Respiratory impedance and corresponding phase-constancy in the 7.5 to 247.5 Hz frequency interval for healthy subjects

This paper presents contributions on respiratory impedance and its phase constancy effects at high frequencies; i.e. 7.5-247.5 Hz. Measurements of 14 healthy volunteers are used to provide the input impedance values. It is shown, via the modulus-phase characteristics, that the impedance poses a typical frequency-independent behavior, known as phase constancy. We propose an electrical ladder network analogue for which we identify a set of parameters from these real-life measurements. The results presented in this paper support earlier theoretical insights on the appearance of phase constancy in ladder networks and the estimated model parameters have meaningful values. The phase constancy implies that the respiratory system is fractal and that the tissue exhibits viscoelastic properties.