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Wearable Device for Continuous, Non-Invasive Monitoring of Vascular Access Health and Fluid Status in Hemodialysis Patients
Richard Neville, David J. Kuraguntla, Samit Gupta, Forrest Miller
GraftWorx, San Francisco, CA

INTRODUCTION: Over 2.5 million patients are undergoing hemodialysis worldwide. A healthy, mature arteriovenous fistula (AVF) is critical for these patients, for whom maintenance of euvolemia is also a major challenge. Clinical outcomes could be improved, and healthcare costs lowered, by preventing fluid overload. This study presents a novel wearable device that enables remote monitoring of AV access health and multiple key fluid status metrics. The SmartPatch system also comprises an end-to-end data path that facilitates secure data transmission and analysis and generates actionable alerts. The aim of this study was to evaluate the systemís ability to accurately and precisely measure Hb and Hct, critical markers for anemia that dictate dialysis treatment. METHODS: 128 patients with arteriovenous fistulas currently undergoing hemodialysis were recruited across three clinical sites. Each of these patients had a SmartPatch device placed on the skin over their fistula. 57 of these patients had their Hb and Hct tested with a HemoCue Hb 201+ device; 21 of these patients were also tested with a Transonic flowmeter to determine volumetric flow rate through the AVF. The remaining 71 patients received a duplex ultrasound or fistulogram to assess percent stenosis of the AVF. A total of 273 sets of multi-sensor data were recorded and analyzed using the GraftWorx data hub and software backend. A randomly selected subset of 157 reads was used to train algorithms for the quantitation of Hb and Hct. These algorithms were then tested on the remaining 116 reads. An algorithm was also developed to identify patients with volumetric flow rates below 1000 mL/min. RESULTS: The SmartPatch system measured Hb and Hct with respective root-mean-square error (RMSE) of 1.20 g/dL and 3.60 Hct compared to reference values obtained from the HemoCue device, whose accuracy has been reported to be between 0.3 and 1.6 g/dL (0.9 to 4.8 Hct). The standard deviations for each read on the same patient-with the same device-were computed and averaged, weighted by group size, as a measure of precision. These precision metrics were computed to be 0.410 g/dL and 1.230 Hct for Hgb and Hct, respectively. Flow rate values obtained from the SmartPatch were compared to flowmeter values taken at a dialysis session within 1-5 days from the patch readings. The SmartPatch was able to reliably identify volumetric flow rate (VFR) values less than 1000 mL/min (sensitivity: 100%, specificity: 75%; n=21). Of the patients who received a duplex ultrasound or fistulogram, 100% of major (>50% stenosis) lesions were detected. CONCLUSIONS: The results of this study illustrate the ability of the wearable SmartPatch system to non-invasively measure volumetric flow rate, blood Hb and Hct in hemodialysis patients with AV fistulas, to a clinically viable degree of accuracy comparable to available methods. This study also showed the ability of the SmartPatch system to detect progression of the degree of stenosis in AV fistulas. Finally, this study demonstrated the efficacy of the end-to-end GraftWorx data path.


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