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Integrated Microsystems to Sense and Control Warfighter Physiology for Military Diver Operations


OBJECTIVE: Develop an integrated microsystems platform that dynamically senses and controls warfighter physiology to enable safe and robust military dive and flight operations. DESCRIPTION: Consequences of inhaling gases at high pressure were originally encountered during undersea salvage and construction over a century ago. Empiric depth and time limits were found to reduce gas bubble formation in tissues that caused the"bends". We continue to limit adverse physiology now expanded to include decompression sickness (DCS), oxygen toxicity, inert gas narcosis, high pressure nervous syndrome (HPNS), hypoxia and high altitude illness primarily by breathing static gas mixtures at prescribed pressures and durations. Longstanding US Navy dive regulations and technologies mandate use of standard gas mixtures, rate of descent, rate of ascent, depth, and bottom time. While dive technology has changed little in the last two decades, recent advances in applied physiology and microsystems technology could coalesce into revolutionary capability. Although trace gases such as nitric oxide (NO) were traditionally considered"poisons", they are now known as naturally occurring biomolecules that play a critical role in cellular signaling and metabolism. The Food and Drug Administration (FDA) has approved NO to treat pulmonary disease, and NO donors such as nitroglycerin have been shown to decrease incidence of DCS through various putative mechanisms. An example within the Defense Advanced Research Projects Agency (DARPA) is inhaled NO to augment operations in hypoxic environments as part of the Rapid Altitude and Hypoxia Acclimatization (RAHA) program. Combining the therapeutic capabilities of trace gases such as NO with in vivo monitoring of pre-symptomatic risk factors such as microbubble formation could reduce the risk of adverse events such as DCS, but requires novel algorithms for dynamic control of pressure-related physiologic conditions, constant physiological feedback, and precise gas administration. Component technologies of interest include but are not limited to: dynamic mixed gas models and control algorithms; physiologic sensors; gas sensors; and gas regulators. Models and algorithms produced under this solicitation should permit increased operation capabilities while minimizing the risk of the following: DCSgas expansion injuries and bubble formation in blood and tissue caused by rapid ascent; oxygen toxicityincreased partial pressure of oxygen (PO2>1.6 ATA) resulting in seizures; inert gas narcosiseuphoria and decrement in intellectual and psychomotor performance related to the lipid solubility of the gas; and hypoxiadecrement in cognition and performance related to low partial pressure of oxygen. The dynamic sensing and control could include but is not limited to such gases as O2, CO2, COx, NO, NOx, H2S, and inert gas diluent. Advanced microsystems technology including chip-scale gas chromatograph / mass spectrometer (to actively and rapidly monitor inspired and expired gases/agents); capacitive micro-machined ultrasonic transducer arrays (for in vivo bubble detection and environmental monitoring); and gas/vapor control elements such as MEMS gas pumps, valves and nebulizers offer new components that could be integrated into a physiologic control system for extreme environments. The therapeutic effects of inhaled pharmaceutical agents on physiology could also be considered. Component technologies could support military open circuit, semi-closed circuit or closed circuit rebreather systems. Military flight operations are also limited by the physiologic effect of breathing gas mixtures across an extreme range of atmospheric pressure. For example, breathing suboptimal gas mixtures has been implicated as the etiology of impaired pilot cognition and unsafe flying conditions in military aircraft equipped with the On Board Oxygen Generation System (OBOGS). Unlike current methods that rely on post-flight diagnostics, continuous assessment of breathing gas and physiology could help determine the etiology and mitigate the operational impact of abnormal pilot physiology within multiple fighter aircraft including the F-22 Raptor and F-35 Joint Strike Fighter. The continuous gas and physiologic monitoring technology developed within this topic could also support pilots within military high-performance jet aircraft. The platform should enable safe operation in this representative profile: (1) insertion via military free fall from 35,000 feet flight level; (2) a brief surface interval; (3) combat dive down to 200 