Biomedical subjects

C Prefaut

Publications and source records attributed to C Prefaut.

At least 37 records · Page 2Linked to original sources

PubMed1997

Non-invasive quantification of diaphragm kinetics using m-mode sonography.

PURPOSE: The standard conditions of spirometry (i.e., wearing a noseclip and breathing through a mouthpiece and a pneumotachograph) are likely to alter the ventilatory pattern. We used "time motion" mode (M-mode) sonography to assess the changes in diaphragm kinetics induced by spirometry during quiet breathing. METHODS: An M-mode sonographic study of the right diaphragm was performed before and during standard spirometry in eight patients without respiratory disease (age 34 to 68 yr). RESULTS: During spirometry, the diaphragm inspiratory amplitude (DIA) increased from 1.34 +/- 0.18 cm to 1.80 +/- 0.18 cm (P = 0.007), whereas the diaphragmatic inspiratory (T1 diaph) increased from 1.27 +/- 0.15 to 1.53 +/- 0.23 sec, (P = 0.015, without change in diaphragmatic total time interval (Ttot diaph). Therefore, the diaphragm duty cycle (T1 diaph/Ttot diaph) increased from 38% +/- 1% to 44% +/- 4% (P = 0.023). The diaphragm inspiratory (DIV) and expiratory (DEV) motion velocity (P = 0.007). CONCLUSION: M-mode sonography enabled us to demonstrate that the wearing of a nose clip and breathing through a mouthpiece and a pneumotachograph induce measurable changes in diaphragm kinetics.

Adult↗

PubMed1997

Changes in maximal exercise ventilation and breathing pattern in boys during growth: a mixed cross-sectional longitudinal study.

The aim of this mixed cross-sectional longitudinal study covering a total age range of 11-17 years, i.e. the entire pubertal growth period, was (1) to specify the changes in maximal breathing pattern during incremental exercise; (2) to determine what parts of the changes are due to anthropometric characteristics, physical fitness and inspiratory or expiratory muscle strength; and (3) to determine if the role of these variables is identical before, during and after pubertal growth spurt. This study was conducted in 44 untrained schoolboys separated into three groups, with an initial age of 11.2 +/- 0.2 years for group A, 12.9 +/- 0.25 years for group B, and 14.9 +/- 0.26 years for group C. These children were subsequently followed for 3 years, during the same time period each year. The maximal inspiratory and expiratory pressures (PI max and PE max) were used as an index of the respiratory muscle strength. During an incremental exercise test, maximal ventilation (VE max), tidal volume (VT max), breathing frequency (fmax), inspiratory and expiratory times (tI max and tE max) and mean inspiratory flow (VT/tI max) were measured at maximal oxygen uptake (VO2max). Our study showed that there was a marked increase with age in VE max, VT max, and VT/tI max, and no significant changes in fmax, tI max and tE max. PI max and PE max showed a general trend towards an increase between 11 and 17 years. The study of the linear correlations between maximal breathing pattern and the anthropometric characteristics, physical fitness and inspiratory or expiratory muscle strength showed that, in the three groups of children, (1) lean body mass was the major determinant of VE max, VT max and VT/tI max and the relationships were significantly different before, during and after the pubertal growth spurt; (2) physical fitness was the main determinant of tI max, tE max and fmax before and after the pubertal growth spurt; and (3) maximal respiratory strength did not play a significant role. In conclusion, this mixed cross-sectional longitudinal study showed, at maximal exercise, a significant increase in VE max during growth due only to a significant increase in VT max and VT/tI max, and that the relationships of anthropometric characteristics and physical fitness with maximal breathing pattern change during growth.

Adolescent↗

PubMed1997

Effect of step duration during incremental exercise on breathing pattern and mouth occlusion pressure.

