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 Modulated Electromyostimulation on the Motor System of Elderly Neurological Patients. Pilot Study of Russian Currents Also Known as Kotz Currents.

In this brief report, we present preliminary findings from a study of the use of electromyostimulation (EMS) in neurological patients. Assuming the approach to be sufficiently effective, we decided to investigate the motor system of elderly neurological patients before and after a course of Russian currents EMS, which were developed for Soviet athletes and cosmonauts. To this point, 19 patients-EMS (n = 11) and control (n = 8)-have successfully completed the study. The study included patients aged 60-90 years with confirmed walking and balance disorders with a history of chronic cerebral ischemia. Patients in the experimental group underwent a course of modulated EMS of the hip and shin muscles from 3 to 9 procedures. Preliminary results of the study showed good patient acceptance of EMS. After the course, the EMS group showed a significant improvement from baseline in the Tinetti Test (+1.4 points, p = 0.0045), Rivermead Mobility Index (+0.5 points, p = 0.0022), and Timed Up and Go Test (-1.2 s, p = 0.0053). There was also a significant improvement in balance quality of 8.6% (p = 0.04). Shin muscle strength, although trending positively, did not change significantly. There was also no change in hip and shin muscles' tone. No significant changes were observed in the control group in the same tests. It can be concluded that stimulation of the hip and shin muscles with Russian (Kotz) currents has a positive effect on the motor system of elderly neurological patients. Significant effects with a course of short duration indicate that this EMS regimen is promising.

Dry immersion induced acute low back pain and its relationship with trunk myofascial viscoelastic changes.

Microgravity induces spinal elongation and Low Back Pain (LBP) but the pathophysiology is unknown. Changes in paraspinal muscle viscoelastic properties may play a role. Dry Immersion (DI) is a ground-based microgravity analogue that induces changes in m. erector spinae superficial myofascial tissue tone within 2 h. This study sought to determine whether bilateral m. erector spinae tone, creep, and stiffness persist beyond 2 h; and if such changes correlate with DI-induced spinal elongation and/or LBP. Ten healthy males lay in the DI bath at the Institute of Biomedical Problems (Moscow, Russia) for 6 h. Bilateral lumbar (L1, L4) and thoracic (T11, T9) trunk myofascial tone, stiffness and creep (MyotonPRO), and subjective LBP (0-10 NRS) were recorded before DI, after 1h, 6 h of DI, and 30min post. The non-standing spinal length was evaluated on the bath lifting platform using a bespoke stadiometer before and following DI. DI significantly modulated m. erector spinae viscoelastic properties at L4, L1, T11, and T9 with no effect of laterality. Bilateral tissue tone was significantly reduced after 1 and 6 h DI at L4, L1, T11, and T9 to a similar extent. Stiffness was also reduced by DI at 1 h but partially recovered at 6 h for L4, L1, and T11. Creep was increased by DI at 1 h, with partial recovery at 6 h, although only T11 was significant. All properties returned to baseline 30 min following DI. Significant spinal elongation (1.17 ± 0.20 cm) with mild (at 1 h) to moderate (at 6 h) LBP was induced, mainly in the upper lumbar and lower thoracic regions. Spinal length increases positively correlated (Rho = 0.847, p = 0.024) with middle thoracic (T9) tone reduction, but with no other stiffness or creep changes. Spinal length positively correlated (Rho = 0.557, p = 0.039) with Max LBP; LBP failed to correlate with any m. erector spinae measured parameters. The DI-induced bilateral m. erector spinae tone, creep, and stiffness changes persist beyond 2 h. Evidence of spinal elongation and LBP allows suggesting that the trunk myofascial tissue changes could play a role in LBP pathogenesis observed in real and simulated microgravity. Further study is warranted with longer duration DI, assessment of IVD geometry, and vertebral column stability.

NAIAD-2020: Characteristics of Motor Evoked Potentials After 3-Day Exposure to Dry Immersion in Women.

As female astronauts participate in space flight more and more frequently, there is a demand for research on how the female body adapts to the microgravity environment. In particular, there is very little research on how the neuromuscular system reacts to gravitational unloading in women. We aimed to estimate changes in motor evoked potentials (MEPs) in the lower leg muscles in women after 3-day exposure to Dry Immersion (DI), which is one of the most widely used ground models of microgravity. Six healthy female volunteers (mean age 30.17 ± 5.5 years) with a natural menstrual cycle participated in this experiment. MEPs were recorded from the gastrocnemius and soleus muscles twice before DI, on the day of DI completion, and 3 days after DI, during the recovery period. To evoke motor responses, transcranial and trans-spinal magnetic stimulation was applied. We showed that changes in MEP characteristics after DI exposure were different depending on the stimulation site, but were similar for both muscles. For trans-spinal stimulation, MEP thresholds decreased compared to baseline values, and amplitudes, on the contrary, increased, resembling the phenomenon of hypogravitational hyperreflexia. This finding is in line with data observed in other experiments on both male and female participants. MEPs to transcranial stimulation had an opposing dynamic, which may have resulted from the small group size and large inter-subject variability, or from hormonal fluctuations during the menstrual cycle. Central motor conduction time remained unchanged, suggesting that pyramidal tract conductibility was not affected by DI exposure. More research is needed to explore the underlying mechanisms.

