Respiratory system mechanics during noninvasive proportional assist ventilation: A model study

Purpose: To assess the accuracies of airway resistance (R-aw) and compliance (C-rs) calculations using the expiratory time constant (RCexp) method as well as the accuracy of P-mus estimation in obstructive lung models. Methods: A Respironics V60 ventilator was connected to an active lung simulator. The driving pressure was maintained at 5-10 cmH(2)O and positive end-expiration pressure (PEEP) was 5 cmH(2)O. Maximal P-mus, estimated based on equations of motion and respiratory mechanical properties, was calculated by the RCexp method to derive respiratory system compliance (C-rs) and inspiratory (R-insp) and expiratory (R-exp) resistance. Results: During PAV, the assist proportion was adjusted to 55% and 40% with P-mus of 5 and 10 cmH(2)O, respectively. P-mus measurement errors were <20% of the preset values in most lung conditions. In the active lung model with PAV, an overestimation of Raw was found in the normal resistance condition, and R-insp was underestimated in the severe obstructive model (P < 0.01). Crs was overestimated significantly except in the severe obstructive model at a P-mus of 10 cmH(2)O (all P < 0.01). Using the RCexp method, the target of <= 20% between the calculated and preset values in airway resistance was achieved in most obstructive models at a P-mus of 5 cmH(2)O. Conclusions: The RCexp method might provide real-time assessments of respiratory mechanics (elastance and resistance) in the PAV mode. With low inspiratory effort, the estimation error was acceptable (<20%) in most obstructive lung models.