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Biomedical subjects

J O Fortrat

Publications and source records attributed to J O Fortrat.

At least 19 recordsLinked to original sources
PubMed2004

Impaired cardiovascular autonomic control in newly and long-term-treated patients with Parkinson's disease: involvement of L-dopa therapy.

In idiopathic Parkinson's disease (PD), autonomic dysfunction is frequent, causing orthostatic hypotension. The respective roles of disease progression and dopaminergic treatment remain unclear. In this study, we investigated the autonomic control of cardiovascular functions and its relation to L-dopa therapy in both newly diagnosed (ND) and long-term-treated (LT) patients. Study subjects were: (1) nine ND patients never having undergone treatment with L-dopa; (2) 18 LT patients who had been receiving L-dopa treatment for a long period. ND patients were investigated before L-dopa treatment and after stabilization of their L-dopa dosage. LT patients were investigated once with their regular treatment and once after a 12-h interruption of L-dopa treatment; (3) nine healthy subjects served as controls. At each test session, blood pressure (BP), heart rate (HR), plasma catecholamines, heart rate variability (HRV), and spontaneous baroreflex sensitivity were assessed in the supine and upright positions. Before receiving L-dopa medication, ND patients had reduced E/I ratios (HR response/deep breathing) and lowered HRV when compared to controls; this was evidence of early effects of the disease on autonomic HR control. Introduction of L-dopa treatment reduced BP, HR, and plasma levels of adrenaline and noradrenaline. Similar changes were found in LT patients when contrasting the short-term treatment interruption and the usual L-dopa dosage. The treatment-linked increase in plasma dopamine also correlated with the decrease in noradrenaline. These results showed that mild impairment of autonomic cardiovascular control occurred early in the course of PD. They also provided evidence that the side effects of L-dopa aggravated the impairment of the autonomic control of BP and HR.

Aged↗
PubMed2001

Smoothed pseudo Wigner-Ville distribution as an alternative to Fourier transform in rats.

Techniques for examining signals in the time and frequency domains are well-established tools. These tools have their limitations; they tell us in a broad sense where the signal component exists in the frequency domain, but they do not tell us how its frequency characteristics change over time. The time-frequency has become a powerful alternative for the analysis of signals. Among various time-frequency distribution methods, one of the most studied is the Wigner-Ville distribution. The aim of this study was to evaluate in conscious rats smoothed pseudo Wigner--Ville distribution (SPWVD) as an alternative to the fast Fourier transform (FFT) in RR intervals and in systolic blood pressure (SBP), before and after adrenergic and cholinergic receptor blockade. Fourteen Wistar rats equipped with telemetry probe were evaluated: (1) under control conditions; (2) after injection of saline (100 microl kg(-1) i.v.); (3) after atenolol (1 mg kg(-1) i.v.); (4) after atropine methyl nitrate (0.5 mg kg(-1) i.v.); and (5) after phentolamine (5 mg kg(-1) i.v.). FFT and SPWVD were applied to RR intervals and SBP time series. Six-minute time series of RR intervals, systolic and diastolic pressures were analysed. The bias and distribution of differences between FFT and SPWVD methods in RR intervals under base conditions were 1.4+/-0.4% (r2=0.94; P<0.01) in LF/LF+HF: 1.5+/-0.5% ( r2=0.92; P<0.01) in HF/LF+HF and 4.8+/-1.9% (r2=0.92; P<0.01) in LF/HF. In SBP the bias and distribution were 1.5+/-0.8% (r2=0.90) P<0.05) in LF/LF+HF and 1.7+/-0.6% (r2=-0.92; P<0.01) in HF/LF+HF. In the frequency domain analysis of RR intervals and SBP there was no difference between FFT and SPWVD. The agreement between the methods demonstrates that in stationary signals both methods can be used interchangeably. SPWVD may be an interesting tool to analyse biomedical signals; it provides a good resolution at high frequency and a good frequency resolution at low frequencies independently if signals remain stationary.