Effect of 5-day dry immersion on the human foot morphology evaluated by computer plantography and soft tissues stiffness measuring.

16 participants have been subjected to Dry Immersion model (DI) for 5 days. DI reproduces the space flight factors such as lack of support, mechanical and axial unloading, physical inactivity, elimination of vertical vascular gradient. Long-term bed rest is also associated with similar factors, so the results of the study may be useful for clinical medicine. Computer plantography and measuring the stiffness of the soft tissues of the foot and superficial muscles of the shin (mm. tibialis anterior and peroneus longus) were performed twice before DI exposure, on the 2nd and 4th days of DI exposure, as well as on the 2nd day of the recovery period. DI exposure effects the parameters under study in two ways: by raising the longitudinal arch and by flattening the transverse arch, which is accompanied by a decrease in the soft tissues stiffness of the foot and superficial muscles of the shin. The work reveals the phenomenon of compensating the longitudinal arch state by changing the characteristics that reflect the transverse arch state. The results of the study for the first time demonstrate the correlation of the foot morphological characteristics with a decrease in stiffness of mm. peroneus longus and tibialis anterior.

Sharp Changes in Muscle Tone in Humans Under Simulated Microgravity.

A decrease in muscle tone induced by space flight requires a standardized assessment of changes to control the state of the neuromuscular system. This study is a step toward the development of a unified protocol, aimed at determining the initial effect of the presence or withdrawal of support on muscle tone, the effects of a 2-h supportlessness in Dry Immersion (DI) experiments, and the changes in muscle tone depending on the site of measurement. To perform measurements of changes in muscle tone, we used a MyotonPRO device. The list of muscles that we assessed includes: trunk - mm. deltoideus posterior, trapezius, erector spinae; leg - mm. biceps femoris, rectus femoris, tibialis anterior, soleus, gastrocnemius; foot - m. flexor digitorum brevis, tendo Achillis, aponeurosis plantaris. The study involved 12 healthy volunteers (6 men, 6 women) without musculoskeletal disorders and aged 32.8 ± 1.6 years. At the start of DI, there was a significant decrease in muscle tone of the following muscles: mm. tibialis anterior (-10.9%), soleus (-9.6%), erector spinae (-14.4%), and the tendo Achillis (-15.3%). The decrease continued to intensify over the next 2 h. In contrast, the gastrocnemius muscle demonstrated an increase in muscle tone (+7.5%) 2 h after the start of DI compared to the immediate in-bath baseline. Muscle tone values were found to be site-dependent and varied in different projections of mm. erector spinae and soleus. In previous experiments, we observed a high sensitivity of the myotonometry technique, which was confirmed in this study. To make it possible to compare data from different studies, a standardized protocol for measuring muscle tone for general use in gravitational physiology needs to be developed.

The First Female Dry Immersion (NAIAD-2020): Design and Specifics of a 3-Day Study.

This article describes procedures and some results of the first study of females undergoing 3-day Dry Immersion. The experiment "NAIAD-2020" was carried out at the Institute of Biomedical Problems (Moscow, Russia) with the participation of six healthy women volunteers (age 30.17 ± 5.5 years, height 1.66 ± 0.1 m, weight 62.05 ± 8.4 kg, BMI 22.39 ± 2.2 kg/m2) with a natural menstrual cycle. During the study, a standard protocol was used, the same as for men, with a minimum period of time spent outside the immersion bath. Before, during and after Immersion, 22 experiments were carried out aimed at studying the neurophysiological, functional, metabolic and psychophysiological functions of the body, the results of which will be presented in future publications. The total time outside the bath for women did not exceed that for men. Systolic and diastolic pressure did not significantly change during the immersion. In the first 24 h after the end of the immersion, heart rate was significantly higher than the background values [F(4,20) = 14.67; P < 0.0001]. Changes in body temperature and water balance were consistent with the patterns found in men. No significant changes in height and weight were found during immersion. All women reported general discomfort and pain in the abdomen and back. The results of this study did not find significant risks to women's health and showed the feasibility of using this model of the effects of space flight in women of reproductive age.

Cardiovascular System Under Simulated Weightlessness: Head-Down Bed Rest vs. Dry Immersion.

