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2 Design Challenge: Simulation of Human Physiology This chapter addresses the simulation of temperature, perspiration, and respiration, described in PETMAN design challenge 3.2.5 (see Appendix B): The study will determine the feasibility of designing a PETMAN system that can simulate fixed skin temperature (by body region), perspiration rate (by body region), and respiration rate (threshold level) and a realistic variability in skin temperature, perspiration rates, and respiration rates based on the amount of physical activity/exertion (objective level) defined in 18.104.22.168-22.214.171.124. This chapter includes a discussion of the relevant PETMAN require- ments (Box 2.1), current technologic capabilities, design challenges and how they might be addressed with current and future technology, costs and benefits of different approaches, and feasibility and potential trade-offs. Current Technologic Capabilities The human-physiology simulation aspects of the PETMAN system may be best categorized as follows: temperature and perspiration, respira- tion and ventilation, and physiology integration. Each of those functions has been simulated to some degree by currently available systems; a few systems incorporate all three. We reviewed all currently available systems that can simulate at least one, and we include here information on technical specifications, images, and references. 25
26 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Box 2.1 Relevant PETMAN Requirements The requirements below outline the desired level of simulating human physiol- ogy in the PETMAN system excerpted from the detailed list of PETMAN system design requirements that appear in Appendix B: 3.3.3 The PETMAN system shall meet the anthropometric requirements of the 50th percentile male in accordance with DOD-HDBK-743A, Military Handbook Anthropometry of U.S. Military Personnel, 13 February 1991. 3.3.4 The PETMAN system shall simulate the following environmental/physiologi- cal conditions under the individual protection ensemble. 126.96.36.199 The PETMAN system shall simulate fixed skin temperature by body re- gion (T) and more realistic variability in body surface temperature based on body region and the level of physical activity/exertion (O). 188.8.131.52 The PETMAN system shall simulate a fixed perspiration rate of 0.4 L/hr (T) and more realistic variability in perspiration rates (range 0.11 to 1.8 L/hr) based on the level of physical activity/exertion (O). 184.108.40.206 The PETMAN system shall simulate a respiration rate of 50 L/min (fixed tidal volume of 1.5 L & breath frequency of 33 breaths/min) (T) and more realistic variability in respiration rates (range 10 to 115 L/min with variable tidal volumes and breath frequencies) based on the level of physical activity/exertion (O). 3.3.13 The PETMAN system shall record the following system parameters over time: skin temperature, respiration rate, perspiration rate, and total mass (in nanograms) of chemical vapor that penetrates/permeates through the protective ensemble. The PETMAN system shall record the start and stop time of each mo- tion in 1 second increments. NOTE: T=threshold (minimum requirement) and O=objective Temperature and Perspiration Several generations of thermal mannequins have been developed in the last 70 years for various commercial and military purposes. Used pri- marily for garment evaluation, early versions manufactured in the 1940s through 1960s were standing, mostly nonarticulated and nonperspiring models. Second-generation variants with movable body parts and append- ages started to appear in the 1970s. The addition of perspiration capability has been more recent in what may be considered third-generation and later
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 27 thermal mannequins. Several documents reviewing those types of man- nequins (also referred to as manikins) and their evolutionary changes are available. Military Systems Information on and specifications of several mannequins constructed by the armed forces of several nations and put into service for assessment of battle dress uniforms, protective ensembles, and other combat-related cloth- ing and equipment are publicly accessible. Two military systems with the most detailed available information are the Uncle Wiggly and Paul manne- quin systems, both housed at U.S. Army facilities. Information on similarly functional U.K. and Canadian systems are discussed in Chapter 1. Uncle Wiggly: Based at the U.S. Army Research Institute of Environmental Medicine (USARIEM) in Natick, Massachusetts, Uncle Wiggly was origi- nally developed in 1984 with a copper-plated shell, cast-aluminum joints, and assorted heaters and sensors (Figure 2.1). Measurement Technology Northwest (in Seattle, Washington) updated the mannequin in 2004 with a thermal-control system consisting of signal conditioning, heater drivers and computer software, and a computer-controlled sweating system. Uncle Wiggly features 19 individual heating zones, each with its own replaceable plug-and-play microcontroller to oversee temperature and fluid control and measurement. Software controls provide automatic steady- state detection; the operator can also program a work-cycle simulation and view instantaneous bar graphs and time-line graphs of any variable. Data updates are shown every second with calculations for number of watts of heat removed. Sweating occurs automatically through a series of valves and hoses that pump water through dozens of âweep holesâ drilled through the metal that allow even and adjustable water distribution along the 19 sections. Motion capability includes the ability to swing arms and legs to simulate walking at speeds up to 3 mph. Testing is conducted in its own chamber that is controlled for temperature, humidity, and wind speed provided by a fan. Paul: Paul (Figure 2.2) is a nonthermal, animatronic mannequin at the U.S. Army Soldier and Biological Chemical Command (SBCCOM) in Natick, â HolmÃ©r, I. 2004. Thermal Manikin History and Applications. European Journal of Applied Physiology 92(6):614-618; HolmÃ©r, I., and H. Nilsson.1995. Heated Manikins as a Tool for Evaluating Clothing. Ann. Occup. Hyg., Oxford University Press 39(6):809-818; Endrusick, T. L., L. A. Stroschein, and R. R. Gonzalez. Thermal Manikin History: United States Military Use of Thermal Manikins in Protective Clothing Research. Measurement Technology Northwest, http://www.mtnw-usa.com/thermalsystems/history.html. Accessed August 9, 2007.