Adrenergic beta-Antagonists↗
PubMed2001

Effect of prolonged head-down bed rest on complex cardiovascular dynamics.

We postulated that a change in complex dynamics of the cardiovascular system could be involved in the orthostatic intolerance observed after simulated weightlessness. Supine recordings of 1024 consecutive pulse intervals and systolic blood pressures were obtained on 7 subjects adapted to a 42 day head-down bed rest (day 22 and 42) but also before and 6 days after head-down bed rest (-6 degrees). Coarse graining spectral analysis was used to extract the non-harmonic (fractal) component from each time series. The power spectral densities of this fractal component are inversely proportional to their frequency (1/f beta). We fitted an inverse power law estimate to the fractal component to determine the spectral exponent beta. The complex dynamics of blood pressure and heart rate variability were also analyzed by correlation dimension and non-linear prediction. Bed rest induced orthostatic intolerance in 4 subjects. There was a significant increase in the spectral exponent beta of RR-interval variability during and after head-down bed rest (before: 1.039 +/- 0.090; during: 1.552 +/- 0.080 and 1.547 +/- 0.100; after: 1.428 +/- 0.040). Analysis of the blood pressure dynamics indicated lower correlation dimensions during head-down bed rest and higher coefficients of predictability after head-down bed rest. Complexity alterations of RR-interval and blood pressure variability were not linked with one another during head-down bed rest. These alterations seemed to be correlated with the orthostatic intolerance observed after bed rest. These results suggest a change of the integration level of cardiovascular autonomic regulation.

Adult↗
PubMed2001

Endocrine responses to 7 days of head-down bed rest and orthostatic tests in men and women.

The objective of this study was to investigate plasma volume (PV), total body water, hormones and hydroelectrolyte responses in eight males (25-40 years) and eight females (25-31 years) during 7 days of exposure to simulated microgravity (-6 degrees head-down bed rest, HDBR). Bed rest is a model that has commonly been used to simulate spaceflight. Heart rate (HR), blood pressure (BP) and vasoactive hormone responses were studied before and after HDBR during a 10-min stand test. No change in total body water and body mass was noted in either sex. The decrease in PV was similar in both men (9.1 +/- 1.4%) and women (9.4 +/- 0.8%). Urinary normetanephrine (NMN) was decreased during HDBR in both sexes. Urinary metanephrine (MN) and plasma catecholamines were unchanged. Daily urinary excretion of urea, an indirect index of protein breakdown, was increased only in the female subjects during HDBR. Plasma active renin (AR) and aldosterone were increased in both sexes, but urinary atrial natriuretic peptide (ANP) and arginine vasopressin (AVP) were unchanged throughout the study. Also, the hormonal responses to 7 days of HDBR were comparable between men and women. Moreover, the results show similar cardiovascular and endocrine responses to standing after HDBR. However, the orthostatic intolerance following HDBR was associated with a blunted increase in noradrenaline (NA) only in the women during the stand test. It is concluded that: (i) 7 days of physical inactivity achieved during HDBR resulted in a reduced sympathetic activity in both sexes and alterations in protein metabolism in women and (ii) standing after HDBR resulted in an attenuated release of noradrenaline in women.

Adult↗
PubMed2000

No effect of venoconstrictive thigh cuffs on orthostatic hypotension induced by head-down bed rest.

