Electrochemical Approach to Measure Physiological Fluid Flow Rates

Srivats Sarathy,M L Raghavan,Srinivasan Rajagopal,Marco A Nino,Abdulsattar H Ghanim,Syed Mubeen

doi:10.3389/fchem.2021.680099

Srivats Sarathy, M L Raghavan + Show 4 more

Open Access

https://doi.org/10.3389/fchem.2021.680099

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Abstract

In vivo measurement of the flow rate of physiological fluids such as the blood flow rate in the heart is vital in critically ill patients and for those undergoing surgical procedures. The reliability of these measurements is therefore quite crucial. However, current methods in practice for measuring flow rates of physiological fluids suffer from poor repeatability and reliability. Here, we assessed the feasibility of a flow rate measurement method that leverages time transient electrochemical behavior of a tracer that is injected directly into a medium (the electrochemical signal caused due to the tracer injectate will be diluted by the continued flow of the medium and the time response of the current—the electrodilution curve—will depend on the flow rate of the medium). In an experimental flow loop apparatus equipped with an electrochemical cell, we used the AC voltammetry technique and tested the feasibility of electrodilution-based measurement of the flow rate using two mediums—pure water and anticoagulated blood—with 0.9 wt% saline as the injectate. The electrodilution curve was quantified using three metrics—change in current amplitude, total time, and change in the total charge for a range of AC voltammetry settings (peak voltages and frequencies). All three metrics showed an inverse relationship with the flow rate of water and blood, with the strongest negative correlation obtained for change in current amplitude. The findings are a proof of concept for the electrodilution method of the flow rate measurement and offer the potential for physiological fluid flow rate measurement in vivo.

Highlights

Electrodilution for Physiological Flow Measurement through arbitrarily shaped structures, material heterogeneity, and significant risks
Thermodilution is the most common technique used in the clinic for blood flow measurement in the heart—the cardiac output
The flow rate of the media could be recovered by appropriate calibration. This is schematically illustrated in Figure 1. (a) The tracer is injected which mixes with the flowing medium, following which (b) the mixture reaches the electrochemical cell and causes a change in the current response. (c) The temporary change in the electrical current causes a peak current. (d) The flowing medium will dilute this response, and (e) the measured current eventually returns to the baseline

Summary

INTRODUCTION

“It was fatal for the development of our understanding of circulation that blood flow is relatively difficult to measure while blood pressure so easy to measure . . . most organs do not need blood pressure, but flow” (Dünser et al, 2013). In 1928, physician-scientist Jarisch aptly summarized this problem in medicine that has endured to this day It is not just the measurement of the rate of blood flow, but that of most physiological flows—the cerebrospinal fluid flow is another such example. In electrodilution, when a small voltage is applied to the flowing media, the introduction and dilution of an injectate will result in a charge transfer (faradaic process) and/or charge redistribution (capacitive process) and release a measurable current change (Park et al, 2019) These temporal changes in current—current dilution—will be related to the blood flow rate because the greater the flow, the quicker the dilution. This study aimed to assess proof of concept for the electrodilution method and develop metrics that best permit the recovery of the blood flow rate

MATERIALS AND METHODS

Experimental Setup

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT