[Short-term exercise-based cardiac rehabilitation induced changes in cardiorespiratory, mechanical and neuromuscular responses to progressive exercise testing]. / Dissociation des réponses cardiorespiratoires et neuromusculaires à l'exercice à la suite de 4 semaines de réentraînement à l'effort chez des patients cardiaques.

Previous studies showed that changes in peak of oxygen uptake value (VO2peak) with training were poorly related to changes in Maximal Tolerated Power output (MTP) among patients with cardiovascular disease. This result could be due to a difference between cardiopulmonary adaptation to training and the skeletal muscle conditioning. OBJECTIVE: The aim of the study was to compare the responses to exercise training of electromyographic activities of vastus lateralis (rms-EMG) and respiratory parameters. METHODS: Nine cardiac patients (64.0±3.1y, 172.9±4.8cm, 83.4±16.3kg, BMI: 27.8±4.5) performed an incremental cycling exercise test to determine MTP, VO2peak and peak values of heart rate, before and after an aerobic training. Ventilatory thresholds were respectively determined as the breakpoint in the curve of carbon dioxide output against oxygen uptake plot (VT1) and the point at which the ratio of minute ventilation to carbon dioxide output starts to increase (VT2). EMGth1 and EMGth2 were defined as the first and the second breakpoints in the rms-EMG - power output relationship. RESULTS: Short-term exercise training (23.7±8.8 days) induced a significant increase in VO2peak (P=0.004), MTP (P=0.015), VT1 (P=0.001) and VT2 (P=0.001). Changes in VO2peak only attained the survival criteria (3.5±2.9mLmin-1kg-1). No significant differences (P>0.05) existed between mean power values of VT1 and EMGth1 (60.5±4.1 vs. 59.2±9.6% of MTP, respectively), or between VT2 and EMGth2 (78.3±5.7 vs. 80.2±5.2% of MTP). After training, EMGth1 occurred significantly before VT1 (60.5±6.2 vs. 64.8±4.8% of MTP, P=0.049). CONCLUSION: This might be taken into account for prescribing exercise rehabilitation according initial clinical limitations of patients.

Impact of prenatal and postnatal exposure to the pesticide chlorpyrifos on the contraction of rat ileal muscle strips: involvement of an inducible nitric oxide synthase-dependent pathway.

BACKGROUND: Prenatal/postnatal exposure to insecticides has been linked to developmental disorders in adulthood. Chlorpyrifos (CPF) is a widely used organophosphorus acetylcholinesterase (AChE)-inhibiting insecticide. The present study established whether prenatal and postnatal exposure to CPF is associated with intestinal motor dysfunction in adult rats. METHODS: Three groups of pregnant rats were exposed to either CPF (1 or 5 mg/kg/day; the CPF1 and CPF5 groups) or vehicle (the control group) by gavage from gestational day 1 until weaning. At weaning, the pups were separated from their dams and individually gavaged (with the same dose) until postnatal day 60. We then measured in vivo intestinal transit and the in vitro contractile responses of ileal smooth muscle strips to electrical field stimulation. Expression of inducible nitric oxide synthase (iNOS) in the ileum was determined using qRT-PCR and immunoblots. Morphometry and AChE assays were also performed. KEY RESULTS: At adulthood, the mean body mass was lower in the CPF1 and CPF5 groups than in controls. CPF5 exposure was associated with weaker in vitro contraction of ileal muscle strips, which was reversed by adding the NOS inhibitor (L-NAME). There was no significant intergroup difference in the mean in vivo transit time. Exposure to CPF was associated with greater iNOS expression, lower AChE activity and reduced circular and longitudinal smooth muscle thickness. CONCLUSIONS & INFERENCES: Prenatal and postnatal exposure to CPF in the rat is associated with weaker contraction of ileal longitudinal smooth muscle via a nitrergic mechanism with increased iNOS expression.

Exercise-based Cardiac Rehabilitation in Coronary Disease: Training Impulse or Modalities?

To compare the effects of 2 short programs with similar training load (TL), based on combined aerobic - resistance training (CT) or aerobic training (AT) on cardiorespiratory responses, 32 patients with coronary heart disease (CHD: 63.8±8.0y, 1.73±0.06 m, 84.8±15.9 kg, Left Ventricular Ejection Fraction: 0.53±0.8) performed 4 weeks of exercise rehabilitation based on CT (n=16) or AT (n=16). Maximal tolerated power (MTP), peak values of oxygen uptake (VO2peak) and heart rate (HRpeak), anaerobic threshold (VT1) were determined during an incremental cycling exercise test before and after training periods. TL, quantified using the session rating of perceived exertion, did not differ between both modalities (CT: 4 438±572 vs. AT: 4 346±592 AU, p=0.300). Improvements in VO2peak were larger after CT (+36.4±24.7% of pre-training VO2peak, i. e., +4.4±2.3 mL.min-1.kg-1, n=14) than observed after AT (+20.1±9.1% of pre-training VO2peak, i. e., +2.6±1.0 mL.min-1.kg-1, n=12) (p=0.014). Additionally, CT significantly improved power (54.6±23.8 vs. 75.1±21.2 watts, p=0.001) and VO2 associated at VT1 (VO2: 9.8±2.5 vs. 12.6±2.9 mL.min-1.kg-1, p=0.001). This might be taken into account when prescribing exercise rehabilitation for CHD patients with different initial clinical limitations.