Orthostatic intolerance (OI) is the most serious symptom of cardiovascular deconditioning induced by head-down bed rest or weightlessness. Wearing venoconstrictive thigh cuffs is an empirical countermeasure used by Russian cosmonauts to limit the shift of fluid from the lower part of the body to the cardio-cephalic region. Our aim was to determine whether or not thigh cuffs help to prevent orthostatic hypotension induced by head-down bed rest. We studied the effect of thigh cuffs on eight healthy men. The cuffs were worn during the day for 7 days of head-down bed rest. We measured: orthostatic tolerance (stand tests and lower body negative pressure tests), plasma volume (Evans blue dilution), autonomic influences (plasma noradrenaline) and baroreflex sensitivity (spontaneous baroreflex slope). Thigh cuffs limited the loss of plasma volume (thigh cuffs: -201 +/- 37 mL vs. control: -345 +/- 42 mL, P < 0.05), the degree of tachycardia and reduction in the spontaneous baroreflex sensitivity induced by head-down bed rest. However, the impact of thigh cuffs was not sufficient to prevent OI (thigh cuffs: 7.0 min of standing time vs. control: 7.1 min). Decrease in absolute plasma volume and in baroreflex sensitivity are known to be important factors in the aetiology of OI induced by head-down bed rest. However, dealing with these factors, using thigh cuffs for example, is not sufficient to prevent OI. Other factors such as venous compliance, microcirculatory changes, peripheral arterial vasoconstriction and vestibular afferents must also be considered.

Adult↗
PubMed2000

Adaptations to a 7-day head-down bed rest with thigh cuffs.

PURPOSE: Thigh cuffs were two elastic strips fixed at the upper part of each thigh, which limits the shift of fluid from the legs into the cardio-thoracic region. The purpose of this study was to examine the effects of thigh cuffs on hormonal and plasma volume responses and orthostatic tolerance during a 7-day head-down bed rest (HDBR). METHODS: Orthostatic tolerance, plasma volume, total body water, blood volume-regulating hormones, and hydro-electrolyte responses were measured in eight healthy men (age range, 25-40 yr), using thigh cuffs 10 h daily during 7 d of -6 degrees HDBR. RESULTS: Thigh cuffs worn during HDBR attenuated the decrease in plasma volume observed after HDBR (thigh cuffs: -5.85 +/- 0.95% vs control: -9.09 +/- 0.82%, P < or = 0.05). During this experiment, there was no significant change in total body water. Thus, the hypovolemia did not result from a loss of water but from a fluid shift from the blood compartment into the interstitial and/or intracellular compartment. Hormonal responses during HDBR and stand test were not modified by the thigh cuffs. Thigh cuffs had no significant effect on the clinical symptoms of orthostatic intolerance after HDBR. CONCLUSIONS: Thigh cuffs worn during HDBR blunted the decrease in plasma volume but did not reduce orthostatic intolerance; thus, they are not a completely effective countermeasure. Furthermore, hypovolemia seems to be necessary but not sufficient to induce orthostatic intolerance after HDBR.

Adult↗
PubMed2000

Fuel homeostasis during physical inactivity induced by bed rest.

The consequences of physical inactivity on fuel homeostasis were evaluated during 7 days of head-down bed rest (HDBR), a model mimicking weightlessness. Eight men (32.4 +/- 1.9 yr; body mass index, 23.9 +/- 0.7 kg/m2) and eight women (27.9 +/- 0.9 yr; body mass index, 20.9 +/- 0.6 kg/m2) underwent an oral glucose tolerance test (OGTT; 1 g/kg) before and after HDBR. The glucose load was labeled with 13C and associated with D-[6,6-2H2] glucose infusion, indirect calorimetry, breath tests, and plasma measurements to determine the glucose turnover and biodisponibility, substrate oxidation, and endocrine responses. Body composition was assessed using H2(18)O dilution. In addition, hormones were measured in daily blood and 24-h urine samples. No change in body composition was noted. Daily fasting insulin increased during HDBR (men, 34%; women, 26%), as did the insulin to glucose ratio (men, 30%; women, 25%). The normetanephrine level dropped (men, 30%; women, 16%), but metanephrine was unchanged. During OGTTs, the insulin response was increased after HDBR (men, 47%; women, 67%), whereas plasma glucose levels were similar. Nonesterified fatty acids and beta-hydroxybutyrate levels were lower. Endogenous glucose production dropped (28%), and exogenous glucose oxidation increased (28%) only in men. Resting energy expenditure was unchanged, but nonproteic respiratory quotient increased (men, 10%; women, 14%). Basal levels of lipid oxidation dropped in both sexes (approximately 90%), but those of carbohydrate oxidation increased in men (40%); as did lipogenesis in women (570%). In response to OGTTs, lipid oxidation was 80% reduced in both sexes after HDBR, but carbohydrate oxidation increased (25%) in men. Lipogenesis occurred in men (304%) and women (74%), but the latter had higher absolute levels. Therefore, 7 days of HDBR resulted in 1) reduced sympathetic activity, 2) insulin resistance suggested at the muscle level in men and at both the muscle and liver levels in women, 3) no changes in glucose biodisponibility, suggesting no alterations in the gastrointestinal function, and 4) a shift toward carbohydrate oxidation in men and a net lipogenesis in women. Such results suggest gender differences in response to sedentary life style and warrant further analysis.

