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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.

International audience; PURPOSE: To evaluate the agreement and diagnostic accuracy of Contrast enhanced magnetic resonance angiography (CE-MRA), Doppler ultrasound (DUS) and Digital subtraction angiography (DSA) in the assessment of carotid stenosis. METHODS: DUS, CE-MRA and DSA were performed in 56 patients included in the Carotide-angiographie par résonance magnétique-échographie-doppler-angioscanner (CARMEDAS) multicenter study with a carotid stenosis ≥ 50%. Three readers evaluated stenoses on CE-MRA and DSA (NASCET criteria). Velocities criteria were used for stenosis estimation on DUS. RESULTS: CE-MRA had a sensitivity and specificity of 96-98% and 66-83% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 94% and 76-84% respectively for carotid stenoses ≥ 70%. The interobserver agreement of CE-MRA was excellent, except for moderate stenoses (50-69%). DUS had a sensitivity and specificity of 88 and 75% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 83 and 86% respectively for carotid stenoses ≥ 70%. Combined concordant CE-MRA and DUS had a sensitivity and specificity of 100 and 85-90% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 96-100% and 80-87% respectively for carotid stenoses ≥ 70%. The positive predictive value of the association CE-MRA and DUS for carotid stenoses ≥ 70% is calculated between 77 and 82% while the negative predictive value is calculated between 97 and 100%. CE-MRA and DUS have concordant findings in 63-72%, and the overestimations cases were recorded only for carotid stenosis ≤ 69%. CONCLUSION: Combined DUS-CE-MRA is excellent for evaluation of severe stenosis but remains debatable in moderate stenosis (50-69%) due to the risk of overestimations.

Dejours[5] was one of the first to comment on the breath-by-breath variations in ventilation (V,:) and gas exchange (oxygen uptake, VO2, and carbon dioxide output, VCO2). It was suggested that the spontaneous variations in alveolar ventilation and perfusion of the lungs, as well as variations in venous blood O2 and CO2 content, were responsible for these breath-by-breath patterns. He observed that all fundamental respiratory variables varied around the mean value. Since that time, there have been many other observations of breath-by-breath variation in the breathing pattern. Lenfant[13] further characterized the pattern of variation, and Hlastala et al.[9] observed cyclical variations in functional residual capacity (FRC). Attempts to quantify the breath-by- breath variation have ranged from computation of autocorrelation functions by Benchetrit and Bertrand,[1] to analysis of run times[2] to more recent methods of spectral analysis,[11],[24] and of chaos theory[6],[15],[17]–[19]. The implication of fractal and/or chaotic behaviour in the breathing pattern has wide ranging consequences including, for chaotic systems, the requirement that the system be deterministic. The purpose of this paper is to explore further whether patterns of breathing are consistent with the properties of fractal or chaotic systems

The reliability of duplex scanning (DS) for the diagnosis of internal carotid artery dissections (ICAD) is not clear.Nine DS signs known to be suggestive for the diagnosis of ICAD were compared between 70 patients with ICAD and 70 matched patients without dissection.Visible internal tapering occlusion, regular eccentric narrowing channel, ectasia beyond the carotid bulb, resistive index asymmetry, blood flow slowdown, ophthalmic artery blood flow inversion, and biphasic flow are more frequent in cases than in controls (p0.001). Atheroma plaques were absent in 80% of ICAD. When DS direct signs and hemodynamic signs were studied, sensitivity was 90% and specificity 60%.Diagnosis of ICAD by DS could be improved if direct signs were combined with hemodynamic signs, giving a high sensitivity and a rather good specificity.

