Validation of the conductance catheter method for measurement of ventricular volumes under varying conditions relevant to cardiac surgery

Abstract

The development of the conductance catheter method has enabled continuous measurement of intraventricular volume in vivo, thus making assessment of pump performance of the heart in vivo possible using pressure-volume analysis. However, this method has not been validated under conditions where pump rate, conductance, viscosity, and temperature of the fluid in the heart chamber is changed as happens in cardiac surgery. To validate the method, pressure-volume data were measured by conductance catheter in a physical model of the human left ventricle. The volume, salinity, viscosity, and temperature of the fluid inside the model were rigorously controlled. The measured pressure-volume data were compared with the actual values to assess the accuracy and dependence of the conductance-measured volumes on salinity, viscosity, temperature, and pump rate. Conductance-measured volumes were not significantly different over a range of heart rates extending from 60 to 100 beats/min, and they were not significantly different over a salinity range of 0.2 to 2 normal saline, a viscosity range of 2.7 to 3.5 centipoise, or over a temperature range of 20 degrees C to 39 degrees C. The percentage errors between actual stroke volumes and conductance-derived volumes were of the order of 10% on average. Our data shows that for a broad range of conditions normally encountered during cardiac surgery, there is no dependence of conductance-measured volume on heart rate, viscosity, temperature, or salinity, provided the correct value of fluid resistivity is used.