Biomedical subjects

F Carré

Publications and source records attributed to F Carré.

At least 37 records · Page 2Linked to original sources

PubMed2000

Pediatric anesthesia monitoring with the help of EEG and ECG.

This paper presents research regarding the monitoring of the brain and the adequacy of anesthesia during surgery. Particular variables are derived from EEG and ECG signals and are correlated to anesthetic gas (sevoflurane) concentration, in pediatric anesthesia. The methods used for parameter extraction are based on change detection theory and time-frequency representation. Preliminary results show that the expired anesthetic gas concentration modulates both the heart rate variability and the duration of the burst suppression. Monitors of the central nervous system and autonomic nervous system activities can be expected to be based on these variables.

Anesthesia, General↗

PubMed2000

Influence of sympathetic heart rate modulation on RT interval rate adaptation in conscious dogs.

The objective was to test if changes in autonomic tone still influenced the RT-RR relationship when full RT adaptation is completed, when heart rate is controlled, and when beat-to-beat variability is abolished by atrial pacing. Eight dogs (8-11 kg) were chronically instrumented with atrial pacing electrodes. Digital ECG (1,000 Hz, 12 bits) were recorded from healthy conscious dogs during spontaneous sinus rhythm and during atrial pacing. The protocol was repeated before and after atenolol (2 mg/kg), prazosin (0.5 mg/kg), or atenolol + prazosin. A vocal incitation was used as sympathetic stimulation. Beat-to-beat quantitative analysis of the RT interval (from QRS apex to end of T wave) was correlated with the preceding RR by linear regression. In spontaneous rhythm, atenolol increased RR (P < 0.001), RT (P < 0.001), and short-term heart rate variability (P < 0.01) and decreased RT-RR slopes (P < 0.001). Prazosin did not significantly modify any parameter. Sympathetic stimulation decreased RR (P < 0.001), RT (P < 0.05), and short-term heart rate variability (P < 0.01) and increased RT-RR slopes (P < 0.001). In atrial pacing, the RT-RR slopes were steeper during pacing than during spontaneous rhythm but were not modified by pharmacological manipulation of the autonomic nervous system. During sinus rhythm the RT-RR relationship is increased by sympathetic stimulation and decreased by beta-blockade. When heart rate modulation and the effects of the time delay in RT rate adaptation are abolished by atrial pacing, the influence of autonomic tone on RT rate adaptation disappears.

Acoustic Stimulation↗

PubMed2000

Comparative effects of bisoprolol and nitrendipine on exercise capacity in hypertensive patients with regular physical activity.

The aim of this study was to evaluate the long-term effects of administering bisoprolol compared with nitrendipine on the duration of the exercise tolerated by male and female patients, aged 18-65 years, having mild to moderate hypertension and taking regular exercise. In this double-blind, randomized prospective study, 96 patients (85 men and 11 women, 48+/-10 years) formed two groups: 49 in the bisoprolol group, and 47 in the nitrendipine group. After a washout period of 14 days, either 10 mg of bisoprolol or 20 mg of nitrendipine was given daily over a treatment period of 12 weeks. During the treatment period, the stability of the physical training was monitored weekly by using a questionnaire. The results of two maximal triangular exercise tolerance tests (ETTs) on an ergometric bicycle performed at D0 under placebo and at D84 under active treatment were compared. No statistical difference was observed between both groups, concerning age, gender, morphologic characteristics, resting cardiovascular parameters, or physical training. Both groups maintained the same training level throughout the study. No significant differences between the groups were noted for duration of ETT [D0 892+/-284 s, D84, 919+/-267 s (NS) vs. D0 929+/-290 s, D84 904+/-324 s (NS)], or maximal work load [D0 190+/-49 W, D84 197+/-48 W (NS) vs. D0 198+/-49 W, D84 196+/-55 W (NS)]. On the other hand, both groups differed in maximal systolic blood pressure [D0 239+/-24 mm Hg, D84 215+/-22 mm Hg (p<0.001) vs. D0 237+/-24 mm Hg, D84 222+/-27 mm Hg (p<0.05)] (p = 0.05), and maximal pulse rate during exercise [141+/-18 vs. 163+/-17] (p<0.001), albeit not in maximal diastolic blood pressure [D0 113+/-13 mm Hg, D84 106+/-17 mm Hg (p<0.05) vs. D0 112+/-13 mm Hg, D84 104+/-15 mm Hg (p<0.05)]. The patient's own perception of the maximal effort (Borg scale) was not significantly different in either of the groups (placebo vs. treatment). Overall, in a population of hypertensive patients taking regular exercise, long-term treatment with bisoprolol produced no significant changes in the duration of peak effort, maximal workload, or the effort perceived by the patients themselves. The effects of regular exercise were comparable in both groups (bisoprolol or nitrendipine). Because previous studies have shown that dihydropyridines do not modify exercise performance in hypertensive patients, it may be concluded that the antihypertensive therapy with bisoprolol is well tolerated in a population of active hypertensive patients during dynamic exercise.

