Alain Varray

Evidence of local exercise-induced systemic oxidative stress in chronic obstructive pulmonary disease patients

Chronic inactivity may not be the sole factor involved in the myopathy of chronic obstructive pulmonary disease (COPD) patients. One hypothesis is that exercise-induced oxidative stress that leads to muscle alterations may also be involved. This study investigated whether exercise localised to a peripheral muscle group would induce oxidative stress in COPD patients. Eleven COPD patients (FEV1 1.15±0.4 L (mean±sd)) and 12 healthy age-matched subjects with a similar low quantity of physical activity performed endurance exercise localised to a peripheral muscle group, the quadriceps of the dominant leg. The authors measured plasma levels of thiobarbituric reactive substances (TBARs) as an index of oxidative stress, the release in superoxide anion (O2·−) by stimulated phagocytes as an oxidant, and blood vitamin E as one antioxidant. Quadriceps endurance was significantly lower in the COPD patients compared with healthy subjects (136±16 s versus 385±69 s (mean±sem), respectively). A significant increase in TBARs 6 h after quadriceps exercise was only found in the COPD patients. In addition, significantly higher O2·− release and lower blood vitamin E levels were found in COPD patients than in controls at rest. This blood vitamin E level was significantly correlated with the resting level of plasma TBARs in the COPD patients. This study mainly showed that quadriceps exercise induced systemic oxidative stress in chronic obstructive pulmonary disease patients and that vitamin E levels were decreased in these patients at rest. The exact relevance of these findings to chronic obstructive pulmonary disease myopathy needs to be elucidated.

Validation of an incremental field test for the direct assessment of peak oxygen uptake in wheelchair-dependent athletes

The aim of this study was to validate an incremental field test performed by wheelchair-dependent (WD) athletes. Nine male paraplegic subjects (mean age: 28.9±4.2 years) performed an incremental field test (FT) and a comparable laboratory test (LT) with their own usual wheelchairs. Both tests started with an initial speed of 4 km.hr-1 and increased by increments of 1 km.hr-1 every minute until volitional exhaustion. The FT was an adapted Léger and Boucher test (ALBT) and was conducted on a 400 m tartan field marked-off every 50 m with pylons. Ventilatory data were collected every 15 s using a portable telemetric system (Cosmed K2, JFB International, Italy). The LT was performed on an adapted treadmill (Sopur, Germany) and ventilatory data were collected every minute using a breath-by-breath automated system (CPX, Medical Graphics, MN, USA). The LT and the FT were not significantly different for duration (8 min 50 ±1 min 24 vs 9 min 55 ±29 s), percentage of maximal heart rate (HR, 86.2±3.9 vs 89.7±5.3%), maximal minute ventilation (Ve, 101.6±28.5 vs 96.8±28.2 l.min-1), and peak oxygen uptake (Vo2 peak, 39.7 + 7.3 vs 36.1 + 5.8 ml.kg-1.min-1) assessed with the CPX and the K2, respectively. We concluded that the FT proposed in the present study is a valid test for direct Vo2 peak assessment in wheelchair athletes using a portable Vo2 telemetric system. Nonetheless, the Léger and Mercier model equation did not accurately predict Vo2 max and further investigation is needed to determine a valid Vo2 max prediction equation for these subjects during the FT.

Recurrence quantification analysis of surface electromyographic signal: Sensitivity to potentiation and neuromuscular fatigue

