Ventilatory thresholds determined from HRV: comparison of 2 methods in obese adolescents.

The development of personalised training programmes is crucial in the management of obesity. We evaluated the ability of 2 heart rate variability analyses to determine ventilatory thresholds (VT) in obese adolescents. 20 adolescents (mean age 14.3±1.6 years and body mass index z-score 4.2±0.1) performed an incremental test to exhaustion before and after a 9-month multidisciplinary management programme. The first (VT1) and second (VT2) ventilatory thresholds were identified by the reference method (gas exchanges). We recorded RR intervals to estimate VT1 and VT2 from heart rate variability using time-domain analysis and time-varying spectral-domain analysis. The coefficient correlations between thresholds were higher with spectral-domain analysis compared to time-domain analysis: Heart rate at VT1: r=0.91 vs. =0.66 and VT2: r=0.91 vs. =0.66; power at VT1: r=0.91 vs. =0.74 and VT2: r=0.93 vs. =0.78; spectral-domain vs. time-domain analysis respectively). No systematic bias in heart rate at VT1 and VT2 with standard deviations <6 bpm were found, confirming that spectral-domain analysis could replace the reference method for the detection of ventilatory thresholds. Furthermore, this technique is sensitive to rehabilitation and re-training, which underlines its utility in clinical practice. This inexpensive and non-invasive tool is promising for prescribing physical activity programs in obese adolescents.

Effects of aqueous hop (Humulus Lupulus L.) extract on vascular reactivity in rats: mechanisms and influence of gender and hormonal status.

Phytoestrogens, naturally occurring plant compounds having oestrogenic and/or anti-oestrogenic activity, are present in many human foodstuffs including hop. Moderate intakes of isoflavonoid phytoestrogens have been associated with a reduction in cardiovascular diseases incidence. So, it is possible that hop (Humulus Lupulus L.) might similarly contribute to the reported health-beneficial effects of moderate beer consumption. Thus, the purpose of this study was to investigate in vitro effects of aqueous hop extract on thoracic vascular reactivity in Sprague Dawley male and female rats. Endothelium-intact thoracic arterial rings from male rats (MALE, n=8), sham-ovariectomized (Sham OVX) female (n=8) and ovariectomized (OVX) female rats (n=8) were used. We assessed the relaxation induced by aqueous hop extract (10(-9), 10(-2)g/l) in aortic rings precontracted with norepinephrine (10(-7)M), in the absence or in the presence of l-NAME (10(-4)M), indomethacin (10(-5)M), thapsigargin (10(-4)M), iberiotoxin (3.10(-8)M), apamin (3.10(-8)M) and TEA (3.10(-4)M). Aqueous hop extract induced relaxation of endothelium-intact thoracic arterial rings in MALE and Sham OVX rats, whereas a weak effect was observed in OVX rats. This vasorelaxation was strongly inhibited in presence of l-NAME, indomethacin and thapsigargin. These data indicated that aqueous hop extract-induced vasodilation, in male and intact female rats, is mediated by NOS activation, cyclooxygenase products and Ca(2+) pathways. Moreover, our results suggested that effect of hop in enhancing vascular reactivity was independent of gender but strongly related to hormonal status.

Physical training decreases total plasma homocysteine and cysteine in middle-aged subjects.

AIMS: The aim of this study was to evaluate whether endurance exercise in middle-aged men induces changes in plasma total homocysteine (tHcy) and total cysteine (tCys), and whether these changes depend on the diet especially on vitamin B(6), folic acid and vitamin B(12) intakes. METHODS: Twelve trained subjects (52.33 +/- 2.4 years) and twelve untrained subjects (56.23 +/- 0.9 years) volunteered for the present study. tHcy and tCys were measured with high-pressure liquid chromatography at rest in both groups and during an incremental exercise performed on a cycle ergometer until exhaustion in the trained subjects. RESULTS: At baseline homocysteinemia and cysteinemia were lower in trained subjects (7.48 +/- 0.4 and 183.45 +/- 13.6 micromol/l) compared with untrained subjects (9.79 +/- 0.4 micromol/l, p < 0.001; 229.01 +/-14.7 micromol/l, p < 0.05, respectively). Incremental exercise also induced a decrease in tHcy and tCys concentrations. Moreover, tHcy concentration was negatively related to the folic acid and B(12) intakes in untrained (r = -0.589, p < 0.05; r = -0.580, p < 0.05, respectively) as well as in trained groups (r = -0.709, p < 0.01; r = -0.731, p < 0.01, respectively) whereas no correlation between tCys and vitamin in the diet was observed. CONCLUSION: This study demonstrates that the combined effects of a chronic physical exercise and a high folate and vitamin B(12) intake could be responsible for the reduction of plasma tHcy and tCys concentrations that might be a key for the prevention of many diseases.

