Evaluation of a new transcardiac conductance method for continuous on-linemeasurement of left ventricular volume

Objective: To evaluate a new, less invasive, conductance method to measure continuous on-line left ventricular volume. End-systolic and end-diastolic volumes obtained with this transcardiac conductance method were compared wi th simultaneous measurements using the conventional intracardiac conductanc e catheter. Design: Controlled animal study. Setting: Research laboratory in a university hospital. Subjects: Six sheep. Interventions: Anesthetized sheep were instrumented and inotropic condition was varied by beta-receptor stimulation (5 mu g/kg/min of dobutamine) and beta-receptor blockade (1 mg/kg of propranolol). In each condition (control , dobutamine, repeat control, propranolol), ventricular volume was varied o ver a wide range by gradual preload reduction using a vena caval balloon ca theter. Measurements and Main Results: We compared the two methods by performing li near regression analysis on simultaneous end-systolic and end-diastolic vol umes obtained during gradual caval occlusions. We statistically analyzed th e intercepts, slopes, and correlation coefficients of the regression equati ons relating the transcardiac and conductance catheter measurements to dete rmine the effects of interanimal variability, inotropic condition, and card iac phase on the relationship between the two methods. The results show an excellent linear correlation between the two methods (mean intercept, -1.82 +/- 1.24 mi; mean slope, 0.787 +/- 0.024 and r(2) = .94), Both slope and i ntercept of the relationship between the two methods show a significant int eranimal and cardiac phase related variability but no significant dependenc e on inotropic condition. Conclusions: The significant interanimal variability indicates that the new method requires individual calibration in each subject. However, the small variability of the regression coefficients with changes in condition indic ates that after initial calibration, end-systolic and end-diastolic volume can be followed accurately even in the presence of large changes in volume and inotropic state. This new method may facilitate quantitative continuous assessment of cardiac function in clinical practice, for example, in the i ntensive care unit.