This study aimed to assess the capacity of recurrence quantification analysis (RQA) to detect potentiation and to determine the fatigue components to which RQA is sensitive. Fifteen men were divided in two groups [8 endurance-trained athletes (END) and 7 power-trained athletes (POW)]. They performed a 10-min intermittent (5s contraction, 5s rest) knee extension exercise at 50% of their maximal voluntary isometric contraction. Muscular fatigue and potentiation were evaluated with neurostimulation technique. Mechanical (peak torque, Pt) and electrophysiological (M-wave) responses following electrical stimulation of the femoral nerve were measured at rest and every 10s throughout exercise. Vastus lateralis muscle activity (root mean square, RMS) was recorded during each contraction, and RMS was normalized to M-wave area (RMS/M). During contraction, muscle activity was analyzed with RQA to obtain the percentage of determinism (%Det). At the beginning of exercise, a significant Pt increase (+52%, P<0.001) was observed in both groups, indicating potentiation. At this time, %Det remained constant in both groups, indicating that RQA did not detect potentiation. Thereafter, Pt decreased in POW from 5min 30s of exercise (-30%, P<0.001), reflecting impairment in excitation-contraction coupling, and %Det increased from 3min 30s (P<0.01). In END, Pt remained high and %Det was unchanged. These two results indicated that RQA detected the peripheral component of fatigue. Conversely, RQA did not detect central adaptation to fatigue since %Det remained constant when a significant increase in RMS/M (P<0.01) appeared in END.

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. Muscle Nerve 27: 170–179, 2003

Influence of lesion level on the cardioventilatory adaptations in paraplegic wheelchair athletes during muscular exercise

Objectives: To characterize the influence of neurological lesion level on the cardiorespiratory and ventilatory responses of two groups of paraplegic athletes during incremental exercise on a treadmill and in the usual conditions for wheelchair exercise.Methods: Cardioventilatory responses evaluated in two groups of paraplegic wheelchair sportsmen designated as high paraplegic athletes (HPA) and low paraplegic athletes (LPA). After 2 min of data collection at rest and 3 min of warm-up at 4 km.h−1, treadmill speed was increased by 1 km.h−1 every minute until exhaustion. During this test, ventilation and its components, as well as respiratory exchanges, were measured breath by breath (C.P.X. Medical Graphics) every minute by taking the mean of the last 20 s of each increment.Results: Spirometric values presented no significant differences between groups. At rest, no significant difference was observed between the two groups for all cardiorespiratory and ventilatory values obtained during the treadmill test. At submaximal exercise, all variables increased with the augmentation in workload. With the exception of R, there were no significant differences in the classic cardiorespiratory parameters (V˙O2, V˙CO2, HR, V˙E) between the two groups of paraplegics. For the ventilatory parameters, we observed significant differences between the two groups, with values of f and It/Trf significantly higher (0.01<P<0.001) and values of Trf and Vt significantly lower (0.01<P<0.001) for HPA versus LPA. We observed changes in breathing pattern, ie, in f, Vt, Trc and It/Trc, were significantly different between groups, with significantly higher values of f and It/Trc for HPA. We noted a ventilatory disturbance which was manifested by values of breathing frequency and tidal volume during exercise that were significantly different between groups. During maximal exercise, we observed no significant differences between the two groups concerning cardiorespiratory and ventilatory values. Despite the absence of significant differences, the more linear time course of the ensemble of HPA flows, the achievement of a greater number of work loads, and the higher maximal values indicate a better capacity for adaptation to exercise in the group of lower thoracic paraplegics.Conclusion: These results raise questions about the influence of neurological level and further research is needed to define with more precision the capacities of readaptation of the different cardiovascular and respiratory functions, as well as the training methods best adapted to the optimization of physical capacities.Spinal Cord (2000) 38, 16–25.

Aerobic metabolism and cardioventilatory responses in paraplegic athletes during an incremental wheelchair exercise