Adolescent↗

PubMed1999

Electrocardiographic predictive factors of long-term clinical improvement with multisite biventricular pacing in advanced heart failure.

Biventricular pacing has recently been proposed for treating patients with drug refractory heart failure and intraventricular conduction delay. The purpose is to restore ventricular relaxation and contraction sequences as homogeneously as possible. The aim of this study was to determine if some factors could predict the long-term clinical effectiveness of that new treatment. This study included 26 patients, aged 66 +/- 7 years, with drug refractory heart failure and wide QRS. Patients were implanted with a biventricular pacemaker. The left ventricle was paced through a coronary sinus tributary. New York Heart Association functional class, exercise tolerance, and left ventricular (LV) ejection fraction were collected at baseline and after pacemaker implantation. Patients were divided into 2 groups: group I = responders; group II = nonresponders. QRS duration and axis at baseline and during biventricular pacing, interventricular conduction time, and LV and right ventricular lead positions were compared between the 2 groups. Group I patients (n = 19) had a mean reduction of 1.3 in functional class and an increase in peak oxygen consumption rate by a mean of 50%. The only parameter that differed between the 2 groups was the QRS duration during biventricular pacing, with a significantly shorter value in group I than in group II (154 +/- 17 vs 177 +/- 26 ms; p = 0.016). Thus, a positive response to biventricular pacing is correlated with the quality of electrical resynchronization. The optimal positions of the right and LV leads would be those that could induce the greatest shortening of QRS duration.

Aged↗

PubMed1999

Kinetics of PCr to ATP and beta-ATP to beta-ADP phosphoryl conversion are modified in working rat skeletal muscle after training.

Kinetics of phosphoryl transfers from PCr to gamma-ATP and from beta-ATP to beta-ADP were measured by magnetization transfer in an in vivo 31P NMR experiment in working rat skeletal hind leg muscles. Two groups were examined. One group was submitted to a 6-week training program of treadmill running. The other group was composed of sedentary animals. Metabolic oxidative capacity and mechanical performance were improved greatly by training as shown previously. Phosphoryl transfer of PCr-->gamma-ATP or beta-ATP-->beta-ADP total fluxes were identical in resting trained and untrained muscles. Under stimulation, the flux of creatine kinase transfer was significantly inhibited by 23% compared with resting level in untrained muscles; by contrast, it was not inhibited and maintained at the high resting level in trained muscles. Thus physiological changes probably linked to a decrease of the production of anions, which could inhibit creatine kinase, were able to maintain creatine kinase flux. The flux of beta-ATP to beta-ADP transfer were enhanced largely in working muscles from 1.4+/-0.8 and 2+/-0.8 at rest to 4+/-1.6 and 6.6+/-2.7 mM s(-1) for untrained and trained muscles respectively; the effect was more pronounced in trained than in untrained muscles. These results showed an acceleration of phosphoryl turnover in working muscles after training, which could contribute to improve oxidative and mechanical performances. Such kinetic measurements of phosphoryl conversion may provide information on ATP turnover in pathophysiologic situations where ADP accumulates because of impaired ATP synthesis (mitochondrial myopathies, lower perfusion level).

