Twitch mouth pressure for detecting respiratory muscle weakness in suspicion of neuromuscular disorder.

Twitch mouth pressure using magnetic stimulation of the phrenic nerves and an automated inspiratory trigger is a noninvasive, non-volitional assessment of diaphragmatic strength. Our aims were to validate this method in patients with suspected neuromuscular disease, to determine the best inspiratory-trigger pressure threshold, and to evaluate whether twitch mouth pressure decreased the overdiagnosis of muscle weakness frequently observed with noninvasive volitional tests. Maximal inspiratory pressure, sniff nasal pressure, and twitch mouth pressure were measured in 112 patients with restrictive disease and suspected neuromuscular disorder. Esophageal and transdiaphragmatic pressures were measured in 64 of these patients to confirm or infirm inspiratory muscle weakness. Magnetic stimulation was triggered by inspiratory pressures of -1 and -5 cmH2O. The -5 cmH2O trigger produced the best correlation between twitch mouth pressure and twitch esophageal pressure (R2 = 0.86; P <0.0001). The best association of noninvasive tests to predict inspiratory muscle weakness was sniff nasal pressure and twitch mouth pressure. Below-normal maximal inspiratory pressure and sniff nasal pressure values suggesting inspiratory muscle weakness were found in 63/112 patients. Only 52 of these 63 patients also had abnormal twitch mouth pressure. In conclusion twitch mouth pressure measurement is a simple, noninvasive, nonvolitional technique which may help to select patients with suspected neuromuscular disorder for invasive inspiratory-muscle investigation.

Respiratory muscle dysfunction in facioscapulohumeral muscular dystrophy.

Respiratory insufficiency in facioscapulohumeral muscular dystrophy has rarely been studied. We compared two age- and sex-matched groups of 29 patients, with and without respiratory dysfunction. Tests in the 29 patients with respiratory dysfunction suggested predominant expiratory muscle dysfunction, leading to ineffective cough in 17 patients. Supine and upright vital capacities were not different (P = 0.76), suggesting absence of diaphragmatic dysfunction. By stepwise regression, only expiratory reserve volume correlated with the Walton and Gardner-Medwin score (R(2) = 0.503; P = 0.001). Compared to controls, patients with respiratory dysfunction had higher values for the Walton and Gardner-Medwin score (6.1 ± 1.9 vs. 3.2 ± 1.2; P <0.0001) and body mass index (26.9 ± 6.0 vs. 22.9 ± 4.0 kg/m(2); P = 0.003) and a smaller number of D4Z4 allele repeats (4.8 ± 1.6 vs. 5.7 ± 1.8; P = 0.05). Mechanical ventilation was required eventually in 20 patients, including 14 who were wheelchair bound. Three patients had acute respiratory failure requiring mechanical ventilation; 16 patients had poor airway clearance, including 10 with sleep apnea syndrome, responsible in 7 for chronic hypercapnia. Two patients presented isolated severe sleep apnea syndrome. Respiratory dysfunction in facioscapulohumeral muscular dystrophy is predominantly related to expiratory muscle weakness. Respiratory function and cough effectiveness should especially be monitored in patients with severe motor impairment and high body mass index.