| Sumario: | BACKGROUND: To investigate patient-ventilator interaction during different levels of noninvasive proportional assist ventilation (PAV) compared with noninvasive pressure support ventilation (PSV). METHODS: Fifteen subjects with severe COPD and hypercapnia were consecutively recruited. After the baseline assessment of unassisted spontaneous breathing, 3 levels of ventilatory support were applied. The proportional assist (PA) and pressure support (PS) levels were set by subject comfort. PA-, PS- or PA+, PS+ were set at 25% more or less of PA or PS (PA- = 75% PA, PA+ = 125% PA, PS- = 75% PS, PS+ = 125% PS). Each level lasted at least 20 min. To demonstrate the patient-ventilator interaction, the neural respiratory drive, respiratory muscle effort, flow signal, and airway pressure were simultaneously monitored. RESULTS: The expiratory cycle delay (time between the termination of the diaphragm electromyogram [EMGdi] signal and the end of the inspiratory flow) progressively increased with increasing assist level in both modes. However, compared with PSV, the expiratory cycle delay was significantly longer in each assist level during noninvasive PAV. The runaway phenomenon was observed in PA+. The time between the peak EMGdi signal and the maximum value of the flow signal and the time difference between the peak EMGdi signal and the maximum value of inspiratory pressure were significantly increased with the increasing assist level of PAV. CONCLUSIONS: The expiratory cycle delay of noninvasive PAV was significantly longer than that of noninvasive PSV in the subjects with COPD with respiratory failure. During the levels of PAV, the lag time between neural respiratory drive and airway pressurization was significantly increased and the "runaway" phenomenon may be observed.
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