Dielectric properties of lung tissue as a function of air content

Dielectric measurements were made on lung samples with different electrode systems in the frequency range 5 kHz-100 kHz. In the case of plate electrodes and spot electrodes, the effects of electrode polarization were partly corrected. An air filling factor F is defined, which is determined from the mass and volume of the sample. The results indicate that the electrical properties of lung tissue are highly dependent on the condition of the tissue. Furthermore they show that the conductivity sigma as well as the relative permittivity epsilon _r decreases with increasing F. This is discussed using histological material. Using a simple theoretical model, the decrease of sigma and epsilon _r is explained by the thinning of the alveolar walls as well as by the deformation of the epithelial cells and blood vessels through the expansion of the alveoli.