We compared the effects of two step durations on breathing pattern, mouth occlusion pressure and "effective" impedance of the respiratory system during incremental exercise. Nine normal subjects (mean age: 27.8+/-1.21 years) performed two incremental exercise tests in randomized order: one test with step increments every 1 min 30s and the other, every 4 min. After a warm-up at 25 W for the 1 min 30 s test, the power was increased by 50 W from 50 W to exhaustion. During the last minute at each power, we measured ventilation (VE), tidal volume (VT), breathing frequency (fR), inspiratory and expiratory time (TI and TE), total time of the respiratory cycle (TTOT), TI/TTOT, mean inspiratory flow (VT/TI), mouth occlusion pressure (P0.1), "effective" impedance of the respiratory system (P0.1/(VT/ TI)) and venous blood lactate concentration ([La]). Our result showed that at maximal exercise the power was significantly higher (p < 0.01) and [La] lower (p < 0.01) in the 1 min 30 s test. At 100, 150 and 200 W, the 4 min test showed significantly higher oxygen uptake (VO2), carbon dioxide output (VCO2), VE, P0.1, fR, VT/TI and HR (p <0.001) and significantly lower TI, TE and TTOT (p<0.01). [La] was significantly higher at 150 W (p<0.05) and 200 W (p<0.001). At the same VCO2, P0.1 was not significantly different between the two tests, whereas VE showed a tendency to be higher (p = 0.08) and P0.1/(VT/TI) was significantly lower during the 4 min test. In conclusion, this study allowed us to quantify the difference in inspiratory neuromuscular output and ventilatory response between 1 min 30s and 4 min tests and showed that different step durations alter the relationship between inspiratory neuromuscular output and mean inspiratory flow.

Adult↗

PubMed1997

Fatigue analysis of human reinnervated muscle after microsurgical nerve repair.

The reinnervated elbow flexors, biceps, and brachialis muscles were compared with the elbow flexors on the healthy opposite side in terms of muscle strength and fatigue in 10 patients who sustained sequelae of a unilateral posttraumatic brachial plexus palsy. The patients had recovered an active elbow flexion against resistance after microsurgical nerve repair. The patients were reviewed with an average postoperative followup of 12 years (range, 7.5-16 years). Despite a statistically significant difference in maximum isometric force, this study showed that after peripheral nerve repair, a partially reinnervated muscle has the same characteristics of fatigue and endurance as a normally innervated muscle, if these muscles exert the same percentage of their own maximum force.

Adolescent↗

PubMed1996

Functional and histologic effects of a free nonvascularised muscle graft implanted into a reinnervated muscle after prolonged denervation.

Striated muscle atrophy and degeneration, which increase with the delay of denervation, represent two of the main causes for poor recovery following delayed nerve repair. The present study, using a rat model, tests the hypothesis that an adjunction of small, free, nonvascularised muscle grafts of contralateral healthy triceps into a chronically denervated triceps improves muscle regeneration and recovery following sciatic nerve repair delayed for 3 months. Our experiments seem to show a relative increase in mechanical properties in animals in which free muscle graft into the triceps was performed 3 weeks following nerve repair. The improvement of the regenerative process of muscles which have suffered a long period of denervation should be considered as an additional therapeutic procedure in the case of late nerve repair.

Animals↗

PubMed1996

Lactate kinetics during passive and partially active recovery in endurance and sprint athletes.

We investigated the effects of passive and partially active recovery on lactate removal after exhausting cycle ergometer exercise in endurance and sprint athletes. A group of 14 men, 7 endurance-trained (ET) and 7 sprint-trained (ST), performed two maximal incremental exercise tests followed by either passive recovery (20 min seated on cycle ergometer followed by 40 min more of seated rest) or partially active recovery [20 min of pedalling at 40% maximal oxygen uptake (VO2max) followed by 40 min of seated rest]. Venous blood samples were drawn at 5 min and 1 min prior to exercise, at the end of exercise, and during recovery at 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 30, 40, 50, 60 min post-exercise. The time course of changes in lactate concentration during the recovery phases were fitted by a bi-exponential time function to assess the velocity constant of the slowly decreasing component (tau 2) expressing the rate of blood lactate removal. The results showed that at the end of maximal exercise and during the 1st min of recovery, ET showed higher blood lactate concentrations than ST. Furthermore, ET reached significantly higher maximal exercise intensities [5.1 (SEM 0.5) W.kg-1 vs 4.0 (SEM 0.3) W.kg-1, P < 0.05] and VO2max [68.4 (SEM 1.1) ml.kg-1.min-1 vs 55.5 (SEM 5.1) ml.kg-1.min-1, P < 0.01]. There was no significant difference between the two groups during passive recovery for tau 2. During partially active recovery, tau 2 was higher than during passive recovery for both groups (P < 0.001), but ET recovered faster and sooner than ST (P < 0.05). Compared to passive recovery, the tau 2 measured during partially active recovery was increased threefold in ET and only 1.5-fold in ST. We concluded that partially active recovery potentiates the enhanced ability to remove blood lactate induced by endurance training.