[Is there a disassociation of ventilatory and electromyographic thresholds in patients with heart disease during a graded cycling exercise?] / Concordance et dissociation des seuils de fatigue électromyographiques et des seuils ventilatoires chez le patient en réadaptation cardiaque.

Exercise prescription was generally based on the determination of ventilatory thresholds (VT1, VT2) during cardiopulmonary exercise testing (CPX). Changes in surface electromyographic activity (EMGth1, EMGth2) were also related to VT1 and VT2 in healthy subjects. OBJECTIVE: To observe the occurrence of EMGth1 and EMGth2 and whether these events accompany VT1 and VT2 during CPX in cardiac patients (CP). METHOD: Thirty-four CP (62.1±7.3years, 172.1±6.3cm, 81.3±15.3kg, BMI: 27.3±4.1) performed a cycle CPX at a 60-rpm cadence. VT1 was determined as the breakpoint in the curve of carbon dioxide output against oxygen uptake plot (V-slope method). VT2 was defined as the point at which the ratio of minute ventilation to carbon dioxide output starts to increase. The root mean square of electromyogram (rms-EMG) was on-line calculated from the real time bipolar surface electromyographic signals recorded from the vastus lateralis. EMGth1 and EMGth2 were defined as the first and the second breakpoints in the rms-EMG-power output relationship. RESULTS: Peak values of oxygen uptake (16.3±4.6mL·min-1·kg-1) and heart rate (106.7±13.8bpm) were reached at 112.9±38.5w (PMT). VT1 and VT2 occurred at 71.1±25.9w (62.5±5.5% PMT) and 87.9±28.6w (78.0±5.1% PMT). All subjects presented two breakpoints in the rms-EMG curve, EMGth1 at 68.0±24.7w and EMGth2 at 88.5±30.1w, i.e. 60.0±7.6 and 78.6±5.0% of PMT. EMGth1 occurred significantly before VT1 (P=0.004, small effect size). No significant difference was observed between EMGth2 and VT2 (P=0.13, small effect size). CONCLUSION: The EMGth1 occurrence before VT1 suggested a role of skeletal muscle conditioning on ventilatory responses, which should be taken into account in cardiac rehabilitation program prescription.

[Heat exchanges and thermoregulation in the neonate]. / Echanges thermiques et thermorégulation chez le nouveau-né.

The newborn's energy expenditure is used in order of priority for: (i) basic metabolism; (ii) body temperature regulation and (iii) body growth. Thermal regulation is an important part of energy expenditure, especially for low birth-weight infants or preterm newborns. The heat exchanges with the environment are greater in the infant than in the adult, explaining the increased risk of body hypo- or hyperthermia. The newborn infant is a homeotherm, but over a long period of time, he cannot maintain the thermal processes. Further developments are expected to improve the infant's thermal environment, with assessment of the various heat exchange mechanisms by conduction, convection, radiation and evaporation. The quantification of the respective parts of these exchanges would improve nursing care through clinical procedures or equipment used to ensure the control of the optimal thermohygrometric conditions in incubators, especially when the likelihood of excessive body cooling is high. The present review focuses on the various body heat exchange mechanisms, the thermoregulation processes of the newborn, and their implications in clinical usage and limitations in the neonatal intensive care unit.

Timing and driving components of the breathing strategy in children with cystic fibrosis during exercise.