3-Hydroxybutyric Acid↗
PubMed1999

Even slight movements disturb analysis of cardiovascular dynamics.

We hypothesized that spontaneous movements (postural adjustments and ideomotion) disturb analysis of heart rate and blood pressure variability and could explain the discrepancy between studies. We measured R-R intervals and systolic blood pressure in nine healthy sitting subjects during three protocols: 1) no movement allowed, 2) movements allowed but not standing, 3) movements and standing allowed. Heart rate and blood pressure were not altered by movements. Movements with or without standing produced a twofold or greater increase of the overall variability of R-R intervals and of the low-frequency components of spectral analysis of heart rate variability. The spectral exponent beta of heart rate variability (1. 123 at rest) was changed by movements (1.364), and the percentage of fractal noise (79% at rest) was increased by standing (91%, coarse-graining spectral analysis). Spontaneous movements could induce a plateau in the correlation dimensions of heart rate variability, but they changed its nonlinear predictability. We suggest that future studies on short-term cardiovascular variability should control spontaneous movements.

Adult↗
PubMed1999

[Fractal analysis and arterial hypertension].

Fractal analysis is a new tool allowing to study the complexity of cardiovascular variability. This approach may be useful for investigating regulatory mechanisms. In fractal terms, homeostasis required an optimal organisation of complexity (beta coefficient close to 1): conversely, some pathological situations have proven to be associated with an altered organisation of fractals (beta coefficient different from 1). Our study aimed at determining if hypertension was associated with an alteration of the fractal component of blood pressure (BP) or heart rate (HR) variability. Eighty-eight subjects referred for high BP entered the study. BP was measured in ambulatory conditions by an automatic device during 24 hours (ABP). BP and HR were then recorded beat-to-beat by a Finapres and an ECG during 30 minutes at rest. The beta coefficient was obtained by coarse-graining spectral analysis from the BP and RR interval time series. This method has proven its interest for breaking down cardiovascular variability into an harmonic component and a non harmonic one, this latter containing fractal elements. Spontaneous baroreflex sensitivity was assessed by the method of sequences. The percentage of fractals contained in BP and RR signals remained relatively stable despite the increasing severity of hypertension. A significant but loose correlation was found between the beta coefficient of RR and ABP (r = 0.23, p = 0.053 with systolic ABP; r = 0.25, p = 0.03 with diastolic ABP). No correlation could be disclosed between ABP and the beta coefficient of BP. The beta coefficient of RR was significantly correlated with the spontaneous baroreflex sensitivity (-0.59, p < 0.0001). It is concluded that it is rather the complexity of HR signal than that of BP which is altered during hypertension. This may suggest that some regulatory processes are lost or less efficient. The correlation reported between the baroreflex gain and the beta coefficient of RR interval may reflect, in fact, an alteration of the parasympathetic drive. Globally, these results emphasise the importance of HR and probably cardiac output in the pathophysiology of high BP.

Baroreflex↗
PubMed1998

Cardiovascular responses to orthostatic tests after a 42-day head-down bed-rest.

