Thoracic electrical bioimpedance in a Lissajous plane: Pre-post smoking changes and PCA of ellipse metrics

Univariate analyses showed no significant pre-post differences for most variables, except for a higher mean |ΔZ| amplitude in men. In PCA space, ellipse area (A) showed consistent differences between pre- and post-smoking distributions across sexes. These differences reflected changes in joint magnitude-phase dispersion rather than statistically significant physiological effects. Inclination, semi-axes, and eccentricity showed substantial overlap between conditions. PCA provided low-dimensional representations that facilitated visualization and comparison of magnitude-phase patterns.
Significance. Representing TEB signals as magnitude-phase Lissajous ellipses provides an intuitive and reproducible geometric representation of breathing. Ellipse area is proposed as a composite geometric descriptor of joint magnitude-phase variability, intended for representation and comparison rather than direct physiological inference. This non-invasive and computationally simple framework uses standard hardware and may support future methodological developments in respiratory signal analysis.&#xD.