Low-magnitude whole body vibration with resistive exercise as a countermeasure against cardiovascular deconditioning after 60 days of head-down bed rest

Comprehensive assessment of physiological responses in women during the ESA dry immersion VIVALDI microgravity simulation

Astronauts in microgravity experience multi-system deconditioning, impacting their inflight efficiency and inducing dysfunctions upon return to Earth gravity. To fill the sex gap of knowledge in the health impact of spaceflights, we simulate microgravity with a 5-day dry immersion in 18 healthy women (ClinicalTrials.gov Identifier: NCT05043974). Here we show that dry immersion rapidly induces a sedentarily-like metabolism shift mimicking the beginning of a metabolic syndrome with a drop in glucose tolerance, an increase in the atherogenic index of plasma, and an impaired lipid profile. Bone remodeling markers suggest a decreased bone formation coupled with an increased bone resorption. Fluid shifts and muscular unloading participate to a marked cardiovascular and sensorimotor deconditioning with decreased orthostatic tolerance, aerobic capacity, and postural balance. Collected datasets provide a comprehensive multi-systemic assessment of dry immersion effects in women and pave the way for future sex-based evaluations of countermeasures.

Running vs. resistance exercise to counteract deconditioning induced by 90-day head-down bedrest

Spaceflight is associated with enhanced inactivity, resulting in muscular and cardiovascular deconditioning. Although physical exercise is commonly used as a countermeasure, separate applications of running and resistive exercise modalities have never been directly compared during long-term bedrest. This study aimed to compare the effectiveness of two exercise countermeasure programs, running and resistance training, applied separately, for counteracting cardiovascular deconditioning induced by 90-day head-down bedrest (HDBR). Maximal oxygen uptake (V˙O₂max), orthostatic tolerance, continuous ECG and blood pressure (BP), body composition, and leg circumferences were measured in the control group (CON: n = 8), running exercise group (RUN: n = 7), and resistive exercise group (RES: n = 7). After HDBR, the decrease in V˙O₂max was prevented by RUN countermeasure and limited by RES countermeasure (−26% in CON p < 0.05, −15% in RES p < 0.05, and −4% in RUN ns). Subjects demonstrated surprisingly modest orthostatic tolerance decrease for different groups, including controls. Lean mass loss was limited by RES and RUN protocols (−10% in CON vs. −5% to 6% in RES and RUN). Both countermeasures prevented the loss in thigh circumference (−7% in CON p < 0.05, −2% in RES ns, and −0.6% in RUN ns) and limited loss in calf circumference (−10% in CON vs. −7% in RES vs. −5% in RUN). Day–night variations in systolic BP were preserved during HDBR. Decrease in V˙O₂max positively correlated with decrease in thigh (r = 0.54 and p = 0.009) and calf (r = 0.52 and p = 0.012) circumferences. During this 90-day strict HDBR, running exercise successfully preserved V˙O₂max, and resistance exercise limited its decline. Both countermeasures limited loss in global lean mass and leg circumferences. The V˙O₂max reduction seems to be conditioned more by muscular than by cardiovascular parameters.

Implementation of exercise countermeasures during spaceflight and microgravity analogue studies: Developing countermeasure protocols for bedrest in older adults (BROA)

Significant progress has been made in the development of countermeasures to attenuate the negative consequences of prolonged exposure to microgravity on astronauts’ bodies. Deconditioning of several organ systems during flight includes losses to cardiorespiratory fitness, muscle mass, bone density and strength. Similar deconditioning also occurs during prolonged bedrest; any protracted time immobile or inactive, especially for unwell older adults (e.g., confined to hospital beds), can lead to similar detrimental health consequences. Due to limitations in physiological research in space, the six-degree head-down tilt bedrest protocol was developed as ground-based analogue to spaceflight. A variety of exercise countermeasures have been tested as interventions to limit detrimental changes and physiological deconditioning of the musculoskeletal and cardiovascular systems. The Canadian Institutes of Health Research and the Canadian Space Agency recently provided funding for research focused on Understanding the Health Impact of Inactivity to study the efficacy of exercise countermeasures in a 14-day randomized clinical trial of six-degree head-down tilt bedrest study in older adults aged 55–65 years old (BROA). Here we will describe the development of a multi-modality countermeasure protocol for the BROA campaign that includes upper- and lower-body resistance exercise and head-down tilt cycle ergometry (high-intensity interval and continuous aerobic exercise training). We provide reasoning for the choice of these modalities following review of the latest available information on exercise as a countermeasure for inactivity and spaceflight-related deconditioning. In summary, this paper sets out to review up-to-date exercise countermeasure research from spaceflight and head-down bedrest studies, whilst providing support for the proposed research countermeasure protocols developed for the bedrest study in older adults.

