We examined mechanisms of ventilator asynchrony and noncapture in a typical ventilator-dependent patient who failed numerous attempts at weaning. As trigger sensitivity was decreased within its usual range, a marked and progressive ventilator response delay occurred which was associated with erratic changes in functional residual capacity as well as dyspnea and tachypnea. This phenomenon varies among ventilators and underscores the importance of understanding technical differences between them. Appropriate ventilator selection is as important as mode selection when attempting to wean patients with advanced chronic obstructive pulmonary disease.