Thigh cuffs are used by Russian cosmonauts to limit the fluid shift induced by space flight. A ground simulation using the head-down bed rest (HDBR) model was performed to assess the effects of thigh cuffs on clinical tolerance and orthostatic adaptation. 8 male healthy volunteers (32.4 +/- 1.9 years) participated twice in a 7-day HDBR--one time with thigh cuffs (worn daily from 9 am to 7 pm) (TC) and one time without (WTC). Orthostatic tolerance was assessed by a 10 minute stand test and by a LBNP test (5 min at -15, -30, -45 mmHg) before (BDC-1) and at the end of the HDBR period (R+1). Plasma volume was measured before and at the end of HDBR by the Evans blue dye dilution technique. Thigh cuffs limits headache due to fluid shift, as well as the loss in plasma volume (TC: -5.85 +/- 0.95%; WTC: -9.09 +/- 0.82%, p0.05). The mean duration of the stand test (R+1) did not differ in the two group (TC 7.1 +/- 1.3 min; WTC 7.0 +/- 1.0 min). The increase in HR and decrease in diastolic blood pressure were slightly but significantly larger without thigh cuffs. Duration of the LBNP tests did not differ with thigh cuffs. Thigh cuffs limit the symptoms due to fluid shift and the loss in plasma volume. They partly reduced the increase in HR during orthostatic stress but had no effect on duration of orthostatic stress tests.

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.

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, P0.05), 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.

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.

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, p0.0001). 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.

This study was aimed to compare the white coat effect and the response to a mental stress. 29 subjects, referred for high blood pressure (BP) were included. Systolic BP (SBP) was recorded beat-to-beat with a Finapres device during 3 periods of at least 5 minutes: 1) rest (alone, in lying position); 2) white coat (5 measurements of BP with a standard mercury sphygmomanometer by the same physician); 3) mental stress (version for computer of the Stroop Word Color Conflict Test). A Coarse-graining spectral analysis was performed to compute the power in the low frequency band (PLF: 0-0.150 Hz) and in the high frequency band (PHF: 0.150-0.500 Hz). SBP was 142 +/- 3.7 during the rest period and increased significantly during the white coat (156.7 +/- 3.9 mmHg) and the mental stress (190.7 +/- 4.8 mmHg) periods. These rises of SBP levels were associated with a rise of PLF, significant only during mental stress (11.3 +/- 1.4, 15.7 +/- 3.7, 17.2 +/- 2.4 mmHg2/Hz, during rest, white coat and mental stress periods, respectively). Moreover, a significant correlation (r = 0.76; p0.0001) was found between the white coat effect (PAS "white coat"-PAS "rest") and the response to stress (PAS "stress"-PAS "rest"). This work shows that white coat effect is not a specific response but may rather represent an increased reactivity to stress. As it is associated with an increased power in the LF band like the response to stress, this white coat effect may involve an activation of the sympathetic system.

It is possible that the pattern of breathing can provide some information about the characteristics of the controller. Benchetrit and Bertrand (1) observed an autocorrelation that was consistent with the hypothesis of a short-term memory in the respiratory control centre. Recently, the newer mathematical techniques of fractal geometry and chaos theory have been applied to studies of the breathing pattern. We described the pattern of ventilation \(\left( {{{\dot V}_E}} \right)\)and gas exchange of humans during exercise to be fractal on the basis of the linearity of the log spectral power versus log frequency relationship (6) during exercise. In this volume, Tuck et al. (15) have described a similar pattern of response for resting ventilatory variability. The linear (so-called 1/f) relationship suggests a long-term correlation. The implication is that the pattern of breathing is influenced over a large number of breaths by past events. As hypothesized for the cardiovascular control mechanisms (2,17), the fractal pattern might be used in effecting control over the homeostasis of the ventilatory events.

The effect of exercise and LBNP countermeasures on the cardiovascular deconditioning response have been evaluated by the study of heart rate variability during progressive LBNP tests before, during (day 15), and after 28 d continuous 6 degrees head-down tilt bed rest. Twelve healthy men (age 27-42 years) were studied in two groups. Six were assigned to a countermeasure regime (CM) consisting of strenuous short-term resistance exercise once per day, 6 days per week from day 7 to day 28, combined with lower body negative pressure (LBNP, -28 mm Hg) for 15 min on days 16, 18, 20, and 22-28. Results were compared with data from six subjects, matched on the basis of maximum oxygen uptake, who received no countermeasures (No-CM). The main effects of bed rest were seen in reductions in RR-interval, and in total spectral power. The results of spectral analysis showed a significant reduction in an index of parasympathetic activity with a nonsignificant increase in a sympathetic indicator. The fractal component of heart rate variability was reduced also, suggesting a change in cardiovascular control mechanisms. Although there were significant differences between CM and No-CM for a number of variables, there were no bed rest by countermeasure interaction effects in the statistical analysis. These results suggested that this particular series of countermeasures was ineffective in preventing at least certain changes indicative of cardiovascular deconditioning with 28 d head-down tilt bed rest.

