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1 Faculte de Medecine Pitie-Salpetriere, UPRES EA 2397, Universite Paris VI Pierre et Marie Curie, Paris, France; Explorations Fonctionnelles Respiratoires, Hopital Pitie-Salpetriere (Assistance Publique-Hopitaux de Paris), Paris, France
2 Faculte de Medecine Pitie-Salpetriere, UPRES EA 2397, Universite Paris VI Pierre et Marie Curie, Paris, France
3 Faculte de Medecine Pitie-Salpetriere, UPRES EA 2397, Universite Paris VI Pierre et Marie Curie, Paris, France; Service de Pneumologie, Hopital Pitie-Salpetriere (Assistance Publique-Hopitaux de Paris), Paris, France
* To whom correspondence should be addressed. E-mail: christian.straus{at}psl.ap-hop-paris.fr.
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 an hypercapnia-induced increase in the automatic respiratory drive on the function of the diaphragmatic corticospinal pathway as inpendently as possible of any other influence. Thirteen healthy volunteers breathed room air, then 5 and 7% hyperoxic CO2. Cervical (cms) and transcranial (tms) magnetic stimulations were performed during early inspiration (I) and expiration (E). Transdiaphragmatic pressure (Pdi) and surface electromyogram of the diaphragm (DiEMG) and of the Abductor Policis Brevis (abpEMG) 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 I and E (air vs 5%CO2 and air vs 7%CO2). DiEMG,tms amplitude increased significantly in response to E-tms (air vs 5%CO2 and air vs 7%CO2) but not in response to I-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 Di to tms, during both inspiration and expiration. This could allow the corticospinal drive to breathe to keep the capacity to modulate respiration in conditions where the automatic respiratory control is stimulated.
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