Non-Invasive Diagnosis of Chronic Exertional Compartment Syndrome using Biological Impedance Measurements
Device Overview:
Chronic Exertional compartment syndrome (CECS) is a pathological condition characterized by increased pressure in one or more compartments of the lower leg, usually in response to swelling or injury of the muscle tissue (OrthoInfo). The lower leg in humans is divided into four muscle compartments, each of which is surrounded by a wall of strong connective tissue called fascia. The pressure buildup occurs because the fascia restricts expansion of the muscle tissue. This can lead to restricted blood flow, ischemia, tissue damage and accumulation of edema in the affected compartment (OrthoInfo). The only method for diagnosing compartment syndrome that is in clinical use is intracompartmental pressure monitoring, which is a highly painful and invasive procedure. The goal of our project is to devise an alternate, more convenient method for sports medicine physicians to differentiate between normal leg compartments and the abnormally pressurized, ischemic leg compartments observed in CECS. A secondary objective for our device is that it should be able to take real-time measurements, thereby solving the problem of user-dependance in the current diagnostic technique.
Our device correlates data from the impedance spectra of the lower leg with the pathophysiological changes observed in CECS and as such will serve as a non-invasive diagnostic tool for the condition that is also capable of taking real-time measurements. The finalized device will comprise two wearable sleeves, each surrounded by a set of electrodes which have been strategically placed to allow for the construction of a 2D image of the axial plane of the lower leg using impedance tomography. The multiple electrodes are connected via a multiplexer circuit to an AD5940 Impedance Spectroscopy Chip (obtained from Analog Devices Inc.). The chip itself will be interfaced with a system controller (Arduino Mega, Raspberry Pi or equivalent). The AD5940 impedance spectroscopy chip is designed to input current of varying frequencies to a set of electrodes on the skin surface and measures the voltage response of the tissue through a seperate set of electrodes. The voltage response is used to calculate an impedance value for each of input current frequency (impedance spectra). The impedance spectra will be stored on the controller, which will have a bluetooth functionality that can be programmed to convey data to a nearby desktop computer. Impedance spectra of the lower leg from before and immediately after exercise will be analysed in MATLAB using a machine learning algorithm designed/trained to identify the differences in impedance spectra for normal and compartment syndrome leg compartments. Impedance tomography may also be used to improve measurement specificity. An intuitive user-interface will be created on a desktop computer, designed to let the physician know whether or not the patient has compartment syndrome, and if possible, the extent/severity of the syndrome. The principles of operation, circuit diagrams and CAD diagrams of our proposed device are provided in the proceeding sections.