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Closed-Loop Control of Respiratory Drive Using Pressure-Support Ventilation

Target Drive Ventilation

Research Center, Respiratory Health Research Unit, Sacré-Coeur Hospital of Montreal; Pediatric Intensive Care Unit, Department of Pediatrics, Sainte-Justine Hospital Research Center, and Department of Medicine, University of Montreal; Department of Adult Critical Care, Sir Mortimer B. Davis Jewish General Hospital, McGill University; Department of Kinanthropology, University of Quebec in Montreal, Montreal, Quebec; Department of Newborn and Developmental Pediatrics, Sunnybrook and Women's College Health Sciences Center; and Interdepartmental Division of Critical Care, University of Toronto, St. Michael's Hospital, Toronto, Ontario, Canada

Correspondence and requests for reprints should be addressed to Dr. Jadranka Spahija, Ph.D., Hôpital du Sacré-Coeur de Montréal, L'Axe de Recherche en Pneumologie, 5400 Boulevard Gouin Ouest, Montréal, PQ, Canada H4J 1C5. E-mail: spahija{at}crhsc.umontreal.ca

By using diaphragm electrical activity (multiple-array esophageal electrode) as an index of respiratory drive, and allowing such activity above or below a preset target range to indicate an increased or reduced demand for ventilatory assistance (target drive ventilation), we evaluated whether the level of pressure-support ventilation can be automatically adjusted in response to exercise-induced changes in ventilatory demand. Eleven healthy individuals breathed through a circuit (18 cm H₂O/L/second inspiratory resistance at 1 L/second flow; 0.5–1.0 L/second expiratory flow limitation) connected to a modified ventilator. Subjects breathed for 6-minute periods at rest and during 20 and 40 W of bicycle exercise, with and without target drive ventilation (the target was set to 60% of the increase in diaphragm electrical activity observed between rest and 20 W of unassisted exercise). With target drive ventilation during exercise, the level of pressure-support ventilation was automatically increased, reaching 13.3 ± 4.0 and 20.3 ± 2.8 cm H₂O during 20- and 40-W exercise, respectively, whereas diaphragm electrical activity was reduced to a level within the target range. Both diaphragmatic pressure-time product and end-tidal CO₂ were significantly reduced with target drive ventilation at the end of the 20- (p < 0.01) and 40-W (p < 0.001) exercise periods. Minute ventilation was not altered. These results demonstrate that target drive ventilation can automatically adjust pressure-support ventilation, maintaining a constant neural drive and compensating for changes in respiratory demand.

Key Words: airflow limitation • diaphragm • electromyography • exercise • mechanical ventilation

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