Cardiovascular responses to orthostatic tests were studied before and after a prolonged 42 day-head-down bed-rest (HDBR;-6 degrees) experiment simulating a long duration space flight. Seven men participating in the experiment underwent stand tests (10 min) and lower body negative pressure (LBNP) tests (5 min at -25, -35, -45 mmHg). Heart rate variability and spontaneous baroreflex response slope (SBS) were analysed to assess autonomic nervous system responses. Changes in plasma volume (PV) were assessed at the end of HDBR. At the end of HDBR, four subjects could not complete the stand tests and one could not complete the LBNP test. A higher stressed heart rate with standing (+ 44% before and + 57% after HDBR) and LBNP exposure (+ 19% before and + 34% after HDBR) were observed. A decrease in blood pressure (BP) reflecting a reduced vasomotor response was only observed with standing (mean BP + 21% before and -8% after HDBR); LBNP was less sensitive probably because it was performed 6 h after the stand test. The PV decreased by 10.6%. A decline in spectrum total power reflecting a reduced variance of RR-interval, a decrease in parasympathetic activity and an increase in sympathetic one were observed at the end of HDBR. The reduced parasympathetic indicator and SBS would suggest that the vagal nerve component of the cardiovascular control had been diminished. Except for a lower BP when standing after HDBR, no significant difference was observed between finishers and non-finishers. Autonomic nervous system changes including reduced vasomotor responses constituted important contributors to the orthostatic intolerance observed here and after space flights. Some autonomic and PV changes seemed to be opposite to those observed with training and would suggest a role of reduced physical activity in cardiovascular changes induced by HDBR.

Adult↗
PubMed1998

Autonomic control of cardiovascular dynamics during weightlessness.

Measuring cardiovascular dynamics is a new method of assessing the autonomic regulation of the cardiovascular system, it provides an easily-implemented non-invasive way of monitoring the effects of weightlessness on this regulatory function. The major findings of studies on cardiovascular dynamics during actual or simulated weightlessness are presented, taking into account the recent consensus on this approach. Future improvements of these studies are discussed.

Aerospace Medicine↗
PubMed1998

Changes in the sympathetic nervous system induced by 42 days of head-down bed rest.

Changes in autonomic nervous system activity could be linked to the orthostatic intolerance (OI) that individuals suffer after a spaceflight or head-down bed rest (HDBR). We examined this possibility by assessing the sympathetic nervous system activity during 42 days of HDBR in seven healthy men. Heart rate variability was studied with the use of power spectral analysis, which provided indicators of the sympathetic (SNSi) and parasympathetic (PNSi) nervous system influences on the heart. Urinary catecholamines and the spontaneous baroreflex sensitivity were measured. Urinary catecholamines decreased by 21.3%, showing a decrease in SNSi. Heart rate variability was greatly reduced during 42 days of HDBR with a drop in PNSi but with no significant changes in SNSi. The baroreflex sensitivity was greatly reduced (30.7%) on day 42 of HDBR. These results suggest a dissociation between the catecholamine response and the SNSi of the heart rate. This dissociation could be the consequence of an increase in beta-adrenergic receptor density and/or activity induced by a decrease in catecholamines during HDBR. The subjects who suffered from OI also had a greater sympathetic response and much lower baroreflex sensitivity when supine than those who finished the stand test. However, the mean response of all subjects indicated that the sympathetic activity (catecholamine excretion) was probably slightly inhibited during HDBR and could contribute to OI.

Adult↗
PubMed1998

White coat effect and reactivity to stress: cardiovascular and autonomic nervous system responses.

