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 (DI_24h, DI_48H and DI_72h), 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 DI_24h. 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 DI_24h 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-β 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 DI_24h. 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 DI_24h 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.

Hemodynamic, autonomic and baroreflex changes after one night sleep deprivation in healthy volunteers

BACKGROUND

Sleep disorders are associated to a number of cardiovascular disturbances that might increase cardiovascular risk. Sleep deprivation, in particular, might, by inducing autonomic dysregulation, raise arterial pressure and hypertensive risk. Available evidence however is contradictory.

METHODS

We tested the main hypothesis that one night sleep deprivation in 24 volunteers might alter hemodynamics (heart rate and Arterial Pressure - AP), autonomic regulation (mono and bivariate spectral analysis of RR and non invasive AP variability) and baroreflex control (spectral index alpha and spontaneous baroreflex slope), performance indices (reaction time) and subjective stress (questionnaires and salivary cortisol). Volunteers were studied in normal living conditions and while kept in isolation and confinement, to test the presence of possible bias related to environmental stress.

RESULTS

Results indicate that there were no differences between normal living conditions and isolation and confinement (Intraclass Correlation Coefficient >0.75 for most variables). Conversely, after one night sleep deprivation subjects felt tired (p<0.05), and performance deteriorated (p<0.05), while cortisol profile was substantially maintained, hemodynamic parameters did not change and HRV and index alpha increased slightly.

CONCLUSIONS

Findings support the contention that one night sleep deprivation, in absence of significant additional stress or disturbances, does not lead to increased arterial pressure values or to changes in autonomic or baroreflex profiles that could conceivably favor hypertension development, but induces the expected increase in tiredness and reduction in performance.

Short-term effects of electrical stimulation superimposed on muscular voluntary contraction in postural control in elderly women

Thirty-two women between 62 and 75 years old were randomized into 3 groups. Each group performed a program of 4 sessions a week over 6 weeks. Group SC (n = 11) climbed up and down stairs, group ES (n = 11) practiced electrostimulation, and group SC + ES (n = 10) superimposed the 2 activities simultaneously. Using a force platform and a seesaw platform, static and dynamic balance in eyes-open and eyes-closed conditions were analyzed before and after the programs for each group. After the programs, the results indicated that dynamic balance improved for the 3 groups, but the contribution of visual information in the control of oscillation amplitude was lower in the SC group than in the ES and SC + ES groups. In the SC + ES group, the electrical stimulation interferes with neurophysiologic afference integration in postural control in relation to voluntary movement. Voluntary exercise appears to be more efficient than electrical stimulation and the superimposed techniques to change balancing tactics in the elderly.

L’électrostimulation surimposée à la contraction musculaire volontaire présente-t-elle un intérêt physiologique chez les sujets âgés ?

OBJECTIVE

To analyze the physiological effects of electrical stimulation with voluntary muscle contraction exercise in postmenopausal women.

MATERIALS AND METHODS

Thirty-two females aged 62 to 75 years were randomly assigned to three groups to perform four activity sessions for six weeks: group ME (N =11) climbed up and down stairs, group ES (N =11) practised electrostimulation, and group ME + ES (N = 10) undertook both activities. Physiological adaptations of body composition (lean and fat masses and bone mineral density), muscular strength (isometric and dynamic), vertical jump and posturokinetic activities (balance and gait) were analysed.

RESULTS

For the three groups, the isometric strength at angle 100 degrees (average increase right and left legs, ME: 19 N.m; ES: 4.5 N.m; ME + ES: 11.5 N.m), the dynamic strength at speed 60 degrees.s(-1) (average increase right and left leg, ME: 15 N.m; ES: 14 N.m; ME+ES: 18.5 N.m) and the vertical jump (ME: 23 mm; ES: 16 mm; ME + ES: 34 mm) increased contrary in the body composition and posturokinetic activities. Nevertheless, the group ME + ES adapted differently on some parameters of bone mineral density (P < 0.05) and dynamic strength (P < 0.01) in relation to the groups ES and ME.

CONCLUSION

Electrostimulation with voluntary muscle contraction exercise could induce different physiologic adaptations compared with electrostimulation or voluntary muscle contraction exercise alone.

