Biomedical subjects

Christian Préfaut

Publications and source records attributed to Christian Préfaut.

13 recordsLinked to original sources

PubMed2003

Aerobic determinants of the decline in preferred walking speed in healthy, active 65- and 80-year-olds.

The preferred walking speed is a common measure of mobility that declines with age and has been related to maximal oxygen uptake (VO(2,max)). The present study determined whether this decline is associated with a higher percentage of the ventilatory threshold in older adults walking at their preferred speed. We compared the preferred walking speed and VO2 at this speed in relation to both VO(2,max) and VO2 corresponding to the ventilatory threshold (TVE) in healthy, physically active sexagenarians (G65, n=10) and octogenarians (G80, n=10) walking on a treadmill. The preferred walking speed was lower in G80 (1.16+/-0.09 m.s(-1)) than in G65 (1.38+/-0.09 m.s(-1); P<0.001). Energy expenditure and the energy cost of walking at the preferred walking speed were not significantly different between the two groups. G80 subjects exhibited significantly higher fractions of VO(2,max) (60.8+/-8.0%) and TVE (74.2+/-7.9%) at the preferred walking speed than G65 (42.9+/-5.0 and 53.2+/-5.7% respectively; P<0.001). Multiple regression analysis showed that the fraction of TVE was the main determinant, with a small contribution of height, in the decline in the preferred walking speed in healthy and active elderly subjects (R2=64%; P<0.001). These findings show that with age, walking at the preferred speed requires a higher fraction of TVE. This increase in the relative physiological effort at preferred walking speed could explain the reduction in this gait speed in healthy older subjects.

Aged↗

PubMed2003

Faster oxygen uptake kinetics at the onset of submaximal cycling exercise following 4 weeks recombinant human erythropoietin (r-HuEPO) treatment.

We tested the hypothesis that prolonged administration of moderate doses of recombinant human erythropoietin (r-HuEPO) accelerates the initial rate of rise in pulmonary O2 uptake (VO2) in response to submaximal exercise and increases the maximal rate of O2 uptake (VO(2,max)). Sixteen endurance-trained athletes were divided into two groups: r-HuEPO- (n=9) or placebo-treated (n=7). r-HuEPO or placebo (saline) injections were given s.c. 3 times a week for 4 weeks. Exercise testing, before and after the 4 weeks, comprised incremental maximal tests and several transitions from rest to 10-min cycling exercise at 65% VO(2,max). VO2 was measured breath-by-breath during all tests. In the r-HuEPO group, resting haemoglobin concentration (+9.6%) and haematocrit (+8.3%), as well as VO(2,max) (+7.0%) and power output (+7.2%) increased significantly (P<0.05) after the 4 weeks, whereas no change was observed in the control group. The time constant of the primary VO2 response was significantly faster (+18%) after the 4 weeks r-HuEPO treatment than before (mean+/-SD; 29.3+/-4.5 vs. 35.7+/-7.4 s, respectively, P<0.05) but was unaffected in the placebo group (34.5+/-7.3 vs. 33.4+/-7.9 s). Collectively, our findings suggest that r-HuEPO contributes both to an acceleration of the dynamic response of VO2 to submaximal exercise and to an increase in maximal exercise capacity.

Adult↗

PubMed2003

Effects of the order of running and cycling of similar intensity and duration on pulmonary diffusing capacity in triathletes.

To study the pathophysiological mechanisms involved in the decrease of post-triathlon diffusing capacity (DLco), blood rheologic properties (blood viscosity: eta(b); changes in plasma volume: deltaPV) and atrial natriuretic factor (ANF) were assessed in ten triathletes during cycle-run (CR) and run-cycle (RC) trials at a metabolic intensity of 75% of maximal oxygen consumption ( VO(2max)). The DLco was measured before and 10 min after trials. ANF and deltaPV were measured at rest, after the cycle and run of CR and RC trials, and at the end of and 10 min after exercise. RC led to a greater deltaDLco decrease, a lower ANF concentration and a lower deltaPV than did CR, whereas for both CR and RC eta(b) was increased throughout exercise and 10 min after. In addition, after CR the deltaDLco decrease was inversely correlated ( r=-0.764; P<0.01) with deltaPV. The association of decreased plasma volume, increased eta(b), and lower ANF concentrations after RC suggested that lower blood pulmonary volume may have caused the greater decrease in Dlco as compared with CR. The inverse correlation between deltaPV and deltaDLco reinforces the hypothesis that fluid shifts limit the post-exercise DLco decrease after the CR succession in triathletes. Lastly, cycling in the crouched position might increase intra-thoracic pressure, decrease thorax volume due to the forearm position on the handlebars, and weaken peripheral muscular pump efficacy, all of which would limit venous return to the heart, and thus result in low pulmonary blood volume. Compared with cycling, running appeared to induce the opposite effects.

