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J Appl Physiol 97: 3-10, 2004. First published March 12, 2004; doi:10.1152/japplphysiol.01099.2003
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Depression of diaphragm motor cortex excitability during mechanical ventilation

Tarek Sharshar,1,3 Ewen T. Ross,1 Nicholas S. Hopkinson,1 Raphael Porcher,2 Annabel H. Nickol,1 Sophie Jonville,1 Mark J. Dayer,1 Nicholas Hart,1 John Moxham,3 Frédéric Lofaso,4 and Michael I. Polkey1

1Respiratory Muscle Laboratory, Royal Brompton and Harefield National Health Service Trust, King's College Hospital, London SW3 6NP; and 3Department of Respiratory Medicine, King's College Hospital, London SE5 9PJ, United Kingdom; 2Département de Biostatistique et Informatique Médicale, Hôpital Saint-Louis, Assistance Publique-Hôpitaux de Paris, 75010 Paris; and 4Service d'Exploration Fonctionnelles, Hôpital Raymond Poincaré, Assistance Publique-Hôpitaux de Paris, 92380 Garches, France

Submitted 9 October 2003 ; accepted in final form 16 February 2004

The effect of mechanical ventilation on the diaphragm motor cortex remains unknown. We assessed the effect of mechanical ventilation on diaphragm motor cortex excitability by measuring the costal and crural diaphragm motor-evoked potential (MEP) elicited by single and paired transcranial magnetic stimulation. In six healthy subjects, MEP recruitment curves of the costal and crural diaphragms were assessed at relaxed end expiration during spontaneous breathing [baseline tidal volume (VTbaseline)] and isocapnic volume cycled ventilation delivered noninvasively (NIV) at three different levels of tidal volume (VTbaseline, VTbaseline + 5 ml/kg liters, and VTbaseline + 10 ml/kg liters). The costal and crural diaphragm response to peripheral stimulation of the right phrenic nerve was not reduced by NIV. NIV reduced the costal and crural MEP amplitude during NIV (P < 0.0001) with the maximal reduction at VTbaseline + 5 ml/kg. Response to paired TMS showed that NIV (VTbaseline + 5 ml/kg) significantly increased the sensitivity of the cortical motoneurons to facilitatory (>9 ms) interstimulus intervals (P = 0.002), suggesting that the diaphragm MEP amplitude depression during NIV is related to neuromechanical inhibition at the level of motor cortex. Our results demonstrate that mechanical ventilation directly inhibits central projections to the diaphragm.

transcranial magnetic stimulation; diaphragm motor-evoked potential depression


Address for reprint requests and other correspondence: M. I. Polkey, Respiratory Muscle Laboratory, Royal Brompton Hospital, Sydney St., London SW3 6NP UK (E-mail: m.polkey{at}rbh.nthames.nhs.uk).






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