BACKGROUND: The most applicable human models of weightlessness are -6° head-down bed rest (HDBR) and head-out dry immersion (DI). A detailed experimental comparison of cardiovascular responses in both models has not yet been carried out, in spite of numerous studies having been performed in each of the models separately. OBJECTIVES: We compared changes in central hemodynamics, autonomic regulation, plasma volume, and water balance induced by -6° HDBR and DI. METHODS: Eleven subjects participated in a 21-day HDBR and 12 subjects in a 3-day DI. During exposure, measurements of the water balance, blood pressure, and heart rate were performed daily. Plasma volume evolution was assessed by the Dill-Costill method. In order to assess orthostatic tolerance time (OTT), central hemodynamic responses to orthostatic stimuli, and autonomous regulation, the 80° lower body negative pressure-tilt test was conducted before and right after both exposures. RESULTS: For most of the studied parameters, the changes were co-directional, although they differed in their extent. The changes in systolic blood pressure and total peripheral resistance after HDBR were more pronounced than those after DI. The OTT was decreased in both groups: to 14.2 ± 3.1 min (vs. 27.9 ± 2.5 min before exposure) in the group of 21-day HDBR and to 8.7 ± 2.1 min (vs. 27.7 ± 1.2 min before exposure) in the group of 3-day DI. CONCLUSIONS: In general, cardiovascular changes during the 21-day HDBR and 3-day DI were co-directional. In some cases, changes in the parameters after 3-day DI exceeded changes after the 21-day HDBR, while in other cases the opposite was true. Significantly stronger effects of DI on cardiovascular function may be due to hypovolemia and support unloading (supportlessness).

Dry immersion as a model of deafferentation: A neurophysiology study using somatosensory evoked potentials.

INTRODUCTION: Dry immersion is a ground-based experiment simulating the effects of weightlessness, and it is a model of acute symmetrical bilateral deafferentation. This exploratory study aimed to investigate the effects of three days of dry immersion (DI) on sensory thresholds and the functioning of lemniscal pathways, assessed by somatosensory evoked potentials (SEPs). METHODS: Twelve healthy male volunteers (32+/-4.8 years) participated in the study. Sensory thresholds and SEPs of the tibial nerve of both limbs were recorded before (D-1) and on the third day of dry immersion (D3). RESULTS: Sensory thresholds significantly decreased on D3 (-20.75 +/-21.7%; z = -2.54; p = 0.0109 on the right side and -22.18+/-17.28%; z = -3.059; p = 0.002 on the left side). The amplitude of P40 responses did not differ between D-1 and D3. Latencies of all central responses until P30 were shortened on D3 (N21 right:-0.57+/-0.31; z = -3.06; p = 0.002; N21 left -0.83+/-0.53; z = -2.94; p = 0.003; P30 right: -1.26+/-1.42; z = -3.059; p = 0.002; P30 left: -1.11+/-1.55; z = -2.27; p = 0.02). CONCLUSION: Three days of dry immersion can induce hyperexcitability of lemniscal pathways. SIGNIFICANCE: This may be explained by a change in the expression of membrane channels and/or medullar plasticity and/or hypersensitization of peripheral sensory receptors induced by this acute deafferentation. Additional studies are needed to further elucidate the mechanisms.

Brain Activity during Mental Imagery of Gait Versus Gait-Like Plantar Stimulation: A Novel Combined Functional MRI Paradigm to Better Understand Cerebral Gait Control.

Human locomotion is a complex sensorimotor behavior whose central control remains difficult to explore using neuroimaging method due to technical constraints, notably the impossibility to walk with a scanner on the head and/or to walk for real inside current scanners. The aim of this functional Magnetic Resonance Imaging (fMRI) study was to analyze interactions between two paradigms to investigate the brain gait control network: (1) mental imagery of gait, and (2) passive mechanical stimulation of the plantar surface of the foot with the Korvit boots. The Korvit stimulator was used through two different modes, namely an organized ("gait like") sequence and a destructured (chaotic) pattern. Eighteen right-handed young healthy volunteers were recruited (mean age, 27 ± 4.7 years). Mental imagery activated a broad neuronal network including the supplementary motor area-proper (SMA-proper), pre-SMA, the dorsal premotor cortex, ventrolateral prefrontal cortex, anterior insula, and precuneus/superior parietal areas. The mechanical plantar stimulation activated the primary sensorimotor cortex and secondary somatosensory cortex bilaterally. The paradigms generated statistically common areas of activity, notably bilateral SMA-proper and right pre-SMA, highlighting the potential key role of SMA in gait control. There was no difference between the organized and chaotic Korvit sequences, highlighting the difficulty of developing a walking-specific plantar stimulation paradigm. In conclusion, this combined-fMRI paradigm combining mental imagery and gait-like plantar stimulation provides complementary information regarding gait-related brain activity and appears useful for the assessment of high-level gait control.

