title: Effect of voluntary facilitation on the diaphragmatic response to transcranial magnetic stimulation.
abstract: We assessed recruitment curves of the surface diaphragm motor-evoked potential (MEP) after transcranial magnetic stimulation during relaxation and at three different levels of facilitation (20, 40, and 60% of maximal inspiratory esophageal pressure) in 10 healthy subjects (six young and four elderly). MEP amplitude recruitment curves varied between individuals during relaxation and at each level of facilitation. Amplitude recruitment curves during relaxation were reproducible in individual subjects. Inspiratory maneuvers caused a decrease in motor threshold and latency and an increase in MEP amplitude, positively correlated to the intensity of facilitation. These changes were similar in young and elderly subjects. The best fit for MEP amplitude recruitment curves for each condition was obtained with a Boltzmann model. The performance of repeated submaximal inspiratory maneuvers did not affect the amplitude recruitment curves of the relaxed diaphragm. We conclude that the recruitment curve of the diaphragm with transcranial magnetic stimulation is repeatable and changes consistently with facilitation and will, therefore, be a robust experimental tool for the investigation of supraspinal pathways to the diaphragm.
authors.affiliation: Respiratory Muscle Laboratory, Royal Brompton and Harefield National Health Service, Trust and King's College Hospital, London SW3 6NP, UK. m.polkey@rbh.nthames.nhs.uk
authors.forename: Tarek
authors.initials: T
authors.lastname: Sharshar
authors.forename: Ewen
authors.initials: E
authors.lastname: Ross
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hopkinson
authors.forename: Mark
authors.initials: M
authors.lastname: Dayer
authors.forename: Annabel
authors.initials: A
authors.lastname: Nickol
authors.forename: Frederic
authors.initials: F
authors.lastname: Lofaso
authors.forename: John
authors.initials: J
authors.lastname: Moxham
authors.forename: Thomas
authors.initials: T
authors.lastname: Similowski
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001921:Brain / Q000502:physiology*; D003964:Diaphragm / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004574:Electromagnetic Fields; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009126:Muscle Relaxation / Q000502:physiology; D011999:Recruitment, Neurophysiological / Q000502:physiology; D015203:Reproducibility of Results