hypoxia (Keramidas et al . ).…”

LunHab: interactive effects of a 10 day sustained exposure to hypoxia and bedrest on aerobic exercise capacity in male lowlanders

“…Bodkin et al 2006), information pertaining to the interactive effects of reduced loading of musculoskeletal and cardiovascular functions and hypoxia on working capacity is relatively scarce. The response was attributable to attenuated convective O 2 transport, as indicated by the lower peak cardiac output, secondary to a more pronounced bedrest-driven hypovolaemic reaction in hypoxia (Loeppky et al 1993;Keramidas et al 2016b). The response was attributable to attenuated convective O 2 transport, as indicated by the lower peak cardiac output, secondary to a more pronounced bedrest-driven hypovolaemic reaction in hypoxia (Loeppky et al 1993;Keramidas et al 2016b).…”

Bed rest and hypoxic exposure affect sleep architecture and breathing stability

“…Specific data related to appetite , insulin sensitivity , bone health (Rittweger et al, 2016), hematology (Keramidas et al, 2016b), peak oxygen uptake (Keramidas et al, 2016a), and skeletal muscle miRNA expression (Rullman et al, 2016), are available elsewhere.…”