Adult↗

PubMed1996

Differences in mouth occlusion pressure and breathing pattern between arm and leg incremental exercise.

The aim of the study was to compare breathing pattern, mouth occlusion pressure, mean inspiratory flow and the ratio of mouth occlusion pressure to mean inspiratory flow at the same power output and carbon dioxide output during arm and leg incremental exercise. Mouth occlusion pressure was used as an index of inspiratory neuromuscular activity and its ratio to mean inspiratory flow as an index of the 'effective' impedance of the respiratory system. Eight normal subjects performed two incremental exercise tests, one with arms, the other with legs, on different weeks and in randomized order, and on two identical cycle ergometers. The power output was increased by steps of 25 W for arms and 50 W for legs every 4 min until exhaustion. At the same power output, oxygen consumption, carbon dioxide output, ventilation, mean inspiratory flow, mouth occlusion pressure, 'effective' impedance (P < 0.001) and respiratory frequency (P < 0.01) were higher during arm exercise than during leg exercise, whereas inspiratory time (P < 0.05) and expiratory time (P < 0.01) were lower. At the same carbon dioxide output, mouth occlusion pressure, ventilation, 'effective' impedance (P < 0.001) and respiratory frequency (P < 0.01) were higher and expiratory time (P < 0.05) was lower during arm exercise. In conclusion, the higher inspiratory neuromuscular activity and impedance of the respiratory system during arm exercise and the differences observed in ventilation and breathing pattern at equal carbon dioxide output seem related to the differences in exercising muscle afferents and the presence of an increased load due to contraction of rib cage muscles to stabilize posture.

Adult↗

PubMed1996

Effects of active recovery on plasma lactate and anaerobic power following repeated intensive exercise.

The purpose of this study was to investigate the effects of active recovery (AR) on plasma lactate concentration [La] and anaerobic power output as measured during repeated bouts of intense exercise (6 s) against increasing braking forces. Ten male subjects performed two randomly assigned exercise trials: one with a 5-min passive recovery (PR) after each exercise bout and one with a 5-min active recovery (AR) at a workload corresponding to 32% of maximal aerobic power. Blood samples were taken at rest, at the end of each exercise bout (S1) and at the 5th minute between bout-recovery (S2) for plasma lactate assay. During the tests, [La]S1 was not significantly different after AR and PR, but [La]S2 was significantly lower after AR for power outputs obtained at braking forces 6 kg (5.66 +/- 0.38 vs 7.56 +/- 0.51 mmol.l-1) and peak anaerobic power (PAnP) (6.73 +/- 0.61 vs 8.54 +/- 0.89 mmol.l-1). Power outputs obtained at 2 and 4 kg did not differ after AR and PR. However, when compared with PR, AR induced a significant increase in both power outputs at 6 kg (842 +/- 35 vs 798 +/- 33 W) and PAnP (945 +/- 56 vs 883 +/- 58 W). These results showed that AR between bouts of intensive exercise decreased blood lactate concentration at high braking forces. This decrease was accompanied by higher anaerobic power outputs at these forces.

Adult↗

PubMed1996

Lactate uptake by skeletal muscle sarcolemmal vesicles decreases after 4 wk of hindlimb unweighting in rats.