Adult↗

PubMed2003

Exercise-induced quadriceps oxidative stress and peripheral muscle dysfunction in patients with chronic obstructive pulmonary disease.

Exercise-induced muscle oxidative stress may be involved in the myopathy associated with chronic obstructive pulmonary disease (COPD). This study was designed to look at whether local exercise induces muscle oxidative stress and whether this oxidative stress may be associated with the reduced muscle endurance in patients with COPD. Quadriceps endurance was measured in 12 patients with COPD (FEV1 = 0.96 +/- 0.14 SEM) and 10 healthy sedentary subjects by repeated knee extensions of the dominant leg. Biopsies of the vastus lateralis muscle were obtained before and 48 hours after exercise. Muscle oxidative stress was measured by lipid peroxidation and oxidized proteins. Muscle antioxidant was evaluated by peroxidase glutathion activity. Quadriceps endurance was significantly reduced in patients with COPD when compared with the healthy control subjects (p < 0.01). Forty-eight hours postexercise, only patients with COPD had a significant increase in muscle lipid peroxidation (p < 0.05) and oxidized proteins (p < 0.05), whereas increased peroxidase glutathion activity was only observed in control subjects (p < 0.05). Both increases in muscle lipid peroxidation and oxidized proteins were significantly and inversely correlated with quadriceps endurance capacity in COPD (p < 0.05). In summary, local exercise induced muscle oxidative stress in patients with COPD, whereas it failed to raise antioxidant activity. In these individuals, muscle oxidative stress was associated with a reduced quadriceps endurance.

Aged↗

PubMed2003

Electrophysiologic changes during exercise testing in patients with chronic obstructive pulmonary disease.

To determine whether skeletal muscle is involved in the exercise limitation of chronic obstructive pulmonary disease (COPD), we investigated electrical adaptations in muscle during incremental cycling exercise testing. Changes in quadriceps activity were compared using surface electromyography (SEMG) and motor point stimulation in ten COPD patients and ten healthy subjects. Patients showed significantly lower exercise capacity, and M-wave duration was increased from exercise onset (P < 0.05) with a parallel decrease in amplitude (P < 0.05). The SEMG power spectrum median frequency was always higher (P < 0.04) in patients and its decline was earlier (P < 0.01). The ratio of the root mean square of the SEMG to oxygen uptake was decreased (P < 0.001) during exercise in patients, although it remained constant in controls. Electromyographic parameters were significantly more involved in the exercise limitation than ventilatory factors. Thus, modified electrical activity in muscle appeared in COPD patients from exercise onset, indicating that skeletal muscle function is clearly implicated in the exercise intolerance of these patients.

Acidosis↗

PubMed2003

Endurance training improves skeletal muscle electrical activity in active COPD patients.

The effect of endurance training on muscle electrical activity during general exercise testing was investigated in physically active patients with chronic obstructive pulmonary disease (COPD). Before and after rehabilitation, patients performed identical incremental exercise tests. Pulmonary gas exchange, venous lactate and pyruvate concentrations, and the quadriceps electromyographic signal were sampled every minute throughout exercise testing. Three weeks of rehabilitation increased exercise capacity without modifying pulmonary function. M-wave amplitude, root mean square (RMS) of electromyographic activity, and RMS/oxygen uptake were increased significantly during post-rehabilitation testing at the same exercise intensity compared to pre-rehabilitation. Median frequency was significantly lower after training. These modifications reflect greater muscle excitability, greater muscle activation for the same level of exercise, and higher recruitment of slow-twitch fibers. Pulmonary rehabilitation in active COPD patients may normalize the electrical activity of skeletal muscles during incremental dynamic exercise. The electromyographic signal confirms neuromuscular changes after endurance training.

Anaerobic Threshold↗

PubMed2003

Training of aerobic and anaerobic fitness in children with asthma.

OBJECTIVE: To assess the effect of a training protocol on aerobic and anaerobic fitness in children with asthma. STUDY DESIGN: Sixteen boys (mean age: 13 years; range: 10-16 years) with mild-to-moderate asthma participated in a rehabilitation program that included 6 weeks of individualized training on a cycle ergometer. Two groups were randomly formed: the control group (CG, n = 7) and the training group (TG, n = 9), which exercised at an intensity set at the heart rate corresponding to the ventilatory threshold, with 1-minute sprints against the maximal aerobic power (MAP) every 4 minutes. Session duration was 45 minutes, 3 sessions per week. Changes in maximal oxygen uptake (VO(2)max), MAP, short-term peak power (PP), and pulmonary function were assessed. RESULTS: Two patients of the training group did not complete the study. Pulmonary function remained unchanged in both groups. Improvement in both aerobic and anaerobic fitness was significant only in the training group (TG vs CG): VO(2)max +18% +/- 2.1% versus +9% +/- 4.5% (P <.05), MAP +32% +/- 5% versus 12% +/- 7% (P <.05), PP +21% +/- 5.7% versus +8.8% +/- 10% (P <.01). CONCLUSION: Exercise training with high-intensity bouts is well tolerated in children with mild-to-moderate asthma. When included in a global rehabilitation program, this type of training improves both aerobic and anaerobic fitness. Anaerobic activities should be considered in sports rehabilitation programs for children with asthma.

