PlanHab: hypoxia exaggerates the bed-rest-induced reduction in peak oxygen uptake during upright cycle ergometry

Abstract

The study examined the effects of hypoxia and horizontal bed rest, separately and in combination, on peak oxygen uptake (V̇o2 peak) during upright cycle ergometry. Ten male lowlanders underwent three 21-day confinement periods in a counterbalanced order: 1) normoxic bed rest [NBR; partial pressure of inspired O2 (PiO2 ) = 133.1 ± 0.3 mmHg]; 2) hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mmHg), and 3) hypoxic ambulation (HAMB; PiO2 = 90.0 ± 0.4 mmHg). Before and after each confinement, subjects performed two incremental-load trials to exhaustion, while inspiring either room air (AIR), or a hypoxic gas (HYPO; PiO2 = 90.0 ± 0.4 mmHg). Changes in regional oxygenation of the vastus lateralis muscle and the frontal cerebral cortex were monitored with near-infrared spectroscopy. Cardiac output (CO) was recorded using a bioimpedance method. The AIR V̇o2 peak was decreased by both HBR (∼13.5%; P ≤ 0.001) and NBR (∼8.6%; P ≤ 0.001), with greater drop after HBR (P = 0.01). The HYPO V̇o2 peak was also reduced by HBR (-9.7%; P ≤ 0.001) and NBR (-6.1%; P ≤ 0.001). Peak CO was lower after both bed-rest interventions, and especially after HBR (HBR: ∼13%, NBR: ∼7%; P ≤ 0.05). Exercise-induced alterations in muscle and cerebral oxygenation were blunted in a similar manner after both bed-rest confinements. No changes were observed in HAMB. Hence, the bed-rest-induced decrease in V̇o2 peak was exaggerated by hypoxia, most likely due to a reduction in convective O2 transport, as indicated by the lower peak values of CO.

Hypoxia and Inactivity Related Physiological Changes (Constipation, Inflammation) Are Not Reflected at the Level of Gut Metabolites and Butyrate Producing Microbial Community: The PlanHab Study

“…Systemic hypoxia was associated with ≈10% reduction of SpO 2 in HAmb and HBR (Keramidas et al, 2016). Combination of hypoxia and inactivity (HBR) resulted in general signs of congestion such as 10% increased mean arterial pressure, 15% increased heart rate, three times larger decrease in plasma volume and concomitant 3-fold increase in mature blood cells, hemoglobin and hematocrit concentrations in comparison to either NBR or HAmb.…”

“…In addition to the present sub-study, other published sub-studies or in preparation focused upon cardiorespiratory, muscular (Debevec et al, 2014), immunological (Keramidas et al, 2016), psycho-neuroendocrine responses (Keramidas et al, 2016; Strewe et al, 2017) next to appetite-regulation (Debevec et al, 2016), skeletal muscle miRNA expression (Rullman et al, 2016) and mineral metabolism (Rittweger et al, 2016) within the same participants.…”

“…The detailed outline of the PlanHab project is given elsewhere (Debevec et al, 2014, 2016; Keramidas et al, 2016; Rittweger et al, 2016; Rullman et al, 2016; Simpson et al, 2016) but is also summarized below for the convenience of the reader.…”

Bed Rest and Hypoxic Exposure Affect Sleep Architecture and Breathing Stability

“…Specific data related to appetite (Debevec et al, 2016), insulin sensitivity (Simpson et al, 2016), 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.…”

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.…”