Wireless monitoring of liver hemodynamics in vivo.

Tony J Akl,Ethan Farquhar,Mark A Wilson,M Nance Ericson,Gerard L Coté

doi:10.1371/journal.pone.0102396

Abstract

Liver transplants have their highest technical failure rate in the first two weeks following surgery. Currently, there are limited devices for continuous, real-time monitoring of the graft. In this work, a three wavelengths system is presented that combines near-infrared spectroscopy and photoplethysmography with a processing method that can uniquely measure and separate the venous and arterial oxygen contributions. This strategy allows for the quantification of tissue oxygen consumption used to study hepatic metabolic activity and to relate it to tissue stress. The sensor is battery operated and communicates wirelessly with a data acquisition computer which provides the possibility of implantation provided sufficient miniaturization. In two in vivo porcine studies, the sensor tracked perfusion changes in hepatic tissue during vascular occlusions with a root mean square error (RMSE) of 0.135 mL/min/g of tissue. We show the possibility of using the pulsatile wave to measure the arterial oxygen saturation similar to pulse oximetry. The signal is also used to extract the venous oxygen saturation from the direct current (DC) levels. Arterial and venous oxygen saturation changes were measured with an RMSE of 2.19% and 1.39% respectively when no vascular occlusions were induced. This error increased to 2.82% and 3.83% when vascular occlusions were induced during hypoxia. These errors are similar to the resolution of a commercial oximetry catheter used as a reference. This work is the first realization of a wireless optical sensor for continuous monitoring of hepatic hemodynamics.

Highlights

Since the first successful liver transplant in 1963 [1], this operation has become a standard treatment for end-stage liver disease and acute liver failure
To verify that the pulsatile signal is tracking the cardiac cycle, we looked at the cardiac cycle peak detected by our system and compared it to the heart rate measured by the arterial pressure catheter
This was performed on data from both animals and the detected heart rate was accurate with a Root Mean Square Error (RMSE) of 3.9 bpm (0.065 Hz)

Summary

Introduction

Since the first successful liver transplant in 1963 [1], this operation has become a standard treatment for end-stage liver disease and acute liver failure. The current standard of care in that period relies on daily blood work and needle biopsies for suspicious results [4] These tests do not allow timely intervention, and complications are often detected after substantial damage is done to the graft, typically necessitating a second surgery including re-transplantation. Our group has developed an implantable telemetry system to monitor both tissue perfusion and oxygenation in the parenchyma of the liver which can be used to quantify stress on the tissue related to vascular complications. Detection of such complications at an early stage should allow for timely medical intervention [8,9,10,11].

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Conclusion