Validation of surface recordings of the diaphragm response to transcranial magnetic stimulation in humans

1 Laboratoire de Physiopathologie Respiratoire, Service de Pneumologie, Groupe Hospitalier Pitié-Salpêtrière, Assistance Publique, Hôpitaux de Paris, 2 Unité Propre de Recherche de l'Enseignement Supérieur EA 2397, Université Pierre et Marie Curie Paris VI, 75013 Paris; and 3 Service de Physiologie Respiratoire et Sportive, Hôpital Charles Nicolle, Centre Hospitalier Universitaire, 76000 Rouen, France The integrity of the central efferent motor pathways to the diaphragm can be assessed by using transcranial magnetic stimulation to measure the latency of the corresponding motor evoked potentials with surface electrodes. Because transcranial magnetic stimulation does not activate the diaphragm alone, signal contamination is a potential problem. To evaluate this issue, surface diaphragmatic motor-evoked potential latencies were compared with latencies recorded from diaphragm needle in 9 healthy volunteers. Surface latencies of muscles likely to contaminate the diaphragm signals (serratus anterior, pectoralis major, and tranversus abdominis) were also recorded. The latencies in response to nonfocal transcranial stimulation from surface electrodes were not significantly different from the needle ones (17 ± 1.3 vs. 17.2 ± 1.1 ms, respectively) but were significantly different from the latencies of the other muscles. In two cases, signal contamination appeared likely (serratus anterior in 1 case, abdominal muscles in 1 case). It is possible to reliably measure the latency of the diaphragm response to transcranial magnetic stimulation with adequately positioned surface electrodes. cerebral cortex