Multi-System Deconditioning in 3-Day Dry Immersion without Daily Raise.

Dry immersion (DI) is a Russian-developed, ground-based model to study the physiological effects of microgravity. It accurately reproduces environmental conditions of weightlessness, such as enhanced physical inactivity, suppression of hydrostatic pressure and supportlessness. We aimed to study the integrative physiological responses to a 3-day strict DI protocol in 12 healthy men, and to assess the extent of multi-system deconditioning. We recorded general clinical data, biological data and evaluated body fluid changes. Cardiovascular deconditioning was evaluated using orthostatic tolerance tests (Lower Body Negative Pressure + tilt and progressive tilt). Metabolic state was tested with oral glucose tolerance test. Muscular deconditioning was assessed via muscle tone measurement. Results: Orthostatic tolerance time dropped from 27 ± 1 to 9 ± 2 min after DI. Significant impairment in glucose tolerance was observed. Net insulin response increased by 72 ± 23% on the third day of DI compared to baseline. Global leg muscle tone was approximately 10% reduced under immersion. Day-night changes in temperature, heart rate and blood pressure were preserved on the third day of DI. Day-night variations of urinary K+ diminished, beginning at the second day of immersion, while 24-h K+ excretion remained stable throughout. Urinary cortisol and melatonin metabolite increased with DI, although within normal limits. A positive correlation was observed between lumbar pain intensity, estimated on the second day of DI, and mean 24-h urinary cortisol under DI. In conclusion, DI represents an accurate and rapid model of gravitational deconditioning. The extent of glucose tolerance impairment may be linked to constant enhanced muscle inactivity. Muscle tone reduction may reflect the reaction of postural muscles to withdrawal of support. Relatively modest increases in cortisol suggest that DI induces a moderate stress effect. In prospect, this advanced ground-based model is extremely suited to test countermeasures for microgravity-induced deconditioning and physical inactivity-related pathologies.

Effects of short-term dry immersion on bone remodeling markers, insulin and adipokines.

BACKGROUND: Dry immersion (DI), a ground-based model of microgravity previously used in Russia, has been recently implemented in France. The aim of this study was to analyze early events in a short-term DI model in which all conditions are met to investigate who is first challenged from osteo- or adipo-kines and to what extent they are associated to insulin-regulating hormones. METHODS: Twelve healthy men were submitted to a 3-day DI. Fasting blood was collected during pre-immersion phase for the determination of the baseline data collection (BDC), daily during DI (DI24h, DI48H and DI72h), then after recovery (R+3h and R+24h). Markers of bone turnover, phosphocalcic metabolism, adipokines and associated factors were measured. RESULTS: Bone resorption as assessed by tartrate-resistant acid phosphatase isoform 5b and N-terminal crosslinked telopeptide of type I collagen levels increased as early as DI24h. At the same time, total procollagen type I N- and C-terminal propeptides and osteoprotegerin, representing bone formation markers, decreased. Total osteocalcin [OC] was unaffected, but its undercarboxylated form [Glu-OC] increased from DI24h to R+3h. The early and progressive increase in bone alkaline phosphatase activities suggested an increased mineralization. Dickkopf-1 and sclerostin, as negative regulators of the Wnt-ß catenin pathway, were unaltered. No change was observed either in phosphocalcic homeostasis (calcium and phosphate serum levels, 25-hydroxyvitamin D, fibroblast growth factor 23 [FGF23]) or in inflammatory response. Adiponectemia was unchanged, whereas circulating leptin concentrations increased. Neutrophil gelatinase-associated lipocalin [lipocalin-2], a potential regulator of bone homeostasis, was found elevated by 16% at R+3h compared to DI24h. The secretory form of nicotinamide phosphoribosyl-transferase [visfatin] concentrations almost doubled after one day of DI and remained elevated. Serum insulin-like growth factor 1 levels progressively increased. Fasting insulin concentrations increased during the entire DI, whereas fasting glucose levels tended to be higher only at DI24h and then returned to BDC values. Changes in bone resorption parameters negatively correlated with changes in bone formation parameters. Percent changes of ultra-sensitive C-reactive protein positively correlated with changes in osteopontin, lipocalin-2 and fasting glucose. Furthermore, a positive correlation was found between changes in FGF23 and Glu-OC, the two main osteoblast-/osteocyte-derived hormones. CONCLUSION: Our results demonstrated that DI induced an unbalanced remodeling activity and the onset of insulin resistance. This metabolic adaptation was concomitant with higher levels of Glu-OC. This finding confirms the role of bone as an endocrine organ in humans. Furthermore, visfatin for which a great responsiveness was observed could represent an early and sensitive marker of unloading in humans.