Effect of a swim training on homocysteine and cysteine levels in rats.

The purpose of this study was to investigate the effects of a 8-week of swim training on total plasma homocysteine and cysteine levels in 16 male Sprague-Dawley rats aged 17 weeks. We also evaluated the activity of hepatic cystathionine beta-synthase (CBS), an enzyme involved in the metabolism of Hcy, the concentration of plasma glutathione, taurine, and a fraction of vitamin B6: the pyridoxal 5-phosphate (PLP). After one week of acclimatization, rats were randomly divided into two groups: 8 non-trained (NTR) and 8 trained rats (TR). Following the training period, body weight gain was lower in TR than in NTR. Plasma homocysteine did not differ among groups while significantly lower plasma cysteine and taurine levels were found in TR (157.83 +/- 8.6 micromol/L; 133.01 +/- 9.32 micromol/L; P < 0.05) compared with data of NTR (176.19 +/- 4.9 micromol/L; 162.57 +/- 8.16 micromol/L; P < 0.05). No significant changes in hepatic CBS activity were observed in TR compared with NTR. Moreover, values for plasma glutathione and PLP concentrations were not affected by training.These results indicate that training reduces plasma cysteine and taurine levels whereas it does not modify other studied parameters. Thus, physical training may regulate cysteine metabolism.

Managing educational resource in medicine: system design and integration.

The objective of this paper is to describe our experience in developing a tool based on web technologies, for storing, managing and providing medical courses written by professors in the medical university of Rennes. The increasing number of documents sent by professors leaded us to build a specific resource management system. We created a relational database, containing all meta information about each available document. Professors provide their courses in various formats. We use natural language parsing techniques to extract information from the text, and provide a proper semantic indexation which will be used by a medical-specific search engine. Then the content of our database is dynamically displayed on a web interface. A user's directory identifies teachers and students, controls the access, tracks the students' navigation and allows an on-line discussion forum. This portal contains 524 courses and we had more than 3,000,000 connections on it last year. We are now integrating its content using the semantic web approach in a larger project: the French Virtual Medical University.

Specific and transfer effects induced by arm or leg training.

The purpose of the present study was to examine both the specific and the transfer effects of a Square Wave Endurance Exercise Test (SWEET) and to investigate the determining factors of transfer effect. A control group (CG, n = 5) and 2 experimental groups were studied. Experimental groups completed 3 days/week a 45 min SWEET over 6 weeks, either with the arms using a wheelchair ergometer (AG, n = 5) or with the legs using a cycling ergometer (LG, n = 5). All subjects performed before and after training two maximal progressive tests: the first one with the arms and the second with the legs. During those tests oxygen uptake (VO(2)) and cardiorespiratory parameters were continuously measured. Specific effects (changes between the tests performed with trained limbs) were observed: the peak power output (W(p)) and VO(2) were significantly increased by both arm (+ 66 %, + 35 %) and leg (+ 17 %, + 14 %) training. At ventilatory threshold (VT), power output (W) and VO(2) were significantly increased with arm (+ 145 % and + 51 %) and leg (+ 53 % and + 46 %) training. Transfer effects (changes between pre and post tests performed with untrained limbs) were observed: W(p) and VO(2) were not increased in AG while W(p) was increased in LG (+ 11 %). At VT, W and VO(2) were increased with arm (+ 19 % and + 23 %) and leg (+ 33 % and + 46 %) training. For AG and LG the VO(2) expressed in percent of the VO(2) peak was increased (+ 19 % and + 33 %, respectively) and the O(2p) was also increased (+ 30 %) for LG. These results show that SWEET training induced specific and transfer effects. Moreover, the initial level of the subjects, the type and the intensity of the training seem to be the major factors for effective observable transfer effects.

