Page 30 - JSOM Fall 2018

Mechanical Forces Experienced by Simulated Patients
Evacuated During Dismounted Military Movement
in Mountainous Terrain

Jonathon Florance, BS *; Cara Florance, PhD 2
1

ABSTRACT
Background: Given a denied or resource­limited area of oper­ acceleration, that potentially can worsen injuries. Several fac­
ations, when air medical evacuation would require extended tors complicate understanding the effects of these mechanical
delay, should dismounted movement through difficult terrain forces. First, impacts can vary depending on mission­specific
dissuade an attempt of immediate ground evacuation? Under­ factors, including mission, enemy, terrain, troops, time, and
standing the magnitude of external forces during dismounted civilian considerations. Second, precise human physiologic ef­
movement would inform planning in such circumstances. fects are difficult to correlate to observed impacts. Human tol­
Objectives: We assessed the mechanical impact experienced erance to acceleration is a function of extrinsic factors such as
during dismounted evacuation from mountainous terrain. magnitude, direction, duration, rate of onset, and positioning
We also describe a protocol using a portable accelerometer of the patient, and also intrinsic factors, including the patient’s
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to evaluate evacuation. Materials and Methods: A triaxial ac­ age, health, and physical conditioning. Therefore, instead of
celerometer and a semiflexible litter were used to collect data direct physiologic effects, we sought to understand the mea­
during the Army Mountain Warfare School Rough Terrain sured impacts of dismounted movement through the context
Evacuation Course. We used the generalized extreme value of other modes of military evacuation so a comparison of
(GEV) distribution, using maximum likelihood estimation, evacuation methods can guide battlefield decisions.
to model maximum acceleration values. Results: It was deter­
mined that the accelerometer should be mounted directly onto Although other investigators have studied acceleration forces in
a mannequin when using semiflexible litters. GEV analysis the context of civilian medical evacuation, none, to our knowl­
from a mannequin­mounted trial revealed that for 1­minute edge, have done so in the context of dismounted tactical mili­
2,3
evacuation intervals, 10% would have a maximum acceler­ tary movement. The secondary objective of this work was to
ation over a value between 2.4g and 3.7g. This interval en­ evaluate and present a protocol that will allow additional and
compasses the maximum acceleration from evacuation using a congruent data collection for different environments to create
Mine­Resistant Ambush Protected (MRAP) vehicle, measured an accurate characterization of dismounted movement in oper­
by the US Army Aeromedical Research Laboratory. The peak ational environments specific to each team. An accelerometer, a
acceleration from a 75­minute, mannequin­mounted trial was device that measures acceleration forces, was used in this study.
5.5g, approximately twice as large as the MRAP maximum. The use of accelerometers during dismounted training can pro­
Conclusion: For the evacuee, the acceleration experienced vide valuable feedback to military personnel who are honing
during dismounted evacuation in mountainous terrain can be skills that may reduce trauma to evacuees.
comparable to MRAP evacuation, especially with sufficient
planning that avoids points of maximum impact. Leaders can Materials and Methods
consider this comparison during planning.
The study design was approved by the Vermont National
Keywords: acceleration; movement; military personnel; emer- Guard State Judge Advocate General. The discrete and nonin­
gencies; warfare; stretchers; transportation; rescue work vasive accelerometer did not alter the existing training curric­
ulum in any form.

Introduction Terrain and Litter Description
This study was conducted in collaboration with the Army
The necessity of conducting military operations in remote Mountain Warfare School. Data collection occurred at the
and austere mountain environments is clear from recent con­ Camp Ethan Allen Training Site in Jericho, Vermont, in April
flicts. Deployed far from logistical support, Special Operations 2017 during the Rough Terrain Evacuation Course culmina­
Forces routinely rely on dismounted movement even when tion exercise. The weather during data collection was 48°F
faced with medical emergencies. Concerned with the pros­ (9°C) and overcast. The terrain was wooded, with steep to
pect of an extended aviation delay, Operators may consider gradually sloping granite faces. The culmination event in­
alternative evacuation that includes dismounted movement. cluded two individual legs, totaling approximately 1 mile or
During such transport, an injured patient on a litter may expe­ 2 hours of patient movement. Soldiers pulled the litter across
rience a mechanical impact, resulting in sudden and transient the ground as a sled, carried the litter over obstacles such as
*Correspondence to jonathon_florance@hms.harvard.edu
1 CPT Florance, US Army National Guard, currently is a student at Harvard Medical School, Boston, Massachusetts. He is a former Special Forces
Officer (C/2/10, B/5/19, SOD­K). He earned his BS at the US Military Academy. Dr Florance is a principal scientist at CoPhysics Corporation.
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