Importance of the Mechanical Forces in the Pathogenesis of Syringomyelia

 

Grant Recipient: Francis Loth, PhD, Department of Mechanical and Industrial Engineering, University of Illinois at Chicago

Project Title: Importance of the Mechanical Forces in the Pathogenesis of Syringomyelia

Dates: September 30, 2005 August 31, 2006

Grant Amount: $50,000

A simplified in vitro model of the spinal canal, based on in vivo magnetic resonance imaging (MRI), was used to examine the hydrodynamics of the human spinal cord and subarachnoid space (SAS) with syringomyelia. In vivo MRI measurements of SAS geometry and cerebrospinal fluid (CSF) velocity were acquired in a patient with syringomyelia and used to aid in the in vitro model design and experiment. The in vitro model contained a fluid-filled coaxial elastic tube to represent a syrinx. A computer controlled pulsatile pump was used to subject the in vitro model to a CSF flow waveform representative of that measured in vivo. Transducers measured unsteady pressure both in the SAS and intra-syrinx at four axial locations in the model.

MRI results indicated that the peak-to-peak amplitude of the SAS flow waveform in vivo was approximately ten fold that of the syrinx and in phase. The in vitro flow waveform approximated the in vivo peak-to-peak magnitude. Peak-to-peak in vitro pressure variation in both the SAS and syrinx was approximately 6 mmHg. Syrinx pressure waveform lead the SAS pressure waveform by approximately 40ms. Syrinx pressure was found to be less than the SAS for ~200 ms during the 860 ms flow cycle. Unsteady pulse wave velocity (PWV) in the syrinx was computed to be a maximum of ~25 m/s. Spinal cord wall motion was found to be non-axisymmetric with a maximum displacement of ~140 m, which is below the resolution limit of MRI.

Agreement between in vivo and in vitro MR measurements demonstrated that the hydrodynamics present in the fluid filled coaxial elastic tube system are similar to those present in syringomyelia. Overall, the in vitro study of the unsteady pressure and flow environment within the syrinx and SAS, provides insight into the complex biomechanical forces present in syringomyelia.

We propose to continue experimentation using this in vitro model of syringomyelia in order to determine the influence of various configuration changes on the hydrodynamic environment within the syrinx and SAS. Our previous research demonstrated a phase shift between the syrinx and SAS pressure that could provide a mechanism for syrinx progression. Thus, the proposed work would examine this potential mechanism under various configurations thought to cause syringomyelia. These configuration changes would represent conditions such as coughing, Chiari malformation, flow obstruction due to vertebra misalignment, changes in atmospheric pressure, and spinal cord tension. We will focus on obtaining measurements that provide a more complete understanding of the role of hydrodynamic forces in syringomyelia pathogenesis. Finally, we will continue research to develop novel MRI techniques that will provide detailed information about patient geometry to better assess syringomyelia and Chiari malformation severity.

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