Hormonal responses to exercise after partial sleep deprivation and after a hypnotic drug-induced sleep.

The aim of this study was to determine the hormonal responses, which are dependent on the sleep wake cycle, to strenuous physical exercise. Exercise was performed after different nocturnal regimens: (i) a baseline night preceded by a habituation night; (ii) two nights of partial sleep deprivation caused by a delayed bedtime or by an early awakening; and (iii) two nights of sleep after administration of either a hypnotic compound (10 mg zolpidem) or a placebo. Eight well-trained male endurance athletes with a maximal oxygen uptake of 63.5 +/- 3.8 ml x kg(-1) x min(-1) (mean value +/- s(x)) were selected on the basis of their sleeping habits and their physical training. Polygraphic recordings of EEG showed that both nights with partial sleep loss led to a decrease (P< 0.01) in stage 2 and rapid eye movement sleep. A delayed bedtime also led to a decrease (P < 0.05) in stage 1 sleep. Zolpidem had no effect on the different stages of sleep. During the afternoon after an experimental night, exercise was performed on a cycle ergometer. After a 10-min warm-up, the participants performed 30 min steady-state cycling at 75% VO(2-max) followed by a progressively increased workload until exhaustion. The recovery period lasted 30 min. Plasma growth hormone, prolactin, cortisol, catecholamine and lactate concentrations were measured at rest, during exercise and after recovery. The concentration of plasma growth hormone and catecholamine were not affected by partial sleep deprivation, whereas that of plasma prolactin was higher (P < 0.05) during the trial after an early awakening. Plasma cortisol was lower (P < 0.05) during recovery after both sleep deprivation conditions. Blood lactate was higher (P < 0.05) during submaximal exercise performed after both a delayed bedtime and an early awakening. Zolpidem-induced sleep did not affect the hormonal and metabolic responses to subsequent exercise. Our results demonstrate only minor alterations in the hormonal responses to exercise after partial sleep deprivation.

Influence of exercise duration on serum insulin-like growth factor and its binding proteins in athletes.

The changes in circulating concentrations of insulin-like growth factors during exercise have to date remained incomplete in their documentation. Therefore, we examined in 25 healthy athletes the effects of three different durations of three types of exercise -- incremental ergometer cycling exercise (ICE), long-distance Nordic ski race (NSR) and a treadmill-simulated soccer game (TSG) lasting 20 min, 3 h, and 2 x 45 min separated by a 15-min half-time rest respectively, on plasma concentrations of growth hormone ([GH]), insulin-like growth factor-1 ([IGF-I]) and its binding proteins 1 and 3 ([IGFBP-1], [IGFBP-3]). Compared to baseline, serum [GH] increased by 15.2-fold after ICE (P < 0.001), 2.9-fold after NSR (P < 0.01) and 4.6-fold after TSG. Serum [IGF-I] rose by 11.9% after ICE (P < 0.001), while it decreased by -14.6% after NSR (P < 0.001) and was unchanged after TSG. Serum [IGFBP-1] was slightly increased (1.7-fold) after ICE (P < 0.01), but increased markedly (11.8-fold) after NSR (P < 0.001) and by 6.3-fold after the second session of TSG (P < 0.01) (it remained unchanged at the end of the first period of TSG, i.e. after 45-min exercise). The [IGFBP-3] increased by 14.7% after ICE (P < 0.001) and by 6% after TSG (P < 0.05) while it did not change after NSR. From our results it would appear that [IGFBP-1] increase to bind free IGF and hinder their insulin-like action during long-term exercise (lasting beyond 45 min). It is suggested that IGFBP-1 might thus contribute both to preventing hypoglycaemic action of IGF and to facilitating glucose uptake by muscle cells when muscle glycogen stores become deplete.

Effects of a selective sleep deprivation on subsequent anaerobic performance.

