General method for describing and extrapolating monotonic transients and its application to respiratory mechanics

The transient response of an overdamped system is a monotonically changing output. We present a rapid method for fitting smooth curves to such responses that is capable of describing multicomponent transients. Confidence intervals on the fitted curves are also obtained. In addition, the curves can be made to extrapolate monotonically. We demonstrate the method by applying it to the flow interruption method commonly used for determining respiratory resistance. If the flow of gas through a resistance is suddenly interrupted the pressure just distal to the point of occlusion immediately changes by an amount reflecting the resistive pressure drop across the resistance that existed just prior to interruption. By extrapolating the signals observed before and after interruption to the midpoint of interruption we are able to estimate the resistance of a test system to within a few per cent