Adenosine Diphosphate↗

PubMed1999

Differential effect of insulin-like growth factor I on in vitro gonadotropin (I and II) and growth hormone secretions in rainbow trout (Oncorhynchus mykiss) at different stages of the reproductive cycle.

The short-term effect of insulin-like growth factor I (IGF-I) on GTH I (FSH-like), GTH II (LH-like), and GH production by cultured rainbow trout pituitary cells was studied in immature fish of both sexes, at early gametogenesis and in spermiating and periovulatory animals. IGF-I had no effect on basal GTH I and GTH II release, whereas it always inhibited basal GH, showing decreasing intensity with the gonad maturation. In absence of IGF-I, GTH I and GTH II cells were always responsive to GnRH, whereas no response was observed for GH cells whatever the sexual stage. The action of IGF-I on the sensitivity to GnRH differs between GTH and GH cells. The former requires a coincubation with IGF-I (10(-6) M)/GnRH to show an increase in sensitivity, independent of the sexual stage. To be responsive to GnRH, the GH cells require longer exposure to IGF-I, the efficiency of which decreases with gonad maturation. The action of IGF-I (10(-6) M) on GTH cell sensitivity to GnRH does not seem to be related to a mitogenic effect or to an improvement in cell survival. It seems to be IGF-I specific, not passing via the insulin receptor. Certain hypotheses on the putative role of IGF-I and GnRH as a link between growth and puberty are suggested.

Animals↗

PubMed1998

Relationships between heart rate and heart rate variability: study in conscious rats.

Heart rate (HR) and heart rate variability (HRV) are risk markers in cardiac disease. HRV is also an index of the sympathovagal modulation of heart rate. Their relations have been rarely analyzed. We aimed to study such relations in normal adult conscious rats by using a novel bradycardic agent, a sinus node inhibitor, S-16257. Placebo-drug crossover designs were used while monitoring HR with telemetry and analyzing HRV in both time and frequency domains. S-16257 (2 mg/kg; n = 10) decreased HR by 29% and markedly increased HRV in parallel. By using various combinations of S-16257, atropine (2 mg/kg), and propranolol (4 mg/kg), a positive relation was shown between RR interval and various indexes of HRV: the slower the HR, the greater the HRV. Nevertheless, there is one exception to this correlation. When S-16257 was associated with both atropine and propranolol, the deep bradycardia was accompanied by a reduction of HRV, which indicates that the physiologic negative correlation between HR and HRV is not an intrinsic property of the pacemaker but is highly dependent on the two components of the autonomic system.

Animals↗

PubMed1998

Blood lactate concentrations during exercise: effect of sampling site and exercise mode.

BACKGROUND: The purpose of the study was to compare blood lactate concentrations determined in blood sampled from three sites (finger capillary, ear-lobe capillary, and forearm vein) during exercise on three different ergometers (a cycle ergometer, a treadmill and an arm-crank ergometer). METHODS: A total of 312 well-trained subjects performed either a six-minute steady-state exercise (n = 219) or an incremental exercise test until exhaustion (n = 93). Blood was sampled from two sites after each exercise test and at the end of each stage of the incremental protocol, 852 pairs of blood samples were analysed. RESULTS: Results showed that, when exercise was performed on a cycle ergometer or a treadmill, no significant differences between venous and ear capillary samples were observed whereas finger capillary values were higher. On an arm-crank ergometer, venous and finger capillary lactate concentrations were usually higher than ear capillary values with some discrepancies depending on the times of sampling. CONCLUSIONS: We conclude that lactate values may differ depending on the sampling site and the type of exercise mode. An ear capillary sample may be preferred because it is less affected by lactate release in the arms and easier to obtain.

Adolescent↗

PubMed1997

Heart rate and heart rate variability, a pharmacological target.

