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Biomedical subjects

Michèle Ramonatxo

Publications and source records attributed to Michèle Ramonatxo.

8 recordsLinked to original sources
PubMed2005

Effects of short vs. prolonged mechanical ventilation on antioxidant systems in piglet diaphragm.

OBJECTIVE: Prolonged controlled mechanical ventilation (MV) is known to induce diaphragmatic oxidative stress that seems to be an important factor reducing force-generating capacity. To better understand the cellular mechanisms involved, this work examined the effect of short vs. prolonged MV on antioxidant defense in the diaphragm. DESIGN AND SETTING: Prospective, randomized, controlled animal study in a university laboratory. METHODS: Eleven piglets (15-20 kg) were assigned to one of two groups: a long-MV group (n=6) ventilated for 3 days or a short-MV group (n=5) ventilated for 3 h. Force frequency curves of the transdiaphragmatic pressure (Pdi) were obtained in vivo by phrenic nerve pacing. Oxidative stress was evaluated by thiobarbituric reactive substance (TBARs) content and the enzymatic antioxidant activity of both superoxide dismutase (SOD) and glutathione peroxidase (GPx) in samples of diaphragm. RESULTS: Pdi decreased in the long-MV group by 30-35% over the 3 days at all frequencies compared to the short-MV group. Diaphragm TBARs content was significantly higher and SOD activity lower in long-MV animals than in short-MV animals after 72 h. GPx activity tended to be lower in diaphragms from long-MV animals, but this difference was not significant. CONCLUSIONS: This study shows that 3 days of MV in piglets is associated with a decrease in antioxidant activity which could emphasize oxidative stress and both contribute to the diaphragm dysfunction caused by MV.

Animals↗
PubMed2005

Changes in respiratory muscle endurance during puberty.

The evaluation of respiratory muscle endurance provides clinically useful information on muscle function, especially in children with respiratory and neuromuscular diseases. However, endurance may be lower in young children than in older children because of the major physical changes of puberty. We thus compared respiratory muscle endurance in 15 healthy pre- and peripubertal children (S1-S2/P1 group) and 14 healthy children near the end of the pubertal process (S4P4 group). All performed a respiratory muscle endurance test threshold load fixed at 50% of the individual maximal inspiratory pressure; (Pi(max)), using a standardized method with a controlled breathing pattern. No significant difference was found between groups for Pi(max). The mean endurance time limit for the S1-S2/P1 group was 138 +/- 20 sec. The S4P4 group was able to breathe with the threshold valve for more than 20 min (1,200 sec) without task failure, except for one girl (385 sec). This study shows that inspiratory muscle endurance is significantly lower in children in early puberty compared to children at the end of the pubertal process. If the underlying mechanisms are not well-known, the present study revealed that if we use the same inspiratory load in prepubertal children as in adults during clinical testing, we are likely to underestimate the susceptibility to task failure of their respiratory muscles. To define a fatigue threshold for the respiratory muscles, as a function of age, thus appears clinically important in further studies, particularly for the management of children with respiratory diseases.

Adolescent↗
PubMed2005

L-arginine improves dystrophic phenotype in mdx mice.

A possible treatment for Duchenne muscular dystrophies would be to compensate for dystrophin loss by increasing the expression of utrophin, another cytoskeletal protein of the muscle membrane. We previously found that L-arginine, the substrate for nitric oxide synthase, significantly increased utrophin level in muscle and targeted it to the sarcolemma. Here, we have addressed the expected benefit in the mdx mice. Magnetic resonance imaging of lower limbs revealed a 35% reduction of the necrotic zones, confirmed by histological staining of muscles. This regression of the necrosis was also supported by the drastic reduction of Evans blue incorporation, a cell impermeable dye. The creatine kinase level in the serum decreased by 57%. Utrophin level increased 2- to 3-fold in muscles. Beta-dystroglycan was relocalised with utrophin to the membrane. In the diaphragm, the most affected muscle in mdx mice, the isometric tension increased by 30%, with regression of collagen and of cytoplasmic lipid overloading. Finally, molsidomine, a therapeutic agent that is converted to a NO donor, also attenuated the dystrophic phenotype. Our results suggest that pharmacological activators of the NO pathway may constitute a realistic treatment for Duchenne and Becker muscular dystrophies.

Animals↗
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↗
PubMed2002

Effects of controlled mechanical ventilation on respiratory muscle contractile properties in rabbits.