The aim of the study was to investigate the effects of a partial sleep deprivation on a subsequent supramaximal exercise evaluated from the 30 second Wingate test, and on the following recovery. To take into account the active muscle mass, the Wingate test was performed against a constant braking force related to the data of a force-velocity test conducted on a Monark cycle ergometer (Model 814 E with weights) one week before the experimental test. Eight highly trained athletes were enrolled for this study. The changes in ventilatory and metabolic responses were analyzed during and upon completion of physical 30 second exercise, taking place after two nights, in other words, after a reference night and after a night with reduced sleep. Partial sleep deprivation was obtained by delaying bedtime until 3 a.m. The 30 second Wingate test was performed between 9 a.m. and noon the following days, using a Monark ergometer (Model 814 F). The analyses of change scores disclosed that there were no main significant effects for measures of ventilation, lactates and pH(v) levels under the two experimental conditions. The peak power, the mean power output and the peak velocity recorded after partial sleep deprivation were not modified in comparison with the values obtained after the reference night. These findings suggest that acute sleep loss did not contribute to alterations in supramaximal exercise.

Effects of gallium chloride on changes in action potentials and contraction in guinea pig ventricular muscle.

The electrophysiological effects of gallium chloride (Ga ) and its activity on arrhythmias induced by digitalis were investigated in guinea pig papillary muscle. KCl microelectrodes were used to record transmembrane electrical activity from Purkinje cells from the papillary muscle of guinea pig hearts during superfusion and electrical stimulation in vitro at 37 degrees C. Myocardial contractility was continuously monitored. Ga was superfused alone in cumulative concentrations(4.5 . 10(-5) to 3.6 . 10(-4) M). Arrhythmias were induced by a superfusion of Digitoxin (7.5 . 10 (-7) M). A superfusion of Ga (4.5 . 10(-5), 9 . 10(-5), 1.8 . 10(-4) M and 3.6 . 10(-4) M) was started 20 min later and maintained for 70 min. Ga alone produced a dose dependent reduction of action potential duration and contractility. Ga potentiated the decrease in the amplitude and duration of the action potential induced by Digitoxin. The incidence of arrhythmias was immediately reduced by two concentrations of Ga (4.5 . 10(-5) and 9 . 10(-5) M) in the digitalized papillary muscles. It is concluded that Ga inhibits calcium movements and has negative inotropic and antidysrhythmic effects.

[Effect of night medical guard on following day vigilance. Influence of hypnotic drug on recovery night and on the vigilance during the following day]. / Effet d'une nuit de garde médicale sur la vigilance du lendemain. Influence d'un hypnotique sur la nuit de récupération et la vigilance dans la journée qui suit.

The consequences of sleep deprivation on vigilance and mood were evaluated in six healthy medical students the day after being on night duty and the following day, after recovering from a full night's sleep. Diurnal vigilance was studied using the Multiple Sleep Latency Test (MSLT) and mood was assessed on an anxiety self-evaluation scale. The study was conducted by means of a double-blind randomized trial to measure the effects of benzodiazepine (lormetazepam, 2 mg) compared to a placebo administered before the night recovery/full night's sleep. Sleep deprivation induced a significant decrease in vigilance the day following the night duty. Sleep latencies were shortened during the morning following the night of recovery/full night's sleep. The values obtained after administering the lormetazepam did not differ significantly from those obtained after administering the placebo. There were no considerable differences in the anxiety evaluation scores before and after the night of recovery/full night's sleep between the two sequences of the trial. This study suggests that a significant lack of sleep (a 36-hour sleep deficit) modifies diurnal vigilance over two nyctohemeral periods. Administration of benzodiazepine with a short half-life after occasional sleep deprivation does not change the reorganization of the sleep-waking cycle.

[Tolerance to exertion after sleep reduction and after taking a hypnotic: zolpidem]. / Tolérance à l'effort après réduction de sommeil et après prise d'un hypnotique: le zolpidem.

