Fig. 2.

Novel technique for continuous CO and LAP monitoring by long time interval analysis of the PAP waveform. First, a cardiac contractions signal [x(t)] is constructed from a 6-min PAP waveform segment [y(t)] based on the impulse ejection model. (PP_j and R_j are, respectively, the pulse pressure and the onset time of PAP upstroke of the jth beat.) Second, y(t) is fitted according to the sum of a constant term with the convolution between x(t) and an impulse response [h(t)]. That is, the constant term and h(t) are estimated so as to optimally fit y(t). The estimated constant term represents average LAP, while the estimated h(t) represents the PAP-LAP response to a single cardiac contraction. Next, the time constant τ of the Windkessel model of Fig. 1 is determined by fitting an exponential to the tail end of h(t) once the faster wave reflections and inertial effects vanish. Finally, average proportional CO is determined similar to invoking Ohm's law and conveniently calibrated with a thermodilution measurement.