Conductance method for time measurement of cross-sectional areas of the aorta

A modified conductance method to determine the cross-sectional areas (CSAs) of arteries in piglets was evaluated in vivo. The method utilized a conduc tance catheter having four electrodes. Between the outer electrodes an alte rnating current was applied and between the inner electrodes the induced vo ltage difference was measured and converted into a conductance. CSA was det ermined from measured conductance minus parallel conductance, which is the conductance of the tissues surrounding the vessel times the length between the measuring electrodes of the conductance catheter divided by the conduct ivity of blood. The parallel conductance was determined by injecting hypert onic saline to change blood conductivity. The conductivity of blood was cal culated from temperature and hematocrit and corrected for maximal deformati on and changes in orientation of the erythrocytes under shear stress condit ions. The equations to calculate the conductivity of blood were obtained fr om in vitro experiments. In vivo average aortic CSAs, determined with the c onductance method CSA((G)) in five piglets, were compared to those determin ed with the intravascular ultrasound method CSA((IVUS)). The regression equ ation between both values was CSA((G)) = -0.09 + 1.00.CSA((IVUS)), r = 0.97 , n = 53. The mean difference between the values was -0.29% +/-5.57% (2 sta ndard deviations). We conclude that the modified conductance method is a re liable technique to estimate the average cross-sectional areas of the aorta in piglets. (C) 1999 Biomedical Engineering Society. [S0090-6964(99)00902- 9].