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The conductance catheter technique was developed in the 1980s to measure instantaneous ventricular conductance. After converting measured conductance to volume signals by use of the classic Baan conductance-to-volume equation, real-time pressure-volume (PV) relations can be obtained. A nonlinear conductance-to-volume conversion equation was proposed by Wei in 2005 to improve the accuracy of the conductance catheter system. This study tested the in vivo applicability of the nonlinear conversion equation, particularly focusing on the effect of deviation in catheter position. By altering catheter position, PV loops obtained by using the classic Baan's equation and the nonlinear equation were compared. The comparison results show that the nonlinear equation indeed compensates for the errors introduced by catheter position deviation, and gives more consistent and reliable PV relations. Moreover, the effect of variations in blood resistivity was analyzed. To obtain consistent and reliable PV relations, the nonlinear equation is suggested for use, and changes in blood resistivity should be carefully monitored.