Measuring Spinal Cord Swelling in a Porcine Model using Fiber Optic Pressure Sensors

Spinal cord swelling is an indication of severe spinal cord injury (SCI) and may have negative effects on neurological outcome. Spinal cord swelling has been observed clinically and in animal models but is still not well understood and has never been mechanically quantified in terms of stress, strain or pressure. The purpose of this study was to evaluate the feasibility of using fiber optic pressure sensors to quantify swelling as a function of pressure in the spinal cord in our established in vivo porcine model of SCI. Fiber optic pressure sensors are suitable for in vivo measurements because they are electrically stable, can operate at body temperature, are highly biocompatible, small in size, and resistive to harsh chemical environments. These sensors are designed to measure pressure in gas and liquid however, the spinal cord is comprised of both fluid and structural elements, such as cerebrospinal fluid and nerve fibers respectively, and is characterized as a soft biological material. Therefore, we hypothesize that when we use these sensors in the spinal cord they may not be measuring fluid pressure but they may be measuring a quantity proportional to bulk stress in the cord instead. To evaluate the feasibility of using these sensors in the spinal cord, fiber optic pressure sensors were inserted directly into the spinal cord of recently euthanized pigs and the spinal cord pressure was measured while a stepwise increasing posterior to anterior force was applied onto the spinal cord. Results show that fiber optic pressure sensors are able to repeatably measure load-related changes in pressure in the spinal cord and most trials showed a strong linear trend between load and pressure. There was large variation in slope between trials however and future work will aim to make these measurements more predictable and to quantitatively relate the measured pressure in the spinal cord to a known applied stress or hydrostatic pressure.