Development and Validation in Porcine and Human Models of a Bioimpedance Spectroscopy System for the Objective Assessment of Kidney Graft Viability

Abstract

This work presents an innovative bioimpedance spectroscopy device, developed as a support tool for decision-making during the evaluation of kidney viability for renal transplantation. Given the increasing demand for organs and the need to optimize donation criteria, the precise and objective assessment of renal graft functionality has become crucial. The device, based on a modular design and adapted to the surgical environment, uses a novel Cole model with a frequency-dependent membrane capacitance, which improves measurement accuracy and repeatability compared to conventional models. Adapting the device for operating room usege involved overcoming significant challenges, such as the need for sterilization and a visual, tactile and acoustic user interface that facilitates device usability. Optimizing the sensing stage has minimized the influence of measurement artifacts, which is crucial for obtaining accurate and representative measurements of renal tissue bioelectrical properties. In addition, a rigorous electrode sterilization protocol was designed, ensuring asepsis during the procedure. The results of tests on porcine renal models demonstrated the device's ability to monitor pathophysiological changes associated with renal ischemia, with a notable improvement against measurement repeatability.

Keywords: Cole model; bioimpedance spectroscopy; ischemia monitoring; kidney transplant.

Figure 3

Probes developed for kidney measurements: (a) Localized measurements (probes number 1 to 6). (b) Longitudinal measurements (probes number 7 to 10). The figure also describes the positioning of the electrodes on a pig kidney in both schemes.

Figure 4

Comparative schematics of the current source and simulated injected current as a function of load impedance: (a) previous device configuration [47]; (b) improved current source proposed in this work.

Figure 5

Comparative schematics of the voltage measurement stage and simulated input resistance as a function of frequency: (a) previous device INA [47]; (b) improved voltage measurement stage proposed in this work.

Figure A1

(a) Details of the electrodes used in the operating room. (b) Packaging for sterilization control. (c,d) Sterile cover and electrode insertion procedure.

Figure A2

English translation of the user manual (page 1).

Figure A3

English translation of the user manual (page 2).

Figure 1

Schematic of the circuit pattern designed for device validation.

Figure 2

Bioimpedance system for the evaluation of renal viability and pathophysiological status.

Figure 6

Example of bioimpedance measurement performed with probe 10: (a) porcine kidney bioimpedance values; (b) human kidney bioimpedance values. To show the agreement between the bioimpedance values and the Cole models, the resulting values of $Z_0$ and $Z_2$ models are also included.

Figure 7

Comparative analysis of localized and longitudinal measurements by means of the reverse repeatability parameter (defined as in Section 2.5, the smaller the better) estimated for: resistance at zero frequency ($R_0$), resistance at infinite frequency ($R_{inf}$), capacitive component associated with the membrane ($C_M$), and characteristic order of the frequency relaxation distribution ($\alpha$) [47].

Figure 8

Comparative analysis of the fitting error of different bioimpedance models: Cole model ($Z_0$), model with parasitic capacitance ($Z_1$), and model with frequency-dependent membrane capacitance ($Z_2$).

Figure 9

Comparative analysis of $Z_0$ and $Z_2$ models by means of the reverse repeatability parameter (defined as in Section 2.5, the smaller the better) estimated for: $R_0$ and $C_m$.

Figure 10

Temporal variation in bioimpedance parameters in a porcine renal model preserved in cold organ preservation solution: (a) $R_0$. (b) $R_{\infty }$. (c) $C_m$ (low frequency). (d) $\alpha$.