28 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT FIGURE 2.1 U.S. Army Research Institute of Environmental Medicineâs (USARIEMâs) Uncle Wiggly thermal mannequin in its own climate-controlled test chamber for measuring thermal and vapor resistance values of clothing ensembles. SOURCE: âModernized manikin: Uncle Wiggly resumes thermal testing after major âorganâ replacement.â The Warrior, March-April 2004. http://www.natick.army. 2-1 mil/about/pao/pubs/warrior/04/marapr/index.htm. Accessed August 7, 2007. Massachusetts, but has been used for testing protective garments in a MIST chamber. Built in 2002 by Creative Engineering, Inc. (in Orlando, Florida). Paul can be programmed for at least 20 motions. Nonmilitary Systems Commercial and academic groups have expended considerable time, effort, and expense to developing increasingly sophisticated and specialized thermal mannequins. Some of the more prominent and innovative manne- â U.S. Army Soldier Systems Center, Vapor Chamber Tests Chem/Bio Protective Prototypes. http://www.amc.army.mil/amc/pa/Aug02Issue.html. Accessed June 13, 2007. â Nilsson, H. O. (2004). Comfort Climate Evaluation with Thermal Manikin Methods and Computer Simulation Models. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3726. Ac- cessed August 8, 2007.
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 29 FIGURE 2.2 U.S. Army Soldier and Biological Chemical Commandâs Paul manne- quin cycling through motions in the Man-in-Simulant Test chamber. SOURCE: âVapor chamber tests chem/bio protective prototypesâ (photo by Curt Biberdorf), http://www.amc.army.mil/amc/pa/Aug02Issue.html. Accessed August 7, 2007. 2-2 quin models are reviewed below. These are loosely categorized into ânonin- tegratedâ systems that use discrete simulations of physiologic functions and âintegratedâ systems that are driven by human-physiology models. Nonintegrated Systems These systems use discrete simulations of physiologic functions. Coppelius and variants: This line of mannequins originated in the VTT Technical Research Centre of Finland Laboratory of Plastics and Fiber Technology. Coppelius (Figure 2.3) features prosthetic joints for externally induced movement and different postures and computer-controlled heating
30 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT FIGURE 2.3 Coppelius mannequin. SOURCE: Used with permission of North Carolina State University. and sweating systems, with 18 individually controlled body sections and 187 sweating glands (distributed over the whole body except the head, hands, and feet). A Coppelius type of mannequin has been developed at the Center for Research on Textile 2-3 Protection and Comfort of North Caro- lina State University through technology exchange with the Finnish VTT group. TOM III and SAM: Toyobo Corporation of Japan has manufactured two types of thermal sweating mannequins, TOM III (1980s) and SAM (1990s). They are differentiated primarily by their sweating mechanisms. TOM III uses water vapor from 220,000 âpores,â whereas SAM sweats liquid water intermittently from 168 sites. SAM measures a broader array of variables (heat dissipation, âskinâ temperature, and so on, in addition to temperature and humidity under clothing) and has more sophisticated computer control than TOM III. â Additional information is available at http://www.tx.ncsu.edu/tpacc/comfort/sweating_ manikin.html.
