Validation of the least squares fitting method (lsf) during nava and psv ventilation

The Least Squares Fitting (LSF) is a computerized method of analysis of respiratory system mechanics. It is based on applying a regression analysis for every sample points of the loop of pressure, flow and volume by fitting the equation Paw= Rrs× V' + VT/Crs+ PEEPtot during inspiration [1]. This technique has been already validated in Controlled Mechanical Ventilation (CMV) and at high level of Pressure Support Ventilation (PSV) [2]. However this method gives unreliable values of resistance (Rrs) and elastance (Ers) in presence of inspiratory muscle activity and in absence of an adequate neuromuscular coupling. We reasoned that NAVA (Neurally-Adjusted Ventilatory Assist) ventilation should assure a better neuromuscular coupling compared to PSV and hence the coefficient of determination (CD) of the above equation should be much higher during NAVA ventilation.