VALIDATION OF THE CONDUCTANCE CATHETER METHOD FOR MEASUREMENT OF VENTRICULAR VOLUMES UNDER VARYING CONDITIONS RELEVANT TO CARDIAC-SURGERY

The development of the conductance catheter method has enabled continu ous measurement of intraventricular volume in vivo, thus making assess ment of pump performance of the heart in vivo possible using pressure- volume analysis. However, this method has not been validated under con ditions where pump rate, conductance, viscosity, and temperature of th e fluid in the heart chamber is changed as happens in cardiac surgery. To validate the method, pressure-volume data were measured by conduct ance catheter in a physical model of the human left ventricle. The vol ume, salinity, viscosity, and temperature of the fluid inside the mode l were rigorously controlled. The measured pressure-volume data were c ompared with the actual values to assess the accuracy and dependence o f the conductance-measured volumes an salinity, viscosity, temperature , and pump rate. Conductance-measured volumes were not significantly d ifferent over a range of heart rates extending from 60 to 100 beats/mi n, 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 percent age errors between actual stroke volumes and conductance-derived volum es were of the order of 10% on overage. Our data shows that for a broa d range of conditions normally encountered during cardiac surgery, the re is no dependence of conductance-measured volume on heart rate, visc osity, temperature, or salinity, provided the correct value of fluid r esistivity is used. (C) 1998 by Excerpta Medica, Inc.