Flow, airway pressure (Paw), and esophageal pressure (Pes) in a patient with severe chronic obstructive pulmonary disease and ventilated with pressure support. The dotted lines indicate the beginning of inspiratory efforts that triggered the ventilator. The thin, black arrows indicate nontriggering inspiratory efforts. Notice the time delay between the beginning of inspiratory effort and ventilator triggering. Ineffective (nontriggering) efforts occurred during both mechanical inspiration and expiration. Those ineffective efforts can easily be identified on the flow waveform; ineffective efforts during mechanical inspiration abruptly increase inspiratory flow, whereas during expiration they result in an abrupt decrease in expiratory flow (open arrows in the flow waveform). The set respiratory frequency is 12 breaths/min, but the patient is making 33 inspiratory efforts per minute.