2-FREQUENCY ANALYSIS OF RESPIRATORY MECHANICS IN ARTIFICIALLY VENTILATED RABBITS

The frequency dependence of respiratory mechanical properties was stud ied in 10 paralyzed, artificially ventilated rabbits, by superimposing a single sinusoidal signal with a frequency of 10, 20 or 30 Hz upon t he ventilator waveform. The tracheal pressure and flow signals were an alyzed both with the usual first order model, which provided total res piratory elastance (Ers) and resistance (Rrs), and by Fourier analysis , which provided respiratory impedance (Zrs) at the breathing frequenc y (0.85 Hz) and at the superimposed oscillation frequency. The real pa rt of Zrs (Re(Zrs)) decreased by 30% from 0.85 to 10 Hz (P<0.001), but did not vary significantly from 10 to 30 Hz. This finding is satisfac torily explained by tissue viscoelasticity. Following a histamine aero sol, the frequency dependence of Re(Zrs) changed very little in three out of four rabbits, but increased substantially in the fourth. In tha t instance, assuming that lung hysteresivity was not markedly modified by histamine, the results suggest inhomogeneous airway obstruction an d/or airway wall shunting.