Time-restricted feeding alleviates cardiac dysfunction induced by simulated microgravity via restoring cardiac FGF21 signaling

Dietary restriction has been well-described to improve health metrics, but whether it could benefit pathophysiological adaptation to extreme environment, for example, microgravity, remains unknown. Here, we investigated the effects of a daily rhythm of fasting and feeding without reducing caloric intake on cardiac function and metabolism against simulated microgravity. Male rats under ad libitum feeding or time-restricted feeding (TRF; food access limited to 8 hours every day) were subjected to hindlimb unloading (HU) to simulate microgravity. HU for 6 weeks led to left ventricular dyssynchrony and declined cardiac function. HU also lowered pyruvate dehydrogenase (PDH) activity and impaired glucose utilization in the heart. All these were largely preserved by TRF. TRF showed no effects on HU-induced loss of cardiac mass, but significantly improved contractile function of cardiomyocytes. Interestingly, TRF raised liver-derived fibroblast growth factor 21 (FGF21) level and enhanced cardiac FGF21 signaling as manifested by upregulation of FGF receptor-1 (FGFR1) expression and its downstream markers in HU rats. In isolated cardiomyocytes, FGF21 treatment improved PDH activity and glucose utilization, consequently enhancing cell contractile function. Finally, both liver-specific knockdown (KD) of FGF21 and cardiac-specific FGFR1 KD abrogated the cardioprotective effects of TRF in HU rats. These data demonstrate that TRF improves cardiac glucose utilization and ameliorates cardiac dysfunction induced by simulated microgravity, at least partially, through restoring cardiac FGF21 signaling, suggesting TRF as a potential countermeasure for cardioprotection in long-term spaceflight.

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

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.

High-Intensity Exercise Mitigates Cardiovascular Deconditioning During Long-Duration Bed Rest

Head-down-tilt bed rest (HDT) mimics the changes in hemodynamics and autonomic cardiovascular control induced by weightlessness. However, the time course and reciprocal interplay of these adaptations, and the effective exercise protocol as a countermeasure need further clarification. The overarching aim of this work (as part of a European Space Agency sponsored long-term bed rest study) was therefore to evaluate the time course of cardiovascular hemodynamics and autonomic control during prolonged HDT and to assess whether high-intensity, short-duration exercise could mitigate these effects. A total of n = 23 healthy, young, male participants were randomly allocated to two groups: training (TRAIN, n = 12) and non-training (CTRL, n = 11) before undergoing a 60-day HDT. The TRAIN group underwent a resistance training protocol using reactive jumps (5–6 times per week), whereas the CTRL group did not perform countermeasures. Finger blood pressure (BP), heart rate (HR), and stroke volume were collected beat-by-beat for 10 min in both sitting and supine positions 7 days before HDT (BDC−7) and 10 days after HDT (R+10), as well as on the 2nd (HDT2), 28th (HDT28), and 56th (HDT56) day of HDT. We investigated (1) the isolated effects of long-term HDT by comparing all the supine positions (including BDC−7 and R+10 at 0 degrees), and (2) the reactivity of the autonomic response before and after long-term HDT using a specific postural stimulus (i.e., supine vs. sitting). Two-factorial linear mixed models were used to assess the time course of HDT and the effect of the countermeasure. Starting from HDT28 onwards, HR increased (p < 0.02) and parasympathetic tone decreased exclusively in the CTRL group (p < 0.0001). Moreover, after 60-day HDT, CTRL participants showed significant impairments in increasing cardiac sympathovagal balance and controlling BP levels during postural shift (supine to sitting), whereas TRAIN participants did not. Results show that a 10-day recovery did not compensate for the cardiovascular and autonomic deconditioning following 60-day HDT. This has to be considered when designing rehabilitation programs—not only for astronauts but also in general public healthcare. High-intensity, short-duration exercise training effectively minimized these impairments and should therefore deserve consideration as a cardiovascular deconditioning countermeasure for spaceflight.

Effects of whole-body vibration on heart rate variability: acute responses and training adaptations

Heart rate variability (HRV) is a noninvasive and practical measure of cardiac autonomic nervous system function, mainly the sympathetic and parasympathetic modulations of heart rate. A low HRV has been shown to be indicative of compromised cardiovascular health. Interventions that enhance HRV are therefore beneficial to cardiovascular health. Whole-body vibration (WBV) training has been proposed as an alternative time-efficient exercise intervention for the improvement of cardiovascular health. In this review, we discuss the effect of WBV both acute and after training on HRV. WBV training appears to be a useful therapeutic intervention to improve cardiac autonomic function in different populations, mainly through decreases in sympathovagal balance. Although the mechanisms by which WBV training improves symphathovagal balance are not yet well understood; enhancement of baroreflex sensitivity, nitric oxide bioavailability and angiotensin II levels seem to play an important role.