Effects of brisk walking on static and dynamic balance, locomotion, body composition, and aerobic capacity in ageing healthy active men

This work analyses the short-term physiological and neurophysiological effects of a brisk walking programme in ageing, healthy, active men. Twenty-one men 63 to 72 years of age were recruited and separated into 2 groups. One group performed a walking programme (WP) (n = 11) and another served as control (C) group (n = 10). The walking programme lasted for twelve weeks and included five sessions per week. Several parameters were assessed before and after the programme for the WP group. The same tests were performed (separated by twelve weeks) in group C. During each assessment, the subjects were put through static and dynamic balance tests, spatio-temporal gait analysis, body composition measurements and determination of aerobic capacity and bone mineral density. The statistic analysis showed a significant improvement in dynamic balance performance, especially in lateral sway when the subjects kept their eyes open, an increase of VO(2) max and loss of fat mass in the WP group. However, no alterations appeared in spatiotemporal gait characteristics, static balance performance, lean mass or bone mineral density (total body and hip). According to these results, this walking programme may have positive effects on preventing ageing subjects from falling.

Neuromuscular effects of three training methods in ageing women

AIM

The present study aimed to compare the effects of 3 strength development methods on muscular mass and muscular strength in healthy ageing women.

METHODS

Thirty-two healthy women, 62 to 75 years old were randomised into 3 groups. The 3 groups performed 4 sessions a week of strength development for 6 weeks. The 1(st) group (SC) climbed up and down 300 stairs per session. The 2(nd) group (ES) followed an electrostimulation programme on the quadriceps muscles. The 3(rd) group (SC+ES) combined stair climbing with electrostimulation. Before and after the 3 programmes, the muscular mass of the leg was assessed using a biphotonic absorptiometry machine. Isometric (angle 20 degrees and 100 degrees ) and isokinetic (60 degrees /s and 240 degrees /s) knee extension torque was measured using an isokinetic dynamometer.

RESULTS

None of the programmes changed the muscular mass. All 3 groups increased isometric (angle 20 degrees, p<0.001; angle 100 degrees, p<0.003) and isokinetic (60 degrees /s, p<0.0001; 240 degrees /s, p<0.0001) knee extension torque. None of the programmes appeared more efficient than the others for muscular mass or muscular strength.

CONCLUSION

Six weeks of activity (SC, ES or SC+ES) improved the isometric and dynamic muscular strength in ageing healthy women. However, this period was too short to change the muscular mass. None of the activities presented a real advantage over the others in ageing women.

Comparison between three strength development methods on body composition in healthy elderly women

The effects of three strength development methods (during 6 weeks) were assessed on the body composition in 32 women, 62 to 75 years old and randomised in 3 groups. The first group (SC) has climbed and come down 300 stairs per session. The second group (ES) followed an electrostimulation programme on quadriceps muscles. The third group (SC+ES) has combined the stairs climbing with electrostimulation. Body composition and bone mineral density (BMD) was assessed using Absorptiometry machine before and after the programmes. None of the programmes has increased significantly BMD. Nevertheless, the SC+ES group BMD enhanced more on the trochanter (p<0,05) and the two legs (p<0,05) than the SC and ES groups BMD (interaction group/time). The combined activity (SC+ES) would deserve to be tested on a longer period.

Cholesterol reduction and increased cardiovascular fitness following a 12 weeks brisk walking

The effects of a walking training programme were assesed on 10 healthy, active men aged 63-69 years. Serum lipids, pulse and blood pressure, maximum oxygen consumption (VO2 max) and anthropometric parameters, were measured before and after this programme. There was a significant fall in LDL (p<0.02) and mean diastolic BP (p<0.005). In spite of the subjects's initial good level of fitness there was still an 8% rise in the mean VO2 max of the group. There was also a significant loss of body fat (P<0.01). These positive physiological effects suggest that brisk walking can be considered as a a useful activity for improving the fitness and general health in this age-range.

Dynamics of cerebral blood flow autoregulation in hypertensive patients

In hypertensive patients, the upper and lower limits of cerebral autoregulation are shifted to higher levels. However, the dynamics of cerebral autoregulation in hypertensive patients are less well known. We compared the dynamics of cerebral autoregulation in 21 treated hypertensive patients (13 men and 8 women; mean age: 48.9+/-13.6 years) and in 21 normotensive subjects (13 men and 8 women; mean age: 51+/-14.5 years) by transcranial Doppler (TCD) of the middle cerebral artery (MCA) during the acute decrease in blood pressure induced by standing up after 2 min in squatting position. MCA maximal outline blood flow velocity (FV), blood pressure (Finapres) and end-tidal PCO2 were continuously monitored and computerised. A cerebral vascular resistance index (CR) was calculated as follows: mean arterial BP/MCA mean FV with normalised changes in CR per second during the blood pressure decrease (CR slope). The CR slope reflecting the rate of cerebral autoregulation did not differ between the two groups and within the hypertensive patients [well controlled (8 patients) and not controlled (13 patients)]. The time to maximum decrease of CR (T1) and the time to full recovery of CR after the initial drop (T2) were also similar in the two groups (controls T1: 11.3+/-3.1 s, T2: 12+/-5.9 s; hypertensive T1: 11.7+/-2.5 s, T2: 10.7+/-4.5 s) and within hypertensive patients. These findings suggest that the dynamics of cerebral autoregulation are well preserved in hypertensive patients, with no difference according to the efficiency of treatment of hypertension.