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 31 Walter: A team at the Institute of Textiles and Clothing of Hong Kong Polytechnic University, in Kowloon, Hong Kong, is using fabric technolo- gies for its thermal sweating mannequin Walter (Figure 2.4). A waterproof but moisture-permeable fabric âskinâ covers 1.5 m2 of surface area and simulates the evaporation of sweat by moisture transfer of internally circu- lated body-temperature water from the mannequin core through tiny pores. The âskinâ can be unzipped and interchanged with different versions to simulate different rates of perspiration. Newton and Huey: Measurement Technology Northwest (MTNW), in Se- attle, Washington, which developed the most recent version of USARIEMâs Uncle Wiggly system, also produces several commercial systems for simu- lation of human physiologic temperatures and sweating. Its Newton and Huey models are constructed of aluminum-filled fiberglass-epoxy and alu- minum, respectively; articulated joints and external frame allow for move- ment. Customizable and independent thermal zonesâ14-45 for Newton Front view Side view FIGURE 2.4â Sweating mannequin Walter. SOURCE: Fan, J., Y. Chen, and W. Zhang. âA Perspiring Fabric Thermal Manikin: Its Development and Use.â Proceedings of the Fourth International Meeting on Thermal Manikins, EMPA Switzerland, Sept. 27-28, 2001. 2-4
32 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT and up to 30 for Hueyâcan be used with an optional removable fabric sweating skin with an output capacity of 50-1,000 mL/h-m2. JUN: Built at Bunka Womenâs University, in Tokyo, with assistance from the Japan Society for the Promotion of Science, JUN incorporates several of the capabilities and features of previously discussed mannequin systems, namely, independently controlled and zoned thermal and sweating systems, fabric âskin,â and externally inducible movement. Separation of the core and a 17-segment external shell allows distinct simulation of core and sur- face temperatures. Integrated Systems Integrated systems are driven by human-physiology models. Advanced Automotive Manikin (ADAM): Actively used for research at the National Renewable Energy Laboratory (NREL), ADAM is another mannequin assembled by MTNW (Figure 2.5). Measuring 61 kg and 175 cm and designed primarily as an automobile occupant, ADAM has 126 individually controlled stand-alone surface zones, each with a surface area of 120 cm2 and integrated heating, temperature-sensing, sweat distribution and dispensing, and a heat-flux gauge and a local controller to manage closed-loop operation. Zone skin temperature is determined by an array of thermistors, and the sweating surface is all metal and optimized for thermal uniformity and response speed. Novel features include wireless control, a 24-V battery pack for two hours of autonomous continued operation, and a respiratory-simulation system for physiologic ventilation and heating with humidification of ambient air at up to 8 L/min. The most unusual aspect of ADAM is its numeric physiologic model., As temperatures are manipulated in ADAMâs environment, the resulting skin heat-transfer rates are reported to a physiologic computer that uses mannequin conditions to generate prescribed and appropriate skin tempera- tures, surface sweat rates, and breathing rates. A loop feedback provides ever-changing measurements for assessment of human thermal comfort in â Advanced Thermal Manikin. Measurement Technology Northwest. http://www.mtnw-usa. com/pdf/ADAM.manikin.specs.pdf. â Paul, H., L. Trevino, G. Bue, J. Rugh, R. Farrington, and C. King. Phase II Testing of Liquid Cooling Garments Using a Sweating Manikin, Controlled by a Human Physiological Model. Doc 2006-01-2239. SAE International. â Farrington, R., J. Rugh, D. Bharathan, H. Paul, G. Bue, and L. Trevino. Using a Sweating Manikin, Controlled by a Human Physiological Model, to Evaluate Liquid Cooling Garments. Doc 2005-01-2971. SAE International.
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 33 FIGURE 2.5 ADAM, the advanced thermal manikin. SOURCE: Burke, R., and R. McGuffin, âDevelopment of an Advanced Thermal Manikin for Vehicle Climate Evaluationâ Proceedings of the Fourth International Meeting on Thermal Manikins, EMPA Switzerland, Sept. 27-28, 2001; R. Burke, Measurement Technology NW. 2-5 a dynamic environment. A separate thermal-comfort model predicts human perceptions of comfort under environmental conditions. Sweating Agile Thermal Manikin (SAM): The Swiss Federal Laboratories for Materials Testing and Research (St. Gallen, Switzerland) has developed SAM, which is equipped with 26 shell parts and 4 heated joints in 30 sepa-
34 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT rately heated sectors constructed of plastic mixed with aluminum powder (Figure 2.6). Electronics and software enable each sector to be heated to a constant temperature or with constant power using just one power supply for all shell parts. The maximal total heating power is 1.2 kW, the equiva- lent of very high-level human muscular activity. One hundred twenty-five sweat outlets are distributed over the man- nequin surface and positioned to ensure roughly human sweat distribution. Special pads cover the outlets to ensure that all water evaporates at low FIGURE 2.6 Sweating Agile Thermal Manikin (SAM). SOURCE: SAM Sweating Agile Thermal Manikin of EMPA, Switzerland.
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 35 sweat rates to simulate insensible sweating or as both vapor and liquid water at higher sweat rates to simulate sensible sweating. Total sweat rate is controlled with a precision balance to measure the reduction in supply- tank water outside SAM; total moisture within clothing is determined by monitoring SAMâs weight. The sweat rate can be varied from 20 mL/h to at least 4 L/h. Heating power, sweat rate, and body movements are linked for active-exercise phases to simulate human activities. Joints at the shoulders, elbows, hips, and knees enable each limb to be moved in a vertical plane. Each limb is connected to a two-axis linear drive mechanism with movement curves defined as series of points with spline interpolation to ensure smooth curving, acceleration, and deceleration. Re- petitive body movements, such as walking and climbing, can be performed during active testing by using a specially developed supporting frame. SAM is positioned in an environmental chamber that can be operated at tempera- tures of â30Â°C to 40Â°C and relative humidity of 30-95 percent. High wind speeds can be simulated by a wind generator positioned in front of SAM. The control unit is positioned on a trolley outside the chamber; heating and sweating supplies are connected through the face. Other Temperature- and Perspiration-Related Systems Several mannequin systems with environmental characteristics and ca- pabilities not covered by the PETMAN specifications are also available. The PyroMan Thermal Protective Clothing Analysis System is an adult- size flame-resistant mannequin system with 122 heat sensors distributed uniformly over the body (excluding hands and feet). Each of PyroManâs sensors covers 0.82 percent of body area and is individually calibrated to ensure accurate reading of temperature and calculation of surface heat flux. The temperature readings, in conjunction with a one-dimensional transient heat-conduction model, are used to determine the heat flux experienced at the sensorâs surface as a function of time. A liquid-integrity testing system has also been described. A liquid-ab- sorbing inner garment is placed over a mannequin and underneath the gar- ment being tested to show penetration by test liquid. Water is the principal challenge agent; it is often treated with a surfactant to increase test severity. The testing duration is usually extended so that clothing design problems or defects will show up more readily. Test results are reported as pass or â Barker, R. L. A Review of Gaps and Limitations in Test Methods for First Responder Protective Clothing and Equipment. January 31, 2005. Prepared for the National Insti- tute for Occupational Safety and Health available at http://www.cdc.gov/niosh/npptl/pdfs/ ProtClothEquipReview.pdf. Last accessed August 7, 2007.
