Compression stockings are widely used to treat a number of vascular conditions ranging from tired, aching legs to lymphedema, ulcer and wound care, and prevention of deep venous thrombosis (DVT). Due to the large number of compression stockings available, differences in measurement techniques, etc., finding the ideal compression stocking for a given patient may prove difficult. Improperly fitted stockings can result in inefficient treatment if too loose, or necrosis and pressure damage if too tight.
In order to account for differing needs among individuals, a closed-loop control system is proposed whereby the amount of compression delivered by a stocking is altered based upon measured physiological variables, Figure 1. The amount of pressure delivered by the compression stocking is dictated by three, independent, 
pneumatically-controlled zones (i.e., these divisions are identical to those currently used in compression stockings). The stocking is meant to be worn with a sensing system. The sensing system currently consists of a portable ultrasound unit for measuring blood flow velocity and a bio-impedance circuit for measuring the degree of lower leg swelling. Future versions of the system will incorporate skin temperature, blood oxygenation, EMG (electromyography), and activity level sensing modules. By measuring changes in the above parameters, we hope to be able to monitor the health of the vascular system.
As this project is still largely in the development phase, many of the sensing modules have not been tested outside of the laboratory. To date, small-scale studies have been conducted that indicate a bio-impedance s
ystem is able to detect small changes in leg volume, Figure 2. Ultimately, changes in the measured physiological variables will be used to assess the performance of compression stockings so that corrective actions may be taken (i.e., increase/decrease in applied pressure), thus mimicking what the body does naturally. Not only will such a system reduce the time and cost of treatment, but it will allow for meaningful data to be collected during normal daily activity. This will lead to a better understanding of the vascular system and associated pathologies, as well as enable the investigation of the effects of different pressure profiles.
