Published ahead of print on May 28, 2003, doi:10.1164/rccm.200203-241OC Am. J. Respir. Crit. Care Med., Volume 168, Number 7, October 2003, 760-769 A more recent version of this article appeared on October 1, 2003
Submitted on March 25, 2002 Trans-Diaphragmatic Pressure Control of Airway Pressure Support in Healthy SubjectsTarek Sharshar1,1 Services d'Explorations Fonctionnelles, de Reanimation Medicale et Centre d\'Innovations Technologiques, Hopital Raymond Poincare, Garches, France, 2 Ecole Superieure d'Ingenieurs en Electrotechnique et Electronique, Noisy le Grand, France, 3 Service de Physiologie-Explorations Fonctionnelles et Institut National de la Sante et de la Recherche Medicale UMR 492, Hopital Henri Mondor, Creteil, France, 4 Departement de Biostatistique et Informatique Medicale, Hopital Saint Louis, Paris, France, 5 Services d'Explorations Fonctionnelles, de Reanimation Medicale et Centre d\'Innovations Technologiques, Hopital Raymond Poincare, Garches, France; Service de Physiologie-Explorations Fonctionnelles et Institut National de la Sante et de la Recherche Medicale UMR 492, Hopital Henri Mondor, Creteil, France * To whom correspondence should be addressed. E-mail: f.lofaso{at}rpc.ap-hop-paris.fr.
We designed a new servoventilator that proportionally adjusts airway pressure (Paw) to transdiaphragmatic pressure (Pdi) generated by the subject during inspiration. Each cycle is triggered by either a preset Pdi increase or a preset inspiratory flow value (whichever is reached first), whereas cycling-off is flow-dependent. We evaluated the servoventilator in seven healthy subjects at normocapnia and three levels of hypercapnia (normocapnia + 3, +6 and +9 mm Hg), comparatively with spontaneous breathing. Triggering was by Pdi in six subjects and flow in one. At all PETco2 levels, time from onset of diaphragm electromyographic activity to inspiratory flow was similar with and without the servoventilator. Paw increased proportionally to Pdi variation during servoventilator breathing. Flow, tidal volume, respiratory rate, intrinsic positive end-expiratory pressure (PEEPi), and esophageal and transdiaphragmatic pressure-time products (PTPs) increased significantly with hypercapnia with and without the servoventilator. Breathing pattern parameters were similar with the two breathing modes, and no differences were found for PEEPi or gastric pressure variation during exhalation. Esophageal and transdiaphragmatic PTP were lower with than without the servoventilator. The Pdi-driven servoventilator was well synchronized to the subjects\' effort, delivering a pressure proportional to Pdi and reducing respiratory effort at normocapnia and hypercapnia. Key words: triggering, servoventilator, respiratory drive
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