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Facilitation of the diaphragm response to transcranial magnetic stimulation by increases in human respiratory drive

¹UPRES EA 2397, Faculté de Médecine Pitié-Salpêtrière, Université Paris VI Pierre et Marie Curie; ²Service Central d'Explorations Fonctionnelles Respiratoires and ³Service de Pneumologie, Assistance Publique-Hôpitaux de Paris, Groupe Hospitalier Pitié-Salpêtrière, 75013 Paris, France

Submitted 11 September 2003 ; accepted in final form 30 April 2004

The human respiratory neural drive has an automatic component (bulbospinal pathway) and a volitional component (corticospinal pathway). The aim of this study was to assess the effects of a hypercapnia-induced increase in the automatic respiratory drive on the function of the diaphragmatic corticospinal pathway as independently as possible of any other influence. Thirteen healthy volunteers breathed room air and then 5 and 7% hyperoxic CO₂. Cervical (cms) and transcranial (tms) magnetic stimulations were performed during early inspiration and expiration. Transdiaphragmatic pressure (Pdi) and surface electromyogram of the diaphragm (DiEMG) and of the abductor pollicis brevis (apbEMG) were recorded in response to cms and tms. During inspiration, Pdi,cms was unaffected by CO₂, but Pdi,tms increased significantly with 7% CO₂. During expiration, Pdi,cms was significantly reduced by CO₂, whereas Pdi,tms was preserved. DiEMG,tms latencies decreased significantly during early inspiration and expiration (air vs. 5% CO₂ and air vs. 7% CO₂). DiEMG,tms amplitude increased significantly in response to early expiration-tms (air vs. 5% CO₂ and air vs. 7% CO₂) but not in response to early inspiration-tms. DiEMG,cms latencies and amplitudes were not affected by CO₂ whereas 7% CO₂ significantly increased the apbEMG,cms latency. The apbEMG,tms vs. apbEMG,cms latency difference was unaffected by CO₂. In conclusion, increasing the automatic drive to breathe facilitates the response of the diaphragm to tms, during both inspiration and expiration. This could allow the corticospinal drive to breathe to keep the capacity to modulate respiration in conditions under which the automatic respiratory control is stimulated.

control of breathing; hypercapnia; nerve conduction; respiratory muscle

This article has been cited by other articles:

				F. Series, W. Wang, C. Melot, and T. Similowski Concomitant responses of upper airway stabilizing muscles to transcranial magnetic stimulation in normal men Exp Physiol, April 1, 2008; 93(4): 496 - 502. [Abstract] [Full Text] [PDF]

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