We investigated the effects of 4 wk of hypodynamia on the rate of lactate transport in skeletal muscle sarcolemmal vesicles from control and hindlimb-suspended rats. Characterization of the sarcolemmal preparations was achieved with a marker enzyme (K+-p-nitrophenylphosphatase) and measurement of 1 mM [U-14C]lactate transport activity under zero-trans conditions with or without a pH gradient or the transport inhibitor alpha-hydroxycinnamate. Preparations from the two groups were not significantly different concerning yield and purification. Based on these results, we used this model to analyze the lactate transport activity after hypodynamia by tail suspension. Hindlimb suspension caused a shift from slow to fast myosin heavy chain isoforms in soleus muscles with a 40% decrease in the citrate synthase activity (from 35.3 +/- 3.7 to 21.4 +/- 2.1 mu mol x g-1 x min-1; P < 0.05). Lactate (1 mM) uptake in vesicles from the two groups was a function of time, and the rate after hindlimb suspension was significantly decreased in the suspended compared with the control group (2.25 +/- 0.44 and 3.50 +/- 0.26 nmol x min-1 x mg protein-1, respectively; P < 0.05). These differences were not observed for a higher lactate concentration (50 mM). These results suggest that the level of physical activity plays a role in the regulation of sarcolemmal lactate transport activity implicated in the exchanges of lactate between producing and utilizing cells, organs, and tissues, which are major ways of carbohydrate energy distribution in humans and others species.

4-Nitrophenylphosphatase↗

PubMed1996

[Cardiac adaptation to muscular exercise in children after complete repair of tetralogy of Fallot].

The aim of this study was to assess cardiac adaptation to muscular exercise in children operated for tetralogy of Fallot. Eight children with a history of tetralogy of Fallot were studied and compared with ten control children. The basal evaluation consisted of an electrocardiogram, spirometry in all cases. Chest X-ray and echocardiography in all operated children. A muscular exercise stress test with incremental load on a bicycle ergometer was carried out with measurement of the cardiac output by CO2 rebreathing (experimental method). Under resting conditions, the two groups were comparable with respect to anthropometrical parameters and respiratory function. The cardiovascular data confirmed the good postoperative results of the children with a history of tetralogy of Fallot; cardiothoracic index of 0.49 to 0.55; sinus rhythm on the electrocardiogram; right ventricular pressures within normal limits; residual instantaneous right ventricular-pulmonary artery pressure gradient less than 25 mmH. On exercise, there was no significant difference with respect to VO2max, maximal heart rate, maximal cardiac output and maximal ventilation. The relationship between cardiac output and oxygen consumption was linear in two groups: y = 8.17x + 1.95 in the control group, y = 8.57x + 2.82 in the operated children. The change in cardiac output on exercise was comparable in the two groups. These observations seemed to be related to the good postoperative haemodynamic result: absence of pulmonary sequellae and right ventricular dysfunction. Despite the normality of the results obtained in this series, exercise stress testing with analysis of cardiac and respiratory adaptation would seem to be necessary in the follow-up of children operated for tetralogy of Fallot to exclude a ventilatory or circulatory limitation.

Adaptation, Physiological↗

PubMed1995

Influence of the delay of denervation on slow striated muscle resistance to slow-to-fast conversion following cross-innervation.

Cross-reinnervation, in cases of nerve repair or nerve transfer, can be the consequence of wrong connections which are surgically induced between the different types of motoneurons (fast and slow). A slow muscle nerve is able to convert a fast muscle virtually completely to the slow fibre type, whereas a fast muscle nerve exerts an incomplete control over the properties of a slow muscle. Our experiments show that following delayed cross-reinnervation, a statistically significant slow-to-fast transformation of the soleus muscle was observed, with a maximum when nerve repair was performed 6 weeks following nerve section in the rat model. Thus, the negative consequences on nerve and muscle relationship due to cross-reinnervation in the case of wrong connections between slow and fast motoneurons after conventional nerve suture or in the case of nerve transfer could be minimised by imposing a delay before nerve repair.

Animals↗

PubMed1995

[Evolution of breathing pattern and ventilation at maximal exercise during growth. Definition of reference values].

