An improved forced oscillatory estimation of respiratory impedance.

A new scheme of estimation is proposed for the determination of the total respiratory impedance (Zr) by forced oscillations. Instead of estimating Zr from the airflow at the mouth and the pressure drop across the respiratory system, Zr can be estimated from cross-power spectra between the electrical signal of the driving apparatus and the measured pressure and flow signals. since the electrical signal is free from any disturbance originating from spontaneous breathing, unlike the conventional techniques the proposed 'indirect' estimation of Zr is not subject to systematic errors caused by the respiratory signal components. This is confirmed both by theoretical analysis and simulation of the forced oscillatory measurement.