Modern indices of left ventricular function require accurate measurement of left ventricular volume (LVV). Although conductance catheter (COND) measurements of LVV have been found to be reproducible under steady state conditions in closed chest animals, after median sternotomy, measurements of LVV are subject to exaggerated variation in parallel conductance (αPVc) outside of the left ventricle. Current calibration methods for measuring αPVc include hypertonic saline injection and quantitative two dimensional echocardiography. Unfortunately, these methods are hampered by imprecision, since frequent changes in αPVc in the open chest make recalibration impractical. Accordingly, a latex wrap technique was developed to insulate the left ventricle from extracardiac sources of αPVc in the open chest. Anesthetized pigs (n = 5) underwent a median sternotomy with insertion of a 6 French COND-micromano-meter combination catheter into the left ventricle. Three conditions were tested: 1) unaltered; 2) metallic retractor outside of the pericardium (metal); and 3) latex wrap between the metal and pericardium. Pressure/COND loops showed that the insulator improved the shape of the loops and decreased αPVc, as measured by an echo-area/COND relationship, whereas metal increased αPVc and produced artifacts in the loops. In conclusion, electrical isolation eliminates distortion of pressure/COND loops related to extracardiac sources of αPVc, therefore allowing for accurate COND measurements in the open chest. ASAIO Journal 1997; 43:M509-M514.
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