Wearable monitoring system assesses peripheral vasculature health
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This document summarizes research on developing a wearable monitoring system to continuously assess peripheral vascular health. It describes work on measuring interface pressure using sensor arrays, blood flow velocity using Doppler ultrasound, and leg volume using impedance plethysmography. The goal is to create minimally invasive, wireless devices that can provide near real-time measurements to improve chronic venous disease diagnosis and treatment monitoring.
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Wearable monitoring system assesses peripheral vasculature health
- 1. A Wearable Monitoring System for Continuously Assessing the Health of the Peripheral Vasculature M. Hegarty 1 , F. Livingston 2 , E. Grant 1,2 , L. Reid 3 1 UNC/NCSU Joint Department of Biomedical Engineering (North Carolina State University), 2 Department of Electrical and Computer Engineering (North Carolina State University), 3 Carolon Company (Rural Hall, NC) This material is based upon work supported under a National Science Foundation Graduate Research Fellowship.
Editor's Notes
- Hello, my name is Meghan Hegarty and I will be presenting our work to date on a wearable monitoring system that can be used to continuously assess the health of the peripheral vascularature. I work under the direction of Dr. Edward Grant at North Carolina State University. For this project, we are working closely with the Carolon Company, which manufactures an advanced line of Vascular Medical Compression Hosiery.
- Chronic venous disease is a major problem in the U.S. and worldwide. The vascular system can be viewed as comprising superficial and deep sub-systems, which are connected by one-way valves. Blood normally flows form the superficial to the deep system and back to the heart. However, if the one-way valves start to break down, retrograde flow can occur. This can result in blood pooling in the lower leg, which causes swelling. If this swelling goes untreated, venous leg ulcers can develop. Unfortunately, the tests used to assess peripheral vascular pathologies are conducted in the very controlled environment of a hospital or medical clinic, and may not give an accurate picture about what is going on with the vascular system. For example, Doppler Ultrasound Assessment often requires that the patient remain seated or standing as still as possible so that the vessel can be tracked appropriately. However, blood flow is obviously going to change as soon as the person starts moving around. Also, there is no easy way to simultaneously collect and synchronize data from multiple instruments, and data cannot be recorded continuously. In response to this need, we are working to create a wearable, wireless sensing garment that can be used to continuously collect information related to the health of a person’s vascular system as they go about their daily life. Currently, we are developing modules to map the compression profile of the stocking, quantify both arterial and venous blood flow velocity, as well as measure leg volume (or the amount of swelling). This information is relayed from the wireless sensing garment to a mobile computing platform where it is stored and processed. Also, information can be relayed to the wearer, such as a suggestion to elevate legs to reduce swelling. This data is later off-loaded to a centralized data base, along with information related to the user’s medical history. Eventually, data mining techniques will be applied to look for trends in the data based upon applied compression.
- Before we begin measuring physiological data, we need an accurate measure of the pressure profile provided by the stocking. Traditionally, the compression profiles of medical compression garments are determined using static measurement techniques such as the HATRA and HOSY. These systems use tension measurements taken at various points to extrapolate interface pressure based upon Laplace’s Law. Unfortunately, traditional testing devices are unable to capture the dynamic effects of compression stockings resulting from their elastic nature. In response to this need, we have proposed an interface-pressure sensing system that can map the compression profile of a stocking in near real-time. This system consists of several arrays of force sensors placed along the course of the limb. We selected locations based upon recommendations from the literature, previous studies, and the measurement locations used to fit compression stockings. Data from these sensors is continuously collected and wirelessly transmitted to a computer running MATLAB where it is stored and analyzed.
- With respect to physiological data, we hope to collect information related to blood flow velocity and leg volume. Previously, we tried to use an array of microphones to listen to blood flow. While this system worked reasonably well for arterial blood flow, we could not detect venous blood flow. This project motivated us to begin working on a portable ultrasound probe. We have created software using MATLAB that allows us to design custom probes based upon the estimated depth of the vessel. We are also developing a wearable probe that contains the power supply, communication hardware, and driver circuitry for Continuous Wave Doppler Ultrasound. The received signal is wirelessly transmitted to a computer for analysis. A block diagram and conceptual probe design are pictured on this slide.
- Impedance plethysmography can be used to measure leg volume. With respect to this technology, a high frequency, low amplitude current is applied between an outer pair of electrodes. An inner pair of electrodes is used to measure changes to the amplitude of this signal, which is related to volume. Previously, we designed a system that can apply a 50kHz, 95uA current to the limb. This system was able to track small changes in resistance (or leg volume) in both laboratory and real-world conditions. We are currently working on a system that can apply signals of varying frequency in order to measure different phenomena. For example, lower frequencies are better at picking up shifts in extra-cellular fluid volume, while higher frequencies might be able to track venous pooling better. A block diagram of the circuit and an initial prototype of the sensor are shown on this slide. We are currently working to characterize the sensing modules. When performance testing is completed, we will conduct small-scale studies in order to validate their use in real-world scenarios. Thank you for listening to my presentation. For more information, please feel free to contact me at mshegart@ncsu.edu.