36 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT fail, depending on the detection of liquid marks on the liquid-absorbing inner garment. Cooling Systems Cooling systems separate from the heating and sweating systems de- scribed above may be necessary for the combination of PETMAN functions. No sophisticated cooling systems for mannequins are available. Current humanoid and android robots, such as ASIMO and Hubo (see Chapter 4), normally use passive forms of heat removal; internal fans to circulate air and exhaust heat have been used infrequently. These robotsâ internal temperatures have been described as âwarm to touchâ and âhot to touchâ with sustained activity (about 35-50ÂºC; personal communication, Dr. J. H. Oh, Korea Advanced Institute of Science and Technology). Cooling systems for human use have been developed for space ex- ploration. The needs of astronauts on extravehicular missions have resulted in cooling garments that assist in thermoregulation. Available liquid cooling and ventilation garments use water at constant flow with vent ducting to remove more than 2000 BTU/h. Sublimator cooling, thermoelectric cooling, and cryogen-based heat-exchange systems are being actively investigated in combination with liquid cooling garments. Descriptions of several feasible technologies applicable to PETMAN have been provided by Grant Bue (National Aeronautics and Space Administration Johnson Space Center), including advanced heat pumps, a mini vapor compressor, âsuper ice,â and vortex tubes. Respiration and Ventilation Respiratory physiology has been simulated for different purposes in different ways at various levels of verisimilitude. Mathematical models are available for numeric modeling of gas-exchange characteristics, and physical âlungsâ have been replicated in isolation and in mannequins for simulation of mechanical aspects of ventilatory function. Mechanical Lung Systems â¢ Physical lung-like systems have been developed for a variety of ap- plications. Mechanical-ventilator training needs and development and testing requirements have resulted in isolated âlungsâ that accurately simulate physicomechanical lung properties, such as airway resistance, lung volume, and compliance. A low-cost, fully mechanical multilobar lung from the University of Canterburyâs Department of Mechanical Engineering (Christchurch, New Zea-
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 37 FIGURE 2.7 PosiChek3 air-supplied breathing apparatus tester. SOURCE: Used with permission of Biosystems LLC, Middletown, Connecticut. land) allows accurate replication of several aspects of a passively breathing lung. â¢ Equipment designed to test self-contained breathing apparatus (SCBA) and gas-mask assemblies are commercially available. Us- ing large pistons or cams, these devices generate substantial airflow and replicate human ventilation to assess mask utility (see Figure 2.7). â Chase, J. G., T. Yuta, K. J. Mulligan, G. M. Shaw, and B. Horn. 2006. A Novel Mechanical Lung Model of Pulmonary Diseases to Assist with Teaching and Training. BMC Pulmonary Medicine 6:21.
38 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Mannequin Lung Systems Technologic advances have generated important opportunities for en- hanced medical education and training in the last two decades. Improved instructional devices are now being used in dedicated environments world- wide to teach safe patient care. Mannequin-based patient simulation is one such instrument, and it has applicability to PETMAN respiration requirements. Human Patient Simulator: Commercialized as a mannequin system with the ability to simulate human patients undergoing anesthesia, the Human Pa- tient Simulator (HPS) from Medical Educational Technologies, Inc. (METI), in Sarasota, Florida, features interconnected cardiovascular, pulmonary, pharmacologic, and metabolic computer models and bellows-driven lungs. Powered externally by a gas-driven pneumatic variable-pressure and vari- able-volume rack system, the lungs are capable of actively metabolizing inspired gases and anesthetic agents and exhaling the expected by-products of cellular metabolism, such as CO2. SimMan and SimBaby: These mannequins feature simple lungs and lack physiologic models. SimMan and SimBaby are manufactured by Laerdal Medical Corp., Wappingers Falls, New York. Costing substantially less than the METI HPS system, these mannequins have ventilatory functions that are powered by external compressors and gases. NeuroDimension Inc. A bellows-less lung system has been developed by personnel at NeuroDimension Incorporated, and the College of Medicine Biomedical Engineering, and McKnight Brain Institute of the University of Florida at Gainesville.10 Using a fixed-volume pressure controller to simulate spontaneous breathing, this model can simulate carinal pressure for simulation of actively breathing or ventilated patients and can simulate tidal volumes of 400 and 500 mL with flow rates of 4.3-5.7 L/min. Physiology Integration Integration of the different aspects of simulated human physiology as required by PETMAN has been accomplished to various degrees in the mannequin systems described above. Temperature and perspiration have been linked in thermal-mannequin programs to simulate metabolic states reflecting different levels of human activity; in the case of NRELâs ADAM, 10â Meka, V. V.Â and J. H.Â vanÂ Oostrom. 2006. Bellows-less Lung System for the Human Pa- tient Simulator. Medical and Biological Engineering and Computing 42(3):413-418.
