Closed-loop control of respiratory drive using pressure-support ventilation: target drive ventilation.

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.