CONDUCTANCE CATHETER MEASUREMENTS OF LEFT-VENTRICULAR VOLUME IN THE INTACT DOG - PARALLEL CONDUCTANCE IS INDEPENDENT OF LEFT-VENTRICULAR SIZE

Objective: It has recently been suggested that conductance catheter pa rallel conductance (alpha V-c) is a function of left ventricular volum e. To confirm this, alpha V-c was measured in this study over a wide r ange of steady state volumes. In addition, conductance derived volumes were compared to those obtained by radionuclide angiography to determ ine if the conductance catheter can be used to measure absolute left v entricular volume accurately in the intact dog heart. Methods: Seven d ogs were anaesthetised and instrumented with left ventricular conducta nce and pressure tip catheters, a flow through rho cuvette to continua lly measure blood resistance, a thermodilution catheter, and a venous catheter for volume infusion/withdrawal. Conductance and angiographic data were acquired at 8(SD 1) variably loaded states. Parallel conduct ance was measured twice at each state using a saline dilution techniqu e and a new non-linear algorithm that allows variability in the observ ations of both maximum and minimum conductance volumes. Results: The m ean value of alpha V-c was 89.1(18.0) ml (71.8 to 111.3 ml) with a mea n within-animal coefficient of variation of 7.3(3.4)%. Multiple linear regression using dummy variables to account for the large interanimal variability did not reveal any relationship between alpha V-c and eit her maximum or minimum left ventricular volume. Furthermore, no differ ence was found when alpha V-c values measured at the lowest and highes t loading levels in each dog were compared. Linear regression showed g ood agreement between conductance and radionuclide derived end diastol ic volumes (slope=0.94, R=0.9, p<0.0001). Conclusions: While alpha V-c varies between animals, it remains constant within any given animal o ver a broad range of left ventricular volumes. Thus the conductance ca theter can provide reliable absolute left ventricular volume measureme nts under steady state conditions.