BackgroundRespiratory mechanics monitoring provides useful information for guiding mechanical ventilation, but many measuring methods are inappropriate for awake patients. This study aimed to evaluate the accuracy of dynamic mechanics estimation using expiratory time constant (RCexp) calculation during noninvasive pressure support ventilation (PSV) with air leak in different lung models.MethodsA Respironics V60 ventilator was connected to an active breathing simulator for modeling five profiles: normal adult, restrictive, mildly and severely obstructive, and mixed obstructive/restrictive. Inspiratory pressure support was adjusted to maintain tidal volumes (VT), achieving 5.0, 7.0, and 10.0 ml/kg body weight. PEEP was set at 5 cmH2O, and the back-up rate was 10 bpm. Measurements were conducted at system leaks of 25–28 L/min. RCexpwas estimated from the ratio at 75% exhaled VTand flow rate, which was then used to determine respiratory system compliance (Crs) and airway resistance (Raw).ResultsIn non-obstructive conditions (Raw≤ 10 cmH2O/L/s), the Crswas overestimated in the PSV mode. Peak inspiratory and expiratory flow and VTincreased with PS levels, as calculated Crsdecreased. In passive breathing, the difference of Crsbetween different VTwas no significant. Underestimations of inspiratory resistance and expiratory resistance were observed at VTof 5.0 ml/kg. The difference was minimal at VTof 7.0 ml/kg. During non-invasive PSV, the estimation of airway resistance with the RCexpmethod was accurately at VTof 7.0 ml/kg.ConclusionsThe difference between the calculated Crsand the preset value was influenced by the volume, status and inspiratory effort in spontaneously breathing.