Altered Venous Function during Long-Duration Spaceflights

Aims: Venous adaptation to microgravity, associated with cardiovascular deconditioning, may contribute to orthostatic intolerance following spaceflight. The aim of this study was to analyze the main parameters of venous hemodynamics with long-duration spaceflight.

Methods: Venous plethysmography was performed on 24 cosmonauts before, during, and after spaceflights aboard the International Space Station. Venous plethysmography assessed venous filling and emptying functions as well as microvascular filtration, in response to different levels of venous occlusion pressure. Calf volume was assessed using calf circumference measurements.

Results: Calf volume decreased during spaceflight from 2.3 ± 0.3 to 1.7 ± 0.2 L (p < 0.001), and recovered after it (2.3 ± 0.3 L). Venous compliance, determined as the relationship between occlusion pressure and the change in venous volume, increased during spaceflight from 0.090 ± 0.005 to 0.120 ± 0.007 (p < 0.01) and recovered 8 days after landing (0.071 ± 0.005, arbitrary units). The index of venous emptying rate decreased during spaceflight from −0.004 ± 0.022 to −0.212 ± 0.033 (p < 0.001, arbitrary units). The index of vascular microfiltration increased during spaceflight from 6.1 ± 1.8 to 10.6 ± 7.9 (p < 0.05, arbitrary units).

Conclusion: This study demonstrated that overall venous function is changed during spaceflight. In future, venous function should be considered when developing countermeasures to prevent cardiovascular deconditioning and orthostatic intolerance with long-duration spaceflight.

Effects of plantar stimulation on cardiovascular response to orthostatism

PURPOSE

Walking is a complex locomotor process that involves both spinal cord reflexes and cortical integration of peripheral nerve input. Maintaining an upright body position requires not only neuromuscular activity but also cardiovascular regulation. We postulated that plantar mechanical stimulation might modulate autonomic nervous system activity and, thereby, impact blood pressure adaptation during standing.

METHODS

Twelve healthy subjects underwent three randomly ordered 45-min 70°-saddle tilt tests while the plantar surfaces of the feet were stimulated using specially engineered Korvit boots in the following modes: (1) no stimulation, (2) disrupted stimulation, and (3) walking mode. Orthostatic tolerance time was measured for each trial. During testing, we obtained an electrocardiogram and measured blood pressure, skin blood flow, and popliteal vein cross-sectional area. We estimated central hemodynamics, baroreflex sensitivity and heart rate variability.

RESULTS

Orthostatic tolerance time was not found to differ significantly between test conditions (37.2 ± 10.4, 40.9 ± 7.6, and 41.8 ± 8.2 min, for no stimulation, disrupted stimulation, and walking mode, respectively). No significant differences between treatment groups were observed for stroke volume or cardiac baroreflex sensitivity, both of which decreased significantly from baseline during tilt testing in all groups. Cardiac sympathetic index and popliteal vein cross-sectional area increased at the end of the tilt period in all groups, without significant differences between treatments.

CONCLUSIONS

Plantar mechanical stimulation is insufficient for immediate modulation of cardiac sympathetic and parasympathetic activity under orthostatic stress.

Effect of Chinese herbal medicine on vascular functions during 60-day head-down bed rest

PURPOSE

Chinese herbal medicine is a promising countermeasure against cardiovascular dysfunction associated with a sedentary lifestyle. We examined the impact of the Chinese herb, Taikong Yangxin, on the micro- and macrovascular dysfunction associated with a 60-day bed rest.

METHODS

Fourteen healthy men were randomly divided into two groups: those given herbal supplement, and the control group; the two groups underwent a 60-day bed rest. The macrovasculature was assessed by sonography. Skin microvascular functions were assessed with laser Doppler. The plasma level of endothelial microparticles (EMPs), markers of endothelial injury, was determined.

RESULTS

Bed rest induced a 33 % decrease in the femoral artery diameter and compliance whereas carotid wall thickness, diameter, and compliance remained unchanged. The early phase of endothelium-dependent vasodilation to ACh was unmodified by bed rest, while the late phase was reduced by 30 % along with a twofold increase in EMPs. In those given Taikong Yangxin, the early phase was amplified by 2.5-fold, and the effects of bed rest on the late phase were prevented.

CONCLUSION

These findings indicate that Taikong Yangxin ameliorates endothelium-dependent vasodilation, likely by improving the NO pathway. The study suggests Taikong Yangxin as a new countermeasure to prevent the changes in microvascular function induced by physical inactivity.