Time/frequency analysis of respiratory mechanics via amplitude modulation of multiple carriers

Time/frequency analysis of nonstationary linear dynamic systems is usually performed using the short-time fast Fourier transform or the wavelet transform. An alternative approach is presented here in which the system to be identified is excited with a superposition of distinct sinusoids, each of which is amplitude-modulated in the output by the time-varying system dynamics. Each component is then filtered out and demodulated separately by application of a recursive time-domain model. The method is applied to the analysis of changing respiratory system impedance simulated by a two-compartment model of the lungs.