Am. J. Respir. Crit. Care Med., Volume 164, Number 3, August 2001, 419-424

Electrical Activity of the Diaphragm during Pressure Support Ventilation in Acute Respiratory Failure

JENNIFER BECK, STEWART B. GOTTFRIED, PAOLO NAVALESI, YOANNA SKROBIK, NORMAN COMTOIS, MAURO ROSSINI, and CHRISTER SINDERBY

Hôpital Ste-Justine, Department of Pediatrics and Department of Medicine, McGill University Health Centre; Meakins-Christie Laboratories, Division of Critical Care Medicine, Department of Medicine, and Centre de Recherche Guy-Bernier, Division of Intensive Care, Hôpital Maisonneuve-Rosemont, Montreal, Quebec, Canada; Fondazione S. Maugeri, Pulmonary Rehabilitation and Respiratory Intensive Care, Pavia, and Bioingegneria, Ospedale Valduce, Costamasnaga, Italy; and Institution of Clinical Neuroscience, Sahlgrenska Hospital, University of Göteborg, Göteborg, Sweden

We compared crural diaphragm electrical activity (EAdi) with transdiaphragmatic pressure (Pdi) during varying levels of pressure support ventilation (PS) in 13 intubated patients. With changing PS, we found no evidence for changes in neuromechanical coupling of the diaphragm. From lowest to highest PS (2 cm H₂O ± 4 to 20 cm H₂O ± 7), tidal volume increased from 430 ml ± 180 to 527 ml ± 180 (p < 0.001). The inspiratory volume calculated during the period when EAdi increased to its peak did not change from 276 ± 147 to 277 ± 162 ml, p = 0.976. Respiratory rate decreased from 23.9 (± 7) to 21.3 (± 7) breaths/min (p = 0.015). EAdi and Pdi decreased proportionally by adding PS (r = 0.84 and r = 0.90, for mean and peak values, respectively). Mean and peak EAdi decreased (p < 0.001) by 33 ± 21% (mean ± SD) and 37 ± 23% with the addition of 10 cm H₂O of PS, similar to the decrease in the mean and peak Pdi (p < 0.001) observed (34 ± 36 and 35 ± 23%). We also found that ventilator assist continued during the diaphragm deactivation period, a phenomenon that was further exaggerated at higher PS levels. We conclude that EAdi is a valid measurement of neural drive to the diaphragm in acute respiratory failure.

Keywords: electromyography; mechanical ventilation; diaphragm; neuromechanical uncoupling

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