The aim of this study was twofold: first, to determine the breathing strategies of children with cystic fibrosis (CF) during exercise, and secondly, to see if there was a correlation with lung function parameters. We determined the tension-time index of the inspiratory muscles (T(T0.1)) during exercise in nine children with CF, who were compared with nine healthy children with a similar age distribution. T(T0.1) was determined as followed T(T0.1) = P0.1/PImax . T(I)/T(TOT), where P0.1 is mouth occlusion pressure, PImax is maximal inspiratory pressure, and T(I)/T(TOT) is the duty cycle. CF children showed a significant decrease of their forced expiratory volume in 1 sec (FEV1), forced vital capacity (FCV), and FEV1/FVC, whereas the residual volume to total lung capacity ratio (RV/TLC) ratio and functional residual capacity (FRC) were significantly increased (P < 0.001). Children with CF showed mild malnutrition assessed by actual weight expressed by percentage of ideal weight for height, age, and gender (weight/height ratio; 82.3 +/- 3.6%). Children with CF showed a significant reduction in their PImax (69.3 +/- 4.2 vs. 93.8 +/- 7 cmH2O). We found a negative linear correlation between PImax and weight/height only in children with CF (r = 0.9, P < 0.001). During exercise, P(0.1), P0.1/PImax, and T(T0.1) were significantly higher, for a same percent maximal oxygen uptake in children with CF. On the contrary, T(I)/T(TOT) ratio was significantly lower in children with CF compared with healthy children. At maximal exercise, children with CF showed a T(T0.1) = 0.16 vs. 0.14 in healthy children (P < 0.001). We observed at maximal exercise that P0.1/PImax increased as FEV1/FVC decreased (r = -0.90, P < 0.001), and increased as RV/TLC increased (r = 0.92, P < 0.001) only in children with CF. Inversely, T(I)/T(TOT) decreased as FEV1/FVC decreased (r = 0.89, P < 0.001), and T(I)/T(TOT) decreased as RV/TLC increased (r = -0.94, P < 0.001). These results suggest that children with CF adopted a breathing strategy during exercise in limiting the increase of the duty cycle. Two determinants of this strategy were degrees of airway obstruction and hyperinflation.

Pattern of rapid-eye movement sleep episode occurrence after an immobilization stress in the rat.

Rapid-eye movement sleep (REMS) in the rat occurs in the form of episodes separated by long (>3 min: isolated REMS episodes, IREMSEs) and short (<3 min: sequential REMS episodes, SREMSEs) intervals. The mechanism clustering SREMSEs is thought to be better suited to increase the amount of REMS when its drive is high. We tested this hypothesis in a new situation by transiently augmenting this drive with a moderate psychogenic stress. After a 90-min immobilization stress, REMS increased by 54% over the rest of the dark phase. This increase was associated with a modest increase in IREMSEs (+40%), but a massive increase in SREMSEs (+300%). Thus, the mechanism that clusters REMS episodes operates in response to a moderate psychogenic stress imposed in standard laboratory conditions and not preceded by sleep deprivation.

Activation of brown adipose tissue thermogenesis increases slow wave sleep in rat.

Considering the thermoregulatory role of slow wave sleep (SWS), we wondered whether the sole increase of brown adipose tissue (BAT) thermogenesis could enhance this sleep state. We tested this hypothesis by administering to rats an agonist (BRL 37,344) of the beta-3 adrenoceptor subtype that is massively localized in BAT cell membrane and that is known to activate BAT thermogenesis. Sleep was electrographically characterized. The temperature of interscapular BAT (Tibat) and cortex (Tco) were also assessed. Tibat significantly increased 2-3 h after BRL injection (but not Tco), concomitantly with SWS (+56-57%). At the maximum of Tibat, a significant positive correlation was found between their changes and those of SWS. We demonstrated for the first time that sleep (and especially SWS) can be affected by the specific activation of BAT.

Influence of incubator humidity on sleep and behaviour of neonates kept at stable body temperature.

UNLABELLED: The influence of incubator air humidity (via passive humidification through use of a water reservoir or via active humidification to 2 and 4 kPa) on sleep and behavioural changes was investigated in 13 neonates. The thermal environment of the incubator was servocontrolled via an interactive device tracking the skin temperature changes of the neonates. Using this servocontrolled skin temperature derivative heating programme, it is believed that an increase in air moisture content (reducing evaporative skin cooling) can be counterbalanced by a fall in neutral air temperature, so as to keep the body thermally constant. This procedure permits the experimental evaluation of the specific effect of air humidity on the thermal equilibrium air temperature and the thermal comfort of neonates without eliciting thermoregulatory mechanisms. Under the experimental conditions, in order to keep body temperature stable an increase in water vapour partial pressure from 1.72 (water reservoir) to 3.99 kPa (produced by a nebulizer) is counterbalanced by a decrease in air temperature of 1.49 degrees C. Within this humidity range, the air temperature must be lowered by 0.05 degrees C when the vapour pressure is increased by 0.08 kPa. The magnitude of this deviation depends on the humidity range and is probably a result of changes in the wetted skin area. CONCLUSION: When body temperature is kept constant, changes in air humidity do not modify sleep, body motility and respiratory and heart rates in neonates.

Assessment of dry heat exchanges in newborns: influence of body position and clothing in SIDS.