The aim of the present study was to investigate the effects of a delayed bedtime (3 a.m.), an advanced rising (3 a.m.), a sleep under placebo and under a hypnotic compound, i.e. 10 mg of zolpidem (Stilnox) on sleep structure and on the adaptations to a subsequent exercise in 8 male athletes. The chronology of these nights was randomized and each treatment administered in a double blind fashion. During each experimental night, subjects were monitored with conventional EEG/EOG/EMG polygraphic recordings. The next day, athletic performance was tested using a bicycle ergometer. A codified exercise was performed and consisted to a 10 min warm up followed by a 30 min steady state cycling corresponding to 75% of predetermined VO2 max. Then the work load increased progressively by steps of 10 W every minute until exhaustion. The recovery lasted 30 min. Heart rate, ventilation, VO2, ERO2 were monitored during all exercise and recovery. Plasma lactates and catecholamines were also measured at the same time. The data concerning sleep recordings showed that both nights with partial sleep deprivation resulted in a drop of time spent in slow wave sleep II (decrease of 55%) and in rapid eye movement sleep (decrease of 45%) while the amount of slow wave sleep III and IV were identical to that observed after the reference night. The sleep onset latency and the amount of sleep in stage I was reduced only after the delayed bedtime. Sleep data under zolpidem did not show any significantly difference in the amount of different sleep stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Met-enkephalin, beta-endorphin and cortisol responses to sub-maximal exercise after sleep disturbances.

The present study compared the effects of partial sleep deprivation and the effects of an intake of a hypnotic compound (zolpidem) prior to bedtime, on sleep and on hormonal and metabolic adaptations to subsequent exercise. Sleep deprivation consisted of a delayed bedtime and an early getting-up time. Eight young subjects, who slept well and were highly trained athletes, were enrolled in this study. Sleep was recorded polygraphically and the following afternoon exercise was performed on a cycle ergometer for 30 min at 75% of maximal oxygen consumption (VO2max) after a 10-min warm up. Met-enkephalin, beta-endorphin, cortisol, and lactate concentrations were measured at rest and during exercise. The data obtained after experimental sleep, with and without medication were compared with those obtained in the reference condition with normal sleep. Both types of sleep reduction decreased the total sleep time, stage 2 sleep, and rapid eye movement sleep, whereas zolpidem administration did not modify either the duration of sleep or the sleep stages. After the reference night, plasma met-enkephalin did not show any significant change at the end of the submaximal exercise, whereas beta-endorphin, cortisol, and lactic acid concentrations increased significantly in all subjects. The changes in concentration in beta-endorphin were significantly related to the changes in cortisol (r = 0.78; P less than 0.01) and to the changes in plasma lactic acid (r = 0.58; P less than 0.05). Cortisol concentrations were also related to lactic acid values (r = 0.94; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of sleep disturbances on subsequent physical performance.

The purpose of the study was to compare the cardiovascular, respiratory and metabolic responses to exercise of highly endurance trained subjects after 3 different nights i.e. a baseline night, a partial sleep deprivation of 3 h in the middle of the night and a 0.25-mg triazolam-induced sleep. Sleep-waking chronobiology and endurance performance capacity were taken into account in the choice of the subjects. Seven subjects exercised on a cycle ergometer for a 10-min warm-up, then for 20 min at a steady exercise intensity (equal to the intensity corresponding to 75% of the predetermined maximal oxygen consumption) followed by an increased intensity until exhaustion. The night with 3 h sleep loss was accompanied by a greater number of periods of wakefulness (P less than 0.01) and fewer periods of stage 2 sleep (P less than 0.05) compared with the results recorded during the baseline night. Triazolam-induced sleep led to an increase in stage 2 sleep (P less than 0.05), a decrease in wakefulness (P less than 0.05) and in stage 3 sleep (P less than 0.05). After partial sleep deprivation, there were statistically significant increases in heart rate (P less than 0.05) and ventilation (P less than 0.05) at submaximal exercise compared with results obtained after the baseline night. Both variables were also significantly enhanced at maximal exercise, while the peak oxygen consumption (VO2) dropped (P less than 0.05) even though the maximal sustained exercise intensity was not different.(ABSTRACT TRUNCATED AT 250 WORDS)

[Disturbance of sports performance after partial sleep deprivation]. / Perturbations de la performance sportive après privation partielle de sommeil.

The changes in cardiac and ventilatory responses were measured in 7 endurance athletes during physical exercise on a bicycle ergometer, taking place after a control night and after a night with partial sleep deprivation in the middle of the night. The results show that, despite the maximal work load was not modified with control, heart rate, ventilation and VE/VO2 ratio (ERO2) were greater at the submaximal (75% of the VO2 max) and maximal work load and oxygen consumption decreased at maximal work, after the night of partial sleep deprivation as compared to the control. These findings suggest that acute sleep loss may contribute to alter the endurance performance by impairment of aerobic pathways.