Reply to Moss et al.: Military and medically relevant
models of blast-induced traumatic brain injury vs.
ellipsoidal heads and helmets
The MIT Faculty has made this article openly available. Please share
how this access benefits you. Your story matters.
Citation
Nyein, M. K. et al. “Reply to Moss et al.: Military and medically
relevant models of blast-induced traumatic brain injury vs.
ellipsoidal heads and helmets.” Proceedings of the National
Academy of Sciences 108 (2011): E83-E83. ©2011 by the
National Academy of Sciences.
As Published
http://dx.doi.org/10.1073/pnas.1102626108
Publisher
National Academy of Sciences (U.S.)
Version
Final published version
Accessed
Thu May 26 06:28:05 EDT 2016
Citable Link
http://hdl.handle.net/1721.1/66975
Terms of Use
Article is made available in accordance with the publisher's policy
and may be subject to US copyright law. Please refer to the
publisher's site for terms of use.
Detailed Terms
LETTER
Reply to Moss et al.: Military and
medically relevant models of
blast-induced traumatic brain injury
vs. ellipsoidal heads and helmets
Moss et al. (1) acknowledge the second main conclusion of Nyein
et al. (2): that a face shield may significantly mitigate blastinduced traumatic brain injury (TBI). However, they obviate the
first and most important finding: that the advanced combat
helmet (ACH) does not amplify the overpressure experienced
by the head, as suggested by Moss et al. in the letter in ref. 3;
therefore, it is safe for blast exposure. As has been shown repeatedly in theater, the ACH provides significant protection
against shrapnel and ballistic threats.
Moss et al. (1) also present two critiques on ref. 2: the lack
of military realism of the blast conditions considered and the
inaccurate reference to their article (3).
The blast conditions used in ref. 2 were based on the previous
finding (4) that the face is the main pathway for the transmission
of stress waves from the blast wave into the brain tissue. It is,
thus, the conditions in front of the face that matter for the
purpose of the study and not those in the back of the head.
Recent field blast tests and simulations of the ACH mounted on
an instrumented dummy head have confirmed the results in ref.
2. The specific blast conditions were such that the simulations
could be replicated under laboratory conditions for the purpose
of model validation.
The letter (1) also states that ref. 2 overlooked a significant
part of ref. 3, because it presented “simulations of blast wave
propagation across an advanced combat helmet (ACH) helmeted head form with and without pads” (1). We do not accept
this premise. The model in ref. 3 does not correspond to a
human head but an ellipsoidal skull. The helmet does not
correspond to the ACH but rather, to a hemiellipsoidal shell.
Moss et al. (3) also claimed to have included a “simplified
face, neck, and body . . . to capture blast-induced accelerations
www.pnas.org/cgi/doi/10.1073/pnas.1102626108
accurately” (3). However, their simulation clearly showed that
this was simply a rigid boundary condition that did not allow for
wave transmission (3). The gap between the cover and the ellipsoid is filled either with air or with material with foam properties. No material property values are given, making the work
impossible to reproduce. Because of the lack of biofidelity and
overall realism of the model as well as the lack of any medical
input, the conclusions portended in that work should be taken
with extreme caution, and they probably have no medical relevance (3). Of particular concern is their statement that “we have
discovered that nonlethal blasts can induce sufficient skull flexure to generate potentially damaging loads in the brain” (3). The
pressure wave amplification or shock underwash in the space
between the cover and the ellipsoid, which their simulation
showed for the case of the air-filled gap, is mired with the same
limitations of the model, and it has caused significant public
concern when it was released on network television news, suggesting that the ACH is unsafe for blast exposure (3).
In summary, we believe that the two main findings in Nyein
et al. (2) are well-supported.
Michelle K. Nyeina,b, Amanda M. Jasona,b, Li Yua,b, Claudio M.
Pitaa,b, John D. Joannopoulosa,c, David F. Moored, and Raul
Radovitzkya,b,1
a
Massachusetts Institute of Technology Institute for Soldier Nanotechnologies and Departments of bAeronautics and Astronautics
and cPhysics, Massachusetts Institute of Technology, Cambridge,
MA; and dDefense and Veterans Brain Injury Center, Walter Reed
Army Medical Center, Washington, DC
1. Moss WC, King MJ, Blackman EG (2011) Distinguishing realistic military blasts from
firecrackers in mitigation studies of blast-induced traumatic brain injury. Proc Natl
Acad Sci USA 108:E82.
2. Nyein MK, et al. (2010) In silico investigation of intracranial blast mitigation with relevance to military traumatic brain injury. Proc Natl Acad Sci USA 107:20703–20708.
3. Moss WC, King MJ, Blackman EG (2009) Skull flexure from blast waves: A mechanism
for brain injury with implications for helmet design. Phys Rev Lett 103:108702.
4. Moore DF, et al. (2009) Computational biology—modeling of primary blast effects on
the central nervous system. Neuroimage 47 (Suppl 2):T10–T20.
Author contributions: M.K.N., A.M.J., L.Y., and C.M.P. performed research; and J.D.J.,
D.F.M., and R.R. wrote the paper.
The authors declare no conflict of interest.
1
To whom correspondence should be addressed. E-mail: rapa@mit.edu.
PNAS | April 26, 2011 | vol. 108 | no. 17 | E83