Abstract The aims of the present study were: (1) to assess aerobic metabolism in paraplegic (P) athletes (spinal lesion level, T4–L3) by means of peak oxygen uptake (V˙O2peak) and ventilatory threshold (VT), and (2) to determine the nature of exercise limitation in these athletes by means of cardioventilatory responses at peak exercise. Eight P athletes underwent conventional spirographic measurements and then performed an incremental wheelchair exercise on an adapted treadmill. Ventilatory data were collected every minute using an automated metabolic system: ventilation (l · min−1), oxygen uptake (V˙O2, l · min−1, ml · min−1 · kg−1), carbon dioxide production (V˙CO2, ml · min−1), respiratory exchange ratio, breathing frequency and tidal volume. Heart rate (HR, beats · min−1) was collected with the aid of a standard electrocardiogram. V˙O2peak was determined using conventional criteria. VT was determined by the breakpoint in the V˙CO2−V˙O2 relationship, and is expressed as the absolute VT (V˙O2, ml · min−1 · kg−1) and relative VT (percentage of V˙O2peak). Spirometric values and cardioventilatory responses at rest and at peak exercise allowed the measurement of ventilatory reserve (VR), heart rate reserve (HRr), heart rate response (HRR), and O2 pulse (O2 P). Results showed a V˙O2peak value of 40.6 (2.5) ml · min−1 · kg−1, an absolute VT detected at 23.1 (1.5) ml · min−1 · kg−1V˙O2 and a relative VT at 56.4 (2.2)% V˙O2peak. HRr [15.8 (3.2) beats · min−1], HRR [48.6 (4.3) beat · l−1], and O2 P [0.23 (0.02) ml · kg−1 · beat−1] were normal, whereas VR at peak exercise [42.7 (2.4)%] was increased. As wheelchair exercise excluded the use of an able-bodied (AB) control group, we compared our V˙O2peak and VT results with those for other P subjects and AB controls reported in the literature, and we compared our cardioventilatory responses with those for respiratory and cardiac patients. The low V˙O2peak values obtained compared with subject values obtained during an arm-crank exercise may be due to a reduced active muscle mass. Absolute VT was somewhat comparable to that of AB subjects, mainly due to the similar muscle mass involved in wheelchair and arm-crank exercise by P and AB subjects, respectively. The increased VR, as reported in patients with chronic heart failure, suggested that P athletes exhibited cardiac limitation at peak exercise, and this contributed to the lower V˙O2peak measured in these subjects.

An innovative maintenance follow-up program after a first inpatient pulmonary rehabilitation

Although the benefits of pulmonary rehabilitation (PR) have been demonstrated in patients with COPD, most studies suggest that short-term programs are insufficient to maintain the benefits beyond a post-discharge period of 6 months to 1 year. We were interested to evaluate the effects of an innovative maintenance intervention compared with a usual after-care. Forty moderate to severe COPD patients, who had just completed their first inpatient PR, were consecutively included in either a maintenance group (MG) or a standard after-care group. The maintenance program was coordinated within a health-care network including self-help associations, and offered weekly activities. We measured the 6-min walk distance (6MWD), the quality of life using the St George Respiratory Questionnaire (SGRQ), the dyspnea, the maximal workload and the health-care utilization. Data were collected at respiratory clinic admission and discharge, and at 6- and 12-month visits after the PR. After 12 months, we found statistically and clinically significant differences in favor of the MG in 6MWD (74 m; p < or = 0.01) and in the three domains of SGRQ: symptom (19%; p < or = 0.01), activity (27%; p < or = 0.01) and impact (32%; p < or = 0.01). The results showed no difference between groups in dyspnea and maximal workload. We also found that the number of days spent in hospital for respiratory disorders was significantly lower in the MG after 12 months (p < or = 0.03). The multidisciplinary management of COPD patients in the post-rehabilitation period within a health-care network including self-help associations seems to be an effective strategy for maintaining, and even improving, the benefits of a first initial structured program.

Respiratory gas exchange indices used to detect the blood lactate accumulation threshold during an incremental exercise test in young athletes

SummaryThe time course of changes in blood lactate concentration and ventilatory gas exchange was studied during an incremental exercise test on a cycle ergometer to determine if the lactate accumulation threshold (LT2) could be accurately estimated by the use of respiratory indices (VT2) in young athletes. LT2 was defined as the starting point of accelerated lactate accumulation. VT2 was identified by the second exponential increase in

Factor analysis of quality of life, dyspnea, and physiologic variables in patients with chronic obstructive pulmonary disease before and after rehabilitation

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