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 39 a rudimentary ventilatory system has also been added. As for simulators in medical education, sophisticated mathematical models of human cardiopul- monary physiology have been engineered to drive accurate and precise lung systems housed in human-shaped mannequins. Documentation of attempts to form an interface between warm, sweating mannequin systems and sys- tems that breathe realistically seems not to be available. Available systems do not address the question of whether mannequin- wide thermoregulation is possible in the context of a multifunction, moving, sensing computer-controlled human-shaped robot. Although a static man- nequin can be warmed and made to sweat appropriately, no commercially available system has the capacity to cool a moving robotâs actuator systems and onboard computers while heating its surface âskin.â The PETMAN requirements for dynamic motion control and balancing of the robot may interfere with thermal and sweating regulation, particularly if the latter must simulate exercise-related physiologic functions realistically (see chap- ters 4 and 6 for more discussion of these potential complications). Design Challenges and How They May be Addressed The human-physiologic simulation aspects of the PETMAN mannequin functions will be restricted by the need to combine physiologic software and engineering requirements (power, space, supply, and exhaust). Those issues are discussed below in the context of relevant PETMAN threshold (T) and objective (O) requirements (provided in italics). Chapter 6 presents further discussion regarding system integration and physical incorporation of physiologic-simulation components into an ensemble-compatible human- shaped package that houses chemical-agent sensors and robotic elements and uses materials that are resistant to toxic chemical materials. Temperature and Perspiration To maintain a constant mannequin âskinâ temperature, the PETMAN system may require heating, cooling, or both. Whereas thermal manne- quins contain only mechanisms necessary to generate heat and perspiration, PETMAN will contain many systems, each of which may have substantial thermal output. Furthermore, the equivalent of a circulatory system may become mandatory under such circumstances if simultaneous heating and cooling are required in different body segments. Regulated heat and sweat generation for simulation of human skin temperatures and perspiration is possible today with dedicated mannequin systems. Mannequin heating is accomplished through heating wires or coils embedded in mannequin body-segment surfaces and controlled by power
40 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT distribution. Mannequin sweating mechanisms use transmission of water as liquid or vapor into conduits and pores with selectable flow rates. Commercially available systems do not have control and management of excess heat in robots or mannequins, because most applications have not required precise thermoregulation. Depending on individual compo- nent characteristics of the PETMAN system, there will probably be a net excess of heat generated by various sources, in which case cooling may be required. Furthermore, the mannequin core, compartment, and surface may vary substantially in temperature, given the nonhomogeneous distribution of components, and will probably require differential heating and cooling. MTNW has described having some experience in temperature regulation through heat exchange between warmed segments and âsweatâ-circula- tion systems that carry cool liquids (personal communication, Rick Burke, MTNW). The followingâelectronic control, mechanical construction, and sys- tem integrationâare some of the key design challenges with respect to temperature and perspiration: Electronic control â¢ ethod of linking temperature and perspiration with respiration, M metabolism, and motion: o ixed heating, sweating, and ventilation output rates (open F loop). o ixed heating, sweating, and ventilation target values (closed F loop, level 1). o ariable heating, sweating, and ventilation output rates and V target values (temperature and perspiration linked through metabolic model). o Zoned heating and sweating (closed loop, level 2). â¢ hermoregulation (concurrent heating and cooling of different T body regions). Mechanical construction â¢ Source of heat (power) and sweat (liquid and gas). â¢ Source of cooling (power and coolant). â¢ Exhaust. â¢ urability (such as susceptibility to freeze damage and heat-related D damage). â¢ Tether or no tether?
