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TECHNICAL PAPERS: Fluids/Heat/Transport

Syringomyelia Hydrodynamics: An In Vitro Study Based on In Vivo Measurements

[+] Author and Article Information
Bryn A. Martin, Wojciech Kalata, Francis Loth, Thomas J. Royston

 University of Illinois at Chicago, Department of Mechanical and Industrial Engineering, Chicago, IL

John N. Oshinski

 Emory University, Department of Radiology and Biomedical Engineering, Atlanta, GA

J Biomech Eng 127(7), 1110-1120 (Jul 29, 2005) (11 pages) doi:10.1115/1.2073687 History: Received January 26, 2005; Revised July 18, 2005; Accepted July 29, 2005

A simplified in vitro model of the spinal canal, based on in vivo magnetic resonance imaging, was used to examine the hydrodynamics of the human spinal cord and subarachnoid space with syringomyelia. In vivo magnetic resonance imaging (MRI) measurements of subarachnoid (SAS) geometry and cerebrospinal fluid 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. Fluid velocity was measured at three axial locations within the in vitro model using the same MRI scanner as the patient study. Pressure and syrinx wall motion measurements were conducted external to the MR scanner using the same model and flow input. Transducers measured unsteady pressure both in the SAS and intra-syrinx at four axial locations in the model. A laser Doppler vibrometer recorded the syrinx wall motion at 18 axial locations and three polar positions. Results indicated that the peak-to-peak amplitude of the SAS flow waveform in vivo was approximately tenfold that of the syrinx and in phase (SAS5.2±0.6mls,syrinx0.5±0.3mls). The in vitro flow waveform approximated the in vivo peak-to-peak magnitude (SAS4.6±0.2mls,syrinx0.4±0.3mls). Peak-to-peak in vitro pressure variation in both the SAS and syrinx was approximately 6 mm Hg. Syrinx pressure waveform lead the SAS pressure waveform by approximately 40 ms. Syrinx pressure was found to be less than the SAS for 200ms during the 860-ms flow cycle. Unsteady pulse wave velocity in the syrinx was computed to be a maximum of 25ms. LDV measurements indicated that spinal cord wall motion was nonaxisymmetric with a maximum displacement of 140μm, which is below the resolution limit of MRI. Agreement between in vivo and in vitro MR measurements demonstrates that the hydrodynamics in the fluid filled coaxial elastic tube system are similar to those present in a single patient with syringomyelia. The presented in vitro study of spinal cord wall motion, and complex unsteady pressure and flow environment within the syrinx and SAS, provides insight into the complex biomechanical forces present in syringomyelia.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Sagittal MRI of head and 3D reconstruction of subcranial subarachnoid space. (a) Patient with Chiari malformation and syringomyelia (T1 image). (b) Healthy subject (T2 image).

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Figure 2

MRI of a patient with Chiari malformation and syringomyelia. (a) Patient’s lower cervical and thoracic region with syringomyelia. (b) 3D view of syrinx with contours, indicating the SAS reconstructed from axial images. (c) MRI images of the spinal canal and syrinx at various axial locations.

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Figure 3

In vitro phantom CSF system model, cross-sectional and side view. The internal syrinx catheter (depicted) is clamped to alter the boundary condition from “open to atmospheric pressure” to “closed to atmospheric pressure.”

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Figure 4

Experimental configuration for the pressure and spinal cord wall motion experiment (top) and MRI experiment (bottom)

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Figure 5

In vitro model flow waveforms measured by pcMRI in the SAS (top) and syrinx (bottom) at positions A, B, and C on the model (measured with system open to the atmospheric pressure)

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Figure 6

In vitro model flow waveforms measured by pcMRI in the SAS (top) and syrinx (bottom) at position A, B, and C on the model (measured with system closed to the atmospheric pressure)

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Figure 7

In vivo patient flow waveforms measured by pcMRI in the SAS (top) and syrinx (bottom) at various vertebrae locations

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Figure 8

In vitro velocity profiles measured by pcMRI in the SAS at various time points during the cardiac cycle (see flow waveform inset)

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Figure 9

In vitro velocity profile obtained from pcMRI at position B indicated at various time points during the cardiac cycle (see flow waveform inset)

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Figure 10

In vivo patient velocity profile obtained from pcMRI measured at T3, indicated at various time points during the cardiac cycle (see flow waveform inset)

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Figure 11

Computed flow difference in the SAS and syrinx measured by pcMRI. Patient measurements between C7 and T3 cervical levels located 6 cm apart. Model measurements obtained between C and B locations, 5 cm apart.

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Figure 12

In vitro pressure versus time measured at four axial locations. (a) external pressure (EP), (b) internal pressure (IP), (c) differential pressure (DP). Measurement 1, 2, 3, and 4 correspond to location 1, 7, 13 and 17 cm on the model as shown in experimental configuration (Fig. 4).

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Figure 13

Ensemble average radial wall displacement as a function of axial location for one cardiac cycle (a) = left wall; (b) = top wall; (c) = right wall, location of left, top, and right wall depicted in Fig. 3 cross-sectional view

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Figure 14

In vitro differential pressure and wall displacement measurements. (a) Differential pressure (internal–external measured at four axial locations. (b) Left wall displacement measured at four axial locations. (c) Top wall displacement measured at four axial locations. (d) Right wall displacement measured at four axial locations.

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Figure 15

In vitro wall displacement measured with low and elevated internal syrinx pressure. (a) Low mean internal syrinx pressure (∼1cmH2O). (b) Elevated mean internal syrinx pressure (∼20cmH2O).

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Figure 16

Variation of pulse wave velocity during the cardiac cycle for the in vitro model as estimated through the Moen-Korteweg equation. Note that zero values indicate the algebraic expression produced an imaginary value for pulse wave velocity.

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