Adolescent↗

PubMed2003

6-minute walk testing is more sensitive than maximal incremental cycle testing for detecting oxygen desaturation in patients with COPD.

STUDY OBJECTIVES: Some respiratory patients exhibit oxygen desaturation during rehabilitative walking but not during maximal cardiopulmonary exercise testing (CPET). We evaluated exercise-induced desaturation during 6-min walk testing (6MWT) in comparison with CPET in patients with COPD and determined the reproducibility of the phenomenon. PATIENTS: We tested 80 consecutive patients with COPD (FEV(1), 62.4 +/- 2% predicted) and 10 patients with supplementary COPD (FEV(1), 59.1 +/- 5% predicted) [mean +/- SEM] to determine the reproducibility. MEASUREMENTS AND RESULTS: First, patients with COPD performed cycle CPET (first CPET [CPET-1]). Three days later, they performed two 6MWTs (first 6MWT [6MWT-1] and second 6MWT [6MWT-2]). Pulse oximetric saturation (SpO(2)) was recorded every minute in both tests. Three groups emerged: desaturation at 6MWT not observed at CPET (DND) [n = 23], desaturation in both tests (n = 16), and no desaturation in either test (n = 41). Second, to evaluate reproducibility, 10 additional subjects with COPD who exhibited desaturation during two successive 6MWTs but not in CPET performed a second CPET (CPET-2) and a single-bout 6MWT (6MWT-3) in a supplementary trial. When two CPETs were performed, lack of O(2) desaturation was noted in both. O(2) desaturation was confirmed in 6MWT-2 and 6MWT-3 (7.4 +/- 1% and 7.4 +/- 1.5%, respectively). CONCLUSION: Twenty-eight percent of patients with COPD presented DND. The phenomenon was reproducible and not protocol dependent, emphasizing the clinical interest of the 6MWT.

Exercise Test↗

PubMed2002

Exhaled nitric oxide level during and after heavy exercise in athletes with exercise-induced hypoxaemia.

Endogenous nitric oxide (NO) is an important mediator of vasodilatation, bronchodilatation and lung inflammation. We hypothesised that the exhaled NO level may be modified in some endurance-trained athletes during and after intense exercise. Nine athletes with exercise-induced hypoxaemia (EIH), 12 athletes without EIH and 10 untrained subjects exercised for 15 min at 90% maximal oxygen consumption (VO(2)max). Exhaled NO was measured during exercise, and after 1 h and 22 h of recovery. Exhaled NO concentration ( C(NO)) decreased significantly during exercise in all subjects and returned to basal values after 1 h of recovery with no further modification. Exhaled NO output (V(NO)) rose significantly during exercise, rapidly dropped down following exercise and was similar to resting values after 1 h and 22 h of recovery. The results also showed that C(NO) and V(NO) were significantly lower in the athletes with EIH in comparison with the untrained subjects (V(NO) was 5.32 +/- 0.77 nmol/min versus 3.61 +/- 0.72 nmol/min at rest, 18.52 +/- 1.50 nmol/min versus 15.00 +/- 2.06 nmol/min during heavy exercise, and 5.52 +/- 1.04 nmol/min versus 3.79 +/- 0.76 nmol/min after 22 h recovery, in untrained subjects and EIH athletes, respectively). These findings do not confirm the hypothesis of pulmonary inflammation associated with EIH. However, potential NO epithelial down-regulation may occur and contribute to the development of gas exchange abnormality in some endurance-trained athletes.

Adult↗

PubMed2002

Effects of streptozotocin-induced diabetes on markers of skeletal muscle metabolism and monocarboxylate transporter 1 to monocarboxylate transporter 4 transporters.

