Evaluating the Feasibility of Quantifying Spinal Cord Swelling as a Function of Pressure Using Fiber Optic Pressure Sensors

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Abstract

Post traumatic spinal cord swelling can occur as a result of a spinal cord injury and may have negative effects on a patient’s neurological outcome. Spinal cord swelling is hypothesized to be associated with an increased pressure in the cord tissue. Experimental measurement of pressure in the in vivo cord would facilitate the study of spinal cord swelling and its effects. The spinal cord is a soft biological tissue consisting of fluid and solid components in which measuring and interpreting pressure is challenging.

The objective of this research was to evaluate the feasibility of using fiber optic pressure sensors to directly measure intraparenchymal cord pressure.

Fiber optic pressure sensors were used to measure intraparenchymal cord pressure in ex vivo pig cords under two conditions. A focal stress was incrementally applied to the cord to simulate sustained compression and decompression (i). Hydrostatic pressure was applied to the cord to simulate swelling (ii). The hydrostatic pressure was applied in three phases: a ramp to increase the pressure, a one hour hold at constant pressure and a ramp to decrease pressure using a fluid filled tank.

During applied focal stress (i), results showed distinct intraparenchymal cord pressure increases and similar trends across trials. Most trials had a linear trend or region with strong correlations (r2 > 0.9) between applied force and intraparenchymal cord pressure. However, when combining all trials, this association weakened (r2 = 0.648).

During ramping applied hydrostatic pressure (ii), the intraparenchymal cord pressure increase followed closely to the pressure in the surrounding fluid. In contrast, during the hold, the intraparenchymal cord pressure gradually increased while the pressure in the surrounding fluid remained unchanged. This resulted in a significant difference between the pressure changes seen in the cord and in the surrounding fluid.

We conclude that the fiber optic pressure sensors are capable of measuring fluid pressure in spinal cord tissue. Based on the content of this thesis, we recommend the use of these sensors to examine relative intraparenchymal cord pressure in events occurring at a rate of 5 N/s up to 300 N in our in vivo porcine model for SCI.

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