OBJECTIVE: We examined in rabbits the effects of more than 48 h of mechanical ventilation on the contractile properties and fiber type adaptations of the respiratory muscles. DESIGN AND SETTING: Experimental prospective study in a university laboratory. ANIMALS AND INTERVENTIONS: Nineteen rabbits were randomly allocated to two groups: control (n=10) or mechanically ventilated (MV; n=9) for 51+/-3 h. MEASUREMENTS AND RESULTS: Respiratory muscles contractile properties were analyzed before and after a fatigue protocol using in vivo isometric 1-s tetanic contraction characteristics in both muscles: peak tetanic force, contraction time, relaxation time, and total contraction time. Both muscle fiber type proportions, diameter, and cross-sectional areas were measured using ATPase staining. The MV rabbits showed significant weight loss in both muscles, accompanied by a reduced peak tetanic force (9.96+/-3.2 vs. 7.44+/-2.2 N for diaphragm of control and MV animals respectively), fatigue resistance index, and increased relaxation time (57.5+/-8.7 vs. 85.8+/-9.4 ms for diaphragm of control and MV animals) and contraction time. These impairments in the MV group worsened after the fatigue runs. Both muscle showed a significant atrophy of type IIa and IIb fibers but a stability in type I fibers cross-sectional area. CONCLUSIONS: Mechanical ventilation in rabbits produces alterations in contractile properties of the diaphragm and 5th external intercostal muscle, increases both muscles fatigue, and promotes atrophy of type II fibers.

Animals↗
PubMed2002

Post-extubation stridor in intensive care unit patients. Risk factors evaluation and importance of the cuff-leak test.

OBJECTIVE: To evaluate the incidence and identify factors associated with the occurrence of post-extubation stridor and to evaluate the performance of the cuff-leak test in detecting this complication. DESIGN: Prospective, clinical investigation. SETTING: Intensive care unit of a university hospital. PATIENTS: Hundred twelve extubations were analyzed in 112 patients during a 14-month period. INTERVENTION: A cuff-leak test before each extubation. MEASUREMENTS AND RESULTS: The incidence of stridor was 12%. When we chose the thresholds of 130 ml and 12% to quantify the cuff-leak volume, the sensitivity and the specificity of the test were, respectively, 85% and 95%. The patients who developed stridor had a cuff leak significantly lower than the others, expressed in absolute values (372+/-170 vs 59+/-92 ml, p<0.001) or in relative values (56+/-20 vs 9+/-13%, p<0.001). Stridor was associated with an elevated Simplified Acute Physiology Score (SAPS II), a medical reason for admission, a traumatic or difficult intubation, a history of self-extubation, an over-inflated balloon cuff at admission to ICU and a prolonged period of intubation. These results provide a framework with which to identify patients at risk of developing a stridor after extubation. CONCLUSION: A low cuff-leak volume (<130 ml or 12%) around the endotracheal tube prior to extubation is useful in identifying patients at risk for post-extubation stridor.

Airway Obstruction↗
PubMed2002

Comparison of the effects of heat and moisture exchangers and heated humidifiers on ventilation and gas exchange during non-invasive ventilation.

OBJECTIVE: To compare the short-term effects of a heat and moisture exchanger (HME) and a heated humidifier (HH) during non-invasive ventilation (NIV). DESIGN: Prospective, clinical investigation. SETTING: Intensive care unit of a university hospital. PATIENTS: Twenty-four patients with acute respiratory failure (ARF). INTERVENTION: Each patient was studied with a HME and a HH in a random order during two consecutive 20min periods of NIV. MEASUREMENTS AND RESULTS: Respiratory rate (RR), expiratory tidal volume (VTe) and expiratory minute ventilation (VE) were measured during the last 5 min of each period and blood gases were measured. Mean pressure support and positive end-expiratory pressure levels were, respectively, 15+/-4 and 6+/-2 cmH(2)O. VE was significantly greater with HME than with HH (14.8+/-4.8 vs 13.2+/-4.3 l/min; p<0.001). This increase in VE was the result of a greater RR for HME than for HH (26.5+/-10.6 vs 24.1+/-9.8 breaths/min; p=0.002), whereas the VT for HME was similar to that for HH (674+/-156 vs 643+/-148 ml; p=0.09). Arterial partial pressure of carbon dioxide (PaCO(2)) was significantly higher with a HME than with a HH (43.4+/-8.9 vs 40.8+/-8.2 mmHg; p<0.005), without significantly changing oxygenation. CONCLUSION: During NIV the increased dead space of a HME can negatively affect ventilatory function and gas exchange. The effect of HME dead space may decrease efficiency of NIV in patients with ARF.

Acute Disease↗