The aim of this study was to elucidate further the precise nature of the so-called "white coat" (WC) effect. We enrolled 88 hypertensive (46 men, 42 women) and 18 normotensive (4 men, 14 women) subjects in whom beat-to-beat blood pressure (BP) and heart rate (HR) were measured with a Finapres device at rest (R period) and during conventional BP measurement (WC period). The WC effect was defined as WC period minus R period values of Finapres systolic BP. Using the same method, we also measured the BP and HR variations induced by mental stress (MS period) and by assuming the standing position (S period). Variability was estimated in the frequency domain for BP (BPV) and HR (HRV) and gave indices of the autonomic nervous system. Pulse wave velocity was taken as an index of arterial distensibility. In hypertensive subjects, the WC effect was significantly and positively correlated with the BP response to stress (0.51, P<.0001) and standing (0.63, P<.0001). An increased BPV was observed in the low-frequency band (0 to 0.150 Hz) during WC, MS, and S periods. In normotensive subjects, the WC effect was very slight and not correlated with the responses to stress and standing. In this group, the WC period was not accompanied with an increased BPV, unlike the stress and standing periods. HRV was similar in normotensives and in hypertensives: decreased, unchanged, and increased during MS, S, and WC periods, respectively. The PWV was significantly increased in the hypertensives relative to the normotensives, even in the quartile of those with the lowest BP (on average similar to that of the normotensives). This work shows that the WC effect is associated with an enhanced BP response to standing and mental stress; these three situations are characterized by an increased BPV in the low frequencies, suggesting a similar modification of the sympathovagal balance. The WC effect may entail an increased risk because it is associated with impaired arterial distensibility.

Adult↗
PubMed1998

Human cardiovascular variability, baroreflex and hormonal adaptations to a blood donation.

1. We studied cardiovascular variability, baroreflex and blood volume regulating hormones to determine the relative roles of autonomic regulation and hormones during blood donation.2. The sympathetic response was studied by measuring the R-R interval and systolic blood pressure variability using coarse graining spectral analysis in eight blood donors. Beat-by-beat R-R intervals and blood pressure were recorded for 20 min before and 5 min after a whole-blood donation of 480+/-10 ml (about 7 ml/kg of blood volume, over 4 min). Plasma catecholamines, vasopressin, atrial natriuretic peptide, endothelin, active renin, osmolality, Na+, K+, haemoglobin and haematocrit were measured just before and after blood withdrawal.3. Blood donation led to increases in the plasma catecholamines (adrenaline, 21+/-2 versus 35+/-3 pg/ml; noradrenaline, 229+/-26 versus 323+/-37 pg/ml; dopamine, 34+/-3 versus 66+/-9 pg/ml) and in systolic blood pressure (130+/-6 versus 140+/-5 mmHg). These changes were independent of ionic or slow endocrine mechanisms. Heart rate, cardiovascular variability and the spontaneous baroreflex sensitivity did not change despite the increase in blood pressure and catecholamines. Thus the peripheral vascular control was probably involved.4. We conclude that the absence of any change in heart rate usually observed during non-hypotensive hypovolaemic stress is probably due to the sympathetic activation being counterbalanced by the high supine vagal tone at the heart and not to the heterogeneous nature of the sympathetic neural response or to changes in sympathetic and parasympathetic activity without any change in autonomic balance.

Adult↗
PubMed1997

Respiratory influences on non-linear dynamics of heart rate variability in humans.

The goal of our study was to determine whether evidence for chaos in heart rate variability (HRV) can be observed when the respiratory input to the autonomic controller of heart rate is forced by the deterministic pattern associated with periodic breathing. We simultaneously recorded, in supine healthy volunteers, RR intervals and breathing volumes for 20 to 30 min (1024 data point series) during three protocols: rest (control), fixed breathing (15 breath/min) and voluntary periodic breathing (3 breaths with 2 s inspiration and 2 s expiration followed by an 8 s breath hold). On both the RR interval and breathing volume series we applied the non-linear prediction method (Sugihara and May algorithm) to the original time series and to distribution-conserved isospectral surrogate data. Our results showed that, in contrast to the control test, during both fixed and voluntary periodic breathing the variability of breathing volumes was clearly deterministic non-chaotic. During all the three protocols, the RR-interval series' non-linear predictability was consistent with one of a chaotic series. However, at rest, no clear difference was observed between the RR-interval series and their surrogates, which means that no clear chaos was observed. During fixed breathing a difference appeared, and this difference seemed clearer during voluntary periodic breathing. We concluded that HRV dynamics were chaotic when respiration was forced with a deterministic non-chaotic pattern and that normal spontaneous respiratory influences might mask the normally chaotic pattern in HRV.