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 41 System integration â¢ Space limitations. â¢ ontrol for heat generation by other systems (such as CPU, trans- C mitters, and sensors). â¢ ompatibility with other systems (device signatures, sources, and C exhaust). â¢ Construction (resistance to chemical agents and cleanability). Size specifications will reduce the possibility of temperature simulation owing to physical restrictions on the layout of heating, sweating, and cool- ing mechanisms and their supply sources and distribution; power limita- tions; exhaust requirements; and requirements imposed by other systems in PETMAN. All these will make meeting the anthropometric requirements extremely challenging even in the case of a tethered system (see chapters 4 and 6 for more discussion). In isolation, mannequin skin temperature can be regulated by body region with current technologies with or without activity-dependent and region-dependent variability. PETMAN mannequin challenges will be re- lated to physical restrictions on the layout, supply sources, and distribution of heating and cooling mechanisms; heating and cooling power limitations; heat and coolant exhaust requirements; interference from other heat sources in the mannequin distribution of heating or cooling to achieve targeted regional mannequin-skin temperatures; integration of control, space, and material requirements with the entire PETMAN system; and temperature regulation under extreme test-chamber conditions. If heating and cooling are required simultaneously in different man- nequin parts, a âcirculatory systemâ will probably be required to establish demand-regulated regional distribution of centrally controlled liquids (or gases) to achieve temperature set points. Heat-exchange systems, liquid nitrogen- or CO2-based systems, and vortex-tube designs are possibili- ties but have not been developed in the context of humanoid mannequin assemblies. In isolation, perspiration can be regulated by body region with or without activity- or region-dependent variability with current technologies. PETMAN mannequin challenges will be related to physical restrictions on layout of the sweating mechanism, supply source, and distribution; sweat pumping-power limitations; sweat exhaust requirements; liquid or vapor interference with other PETMAN systems (for example, the effect of un- der-ensemble moisture on agent-detection sensors; integration of control, space, and materials requirements with the entire PETMAN system; and simulating sweating under extreme test-chamber conditions. The PETMAN mannequin requirement for perspiration has described
42 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT water and water vapor as acceptable sweat equivalents (current sweating mannequins use only water or water vapor), so the feasibility analysis does not address the biochemical and physiologic replication of electrolytes, oils, and other constituents of human sweat and their accompanying chemical reactivity and biomechanical implications. Current thermal sweating mannequins and human-physiologic simula- tion mannequins are capable of continuous recording of skin temperature, respiration rate, and perspiration rate in time in one second increments. Respiration and Ventilation Positive-pressure mechanical simulation of human respiration and ven- tilation with regulatory mechanisms is possible now with dedicated man- nequin systems. Mannequin respiration and ventilation are accomplished through âlungâ reservoirs in the mannequin thoracic cavity that are pow- ered by external pneumatics or bellows. These lungs create chest-wall movement and simulated air or gas movement transmitted through either a nonanatomic pneumatic or an anatomic airway system. Depending on the mannequin system, gas exchange (for example, oxygen consumption and CO2 exhalation) can also be simulated. Software controls range from simple respiratory rate and volume regulation to automated determination of pulmonary measures corresponding to whole-mannequin conditions, such as cardiac arrest or septic shock. Size specifications will limit respiration and ventilation simulation be- cause of design limitations imposed by whether a pneumatic or actuated chest-wall movement system is implemented (see below), power limitations, and interference with other PETMAN subsystems. The PETMAN mannequin requirement for respiration and chest- wall movement has been described as predicated on the need to replicate under-ensemble conditionsâsuch as compartment âhot spots,â pressure differentials, and airflowâthat may affect ensemble leakage or penetration and agent transport and distribution in the ensemble. The issue of respira- tory system air flow at 50 L/min can be addressed either with or separately from chest-wall movement. Specifically, the requirements theoretically could be met at different levels (Figure 2.8) with a unified mannequin respiratory system or with discrete but linked component systems. Unified System (Anatomically Correct) A respiratory system based on human anatomy and depending on nega- tive intrathoracic pressures will be one candidate for PETMAN airflow and chest-movement needs. Like human respiration and ventilation, this type of system would require a true self-contained intrathoracic bellows system