Diabetes is known to alter both oxidative and glycolytic pathways in a fiber type-dependent manner. In various skeletal muscles of normal rats, monocarboxylate transporter 1 (MCT1) has been found to be highly correlated to lactate uptake, as well as to oxidative capacity, whereas the distribution and characteristics of MCT4 make it a good candidate for the extrusion of lactic acid from glycolytic muscle cells. Since a previous study found decreased sarcolemmal lactate uptake in streptozotocin (STZ)-diabetic rats, we investigated the presence of MCT1 in relation to enzymatic markers of both oxidative and glycolytic pathways, as well as MCT4 content, in STZ-diabetic rats. Soleus (SOL), red tibialis anterior (RTA), extensor digitorus longus (EDL), heart, and preparations of purified sarcolemmal vesicles (SV) from control and STZ-diabetic rats were harvested for MCT1 and MCT4 content, citrate synthase activity (CS), and lactate dehydrogenase (LDH) isozymes. Basal blood lactate concentration was increased by 38% in the diabetic rats (close to 1.91 mmol/L). However, no change was found in either MCT1 or MCT4 content in these rats. The diabetic rats presented fiber type-specific decrease in CS activity. We noted a redistribution in LDH isozymes in diabetic muscles with a general increase in type H-LDH. Regression analyses indicated (1) a strong relationship between LDH-4 and LDH-5 and (2) MCT1 was still correlated with CS activity in diabetic muscles. These results suggest that diabetes-induced hyperlactatemia is not associated with changes in MCT1 or MCT4 expression, but with alterations of oxidative and glycolytic enzymes.

Animals↗

PubMed2002

Effects of an enhanced heart rate reserve on aerobic performance in patients with a heart transplant.

OBJECTIVE: The aim of this study was to investigate whether a high-intensity warm-up at the start of a graded, symptom-limited exercise test would enhance heart rate reserve and thus improve the aerobic performance of orthotopic heart transplant patients. DESIGN: Adrenal and cardiorespiratory responses were compared in 10 orthotopic heart transplant patients who performed two graded, symptom-limited exercise tests on an ergocycle. RESULTS: At the start of the graded, symptom-limited exercise test, high intensity increased the norepinephrine level more than usual intensity between rest and the third minute of exercise. This higher norepinephrine level was followed by a higher heart rate response from the fourth minute of exercise. Heart rate reserve was enhanced during high-intensity exercise, without any significant change in peak oxygen uptake. CONCLUSIONS: This specific warm-up enhanced heart rate reserve during a graded, symptom-limited exercise test on an ergocycle. Mechanisms more important than limited heart rate reserve are involved in the limitation of exercise tolerance in orthotopic heart transplant patients.

Adrenergic alpha-Agonists↗

PubMed2002

Effect of training on the GH/IGF-I axis during exercise in middle-aged men: relationship to glucose homeostasis.

The aim of this study was to compare circulating levels of growth hormone (GH), IGF-I, and IGF-binding protein (IGFBP)-1 and IGFBP-3 in response to a long-duration endurance exercise in trained vs. sedentary middle-aged males and to determine whether a relationship with glucose homeostasis exists. Seven trained men (Tr) were compared with seven age-matched sedentary men (Sed) during two trials of 60 min of cycling exercise performed below (-VT) and above (+VT) the ventilatory threshold. Insulin sensitivity (S(I)) was higher in Tr than in Sed (P < 0.001). Basal GH, IGF-I, and IGFBP-1 and -3 were higher in Tr (P < 0.05). During +VT, Tr had a threefold higher GH response, whereas their blood glucose level was better maintained (P < 0.05). Basal IGFBP-1 was correlated with S(I) (P < 0.01). These data indicate that endurance training in middle-aged men increased the activity of the GH/IGF-I system and improved glucoregulation both at rest and during high-intensity endurance exercise.

Adaptation, Physiological↗

PubMedDate not supplied

Gender difference in coping strategies among patients enrolled in an inpatient rehabilitation program.

BACKGROUND: Previous research has not addressed gender differences in coping strategies among patients with mild to moderate chronic obstructive pulmonary disease (COPD) who are enrolled in inpatient and multidisciplinary rehabilitation programs. METHODS: The coping strategies of 182 consecutive patients (61 women aged 61.1 years; 121 men aged 62.7 years) with mild to moderate COPD were assessed on admission and then at discharge after 29 days of pulmonary rehabilitation, using the Coping Inventory for Stressful Situations. A one-way analysis of variance for repeated measures was used to test the differences in coping scores. RESULTS: During the rehabilitation program, problem-focused strategies increased (+2.54 [95% confidence interval: 1.41-3.67] with F=23.77, P<.0001), emotion-focused strategies decreased (-2.75 [95% confidence interval: -4.06, -1.45], F=15.37, P<.001), and avoidance strategies were differently (t=2.97, P<.05) influenced in women (+2.43 [95% confidence interval: .66-4.19]) compared with men (-1.30 [95% confidence interval: -2.82-.22]). The prevalence of COPD in women is increasing, and rehabilitation professionals need a greater awareness of how women cope differently than men with this disease.

Adaptation, Psychological↗