ObjectiveAirway occlusion pressure at 0.1 sec (P0.1) is an index of respiratory center output. During pressure-support ventilation, P0.1 correlates with the mechanical output of the inspiratory muscles and has an inverse relationship with the amount of pressure-support ventilation. Based on these observations, we designed a closed-loop control which, by automatically adjusting pressure-support ventilation, stabilizes P0.1, and hence patient inspiratory activity, at a desired target. The purpose of the study was to demonstrate the feasibility of the method, rather than its efficacy or even its influence on patient outcome.DesignProspective, randomized trial.SettingA general intensive care unit of a university hospital in Italy.PatientsEight stable patients intubated and ventilated with pressure-support ventilation for acute respiratory failure.InterventionsPatients were transiently connected to a computer-controlled ventilator on which the algorithm for closed-loop control was implemented. The closed-loop control was based on breath by breath measurement of P0.1 and on comparison with a target set by the user. When actual P0.1 proved to be higher than the target value, the P0.1 controller automatically increased pressure-support ventilation, and decreased it when P0.1 proved to be lower than the target value. For safety, a volume controller was also implemented. Four P0.1 targets (1.5, 2.5, 3.5, and 4.5 cm H2O) were applied at random for 15 mins each.Measurements and Main ResultsThe closed-loop algorithm was able to control P0.1, with a difference from the set targets of 0.59 plus minus 0.27 (SD) cm H2O.ConclusionsThe study shows that P0.1 can be automatically controlled by pressure-support ventilation adjustments with a computer. Inspiratory activity can thus be stabilized at a level prescribed by the physician.(Crit Care Med 1996; 24:771-779)