CARDIAC-RELATED CHANGES IN LUNG RESISTIVITY AS A FUNCTION OF FREQUENCY AND LOCATION OBTAINED FROM EITS IMAGES

ECG-gated electrical impedance tomographic spectroscopy (EITS) measure ments of the lungs were taken on seven normal subjects in the frequenc y range 9.6 kHz to 614.4 kHz. The results show that in late systole th e resistivity rho' relative to the R-wave (i.e. rho' = I at the R-wave ) decreases consistently within the lung. In addition there arises an increase in rho' in early systole towards the periphery of the lung. F requency behaviour of rho' changes with location. At all times after t he R-wave, in the centre of the lung rho' is higher at higher frequenc y f whereas in the periphery it is lower at higher f. The principal de crease in rho' can be explained by increasing pulmonary blood volume d ue to cardiac contraction. The early systolic increase is presumably d ue to venous return to the left atrium locally leading blood output fr om the right ventricle which is delayed by the windkessel effect. Base d on a model taking extracapillary and capillary blood volume increase into account, the change in frequency behaviour of rho' is explained by regional variations in extracapillary blood vessel size determining the relative contributions of extracapillary blood volume change and capillary blood volume change to rho' at a certain frequency.