A dramatic decrease of sudden infant death syndrome (SIDS) has been noted following the issuance of recommendations to adopt the supine sleeping position for infants. It has been suggested that the increased risk could be related to heat stress associated with body position. In the present study, the dry heat losses of small-for-gestational-age newborns nude or clothed were assessed and compared to see whether there is a difference in the ability to lose heat between the prone and supine positions. An anthropomorphic thermal mannequin was exposed to six environmental temperatures, ranging between 25 and 37 degrees C, in a single-walled, air-heated incubator. The magnitudes of heat losses did not significantly differ between the two body positions for the nude (supine 103.46 +/- 29.67 vs. prone 85.78 +/- 34.91 W/m(2)) and clothed mannequin (supine 59.35 +/- 21.51 vs. prone 63.17 +/- 23.06 W/m(2)). With regard to dry heat exchanges recorded under steady-state conditions, the results show that there is no association between body position and body overheating.

Reliability of a new device to assess the oxygen consumption of human respiratory muscles.

PURPOSE: This study tests the reliability of a new device for assessing the oxygen consumption of the respiratory muscles (VO2 resp.). METHODS: Fourteen healthy male volunteers participated in the study. The device consists of an expandable external ventilatory dead space created with pieces of plastic tubing and a spirometer filled with 100% oxygen. It also incorporates a carbon dioxide absorber. Total VO2 (VO2 tot.) was recorded from the spirometric closed circuit and ventilation (V(E)), from the spirometer tracing. For each subject the test procedure was carried out in duplicate (T1 and T2) after an overnight fast. The dead space was increased at a constant rate of 260 mL every 90 s, and VO2 tot. and V(E) increased progressively. Because log VO2 tot. was linearly related to V(E), we calculated the slope value (log VO2-V(E)) and the Y-intercept (VE = 0) of the semilog regression representing, respectively, VO2 resp. and metabolic VO2 (VO2 met.). RESULTS: When compared with values in the literature, these values did not differ from those recorded in subjects of a similar age group. The VO2 resp. and VO2 met. calculated in T1 and T2 were not different (VO2 resp. = 0.0066 +/- 0.0005 for T1 vs 0.0067 +/- 0.0005 log mL x min(-1)/L x min(-1) for T2 and VO2 met. = 269.3 +/- 28.6 for T1 vs 281.9 +/- 24.1 mL x min(-1) for T2). The coefficients of variation were: 25% at T1 and 23% at T2 for VO2 resp. and 34% at T1 and 29% at T2 for VO2 met. Moreover, significant correlations (r = 0.96, P < 0.001 for VO2 resp., r = 0.95, P < 0.001 for VO2 met.), high coefficients of determination (r2 = 0.92 for VO2 resp., r2 = 0.90 for VO2 met.) and negligible SEE (0.0005 for VO2 resp., 0.2 mL x min(-1) for VO2 met.) were found between the two tests. When we plotted the mean values of VO2 resp. and VO2 met. measured at T1 and T2 against their respective differences, more than 95% of the slight differences ranged between the limits defined by mean value +/- 2 SD, reflecting the small discrepancy between duplicate measurements. CONCLUSION: The results confirm that the test performed with this device is useful and reliable for assessing the VO2 resp. in healthy subjects.

Humidity control tool for neonatal incubator.

In the first days of life, the daily evaporative loss from premature neonates can reach up to 20% of body mass. Such loss can be reduced by increasing the air humidity inside the incubator. Neither passive humidification nor open loop systems allow high humidity rates to be maintained or easily controlled: at 34 degrees C, the maximum levels vary with the system from 40% to 77% of relative humidity. The skin evaporative exchanges between the neonate and the environment are directly proportional to the water vapour partial pressure difference between the neonate's skin and the air. An active closed loop system has been designed, which permits reliable and accurate control of humidity according to the water vapour partial pressure set, between 1 and 6 kPa, in an air temperature range of 28-39 degrees C. It is characterised by variations of about 0.05 kPa around the set value and a maximum humidification speed of 0.25 kPa min-1. The algorithm is based on optimal control and the dynamic programming principles. Test results place this active system above usual systems for its power, precision and adaptability. It is an exploitable tool in fundamental and clinical research, to precisely study the humidity effects on neonatal comfort and thermo-regulation evolution.

Skin derivative control of thermal environment in a closed incubator.

Defining a thermoneutral environment remains difficult because thermoneutrality depends on both physical and physiological factors. A servocontrolled skin temperature derivative (SCS) heating device has been designed to control the thermal environment in closed incubators without the necessity of setting an air or skin reference temperature. The thermal environment obtained with the SCS program is controlled only by the neonate's skin temperature changes. For each neonate, the program allows the attainment of a specific individual thermal equilibrium (Teq). Although the mean value of the thermal equilibrium level measured on 29 neonates does not differ significantly from the neutral air temperature defined from the charts of other researchers, individual values of Teq differed greatly among neonates of similar birthweight and postnatal age. When compared with on/off heating programs, the SCS system permits greater quiet sleep occurrence and seems to provide an optimal thermal environment. The results suggest that the skin temperature derivative heating program takes into account both the ambient and physiological factors affecting body temperature regulation of each neonate.