The aim of the study was to define the changes of parameters of breathing pattern and ventilation (VE) as a function of age during maximal exercise in children. A multi-longitudinal survey was conducted in forty four untrained schoolboys, divided in three groups with initial age of 11.2 years for group I, 12.9 years for group II, and 14.9 for group III. These children were subsequently followed three years ago at the same period. The range age was thus 11.2 to 16.9 years. This study showed that, during growth, ventilation (VE max), tidal volume (VT max) and mean inspiratory flow (VT/TI max) increased significantly with age, that inspiratory frequency (f max) decreased, that inspiratory, expiratory and total time of the respiratory cycle (TI max, TE max, TTOT max) increased slightly and that the inspiration fraction (TI/TTOT max) was identical at 11 and 17 years. Furthermore we observed that the peak height velocity and peak tidal volume velocity took place at the same age, i.e., 14 years and that those of weight and VT/TI at the same age of 15 years. In conclusion, this study allowed us to define reference values for breathing pattern at maximal exercise in sedentary boys and to specify the relation between growth and parameters of breathing pattern in these children.

Adolescent↗

PubMed1995

[Effect of hypodynamia on initial speed of lactate transport in skeletal muscle sarcolemmal vesicles in rats].

Skeletal muscle sarcolemmal vesicles from control (C) and hindlimb suspended (S) rats were used to investigate the effect of unweighting on the lactate transporter activity. Sarcolemmal preparations were not different between the two groups. The efficiency of 4 weeks of hindlimb suspension was confirmed by a 40% decrease of citrate synthetase activity and a shift towards faster myosin isoforms in soleus muscle. The time course of 1 mM lactate uptake showed that the equilibrium was reached faster in group C (20 s) than in group S (40 s). The initial rate of 1 mM of lactate uptake decreased significantly (p < 0.05) after 4 weeks of hindlimb suspension. The initial rate of 50 mM lactate uptake did not differ significantly between the two groups. We conclude that 4 weeks of unweighting decreases significantly the skeletal muscle sarcolemmal lactate transport activity in rats. This result suggests that the level of physical activity probably plays a role on lactate transport regulation in muscle.

Animals↗

PubMed1994

Sickle cell trait as a limiting factor for high-level performance in a semi-marathon.

Of 1506 black males participating in the first Abidjan semi-marathon, 123 subjects with sickle cell trait (SCT) were detected, i.e., 8.7%. Twenty-nine of these subjects with hemoglobin S (HbS) were ranked among the first 332 participants to finish the race, a percentage of 8.2. These percentages did not significantly differ from the prevalence of SCT observed in the general Ivory Coast population (12.0%). Only one subject with SCT was found among the 22 internationally-ranked athletes. The concentration of HbS found in this athlete (37.7%), his mean globular volume (87 fl), and his hemoglobin concentration (13.8 g/100 ml) suggest the coexistence of alpha-thalassemia with SCT. These results indicate that the percentage of SCT individuals participating in a semi-marathon is equal to the prevalence of SCT found in the local population. Furthermore, the general ranking of SCT individuals is comparable to that of non-SCT individuals. Nevertheless, at the level of internationally-ranked performance, no subject with SCT only, was ranked; the one ranked subject with SCT presented an associated alpha thalassemia. We thus hypothesize that SCT may be a limiting factor for high level performance in a semi-marathon and alpha-thalassemia, an enhancing factor for subjects with SCT to succeed in long distance races.

Adolescent↗

PubMed1994

Performance and metabolic effects of benzodiazepine during submaximal exercise.

The present study examined whether benzodiazepine (BZ) intake alters performance and selected hormonal and metabolic variables during submaximal exercise. Seven triathletes completed two cycling trials at 85% maximum O2 uptake starting 3 h after an ingestion of either a placebo (PLA) of gelatin or BZ (1.5 mg lorazepam) and continuing until exhaustion, according to a double-blind randomized protocol. Blood samples were collected at rest; 5, 10, and 15 min; and exhaustion for dopamine (DA), norepinephrine (NE), epinephrine (Epi), adrenocorticotropic hormone (ACTH), cortisol (CORT), insulin (INS), free fatty acid, blood glucose, and lactate (La) determinations. Time of cycling was not significantly changed after BZ or PLA administration (22.9 +/- 2.5 vs. 23.5 +/- 3.8 min, respectively). A decrease in CORT and an increase in INS (P < 0.05) were observed with BZ before cycling. In comparison with rest, exercise resulted in a decrease in INS and an increase in all the other variables investigated (P < 0.001), but DA, NE, Epi, ACTH, CORT, La, and free fatty acid were significantly less elevated under BZ (P < 0.05). No change was found in glucose and INS levels between the two treatments at the end of the test. There was a strong correlation under both PLA and BZ conditions between DA, NE, Epi, and ACTH and also between Epi and La levels. From these data, BZ intake did appear to alter metabolism but did not influence performance during intense submaximal exercise.