The aim of this study was to determine what effects social isolation and confinement stress had on the volume regulating hormones. In six healthy male subjects, during a 28-d isolation and confinement study (ESA-ISEMSI'90), hematocrit, blood pressure and resting heart rate, plasma cortisol, renin, aldosterone, arginine vasopressin levels besides the electrolyte (Na+, K+) balance and plasma creatinine were measured. During the confinement, an elevated systolic blood pressure (p0.01) was observed together with an increase in MHPG corresponding to an elevated mental work load. The pattern displayed by volume regulating hormones (increased values for renin, aldosterone (p0.05) and arginine vasopressin) was not only characteristic of confinement stress but also reflected changes in the water and electrolyte metabolism. The increased creatinine levels seen throughout the study were regarded as consequences of hypohydration, and an enhanced muscular catabolism due to reduced physical activity. A similar pattern of hormone modifications was obtained in a head down tilt of the same duration, indicating that some of the described modifications are probably related to isolation and confinement stress.

In the ISEMSI confinement experiment we observed three main reactions concerning blood volume regulation: first, a stress activation produced by the high workload that the subjects had to accomplish, both before the isolation period and during the two first weeks of isolation; second, a typical defense reaction to the environment occurred, at least during the two initial days of isolation and later perhaps between crew members themselves; and third, a change in blood volume regulating hormone levels may have been the result of the increase of sympathetic system activity and of dehydration. Confinement is certainly a good and valid method to simulate space station life (with the absence of weightlessness). So, it is interesting to use these confinement studies to perform biological and physiological experiments to obtain greater knowledge, but also to prepare and validate new scientific protocols or new scientific equipment suitable for spaceflights. Even more so, confinement is a good way to prepare and train crew members for long-term space missions. It would seem desirable to confirm the scientific results obtained during the ISEMSI campaign, and especially those for the regulation of the blood volume. This will be done during the next confinement experiment, called EXEMSI, in which four subjects will be subjected to 60 days of confinement.

The purpose of the present study was to investigate the basic fractal nature of the variability in resting heart rate (HRV), relative to that in breathing frequency (BFV) and tidal volume (TVV), and to test the hypothesis that fractal HRV is due to the fractal BFV and/or TVV in humans. In addition, the possible fractal nature of respiratory volume curves (RVC) and HRV was observed. In the first study, eight subjects were tested while they sat quietly in a comfortable chair for 60 min. Beat-to-beat R-R intervals, i.e., HRV, and breath-by-breath BFV and TVV were measured. In the second study, six subjects were tested while they were in the supine position for 20-30 min. The RVC was monitored continuously together with HRV. Coarse-graining spectral analysis (Yamamoto, Y., and R. L. Hughson, Physica D 68: 250-264, 1993) was applied to these signals to evaluate the percentage of random fractal components in the time series (%Fractal) and the spectral exponent (beta), which characterizes irregularity of the signals. The estimates of beta were determined for each variable only over the range normally used to evaluate HRV. Values for %Fractal and beta of both BFV and TVV were significantly (P < 0.05) greater than those for HRV. In addition, there was no significant (P > 0.05) correlation between the beta values of HRV relative to either BFV (r = 0.14) or TVV (r = 0.34). RVC showed a smooth oscillation as compared with HRV; %Fractal for RVC (42.3 +/- 21.7%, mean +/- SD) was significantly (P < 0.05) lower than that for HRV (78.5 +/- 4.2%).(ABSTRACT TRUNCATED AT 250 WORDS)