1. Conclusion/Discussion
EVALUATION OF SLEEP QUALITY AND AXONAL INJURY IN OIF/OEF VETERANS WITH A HISTORY OF BLAST EXPOSURE
Sheehy, CJ; Powers, K; Storzbach, D; Sun, SM; Huckans, M; O’Hearn, DJ; Rooney, W; Simon, J; Murchison, C; Boudreau, EA.
Portland Veterans Affairs Medical Center and Oregon Health & Science University, Portland OR
Introduction
Results **
The association between mild traumatic brain injury (mTBI) and sleep disturbance has been well described. However, further characterization of the nature and extent of these sleep disturbances is needed using both qualitative and quantitative measures. This study, which was part of a broader investigation of neurocognitive changes in blast exposed Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF) Veterans, was designed to evaluate subjective sleep quality, and in a subgroup of subjects, begin investigating the role of axonal injury in sleep disruption.
PSQI: Consistent with our previous interim report, subjects in both non-blast exposed and blast exposed groups had elevated PSQI scores (Group 1 = 7.7; Group 2 = 11.3). However, when the two groups were compared using an independent sample t-test, the blast exposed group had significantly higher global PSQI scores (p = 0.002).
DTI: When we evaluated the imaging data, our preliminary analysis showed a significant relationship between global PSQI scores and axonal integrity in the left posterior limb of the IC, and the right centrum semiovale.
DTI Measures
Global PSQI Correlation
Significance
(2-tailed)
Fractional Anisotropy
Left Post. Limb IC
Right CO
0.577**
-0.145
0.024**
0.605
Mean Diffusivity
-0.293
0.683**
0.290
0.005** λ1
-0.006
0.691**
0.983
0.004**
Conclusion/Discussion
Blast exposure is associated with poorer sleep quality in OIF/OEF Veterans. While the results of the imaging portion of this study needs to be interpreted very cautiously due to the small number of subjects, the data suggests that axonal injury as measured by DTI may be a useful biomarker for neuronal pathways associated with blast-related sleep disruptions.
Methods
Eighty-five OIF/OEF Veterans were evaluated in the following groups: deployed, non-blast exposed (Group 1; 21 subjects); and deployed, blast exposed (Group 2; 45 subjects). All subjects were at least one year s/p last blast exposure. None of the subjects had abnormalities on standard clinical imaging sequences. Each subject completed a battery of neurocognitive tests including the Pittsburg Sleep Quality Index (PSQI, Buysse et al, 1989). In addition, a subgroup of 16 subjects (8 subjects from Group 1; 8 subjects from Group 2) underwent evaluation for axonal injury using high-field strength diffusion tensor imaging (DTI; Siemans MAGNETOM 7 Tesla instrument using diffusion tensor acquisition – spin-echo echo-planar- including accompanying phase images using 2 mm thick isotropic voxels and 32 gradient directions). Regional diffusion values were determined using FSL Tools (FMRIB Software Library) and DTI Studio Processing Tools and Environment.
Table 1: In order to evaluate the relationship between sleep quality and axonal integrity, a partial correlation analysis was performed between the global PSQI score and three DTI parameters. Significant findings were only observed in two regions, the posterior limb of the internal capsule and the right centrum semiovale (CO). FA = fractional anisotropy (a calculated value that is between 0 – 1); MD = Mean Diffusivity (a measure of the total amount of diffusion occurring); λ1 = axial diffusivity (a measure of the amount of diffusion occurring parallel to the axon, a generally accepted measure of axonal integrity).
References
Schwab et al, The Brief Traumatic Brain Injury Screen (BTBIS): Investigating the validity of a self-report instrument for detecting traumatic brain injury (TBI) in troops returning from deployment in Afghanistan and Iraq. Neurology, 66(5) Supp. 2, A235.
Buysse DJ, Reynolds CF, Monk TH, et al. The Pittsburgh Sleep Quality Index: a new instrument for psychiatric practice and research. Psychiatry Res. 1989;28:193–213.
**This research has been supported by a grant from the Department of Veteran’s Affairs Rehabilitation Research & Development Service. Merit Review Study No. B5060R
“Multidiscipline Assessment of Blast Victims for Cognitive Rehabilitation”, Daniel Storzbach, Principal investigator.
Figure 1: The color directional map from an axial slice acquired in one blast exposed subject. An ellipsoid region-of-interest corresponding with the right centrum semiovale is shown in white.
Analysis: Regional diffusion values were determined using FSL software and DTI Studio Processing Tools and Environment and included calculation of mean diffusivity, fractional anisotropy, and the three eigenvalues (λ1, λ2, λ3), for measures of axial and radial diffusivity. The generation of a color directional map like the one shown in this figure is a key step in DTI processing as it involves color coding the fibers by the direction in which they are oriented.