Page 93 - JSOM Spring 2020

Low-Level Blast Exposure in Humans

A Systematic Review of Acute and Chronic Effects

Heather G. Belanger, PhD *;
1
F. Bowling, BHS, NRP, ATP ; Eveline F. Yao, MS, MD, MPH 3
2

ABSTRACT
There is growing concern that military breaching and training with artillery or mortar firing, grenades, and shoulder-fired
and firing artillery and mortars, grenades, and shoulder-fired weapons (e.g., Carl Gustaf recoilless rifle). Based on data from
weapons may have some type of cumulative deleterious effects. tests on human tympanic membranes, a single exposure < 4 psi
There are anecdotal reports of those with repetitive exposure is considered safe without protection, and this value is used to
2
to low-level blast complaining of various symptoms, as well as dictate safety protocols. However, safety thresholds for brain
increasing empirical evidence. The purpose of this report is to injury remain unknown.
provide a systematic review of the literature on repetitive low-
level blast as it pertains to military and police training proto- Concern about cumulative effects of low-level blast exposure
cols. An extensive literature search was conducted, resulting is analogous to the concern that subconcussive blows to the
in detailed review of 18 studies. Results suggest few consis- head in sports may have deleterious long-term effects. As
3,4
tent findings, likely due to the heterogeneity of methods, high with subconcussive blows, the difficulty lies in defining the
risk of bias, and lack of reliance on objective blast-exposure construct. If the lower boundary of concussions is unclear,
data. Adverse effects, when present, dissipated over time. All defining a “subconcussive” blow is clearly more problematic.
studies that used blast gauges found significant associations, How does it differ from any blow to the head? What force is
though only a subset actually reported using the blast-gauge required to be considered a subconcussive blow? What is the
data (to correlate objective exposure with outcomes). When threshold level of blast exposure that is tolerable and how can
comparing studies within an outcome domain (e.g., cognitive), this be determined?
findings were largely inconsistent. Research with larger sam-
ple sizes, followed longitudinally, is needed. Subconcussive blows to the head in the sports arena and blast
exposure differ in that there is no physical impact to the head
Keywords: blast; low-level blast; concussion; traumatic brain with blast (instead, there is overpressure). The need for some
injury; biomarker; neuropsychological objective way to assess cumulative exposure is apparent.
Concerns about the possible effects of repetitive head trauma
and the development of chronic traumatic encephalopathy
highlight the importance of developing a clear scientific un-
Introduction
derstanding of these issues. Does a force that does not nec-
5
Mild traumatic brain injury (mTBI) or concussion has become essarily alter consciousness, either alone or repetitively, have
an increasingly problematic and publicized injury within the some type of adverse impact, either in the short or long term?
Department of Defense (DoD) and the Veterans Health Ad-
ministration; mTBI incidence is high and there are concerns Animal models suggest a single blow with a level of force
for possible long-term sequelae. Because of reports of asso- that typically does not cause cellular damage can nonetheless
ciations between duration of low-level blast exposure and cause damage when repeated several times within short pe-
1
6
7–9
clinical symptoms and because of more recent scientific and riods. Neuroimaging studies and some neuropsychological
10
media attention on concussion and mTBI, there is growing studies suggest blast exposure has unique and independent
concern that long-term exposure to blast may have deleterious adverse effects on military veterans. Given these suggestive
effects. Certain occupations, like law enforcement and military findings, it is imperative to gain a better understanding of any
breachers, tend to have particularly chronic exposure. Such adverse effects of blast exposure, particularly repetitive low-
exposure might come from training with explosive breaching, level blast exposure that does not overtly cause TBI. Our pur-
whereby an explosive charge is detonated at relatively close pose in this paper is to systematically examine the literature on
distance to open a locked door and/or to take down a wall any potential acute and chronic effects of repetitive, low-level
to gain quick access to a structure. Military personnel also blast exposure to share lessons learned to date and provide
engage in such training but might also be exposed via training insight for the design of future studies.
*Correspondence to USSOCOM Command Surgeon’s Office, 7701 Tampa Pointe Blvd, MacDill AFB, FL 33621-5323 or heather.belanger.ctr@
socom.mil
1 Dr Belanger is with the Defense and Veterans Brain Injury Center (DVBIC); Special Operations Command (SOCOM); Surgeon General’s Office;
2
and Department of Psychiatry and Behavioral Neurosciences, and Department of Psychology University of South Florida, Tampa, FL. F. Bowling
3
is with SOCOM, Special Operations Forces Acquisition, Technology and Logistics – Science and Technology (SOF AT&L-ST). Col Yao, USAF,
MC, CFS, is with SOCOM, Surgeon General’s Office, Tampa, FL.
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