A method and device for generating a signal that mirrors changes in the level of effortexerted by respiratory muscles of patients on mechanical ventilatory supportcomprising: monitoring and storing airway pressure (P), rate ofgas flow (F), and volume of gas flow (V), and generating a composite pressure signalusing resistive pressure units (K) determined from elapsed dataand selected to minimize step changes in the calculated signal and elastic pressureunits (K) determined from elapsed data by steps comprising: - scanningstored F or P during exhalation and identifying where their trajectorytransiently reverses direction to detect transients； - selecting points withinthe exhalation that are at preselected distances away from the transients； -calculating the value of K required to force the values of the calculatedsignal at said selected points in elapsed breaths to be substantially equal whenthe selected value of K is used as the flow coefficient.
