Gopakumaran B, Petre J H, Krucinski S, Murray P A
Department of Biomedical Engineering, Ohio State University, Columbus 43210, USA.
Biomed Instrum Technol. 1996 Sep-Oct;30(5):427-38.
The authors propose using a multi-electrode conductance catheter to measure continuous right ventricular volume. True ventricular volume measurements are affected by four main sources of error. 1) field non-uniformity, 2) catheter curvature, 3) blood conductivity changes, and 4) leakage of current through surrounding tissues. Three-dimensional finite-element models were developed to investigate the effects of these sources of error and to devise schemes for correcting them. The models include an axisymmetric cylindrical model, a rectangular block model, and a heart model with left and right ventricular chambers. The heart model is built from conical primitives, with major dimensions derived from the literature. Finite-element simulations showed that volume measurements were underestimated due to field nonuniformity to as much as 1/25th actual volume in segments near the exciting electrodes. The extent of underestimation in a segment decreased with increasing distance of the segment from the exciting electrodes and increased for larger segmental volumes. Catheter curvature overestimated measured volume by as much as 4.5 times when the curvature was increased from 0.0 to 1.25 (from a straight catheter to a very curved one). The leakage of current through surrounding tissues overestimated volume by nearly 30%. The sensitivity of volume measurement to blood resistivity changes was found to be very high, at 70%. Correction factors established with the computer models compensate for field nonuniformity. Mathematical mapping of the curved catheter onto a fictitious straight catheter corrects for the catheter curvature error. Correction for both nonuniform field and catheter curvature allowed measurement of total ventricular volume with an error of 7%. Leakage current is determined by using different frequencies to build the catheter electric field and to separate tissue and blood resistance paths. Using this scheme, the percentage overestimation in volume measurement due to leakage could be determined with an accuracy of 85%. The proposed correction scheme for blood conductivity changes involves the in-vivo measurement of blood conductivity with the catheter itself. It was found that blood conductivity could be determined with insignificant error (< 0.5%) so long as the blood volume around the exciting electrodes had a radius of more than the electrode spacing.
作者们提议使用多电极电导导管来测量右心室的连续容积。真正的心室容积测量受到四个主要误差来源的影响。1）场不均匀性，2）导管曲率，3）血液电导率变化，以及4）电流通过周围组织的泄漏。开发了三维有限元模型来研究这些误差来源的影响，并设计校正方案。这些模型包括一个轴对称圆柱模型、一个矩形块模型和一个带有左右心室腔的心脏模型。心脏模型由锥形基本体构建而成，其主要尺寸来自文献。有限元模拟表明，由于场不均匀性，在靠近激励电极的节段中，容积测量值被低估多达实际容积的1/25。节段中低估的程度随着该节段与激励电极距离的增加而减小，并且对于较大的节段容积会增加。当曲率从0.0增加到1.25（从直导管到非常弯曲的导管）时，导管曲率会使测量容积高估多达4.5倍。电流通过周围组织的泄漏使容积高估了近30%。发现容积测量对血液电阻率变化的敏感度非常高，为70%。通过计算机模型建立的校正因子可补偿场不均匀性。将弯曲导管数学映射到虚拟的直导管上可校正导管曲率误差。对场不均匀性和导管曲率进行校正后，总心室容积测量的误差为7%。通过使用不同频率构建导管电场并分离组织和血液电阻路径来确定泄漏电流。使用该方案，由于泄漏导致的容积测量高估百分比的确定精度可达85%。针对血液电导率变化提出的校正方案涉及使用导管本身在体内测量血液电导率。结果发现，只要激励电极周围的血液容积半径大于电极间距，就可以以微不足道的误差（<0.5%）确定血液电导率。
