Page 28 - Journal of Special Operations Medicine - Spring 2016

other venipunctures, immunizations), standing for long in military relevant environments (e.g., physical work,
periods (e.g., military formations), and physically de- heat, cold, altitude), we are corroborating the observa-
manding training or exercises, especially in hot environ- tions in case 9 that are consistent with a capability for
ments. More importantly, 4% of military syncope cases providing Soldiers with real-time military goal-directed
can result in serious debilitating injuries, including con- physical training and assessment of performance status.
cussions, cerebral lacerations, skull and vertebral frac-
tures, and/or other intracranial injuries. Given these Conclusion
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health threats, a simple diagnostic technology that could
provide a predictive capability forewarning imminent There are several unique aspects of the CRI that make it
collapse would prove invaluable in preventing physical ideal for clinical and performance applications. It can be
collapse and potentially serious injury in military op- easily and noninvasively determined using a PPG-based
erations. Case 7, the patient with POTS, supports the device and needs no reference baseline; it can be cal-
usefulness of a continuous, real-time measure of com- culated after 30 heartbeats and continuously thereafter.
pensatory reserve as a sensitive and specific assessment It is easy to use and understand, with lower numbers
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of orthostatic instability when vital signs measurements representing diminishing reserve and higher numbers
are neither available nor stable. indicating volume repletion. Importantly, the CRI al-
gorithm can distinguish individuals who have low tol-
The data generated from case 8 demonstrate that mea- erance to central hypovolemia, thus providing the first
surement of the CRI can quantify in real time the com- monitoring capability, to our knowledge, for early de-
promise to compensate for blood loss during heat stress tection of those at highest risk for shock, fainting, or
that commonly accompanies military activities. An el- physical fatigue. Last, CRI requires no reference mea-
evation in core temperature of 1°C caused a greater than surement to normovolemia, with a scale that represents
30% reduction in the reserve to compensate for reduced the same information for individual subjects. Unlike
10
central blood volume. Based on hemorrhage estimates, other parameters, which are based on raw, uninter-
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a blood loss of only approximately 1,000mL caused this preted information that requires synthesis by the care-
individual to decompensate in the heat, which normally giver, CRI provides a single new parameter that trends
would require approximately 1,500mL under normo- volume change. Results presented here from a series of
thermic conditions. Most significant is that the time to nine distinctly different physiologic scenarios demon-
the early decompensatory phase of shock was reduced strate that the ability of each Soldier to sustain an injury
by nearly 50% in heat, dramatically limiting the time or mission-critical performance depend on the reserve to
that a medic has to intervene with effective field care. compensate for physiologic compromise. Measurement
The observation of case 8 has been recently corroborated of the compensatory reserve can anticipate a trajectory
by findings that the CRI accurately tracks the ability of of outcome (e.g., shock, fainting, heat stress) resulting
military personnel to compensate for blood loss when from hemodynamic changes secondary to intravascular
exposed to heat stress and physical activity conditions. volume loss well in advance of changes in traditional
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As such, real-time measurement of the compensatory re- vital signs. If we continue to find that measurement
serve could provide an improved decision-support tool of the compensatory reserve anticipates hemodynamic
for Combat Medics and unit commanders. compromise or decompensation in advance of changes
in standard clinical metrics or subjective symptoms in
In case 9, we were able to demonstrate that measure- traumatically injured patients, we hypothesize that CRI
ment of the CRI provided a capability to quantitatively will dramatically change how patient volume status is
assess the magnitude of compromise to the body’s re- assessed and monitored in military and civilian acute
serve to compensate for the metabolic and thermoreg- care and emergency medicine scenarios.
ulatory demands of performing progressive increases
of work intensity in the heat. Such an application has Acknowledgments
significant implications for assessment of field per-
formance and warfighter combat readiness. The CRI The authors thank Ms Mariam Calderon and Ms Jessie
technology could provide a decision-assist tool for com- Fernandez for their assistance in the editorial prepara-
manders to assess the risk of their units’ ability to meet tion of the manuscript and Dr Craig Crandall and Dan
the demands for a successful mission. In addition, the Gagnon for their contribution of data to case 8.
recovery of compensatory reserve following exercise
(Figure 9) suggests the potential use of CRI monitoring Funding
as a sensitive field hydration monitor that could be used
for directing effective fluid replacement. With future in- This work was supported by the US Army Medical Re-
vestigations designed to study the effectiveness of the search and Materiel Command Combat Casualty Re-
CRI in monitoring healthy individuals during activities search Program (Grants D_009_2014_USAISR, W81X

12 Journal of Special Operations Medicine Volume 16, Edition 1/Spring 2016