Method and apparatus for non-invasively determining the time onset (Tonset)and end (Tend) of patient inspiratory efforts. A composite pressure signal isgenerated comprising the sum of an airway pressure signal, a gas flow pressuresignal obtained by applying a gain factor (Kf) to a signal representing gasflow rate and a gas volume pressure signal obtained by applying a gain factor(Kv) to a signal representing volume of gas flow. Kf <；/sb>； and Kv values areadjusted to result in a desired linear trajectory of composite pressure signalbaseline in the latter part of the exhalation phase. The current compositepressure signal is compared with (i) selected earlier composite pressuresignal values and/or (ii) value expected at current time based onextrapolation of composite pressure signal trajectory at specified earliertimes and/or (iii) the current rate of change in the composite pressure signalwith a selected earlier rates of change. The differences obtained by thecomparison are compared with selected threshold values. T<；sb>；onset isidentified when at least one of the differences exceeds the threshold values.
