A clinically relevant wireless pressure sensor for acute compartment syndrome

Abstract

Acute compartment syndrome (ACS) is a surgical emergency requiring rapid diagnosis and intervention. ACS occurs after traumatic injury when edema causes the pressure within a myofascial compartment to rise above capillary perfusion pressure. Circulation in the compartment is compromised, leading to cellular anoxia, muscle ischemia, tissue death, and limb loss. To aid in the diagnosis of ACS we have developed a small, simple, inexpensive, wireless, implantable sensor technology for monitoring intracompartmental pressure. When placed under hydrostatic load, the resonant frequency of the sensor changes proportional to the change in pressure. An analytical model was created and validated to predict the electrical characteristics of the novel coil geometries which comprise our sensors. Using this model, we designed sensors of clinically relevant size and frequency. Sensors were then tested under physiologically relevant pressure changes, and finally they were validated in an in-situ simulation of ACS. Results showed that the analytical model predicts coil properties and sensor performance to within a 10% error in almost all cases. Under physiologic conditions, sensors were sensitive to pressure changes to within 11% error. Performance of sensors in situ correlated well to benchtop testing. During simulated ACS in a fresh cadaver, sensors were sufficiently sensitive to monitor intracompartmental pressures. From this work, we developed and validated an analytical model of the electrical characteristics of a planar, stadium-geometry Archimedean spiral, both as a single coil, and in an anti-aligned inductive pair. We identified a dielectric material with unique properties favorable to hydrostatic compression and refined a clinically relevant configuration appropriately sized for clinical use. Each of these components was tested and validated comprehensively for use in a clinical setting. This work has provided several of the elements needed for a functional, clinically relevant, pressure sensor and a validated model of the electrical characteristics for novel stadium geometry Archimedean spirals for use in implantable sensors.