Heart rate varies with respiration, blood pressure, emotion, etc., and heart rate variability (HRV) is presently one of the best indices to predict fatal issues in cardiac failure and after myocardial infarction. HRV depends on various reflexes. In addition, parallel studies of HRV and the myocardial adrenergic and muscarinic transduction system in experimental models of cardiac hypertrophy (CH) have suggested that the myocardial phenotype at the sinus-node level may also play a role. A transgenic strain of mice with atrial overexpression of the beta 1-adrenergic receptors was generated with attenuated HRV, which demonstrates that the phenotype itself is a determinant of HRV. HRV is explored by noninvasive techniques, including simple determination of the standard error of the mean, time-domain analysis, and Fourier transformation. We recently developed a time and frequency domain method of analysis, the smoothed pseudo-Wigner-Ville transformation, which allows better exploration of nonstationarity. Nonlinear methods have also been applied due to the extreme complexity of the biological determinants, and have provided evidence of a chaotic attractor in certain conditions. It is proposed that in steady state a very simple process, which is not completely deterministic, could better explain intermit interval regulations than chaotic behavior. In contrast, under extreme circumstances the regulation proceeds using chaotic behavior. Arrhythmias and HRV can be quantitated in 16-month-old unanesthetized spontaneously hypertensive rats (SHR). Ventricular premature beats are more frequent in SHR than in age-matched controls; they disappear after converting enzyme inhibition (CEI) relative to the reduction of both cardiac hypertrophy and ventricular fibrosis. HRV is attenuated in SHR, as it is in compensatory CH in humans. When CH is prevented, HRV returns to normal. CEI is therefore antiarrhythmic. Another pharmacological application of this concept concerns the bradycardic agents that may improve HRV.

Animals↗

PubMed1997

Compensated cardiac hypertrophy: arrhythmogenicity and the new myocardial phenotype. I. Fibrosis.

The high incidence of arrhythmias in compensated cardiac hypertrophy is related to two independently regulated components-fibrosis and the adaptational phenotypic changes in membrane proteins linked to cardiac hypertrophy, and fibrosis. During the regression of hypertensive cardiopathy in middle-aged spontaneously hypertensive rats, the roles of cardiac hypertrophy and fibrosis can be analysed separately, revealing that both correlate independently with arrhythmias. In an experimental model of myocardial infarction it is possible to prevent arrhythmias with propranolol at the same time as cardiac hypertrophy, despite ventricular fibrosis. Fibrosis would appear to create arrhythmias both by anatomical uncoupling and by a re-entry mechanism generated by the zig-zag propagation of the transverse waveform. Triggered activity and automaticity depend on the membrane phenotype of the cardiocyte. They also play an important role, which is aggravated by myocardial heterogeneity.

Animals↗

PubMed1997

Cardiac hypertrophy, arrhythmogenicity and the new myocardial phenotype. II. The cellular adaptational process.

Ventricular fibrosis is not the only structural determinant of arrhythmias in left ventricular hypertrophy. In an experimental model of compensatory cardiac hypertrophy (CCH) the degree of cardiac hypertrophy is also independently linked to ventricular arrhythmias. Cardiac hypertrophy reflects the level of adaptation, and matches the adaptational modifications of the myocardial phenotype. We suggest that these modifications have detrimental aspects. The increased action potential (AP) and QT duration and the prolonged calcium transient both favour spontaneous calcium oscillations, and both are potentially arrhythmogenic and linked to phenotypic changes in membrane proteins. To date, only two ionic currents have been studied in detail: Ito is depressed (likely the main determinant in AP durations), and If, the pacemaker current, is induced in the overloaded ventricular myocytes. In rat CCH, the two components of the sarcoplasmic reticulum, namely Ca(2+)-ATPase and ryanodine receptors, are down-regulated in parallel. Nevertheless, while the inward calcium current is unchanged, the functionally linked duo composed of the Na+/Ca2+ exchanged and (Na+, K+)-ATPase, is less active. Such an imbalance may explain the prolonged calcium transient. The changes in heart rate variability provide information about the state of the autonomic nervous system and has prognostic value even in CCH. Transgenic studies have demonstrated that the myocardial adrenergic and muscarinic receptor content is also a determining factor. During CCH, several phenotypic membrane changes participate in the slowing of contraction velocity and are thus adaptational. They also have a detrimental counterpart and, together with fibrosis, favour arrhythmias.

Action Potentials↗

PubMed1996

Improvement of muscular oxidative capacity by training is associated with slight acidosis and ATP depletion in exercising muscles.

