Real Time Physiological Status Monitor for MicroClimate Control

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Biotechnology OBJECTIVE: The Defense Threat Reduction Agency (DTRA) seeks to develop a ruggedized non-invasive real time physiological status monitor (RT-PSM) that can control an Army microclimate cooling system to mitigate thermal stress injuries, increasing mission performance and system efficiency. DESCRIPTION: Warfighters operating in non-permissive environments in Level 1/A Personal Protective Equipment (PPE) are vulnerable to heat injuries. Even at low activity levels, mission performance and user health can be severely compromised. The requirements to wear PPE further exacerbates a Warfighter's thermal strain, diminishing the rejection of metabolic heat to the ambient environment. As a result, body heat is stored, core temperature rises, and physical and cognitive function can be significantly degraded. Depending on the environmental conditions, activity level, thermal characteristics of the protective clothing, duration of exposure, and individual tolerance to the heat, personnel may experience symptoms ranging from physical discomfort to more severe life-threatening conditions. To mitigate these risks, current cooling solutions are being implemented under PPE utilizing a cooling vest and portable vapor compression system. This provides a steady state heat flux, which can be effective for shorter duration missions, but proves detrimental over longer missions due to inefficiencies in cooling the user. This is due to vasoconstriction within the skin limiting the effective heat transfer to reduce elevated core body temperatures. Utilizing heat stress biomarkers measured by a RT-PSM, a microclimate cooling system can increase cooling efficiency and time on target whilst minimizing power consumption and cognitive loading [1]. Current RT-PSMs utilize a combination of skin temperature, core temperature (typically estimated), heart rate, and skin heat flux to estimate the thermal strain [2]. When the data is fused, a general physiological strain index (PSI) can be calculated. Utilizing a generalizable modified PSI for the cooling system may not be satisfactory as individual thermal strains are so variable [3]. An innovative solution is required to ensure that reliable, valid metrics are being measured and tailored to each individual's needs based on their respective thermophysiological responses to the cooling garment. In summary, the proposed sensor system should provide insight to the real time thermal strain of the end user using a novel combination of sensors. These sensors should then feed into an accessible algorithm that may be used for optimizing the control of a microclimate cooling system to ensure users can effectively perform their mission set while managing thermal strain. PHASE I: The goal of the Phase I effort is to design and develop a RT-PSM sensor suite, algorithm, and Data Acquisition module by which thermal strain can be measured accurately. The proof of concept should demonstrate reliable signal sampling and sensor fusion in an output that is relevant for a liquid cooled vapor compression microclimate system. This includes investigation into relevant form factors by which the sensors can be implemented. PHASE II: Develop integrated sensor suite and algorithm to perform cooling functions with simulated micro climate system optimizing for human performance. The proof of function system should be validated in a relevant environment. This validation should include the ability to modify algorithm outputs to tailor cooling system parameters for individual user optimization. By the end of Phase II the sensor suite and algorithm should be capable of providing relevant heat stress indicators and controlling a microclimate cooling system according to those metrics to reduce heat stress injury risk. PHASE III DUAL USE APPLICATIONS: PHASE III: A Phase III effort would focus on ruggedization, reliability, and further algorithm optimization of the sensor solution for both Army and commercial markets. Algorithms would be refined for reliability across larger subject populations and validated in simulated operational environments in conjunction with Army testing events. PHASE III: DUAL USE APPLICATIONS: Multiple industries must contend with heat stress related injuries, such as construction, agriculture, and first responders. Coupling a reliable RT-PSM heat stress indicator with microclimate cooling system would increase safety, productivity, and mission duration. REFERENCES: 1. Xu, Xiaojiang, et al. Simulation of a biofeedback microclimate cooling system using a human thermoregulation model. US Army Research Institute of Environmental Medicine Natick United States, 2017. ; 2. Lee, Jason KW, et al. "Biomarkers for warfighter safety and performance in hot and cold environments." Journal of science and medicine in sport (2022). ; 3. Buller, Mark J., Alexander P. Welles, and Karl E. Friedl. "Wearable physiological monitoring for human thermal-work strain optimization." Journal of applied physiology 124.2 (2018): 432-441. KEYWORDS: Microclimate; PPE; Core Temperature; skin temperature; monitoring; cooling; control systems; algorithm