Adult↗
PubMed1997

Orthostatic tests after a 4-day confinement or simulated weightlessness.

Besides microgravity, inactivity is likely to play a role in the cardiovascular deconditioning after space flights and weightlessness simulations. The aim of the study was to compare the effects of a 4-day head-down bed rest (HDBR) (-6 degrees) and a 4-day confinement (C) on cardiovascular responses to orthostatic stress. Eight male subjects underwent head-up tilt (HUT) (+60 degrees) and lower-body negative pressure (LBNP) (-20, -30, -40 and -50 mmHg) before (D-1) and at the end (R1) of each situation. Blood pressure, heart rate variability (HRV) and spontaneous baroreflex slope (SBS) were determined. The HDBR reduced orthostatic tolerance, as five subjects presented orthostatic hypotension during the HUT at R1, compared with two subjects at D-1. These same two subjects presented orthostatic hypotension after confinement. The main findings, after HDBR, included reductions in RR interval and total spectral power and a decrease in the parasympathetic indicator (PNS) in favour of a decrease in vagal tone; the increase in the sympathetic indicator (SNS) was not significant. After confinement, the RR interval was also significantly reduced and PNS decreased, but not significantly. RR interval and PNS were further reduced during HUT and LBNP, reflecting a withdrawal of parasympathetic activity. SBS was reduced after HDBR (P < 0.05) and confinement (P = 0.05), with a further reduction during HUT and LBNP without difference between D-1 and R1. This experiment showed that a 4-day HDBR leads to impaired baroreflex function and changes in autonomic balance, which may contribute to orthostatic intolerance. Although less significant, similar patterns of changes in the autonomic nervous system were observed after confinement, suggesting an influence of the inactivity in cardiovascular deconditioning.

Adult↗
PubMed1997

Cardiovascular and hormonal changes induced by a simulation of a lunar mission.

BACKGROUND: This is the first simulation of a 14-d lunar mission including 6 d on the Moon. HYPOTHESIS: We hypothesized that a lunar gravity simulation in the middle of a head-down tilt (HDT) might result in some reversal of body fluid/hormonal responses, and influence cardiovascular deconditioning. METHODS: Six men (28 +/- 2.5 yr) were placed in bed rest (BR): in (HDT) (-6 degrees) to simulate microgravity during the travel (two 4-d periods), and in head-up tilt (HUT) (+10 degrees) (6-d period) to simulate lunar gravity (1/6 g). Muscular exercise was performed during the HUT period to simulate 6 h of lunar EVA. Heart rate variability (HRV) and hormonal responses were studied. RESULTS: An orthostatic arterial hypotension was observed after the BR (tilt test) in 4 of the 6 subjects. Plasma volume measured at D14 decreased by -11.1% (vs. D-3, sitting position). A decrease in atrial natriuretic peptide (26 +/- 3.5 pg.ml-1 (D14) vs. 37.9 +/- 3.5 pg.ml-1 (D-3, sitting) and an increase in plasma renin activity (198 +/- 9.2 mg.L-1.min-1 (D14) vs. 71 +/- 9.2 mg.L-1.min-1 (D-3, sitting) were observed during the BR, more pronounced in HUT at 7:00 p.m. Sympathetic-parasympathetic balance (HRV) at rest showed a decrease in parasympathetic indicator and an increase in sympathetic indicator in BR (p < 0.05), without differences within HDT and HUT periods. CONCLUSION: These changes were mostly similar to those reported in spaceflights, and HDT. Although the exposure to 1/6 g with exercise modified some hormonal and body fluid responses, this partial gravity simulation was not sufficient to prevent the decrease in orthostatic tolerance observed here as well as after Apollo lunar missions.

Adult↗