Metabolic and mechanical properties of female rat skeletal muscles, submitted to endurance training on a treadmill, were studied by a 60-min in vivo multistep fatigue test. 31P-NMR was used to follow energy metabolism and pH. Mechanical performance was greatly improved in trained muscles. The oxidative capacity of the skeletal muscles was evaluated from the relationship between ADP calculated from the creatine kinase equilibrium and work and from the measure of the rate of phosphocreatine (PCr) resynthesis following exercise. In trained muscles, ADP production was lower per unit of mechanical performance, showing an improvement of oxidative metabolism. However, the PCr resynthesis rate was not modified. Slight acidosis and ATP depletion were observed from the beginning of the fatigue test. These modifications suggest changes of the creatine kinase equilibrium favoring mitochondrial ATP production. Our results indicate that muscle status improvement could be accompanied by ATP depletion and minimal acidosis during contraction; this would be of particular importance for objective evaluation of muscle regeneration processes and of gene therapy in muscle diseases.

Acidosis↗

PubMed1996

Energy consumption of paraplegic locomotion using reciprocating gait orthosis.

The energy cost of walking using a reciprocating gait orthosis (RGOII) with functional electrical stimulation (FES) was assessed in 14 patients with spastic complete paraplegia from six rehabilitation centres. Before and after training asing RGOII with FES, the subjects performed a progressive maximal test on an arm-crank ergometer to obtain their laboratory peak oxygen uptake (LVO2peak), heart rate (HR) and blood lactate concentration changes. At the end of the training session, oxygen uptake (VO2) was measured during a walking test with orthosis at different speeds (6 min steady state at 0.1 m.s-1, followed by 2-min stages at progressively increasing speeds up to exhaustion). Of the subjects 4 repeated this test using orthosis without FES. At a speed of 0.1 m.s-1, VO2 represented 47 (SD 23)% of LVO2peak, mean HR was 137 (SD 21) beats.min-1 and mean blood lactate concentration 2.4. (SD 1.4) mmol.l-1. Maximal speed ranged from 0.23 to 0.5 m.s-1. At maximal speed, VO2 was 91 (SD 18)% of LVO2peak, mean HR reached 96 (SD 7)% and mean blood lactate concentration only 52 (SD 19)% of the maximal values measured during the laboratory test. Walking without electrical stimulation induced an increase in HR but there was no difference in VO2 and blood lactate compared to walking with stimulation. The training period did not result in any improvement in maximal physiological data. We concluded that the free cadence walking speed with orthosis remains much lower than that of able-bodied people or wheelchair users. The metabolic cost at a given speed is much higher even if, using a stimulation device, the cardiovascular stress is reduced.

Adult↗

PubMed1996

Expression of the cardiac ryanodine receptor in the compensated phase of hypertrophy in rat heart.

OBJECTIVES: Abnormal calcium handling is a general feature of cardiac hypertrophy and alteration in the expression of SR proteins has been suggested to be involved in this alteration. To determine the expression of the cardiac ryanodine receptor (Ry2) gene during compensatory hypertrophy, we studied the mRNA and protein accumulation in left ventricles from rats with 30 to 100% hypertrophy. METHODS: Cardiac hypertrophy was obtained after 1 month of aortic constriction. Ry2 mRNA was analyzed by RNase protection assay, Northern and slot blots, and Ry2 protein by high-affinity [3H]ryanodine binding and Western blot. RESULTS: We demonstrate that: (1) the cardiac Ry2 mRNA concentration is decreased by 50% in severe hypertrophy; (2) both the density of the high-affinity sites and the Ry2 protein level are decreased by 25%; (3) the decrease in the mRNA and protein levels and the number of high-affinity sites are highly correlated to the severity of hypertrophy. CONCLUSION: Our results suggest that, as for SR Ca(2+)-ATPase, there is either a downregulation or a lack of upregulation of the gene coding for the Ry2 in compensatory hypertrophy. The decreased density of Ry2 may alter SR Ca2+ transport and contribute to the impaired Ca2+ handling by slowing the Ca2+ movements.

Animals↗

PubMed1996

Decreased heart rate variability in transgenic mice overexpressing atrial beta 1-adrenoceptors.

