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Operator State Monitoring: Minimally Intrusive Monitoring of Peripheral and Cerebral Blood Oxygen as Well as Pulse and Respiratory Rates in Future Vertical Lift Aircrew


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Military Operational Medicine OBJECTIVE: Develop and demonstrate nonintrusive technology to monitor cerebral blood oxygen, pulse oximetry, pulse rate, respiration rate, and possible impact trauma of Army aviators during flight. DESCRIPTION: The Army’s Future Vertical Lift (FVL) program, which includes SOCOM, is developing aircraft with dramatically expanded performance envelopes that will increase environmental stress on aircrew personnel during flight (1). The enhanced performance capabilities of FVL aircraft and their consequent stresses on the Army aviator will require near real-time actionable information characterizing the aviator’s physiological status, information that must be obtained without adversely impacting aviator performance in any way for the duration of the mission (3). With the increased speed, agility, and altitude of the FVL aircraft, blood oxygen levels are an increasingly crucial parameter to monitor. The literature identifies well-established differences in the spectra of arterial (i.e., oxygenated) blood verses venous (i.e., deoxygenated) blood (5). This difference in spectra underlies conventional pulse oximetry, which is widely used to monitor the percent oxygen saturation of peripheral blood. Such conventional pulse oximetry measurements are typically limited to measuring blood oxygen in tissue that can be transilluminated, such as the finger or earlobe. However, it has been well established that, for any of a large number of reasons, peripheral blood oxygen saturation can differ markedly from the blood oxygen saturation in the central nervous system (5). Thus, current pulse oximetry technology, limited to peripheral blood oxygen saturation, is incapable of monitoring cerebral blood oxygen levels. Moreover, the increased physiological stresses that FVL aircraft will impose make peripheral blood oxygen saturation an even less reliable and trustworthy indicator of cerebral blood oxygen. Clearly, for the FVL aviator, precise monitoring of central blood oxygen is far more important than approximations extrapolated from peripheral oxygen saturation measurements. Thus, there is a need for technology that provides reliable measures of central blood oxygen. Recent developments in near infrared transcranial spectroscopy (NIRS) suggest a way forward to meet this need. Furthermore, the capabilities of FVL aircraft make it essential to determine quickly and reliably whether the pilot is in some way compromised, traumatized, incapacitated, unresponsive, or possibly even dead. Because of these contingencies, there is a need for technology to monitor respiration rate, pulse rate, as well as physiological transients such as the possible occurrence of ‘hydrostatic shock,’ a pressure wave that can indicate the occurrence of a blunt force trauma or even a penetrating wound. While the hydrostatic shock may not itself produce tissue damage, the detection of such a shock would be important for operator state monitoring (OSM) and interpreting the ensemble of OSM signals. Thus, the technology being developed here should support potential integration with current and projected near-term OSM innovations (4). To meet specific Army aviation requirements and to integrate with existing Army kits and equipment, significant engineering and algorithm development is anticipated. Additionally, the technology will need to be hardened to mitigate the rotary-wing vibration environment. Furthermore, software enhancements are likely necessary to integrate with the Army's specific software frameworks and possible fusion and/or comparison with other OSM data, flight information, and other factors. If fielded, the technology may require secured communication methods. PHASE I: Given its short duration, Phase I will not incorporate human testing but will focus on the identification, design and development of an initial proof-of-concept prototype to record such essential physiological OSM parameters as peripheral blood oxygen saturation, cerebral blood oxygen, respiration rate, heart rate and other relevant metrics as well as the identification of pathways for the implementation of hydrostatic shock detection consequent to blunt force or penetrating trauma. To accelerate product development during this phase, an expert workshop targeting OSM in military and civilian aviation will clarify current and emerging near term needs and technology. The proposed prototype Phase I designs should have a compact, low profile, minimally intrusive footprint potentially compatible with the Army helicopter pilot's current helmet. PHASE II: Phase II will be devoted to the construction, refinement, characterization, and demonstration of the functionality of prototypes designed in Phase I. During Phase II, hydrostatic shock detection capability will be incorporated into the candidate prototype form factors. Essential signal processing, database management, analysis, and display software will be designed and developed. Norms, standards, or ‘Red Lines’ for the prototype’s physiological signals will be demonstrated. Simultaneous displays of cerebral blood oxygen, pulse oximetry, heart rate, and respiration rate for near-real time aviator self and supervisory monitoring will be developed. Additionally, during Phase II, functionality during surrogate mission simulations lasting up to 8 hours in at least 6 Warfighters will be demonstrated. A strategy and plan for FDA approvals will be developed and initiated, and a plan for self and crewmate monitoring will be formulated. Additional candidate OSM variables to interface with the prototype will be identified. Four copies of the prototype devices are to be delivered to USAARL for further test and evaluation. PHASE III DUAL USE APPLICATIONS: The end-state of this work is an FVL-enabling technology that monitors, in real-time, the medical and physiological status of the pilot and aircrew. This goal is closely aligned with initiatives and goals within the PEO Aviation office to improve aviator safety and situational awareness by reducing cockpit workload and stress. As the technology developed here demonstrates capability within FVL aircraft, it will be integrated into PEO Aviation's enduring fleet aircraft, and more broadly into aircraft platforms across the DoD. Notably, this technology supports the achievement of a validated requirement for FVL aircraft to include operator state monitoring interfaces that enable supervised autonomy. The developer will identify public and private sector funding to support additional necessary R&D as well as the FDA approval plan as required. The developer will be encouraged to coordinate with USAARL to acquire a limited air worthiness certification to enable flight tests and evaluations of the viable prototype(s) as this technology is transitioned to the Army, other DoD partners, and to the private sector, including commercial aviation. REFERENCES: 1. Curry, I. (2022). FVL performance envelope: Implications for aircrew physiology and performance (USAARL Technical Memorandum 2023-01). U.S. Army Aeromedical Research Laboratory. 2. Courtney, M., & Courtney, A. (2008). Scientific evidence for hydrostatic shock. arXiv preprint arXiv:0803.3051. 3. Duffy, M. J., & Feltman, K. A. (2023). A systematic literature review of operator state detection using physiological measures (USAARL-TECH-TR--2023-11). U.S. Army Aeromedical Research Laboratory. 4. Kelley, A., McAtee, A., Duffy, M., & Feltman, K. (2023). Evaluation of inter-subject variability in physiological metrics and workload perception: Implications for operator state monitoring (USAARL-TECH-TR--2023-16). U.S. Army Aeromedical Research Laboratory. 5. Temme, L., Eshelman, R., Bowers, B., Hayes, A., Adaway, C., St Onge, P., McAtee, A., Ard, D., Petrassi, F., Murty, S., Goldie, C., White, S. & Paul, S. (2020). The portable helicopter oxygen delivery system in the altitude chamber: A comparison between peripheral and regional blood oxygen saturation (USAARL-TECH-FR--2020-39). U.S. Army Aeromedical Research Laboratory. Note: USAARL publications are available for the USAARL Science Information Center:, 334-255-6067 KEYWORDS: Future Vertical Lift, Army Aviators, Physiological monitoring, Cerebral oximetry, Respiration, Pulse oximetry, Operator state monitoring
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