Page 49 - JSOM Winter 2023

Optimizing Brain Health of
United States Special Operations Forces

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Brian L. Edlow, MD *; Natalie Gilmore, PhD ; Samantha L. Tromly, BS ; Katryna B. Deary, NP ;
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Isabella R. McKinney, BS ; Collin G. Hu, DO ; Jessica N. Kelemen, BA ; Chiara Maffei, PhD ;
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Chieh-En J. Tseng, PhD ; Gabriel Ramos Llorden, PhD ; Brian C. Healy, PhD ;
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Maryam Masood, MS ; Ryan J. Cali, BS ; Timothy Baxter, MSc ; Eveline F. Yao, MD ;
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Heather G. Belanger, PhD ; Dan Benjamini, PhD ; Peter J. Basser, PhD ; David S. Priemer, MD ;
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W. Taylor Kimberly, MD, PhD ; Jonathan R. Polimeni, PhD ; Bruce R. Rosen, MD, PhD ;
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Bruce Fischl, PhD ; Nicole R. Zürcher, PhD ; Douglas N. Greve, PhD ; Jacob M. Hooker, PhD ;
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Susie Y. Huang, MD, PhD ; Adam Caruso, MPS ; Gregory A. Smith, BS ; Timothy G. Szymanski, MS ;
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Daniel P. Perl, MD ; Kristen Dams-O’Connor, PhD ; Christine L. Mac Donald, PhD ; Yelena G. Bodien, PhD 34
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ABSTRACT
United States Special Operations Forces (SOF) personnel are surveillance of blast exposure frequency and magnitude, an
frequently exposed to explosive blasts in training and combat. inability to distinguish between the effects of blast and blunt
However, the effects of repeated blast exposure on the human trauma, and inadequate baseline (i.e., pre-exposure) assess-
brain are incompletely understood. Moreover, there is cur- ments. Without comprehensive baseline data on Operators at
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rently no diagnostic test to detect repeated blast brain injury the time of selection, longitudinal measurements of blast- related
(rBBI). In this “Human Performance Optimization” article, we changes in brain structure and function are not possible. 6
discuss how the development and implementation of a reli-
able diagnostic test for rBBI has the potential to promote SOF There are also fundamental gaps in knowledge about the
brain health, combat readiness, and quality of life. mechanisms by which RBE may cause brain injury. Biome-
chanical, computational, and animal models have begun to
Keywords: blast overpressure; brain injury; special opera- reveal how blast waves penetrate the skull and affect under-
tions forces; sof; human performance optimization lying brain tissue. 9-19 These studies suggest that, depending
on the head’s orientation with respect to the blast, overpres-
sure waves may enter the intracranial vault via the ear ca-
nals, orbits, nasal sinuses, and foramen magnum, injuring the
Introduction
nearby cerebellum, orbitofrontal lobes, temporal lobes, and
United States (U.S.) Special Operations Forces (SOF) person- brainstem. 9,20,21 Focal injury within these regions may explain
nel experience high levels of blast exposure during training several symptoms reported by military personnel with RBE,
and combat. The cumulative effects of repeated blast expo- which include dizziness (cerebellum), behavioral dysregulation
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sure (RBE) on SOF brain health and performance are not fully and aggression (orbitofrontal lobes), memory loss (temporal
understood. Consequently, there is no diagnostic test to iden- lobes), autonomic dysfunction, and insomnia (brainstem).
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tify brain injury resulting from RBE, which we refer to as re- The proposed mechanism of focal blast-induced brain injury
peated blast brain injury (rBBI). In this “Human Performance is supported by advanced neuroimaging studies, which have
Optimization” article, we discuss why the development of a identified structural brain abnormalities in close proximity to
diagnostic test for rBBI is essential for optimizing SOF brain openings in the skull. 23
health. We first review the state of the science in blast-related
brain injury, with a focus on biomechanical, pathological, Several lines of evidence suggest that blast overpressure also
and neuroimaging data. Second, we discuss current technical, causes diffuse brain injury. Biomechanical studies indicate that
scientific, logistical, and social barriers to developing and dis- blast overpressure waves penetrate the helmet and dynami-
seminating a diagnostic test for rBBI and propose strategies cally deform the skull, creating pressure gradients that sweep
to overcome them. Third, we consider how the extraordinary through the brain (Figure 1). 12,24,25 Consistent with biomechan-
cognitive and physical demands of training and combat im- ical evidence for diffuse brain injury, recent histopathology
pact access to diagnostic testing and the delivery of medical and neuroimaging studies in individuals with blast exposure
care for SOF personnel. Finally, we propose an operational have revealed lesions throughout the thalamus, hypothalamus,
definition for rBBI, which is distinct from mild traumatic brain basal forebrain, and cerebral cortex at tissue interfaces such
injury (mTBI) and traumatic encephalopathy syndrome. 4,5 as the grey-white matter junction. 13,19,23,26,27 Blast overpressure
may cause compression and shearing of neurons and glia at
these interfaces, where there is a change in brain tissue den-
State of the Science
sity. 28,29 Radiologic-pathologic correlation studies of military
The effects of repeated blast exposure on the human brain are personnel exposed to blasts indicate that astroglial scarring
not fully understood. Current studies are limited by incomplete at the grey-white junction is associated with rBBI and may
*Correspondence to bedlow@mgh.harvard.edu
Author bios and affiliations on page 56.
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