MNX (Medium Duration Nutrition and Resistance-Vibration Exercise) Bed-Rest: Effect of Resistance Vibration Exercise Alone or Combined With Whey Protein Supplementation on Cardiovascular System in 21-Day Head-Down Bed Rest.

Patrick Guinet,James Patrick Macnamara,Benjamin D Levine,Matthieu Berry,Marie-Pierre Bareille,Nastassia Navasiolava,Françoise Larcher,Marc-Antoine Custaud,Anne Pavy-Le Traon

doi:10.3389/fphys.2020.00812

Abstract

Current inflight countermeasures do not completely prevent bone and cardiovascular changes induced by microgravity. High load Resistance Exercise combined with whole body Vibration (RVE) demonstrated benefits on bone and cardiovascular system during previous Head-Down Bed Rest (HDBR) studies. We examined the effectiveness of RVE alone or combined with a nutritional supplementation of Whey protein (NeX) on cardiovascular deconditioning. Eight male subjects (age 34 ± 8 years) in a crossover design completed three 21-day HDBR campaigns (Control-CON, RVE, and NeX). Pre and post HDBR Orthostatic Tolerance (OT) was evaluated by a 15-min head-up tilt test followed by increasing levels of Lower Body Negative Pressure (LBNP). Heart rate (HR), blood pressure (BP), and Sympathetic Index (ΣI) through spectral analysis were measured during OT test. Plasma Volume (PV), and Maximal Oxygen Uptake (VO2max) were measured before and after each campaign. Left ventricular mass, left ventricular end diastolic (LVEDV), end systolic (LVESV), stroke (SV) volumes, and circumferential deformation at rest and during an orthostatic stress simulated by a 30 mmHg LBNP were measured by cardiac MRI. RVE failed to prevent any change in these variables and NeX did not have any additional effect over exercise alone. In the 3 groups, (1) OT time dropped similarly (bed rest p < 0.001), (2) HR and ΣI were increased at rest at the end of HDBR and HR increased markedly during LBNP-tilt test, with inability to increase further the ΣI, (3) PV dropped (bed rest p < 0.001), along with LVEDV, LVESV and SV (p = 0.08, p < 0.001, and p = 0.045, respectively), (4) Left ventricle mass did not change significantly, (5) Deformation of the heart assessed by global circumferential strain was preserved and early diastolic circumferential strain rate was increased during orthostatic stress at the end of HDBR, illustrating preserved systolic and diastolic function respectively, without any difference between groups. Despite the drop in PV and LV volumes, RVE and NeX tended to alleviate the decrease in VO2max. In conclusion, RVE and NeX failed to prevent the cardiovascular deconditioning induced by a 21 day-HDBR.

Highlights

Head-Down Bed Rest (HDBR) accurately reproduces several of the physiological changes induced by microgravity, including many cardiovascular, muscle and bone alterations (Pavy-Le Traon et al, 2007; Hargens and Vico, 2016; Mulavara et al, 2018)
Hemodynamic and Autonomic Responses to Tilt (Table 1 and Figure 5) No significant differences were found in Resistive Vibration Exercise (RVE) and NeX compared with control group and between countermeasures
Despite reduction in size during bedrest, deformation of the heart assessed by Global circumferential strain (GCS) was preserved and GCSRE was enhanced during orthostatic stress, illustrating preserved systolic and diastolic function, respectively

Summary

Introduction

Head-Down Bed Rest (HDBR) accurately reproduces several of the physiological changes induced by microgravity, including many cardiovascular, muscle and bone alterations (Pavy-Le Traon et al, 2007; Hargens and Vico, 2016; Mulavara et al, 2018). Cardiovascular deconditioning resulting from spaceflight and HDBR includes increased resting heart rate (HR), orthostatic intolerance (OI), and decreased maximal oxygen uptake (VO2max) (Bungo et al, 1985; Convertino, 1994; Pavy-Le Traon et al, 2007). Exercise training has prevented cardiac deconditioning during bed-rest but has not improved orthostatic tolerance (OT) without concurrent volume loading, emphasizing the dual contributions of plasma volume (PV) and cardiac remodeling to the cardiovascular adaptation to microgravity (Shibata and Perhonen, 2010; Hastings et al, 2012; Ploutz-Snyder et al, 2018). Further understanding of cardiac response to orthostatic stress and interventions that can prevent both cardiac deconditioning and OI are needed

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