Gopakumaran B, Osborn P, Petre J H, Murray P A
Biomedical Engineering Center, The Ohio State University, Columbus, USA.
J Clin Monit. 1997 Nov;13(6):363-71. doi: 10.1023/a:1007407807068.
To propose and verify a technique by which blood resistivity can be measured continuously and instantaneously with a conductance catheter used to measure ventricular volume by intracardiac impedance volumetry.
Intracardiac impedance volumetry involves the measurement of ventricular blood volume using a multi-electrode conductance catheter. Ventricular volume measurement with the conductance catheter requires the value of blood resistivity. Previously, blood resistivity has been determined by drawing a sample of blood and measuring resistivity in a separate measuring cell. A new technique is proposed that allows the resistivity of blood to be measured with the conductance catheter itself. Two adjacent electrodes of the catheter are chosen to establish a localized electric field. With a localized field, the resistance measured between the adjacent electrodes bears a constant ratio (resistivity ratio) to the resistivity of blood. Finite element cylindrical models with exciting electrodes were created to determine the resistivity ratio. Blood resistivity was determined by dividing the resistance found due to the localized electric field by the resistivity ratio. The proposed scheme was verified in cylindrical physical models and in in vivo canine hearts.
Finite element simulations showed the resistivity ratio to be 1.30 and 1.43 for two custom-made catheters (Ohmeda Inc. and Biosensors Inc., respectively). The resistivity ratio remained constant as long as the cylindrical volume of blood around the adjacent electrodes had a radius larger than the electrode spacing. In addition, this ratio was found to be a function of electrode width. The new technique allowed us to measure saline resistivity with an error, -0.99+/-0.25% in a physical model, and blood resistivity with an error, -0.625+/-2.75% in an in vivo canine model.
The new in vivo technique can be used to measure and track blood resistivity instantaneously and continuously without drawing blood samples.
提出并验证一种技术，通过用于心内阻抗容积法测量心室容积的电导导管连续即时测量血液电阻率。
心内阻抗容积法涉及使用多电极电导导管测量心室血容量。用电导导管测量心室容积需要血液电阻率值。此前，血液电阻率是通过抽取血样并在单独的测量池中测量电阻率来确定的。提出了一种新技术，可使用电导导管本身测量血液电阻率。选择导管的两个相邻电极建立局部电场。在局部电场中，相邻电极之间测量的电阻与血液电阻率具有恒定比例（电阻率比）。创建带有激励电极的有限元圆柱模型以确定电阻率比。通过将局部电场产生的电阻除以电阻率比来确定血液电阻率。在圆柱物理模型和体内犬心模型中验证了所提出的方案。
有限元模拟显示，两种定制导管（分别为Ohmeda公司和Biosensors公司）的电阻率比分别为1.30和1.43。只要相邻电极周围的圆柱形血液体积半径大于电极间距，电阻率比就保持恒定。此外，该比例是电极宽度的函数。新技术使我们能够在物理模型中以-0.99±0.25%的误差测量盐水电阻率，在体内犬模型中以-0.625±2.75%的误差测量血液电阻率。
新的体内技术可用于即时连续测量和跟踪血液电阻率，无需抽取血样。