Heart rate variability (HRV) depends on various reflexes, including the baroreflex or respiratory reflex. Experimental studies have suggested that the sinoatrial node density in G protein-linked receptors may be involved. Transgenic mice, with a specific eightfold atrial overexpression of human beta 1-adrenoceptor (beta 1-AR), have been generated to evaluate the role of the atrial beta 1-AR density on HRV. The heart rate was monitored using telemetry, and the signal was analyzed using a quantitative time-frequency domain analysis, the smoothed pseudo-Wigner-Ville method, and phase portrait maps. 1) Heart rate was unchanged, but the two normal components of HRV were decreased in transgenic mice. Transgenic mice have an unshortened life span and no arrhythmias. 2) Challenge of the animals by propranolol showed no modulation of the HRV in transgenic mice compared with controls. 3) In isolated atrial strips from transgenic mice, basal contractility was increased and there was no isoproterenol-induced inotropic effect. 4) The basal level of adenosine 3',5'-cyclic monophosphate production was lowered in transgenic mice, suggesting a shift in adenylate cyclase isoforms.

Adenylyl Cyclases↗

PubMed1996

Linear and non-linear analyses of heart rate variability: a minireview.

To complete traditional time- and frequency-domain analyses, new methods derived from non-linear systems analysis have recently been developed for time series studies. A panel of the most widely used methods of heart rate analysis is given with computations on mouse data, before and after a single atropine injection.

Animals↗

PubMed1995

Molecular and cellular biology of the senescent hypertrophied and failing heart.

During aging, experimental studies have revealed various cellular changes, principal among which is myocyte hypertrophy, which compensates for the loss of myocytes and is associated with fibrosis. The expression of alpha-myosin heavy chain is replaced by that of the isogene beta-myosin, which leads to decreased myosin adenosine triphosphatase (ATPase) activity. In consequence, contraction is slower and more energetically economical. The Ca(2+)-ATPase of the sarcoplasmic reticulum and Na+/Ca2+ exchange activity are decreased, which probably explains the reduced velocity of relaxation. Membrane receptors are also modified, since the density of both the total beta-adrenergic and muscarinic receptors is decreased. The senescent heart is able to hypertrophy in response to overload and to adapt to the new requirements. Similar alterations are observed both in the senescent heart and in the overloaded heart, in clinical as well as in experimental studies; however, differences do exist, especially in terms of fibrosis and arrhythmias.

Adaptation, Physiological↗

PubMed1995

Decrease in beta 1-adrenergic and M2-muscarinic receptor mRNA levels and unchanged accumulation of mRNAs coding for G alpha i-2 and G alpha s proteins in rat cardiac hypertrophy.

During compensatory cardiac hypertrophy in the rat, hemodynamic overload induces a parallel decrease in the densities of both beta 1-adrenergic (beta 1-AR) and M2-muscarinic (M2-MR) receptors in the left ventricle, but the total number of receptors remains unchanged. It is not known whether this reduction is transcriptionally or translationally regulated, or if the functionally closely linked alpha-subunits of G protein (G alpha s and G alpha i-2) partake in this regulation. In order to resolve these questions, the absolute concentrations of mRNAs for both receptors and for G alpha s and G alpha i-2 were quantified by slot blot analysis of the left ventricles of adult rats 5 weeks after aortic banding. The results showed a significant decrease of both receptor mRNA levels in hypertrophied left ventricle (beta 1-AR: -48%; M2-MR: -42%) that paralleled the reduction in receptor protein densities and was negatively correlated with the left ventricular weight/body weight ratio (LVW/BW). By contrast, the relative levels of G alpha s and G alpha i-2 mRNAs remained unchanged, and both accumulated proportionally to the increase in LVW/BW. These results show that the beta 1-AR and the M2-MR were pretranslationally regulated. This suggests the hypothesis that the corresponding genes do not follow the general increase in transcriptional activity. By contrast, the genes coding for G alpha s and G alpha i-2 may follow the general pattern of activation during hypertrophy. Receptors and coupling proteins belong to two different groups of genes that are controlled by distinct mechanisms of regulation.

Animals↗