Changes in kinetics of cerebral auto-regulation with head-down bed rest

Thoraco-cephalic fluid shift induced by weightlessness may influence cerebral autoregulation. Our objective was to assess effects of simulated weightlessness by a 7-day head-down bed rest (HDBR) on the kinetics of cerebral blood flow (CBF) autoregulation in eight healthy women (27.9 +/- 0.9 years). This was studied by transcranial Doppler (TCD) of the middle cerebral artery (MCA) during the sudden decrease in blood pressure (BP) induced by quickly deflating thigh cuff aftera 4-min arterial occlusion before (D - 3), during (D2, D5) and after the HDBR (D + 1). BP (Finapres) and MCA maximal blood flow velocity were continuously recorded. Cerebrovascular resistance (CR) was expressed as the ratio of mean BP to mean MCA velocity. The CR slope was defined as changes in CR per second during the BP decrease. The magnitude of the relative decrease in mean BP and MCA velocity as well as the CR slope did not differ significantly before, during and after the HDBR, showing no major impairment of cerebral autoregulation during short-term HDBR. The time to maximum decrease in CR (T1 in s), corresponding to the maximum vasodilation was reduced on D2 (7-2 +/- 0.6) versus D - 3 (9.9 +/- 1-3), D5 (9-6 +/- 0.8) and R + 1 (11.7 +/- 11) probably as a result of the fluid shift. We also looked if the responses during the thigh cuff release differed in women according to their tolerance to the 10 min stand test performed after the HDBR: T1 was larger in the five women who presented orthostatic intolerance suggesting that some differences in cerebral autoregulatory responses may be related to orthostatic intolerance.

Effects of cosmonaut vestibular training on vestibular function prior to spaceflight

The purpose of this study was to quantify the effects of repetitive Coriolis and cross-coupled stimulations, similar to the vestibular training the cosmonauts are exposed to prior to their spaceflight. on vestibular function in control subjects on Earth. Ten volunteers were passively rotated in yaw on a rotating chair while executing standardized pitch head-and-trunk movements. The chair stopped to change direction after 12 head-and-trunk movements were made. The runs were grouped in sessions of ten,which were repeated daily for 10 days. The severity of motion sickness was assessed by subjective judgment and measurements of skin pallor and salivary total protein concentration, and nystagmus was recorded. The severity of motion sickness and nystagmus decreased during cosmonaut vestibular training (CVT). One month after the end of CVT, nystagmus responses were still about 20-30% lower than control values. These results indicate that CVT induces a habituation of vestibular responses. One important implication of this experiment concerns space studies on cosmonauts who are exposed to such vestibular training prior to their spaceflight.

Balance and gait analysis after 30 days -6 degrees bed rest: influence of lower-body negative-pressure sessions

Five volunteers took part in -6 degrees head-down bed-rest experiments for 30 d. In the first experiment, three subjects underwent several sessions of lower-body negative-pressure (LBNP) per day, with two others serving as controls. In the second, the LBNP group of the first experiment became the control and vice versa. Two experimental protocols analyzed the bed-rest-induced modifications of balance and gait and the efficiency of LBNP in counteracting these modifications. A kymographic method allowed the measurement of walking parameters. Anteroposterior and lateral sways were successively studied with both a force platform (static condition) and a rocking platform (dynamic condition). The tests were performed 2 d before the bed-rest period, and over the 1st, 3rd and 4th days of the recovery period. When the subjects were controls, bed rest decreased step length, walking velocity, and balance stability. LBNP completely counteracted the bed-rest-induced modifications of gait and static balance and of dynamic balance for the lateral sway. As LBNP was ineffective in counteracting the modifications of the anteroposterior sway, dynamic balance deficiency was independent of the beneficial effect of LBNP on the decreased orthostatic tolerance induced by -6 degrees head-down bed rest. The results indicate that head-down bed rest, like spaceflight, induces certain sensorimotor changes involved in the decrease of gait and balance performance.