title: Corticospinal control of respiratory muscles in chronic obstructive pulmonary disease.
abstract: Patients with chronic obstructive pulmonary disease (COPD) face an increased respiratory load and in consequence have an elevated respiratory drive. We used transcranial magnetic stimulation (TMS) to investigate associated changes in corticospinal excitability both at rest and during voluntary facilitation at different levels of inspiratory effort. Diaphragm and abdominal motor thresholds were significantly lower in COPD than healthy controls, but the quadriceps response was the same. In patients there was a significant increase in diaphragm response from rest during 20% inspiratory efforts but no further increase with greater efforts. In controls there was a further stepwise increase at 40% and 60% of inspiratory effort. The cortical silent period was significantly shorter in COPD. Using paired stimulation to study intracortical inhibitory and excitatory circuits we found significantly less excitability of intracortical facilitatory circuits in patients at long (>7 ms) interstimulus intervals. These results suggest that there is a ceiling effect in motor control output to the respiratory muscles of patients with COPD.
authors.affiliation: Respiratory Muscle Laboratory, Royal Brompton Hospital, London SW3 6NP, UK. n.hopkinson@ic.ac.uk
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hopkinson
authors.forename: Tarek
authors.initials: T
authors.lastname: Sharshar
authors.forename: Ewen T
authors.initials: ET
authors.lastname: Ross
authors.forename: Annabel H
authors.initials: AH
authors.lastname: Nickol
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Dayer
authors.forename: Raphaël
authors.initials: R
authors.lastname: Porcher
authors.forename: Sophie
authors.initials: S
authors.lastname: Jonville
authors.forename: John
authors.initials: J
authors.lastname: Moxham
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
mesh_terms: D000009:Abdominal Muscles / Q000503:physiopathology; D000368:Aged; D003964:Diaphragm / Q000503:physiopathology; D004558:Electric Stimulation / Q000379:methods; D004574:Electromagnetic Fields; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D016555:Matched-Pair Analysis; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000503:physiopathology; D009433:Neural Inhibition / Q000502:physiology; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D011712:Pyramidal Tracts / Q000503:physiopathology*; D011999:Recruitment, Neurophysiological / Q000502:physiology; D012016:Reference Values; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000503:physiopathology*