Parameter estimation of respiratory impedance measured by forced complex-wave oscillations

Respiratory impedance data measured using the forced oscillation method were analyzed using an equivalent circuit model and the following conclusions were obtained: 1) Use of the complex wave oscillation method provided a measurement range of over 9 cmH2O/1/s with a resolution of 0.13 cmH2O/1/s. 2) The respiratory system was expressed as a two-compartment model. By expressing the circuit characteristics as phasor loci, a method was shown whereby individual impedance parameter values could be derived from the measured impedance phasor loci. 3) Under enflurane anesthesia, the model parameter values were derived as R1 = 1.2, R2 = 1.6 cmH2O/1/s, C1 = 0.02, C2 = 0.041/cmH2O and L = 0.065 cmH2O/1/s2.