Long-Term Associations of Subconcussive Blast Exposure With Brain Function and Structure

OBJECTIVE: To determine the characteristics of subconcussive blast exposure associated with differences in brain structure and brain function. SETTING: Veterans Affairs Health Care System. PARTICIPANTS: Combat-exposed veterans (n = 107) without history of blast-related traumatic brain injury (TBI) or military TBI volunteered to participate. DESIGN: Observational study. MAIN OUTCOMES AND MEASURES: Connectome metrics describing the functional brain connectome, the unique brain network present at rest for individuals, were measured using magnetoencephalography. Regional brain volumes were calculated from anatomical magnetic resonance imaging using FreeSurfer. The Salisbury Blast Interview evaluated lifetime blast exposure. RESULTS: Several blast characteristics were associated with the functional connectome. The average severity of exposures was related to slowing of oscillatory communication (average pressure, parameter estimate = -4.41, P < .05 corrected). By contrast, the frequency of exposures was associated with topological differences including the number of active brain regions (number of blast exposures, parameter estimate = 0.01, P < .05 corrected) and the composition of core subnetworks (number of close-range blast exposures, parameter estimate = 0.0005, P < .05 corrected). Subconcussive blast exposure was unrelated to brain volumes. CONCLUSION: These results demonstrate that cumulative burden of subconcussive blast exposures is associated with long-term brain function. Independent relationships with the functional connectome were observed for both the average severity and the frequency of subconcussive blast exposures. This contrasts with previous work combining concussive and subconcussive blast demonstrating the highest severity across all exposures was most relevant to long-term brain function. A critical implication of these results is that long-term brain function may be associated with blast exposure, even in the absence of acute clinical effects or noticeable symptoms. This renders subconcussive blast exposure an invisible neurological insult with potential long-term implications for brain function. As military occupational blast exposure (MOBE) is primarily subconcussive in nature, this has direct implications for its conceptualization, regulation, and monitoring.