feet sea water (FSW) for at least 120 minutes duration, surface and immediately begin a second dive of variable, increasing depth with minima at 100 FSW (for at least 10 minutes), 150 FSW (for at least 10 minutes), and 200 FSW (for at least 20 minutes) without decompression obligation; (4) brief surface interval; and (5) extraction in an unpressurized aircraft below 14,000 feet mean sea level. PHASE I: Define the gas mixtures suitable for the representative dive and flight profile. Explore and develop requirements for the dynamic mixed gas model and control algorithm. Develop a high level model and control algorithm, to be informed by Phase II in vivo experimentation and data collection. Select representative component microsystem technologies for proof of concept and development. Design a breadboard mixed gas platform for use in simulated dive and flight profile(s) within a chamber. Develop the military and Occupational Safety and Health Administration (OSHA) regulatory approval plan for the component technologies and integrated device. Phase I deliverables: A report defining (1) Opportunities and limitations of selected gases; (2) current state-of-the-art and limitations of component technologies including model/algorithm, physiologic sensors, gas sensors, and gas control components; (3) high level model and control algorithm; (4) detailed design of breadboard system; and (5) proposed animal chamber testing and regulatory approval plan. PHASE II: Develop, demonstrate, and validate a dynamic model and control algorithm using a small animal model. Build a breadboard mixed gas system that includes the necessary control algorithm, physiologic sensors, gas sensors, and gas control components for use in chamber experiments. The breadboard system shall be demonstrated using the defined profile. At the conclusion of Phase II the performer shall provide a detailed plan for algorithm optimization, hardware miniaturization and integration into a prototype device, and transition of a man-portable prototype device into operationally relevant environments. As such, full and traceable documentation of in vivo testing that meets regulatory requirements must be provided in order to move to Phase III. Phase II deliverables: (1) Dynamic mixed gas model and control algorithm that enables extreme combat diving and high altitude flight with limited risk of complications; (2) breadboard system that includes the necessary algorithm, physiologic sensors, gas sensors, and gas control components; (3) prototype integrated microsystem device design; and (4) detailed regulatory approval, transition, and commercialization plan. PHASE III: Phase III commercial application will focus on exploration and extraction of undersea oil, gas, and minerals. Improved deep water site access, operations, and safety should limit cost and environmental impact of production of natural resource necessary for US economic and military viability. Phase III military application will focus on robust military diving and flight operations. Specific applications include expanded special operations and EOD capabilities. REFERENCES: 1) Bennett and Elliott's physiology and medicine of diving (5th ed.). Bennett, P; Rostain, J. United States: Saunders Ltd (2003). 2) The future of diving: 100 years of Haldane and beyond. Lang, M. Brubakk, A. ed.; Washington, D.C.: Smithsonian Institution Scholarly Press, 2009. (ISBN: 9780978846053). 3) DARPA Rapid Altitude and Hypoxia Acclimatization (RAHA) and Surviving Blood Loss (SBL) programs:; 4) Inhaled NO as a therapeutic agent. Bloch KD, Ichinose F, Roberts Jr. JD, Zapol WM. Cardiovascular Research 2007. 75:339-48. 5) Exogenous nitric oxide and bubble formation in divers. Dujic Z, Palada I, Valic Z, Duplancic D, Obad A, Wisloff U, Brubakk AO. Med Sci Sports Exerc. 2006. Aug;38(8):1432-5. 6) Hydrogen sulfide and nitric oxide are mutually dependent in the regulation of angiogenesis and endothelium-dependent vasorelaxation. Coletta C, Papapetropoulos A, Erdelyi K, Olah G, Mdis K, Panopoulos P, Asimakopoulou A, Ger D, Sharina I, Martin M, Szabo C. PNAS. 2012. Jun; 109 (23): 91619166. 7) Assessment of extravascular lung water and cardiac function in trimix SCUBA diving. Marinovic J, Ljubkovic M, Obad A, Breskovic T, Salamunic I, Denoble PJ, Dujic Z. Med Sci Sports Exerc. 2010. Jun;42(6):1054-61. 8) Representative chip-scale gas chromatograph developed within DARPA Micro Gas Analyzer (MGA) program: 9) Capacitive Micromachined Ultrasonic Transducers for Therapeutic Ultrasound applications. Wong SH, Kupnik M, Watkins RD, Butts-Pauly K, Khuri-Yakub BT. IEEE Transactions on Biomedical Engineering 2010. Jan;57(1):114-23.
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