Adrenocorticotropic Hormone↗

PubMed1992

Caffeine increases maximal anaerobic power and blood lactate concentration.

The aim of this study was to specify the effects of caffeine on maximal anaerobic power (Wmax). A group of 14 subjects ingested caffeine (250 mg) or placebo in random double-blind order. The Wmax was determined using a force-velocity exercise test. In addition, we measured blood lactate concentration for each load at the end of pedalling and after 5 min of recovery. We observed that caffeine increased Wmax [964 (SEM 65.77) W with caffeine vs 903.7 (SEM 52.62) W with placebo; P less than 0.02] and blood lactate concentration both at the end of pedalling [8.36 (SEM 0.95) mmol.l-1 with caffeine vs 7.17 (SEM 0.53) mmol.l-1 with placebo; P less than 0.01] and after 5 min of recovery [10.23 (SEM 0.97) mmol.l-1 with caffeine vs 8.35 (SEM 0.66) mmol.l-1 with placebo; P less than 0.04]. The quotient lactate concentration/power (mmol.l-1.W-1) also increased with caffeine at the end of pedalling [7.6.10(-3) (SEM 3.82.10(-5)) vs 6.85.10(-3) (SEM 3.01.10(-5)); P less than 0.01] and after 5 min of recovery [9.82.10(-3) (SEM 4.28.10(-5)) vs 8.84.10(-3) (SEM 3.58.10(-5)); P less than 0.02]. We concluded that caffeine increased both Wmax and blood lactate concentration.

Adult↗

PubMed1991

Effects of moderate exercise on the pharmacokinetics of caffeine.

The effect of moderate exercise on the kinetics of caffeine in 12 healthy volunteers-6 heavy coffee drinkers (HD) and 6 light coffee drinkers (LD) has been studied. Kinetics at Rest was measured first (R): the subjects remained at rest for 8 h after a single 250 mg dose of caffeine. One week later, the Exercise Kinetics (E) was measured under the same conditions, but with the subjects performing moderate exercise (30% of VO2 max) during the first hour of the study. Exercise raised the maximal plasma caffeine concentrations (R: 7.28: E: 10.45) and reduced both the half-life (R 3.99 h: E 2.29 h) and the volume of distribution (R 37 l: E 20.9 l). Both during exercise and at rest. HD had a greater half-life elimination and volume of distribution than LD. The results suggest potentiation of the effects of caffeine during exercise and an increase in its distribution due to regular heavy coffee intake.

Administration, Oral↗

PubMed1991

Blood lactate increase during the force velocity exercise test.

Venous blood lactate concentration was measured during the force velocity exercise test in order to determine whether this test is strictly alactic or whether it draws upon lactic anaerobic metabolism. Nine trained male subjects, aged from 23 to 29 years, participated in this study. Two blood samples were drawn at rest, and then for each work load (1 kg to 10 kg): at the end of each sprint (S1) and at the 5th minute of recovery (S2). From the first braking force, venous blood lactate concentration increased very significantly during the force velocity test (p less than 0.001) and, once the peak of power has been obtained, the venous blood lactate concentration remained steady. The lactate increase for each load (delta[LA]) decreased significantly (p less than 0.01). From the beginning of the exercise to the peak of power, a significant positive correlation between the increase of power and the increase of blood lactate concentration measured at S2 existed (r = 0.71, p less than 0.001), whereas there was a negative correlation between the decrease of delta[LA] and the increase of power (r = -0.45, p less than 0.01). In conclusion, the repetition of sprints during the force velocity test induced a recruitment of lactic anaerobic metabolism. Maximal power must be considered as an alactic and lactic anaerobic power. The consequences of lactate accumulation in muscle may be a limitation of the maximal anaerobic power.

Acceleration↗