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 43 lung lung lung lung actuator +/- tether Unified-system chest expansion Component-system chest expansion FIGURE 2.8 Comparison of systems that simulate human respiration and ventila- tion. Axial cross-sections of mannequin thoracic cavity are shown. (diaphragm, compliant chest, and lungs) capable of inducing sufficient negative pressure to draw air from the environment into the chest cavity 2-8 and then exhale it. Such a system, with internalized pneumatic systems to drive mannequin breathing, has not been reported in commercially avail- Good version from Word document able mannequins but could be made available with short-term research and development. Component Systems (Nonanatomic) If movement of air through the mannequinâs nose, mouth, airway, and lungs is handled separately from chest-wall movement, two nonanatomic mechanisms may be used to achieve each objective independently: airflow and chest movement. â¢ Current METI mannequins use an extrathoracic (tether-connected) bellows system to generate both negative pressure to draw air in and positive pressure to exhale. Their bellows mechanism works with a simple airway (basic but accurate facial features, oropha- ryngeal and nasopharyngeal structures, dentition, tracheal and bronchial structures, and bag-reservoir lungs) for adequate simu- lation of human respiratory and ventilatory airflow. Less critical breathing-related biophysical propertiesâsuch as airway resis- tance, dead-space ventilation, and positive end-expiratory pres- sure (PEEP)âcould be replicated with refinements of mannequin anatomy. (Alveolar metabolism of inhaled materials, exhalation of human gaseous metabolic products, and mask-seal and air- way or alveolar absorption of agent will not be addressed in this analysis.) Separate from bellows mechanisms, a piston- or cam-based
44 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT system (as used in respiratory-mask testing systems manufactured by ATI and Biosystems) may generate negative inspiratory forces sufficient for PETMAN respiration and ventilation simulation. Published specifications describe flow up to 102 L/min through a standard SCBA mask assembly. Space and power requirements will probably be greater than for bellows systems because of the mechanisms and higher pressures and flow volumes generated. Another theoretical alternative is to interpose a two-way jet ventilator system in the mouth of the mannequin; the inward-facing and outward-facing jets would simulate inspiration and exhalation, respectively. Disadvantages include nonphysiologic airflow patterns and outlet pressures. â¢ Mannequin chest expansion can be independently accomplished with intrathoracic actuators (see Figure 2.8). METI has announced a self-contained, untethered battery-operated mannequin that cre- ates chest-wall movement without lung pneumatics). Current mannequins that simulate human physiology are capable of continuous recording of skin temperature, respiration rate, and perspiration rate in one second increments. Physiology Integration Chapter 6 discusses PETMAN system integration in detail. This sec- tion is limited to the integration of human-physiology simulation into the entirety of PETMAN. Mannequin breathing, surface temperature, and per- spiration may be integrated at several levels: full dynamic, limited dynamic, or preset integration. Full Dynamic Integration: Comprehensive linking and feedback control of all PETMAN systems with human-physiology simulation would be neces- sary for a mannequin capable of detecting chemical agents and responding in a manner that resembles human pathophysiology, for example, a reduc- tion in heart rate caused by sarin exposure. This level of integration will be difficult to achieve. Limited Dynamic Integration: PETMAN human-physiology simulation may be designed to operate discretely from sensor systems but able to self-regu- late to achieve target vitals signs and perspiration rate. Physiologic models accomplishing this have been described by NREL and MTNW, whose ADAM mannequin is not complicated by additional onboard systems that generate heat and drain power. Use of a âmetabolismâ model to drive physiologic simulation is a potential solution (see Figure 2.9).
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 45 Mannequin robotic âMetabolismâ Respiration and model ventilation activity and movement Circulation Mannequin subsystem Surface temperature heat signatures (heating and/or cooling) Perspiration FIGURE 2.9 Diagram of potential mannequin âmetabolismâ model. Preset Integration (Pseudophysiology): The least complicated method of 2-9 linking the different human-physiology simulation components is to define preset states (such as âresting,â âwalking,â ârunning,â and âcrawlingâ) and their corresponding physiologic characteristics. Setting respiratory rate, tidal volume, surface temperature, and sweating rate for a defined activity simplifies feedback to achieve target values. Fitting the component subsystems necessary only for human-like ther- moregulation, sweating, respiration, and ventilation should be possible in a mannequin sized as a 50th percentile male. For example, iStan is completely self-contained, has skin made of thermoplastic elastomer, has a realistic weight, and uses pressurized water to create sweating. An area is also avail- able in the belly to allow for additional simulation capabilities.11 However, as discussed in more detail in Chapter 6, successful posi- tioning and complete packaging of the physiologic simulation subsystems alongside the sensor, robotics, and power systems needed to meet all PET- MAN requirements are likely not feasible with current technologies without a tether. In any size state-of-the art robots, actuators fill the volume of the arms, legs, shoulders and hips, but space is typically available in the torso and head. In a 50th percentile male-sized PETMAN that meets all the objective requirements, about 3 L in the head and about 20 L in the torso would be available for all the other capabilities. The water for respiration, sweating, and cooling could be stored in the head. The torso space would be availableâbut insufficientâfor all the remaining computer, electronic, heating, sensing, and battery components. Approximately 24 L of the man- nequin would be needed to house just the batteries to power PETMAN for 12 hours. 11â Presented by Carlos Moreno, Medical Education Technologies, Inc.
46 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT On the basis of the extensive physical-activity requirements speci- fied for PETMAN, the onboard processing and robotic actuation (whether pneumatic, electric, or hydraulic) involved will require substantial energy stores and generate considerable heat and exhaust. Although a breathing- mannequin system at rest could potentially be made to thermoregulate and perspire appropriately in all its body segments, the technology to control mannequin heating and cooling dynamically to achieve the same homeo- stasis within the limits of operational testing is not now available. Cost-Benefit Analysis and Trade-offs The PETMAN requirements related to human physiology are analyzed in Table 2.1. The analysis includes discussion of the technical benefit, cost impact (disadvantages), near-term availability, and feasibility. Feasibility and Potential alternatives Based on the information presented earlier in this chapter, it is feasible to simulate the independent components of physiologic conditions under the IPE (requirement 3.3.4, Appendix B) at least the threshold levels. However, given the space available in the mannequin (50th percentile male anthropometrics) and the heating, cooling, and sweating system require- ments (power, supply, and exhaust demands), it is not feasible with current technologies to meet the human physiologic requirements with additional chemical sensing and robotics operational requirements in an autonomous nontethered PETMAN system. Conclusion 2-1a: Simulation of chest-wall movement associated with respiration is feasible. Conclusion 2-1b: Simulation of human respiration and ventilation with chest movement and respiratory tract airflow through external (tether- connected) pneumatics is feasible. Conclusion 2-1c: Internalization of all systems necessary to generate chest-wall movements and simulated respiration and ventilation in the mannequin will require additional research and development. Recommendation 2-1: The role of simulated respiratory tract airflow in the mannequin during IPE testing should be further clarified. Distinct from simulation of respiratory chest-wall movement for re-creation of under-ensemble airflow, the generation of accurate mannequin inspira- tory and expiratory airflow through a mask respirator will require ad-
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 47 ditional development and may duplicate current protocols for testing of IPE mask respirators in isolation. Conclusion 2-2a: Simulation of human activity-dependent skin tem- peratures and sweating (with water as a sweat equivalent) should be feasible when space, power, electric, and exhaust requirements of other PETMAN subsystems are housed outside the mannequin via a tether. Conclusion 2-2b: Integration of activity-dependent human-like skin temperatures and sweating into mannequin wide thermoregulation with differential heating and cooling through a circulatory system has not been achieved. That is, a static mannequin can be warmed and made to sweat appropriately, but no commercially available system has the capacity to cool a moving robotâs actuator systems and onboard computers while heating its surface âskin.â However, based on the currently available systems, this requirement may be feasible with ad- ditional short-term research and development. Recommendation 2-2: Inasmuch as mannequin-wide thermoregulation is by definition an all-or-none proposition, its feasibility analysis does not lead to recommendations regarding potential alternatives or sacri- fices in performance requirements. Conclusion 2-3a: Mannequin respiration, skin temperature, and sweat- ing should be controlled through either preset physiologic characteristics for defined IPE test activity states or a mannequin metabolism model designed to operate without physiologic linkage to sensor systems. Conclusion 2-3b: Integration and installation of the necessary sys- tems to achieve all human-physiology simulation requirements into a PETMAN that meets all specified operational requirements will en- counter substantial challenges with the use of technologies that are currently available or are expected to be available in the near future. The presence of a tether may relieve someânot allâobstacles to this objective. Recommendation 2-3: A phased development project with progression through transitional stages may alleviate several technologic hurdles that need to be overcome if all human-physiology simulation require- ments are to be met in a robotic sensing PETMAN. The above conclusions are in accordance with the feasibility analyses of other PETMAN system considerations, such as robotics (see Chapter 4) and systems integration (see Chapter 6).
48 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Table 2.2 Cost-Benefit Analysis of Simulating Human Physiologic Characteristics as Part of PETMAN System Requirement Requirement Number Description Technical Benefit 3.3.1 Tethered (T) Easier, cheaper solution to power, thermal, mechanical issues Untethered (O) No modification of IPE; potentially more realistic test challenge 3.3.3 Anthropometric Compatibility with protective requirements of 50th ensemble percentile male 220.127.116.11 Fixed skin-temperature Intended to be easier to simulation by body achieve than variable region (T) temperature based on region and activity
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 49 Cost Impact/ Near-term Disadvantages Comments Availability Feasibilitya Requires Assume not just Would still 3 nonstandard a simple tether: require modification of IPE mechanical, power, integrating coolant interface subsystems but appears feasible in 1-2 years Power, thermal, âÂ Â â 1 mechanical challenges; probably insurmountable in required timeframe Space limitations â â 1 leading to restrictions on every system Maintaining skin Not much easier Heating 3 at controlled than variable subsystems temperature, skin temperature; are available whether fixed challenge is in from several or model-based, system integration mannequin requires both manufacturers; heating and cooling cooling regulation methods could be adapted from spacesuit technology continued
50 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Table 2.1 Continued Requirement Requirement Number Description Technical Benefit Variable skin-temperature More accurate simulation simulation by body region of temperature in IPE, and level of physical activity hence realistic simulation or exertion (O) of IPE internal and external environmental challenges 18.104.22.168 Fixed perspiration rate (T) Intended to be easier or cheaper to achieve than variable perspiration rate Variability in perspiration Accurate simulation of rate based on level of moisture environment in IPE, physical activity or exertion capturing moisture effect on (O) agent behavior 22.214.171.124 Fixed respiration rate: (a) Small increase in accuracy of combined simulation of agent transport in IPE and in IPE mask
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 51 Cost Impact/ Near-term Disadvantages Comments Availability Feasibilitya Maintaining skin Not much more Heating 3 at controlled difficult than fixed subsystem temperature, skin temperature; are available whether fixed challenge is in from several or model-based, system integration mannequin requires both manufacturers; heating and cooling cooling regulation methods could be adapted from spacesuit technology Complex Not much Subsystems 3 liquid-delivery less difficult are available system available than variable from several from several perspiration rate; mannequin manufacturers challenge is in manufacturers system integration Â â Not much more Subsystems 3 difficult than fixed are available perspiration rate; from several challenge is in mannequin system integration manufacturers Pneumatic or Current Potentially 3 actuated system mannequin applicable that simulates systems use subsystem also chest motion while positive pressure, available from driving respiratory unlike humans respiratory- flow mask testing companies continued
52 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Table 2.1 Continued Requirement Requirement Number Description Technical Benefit Fixed respiration rate: (b) Accuracy of simulation of respiratory flow only agent transport in IPE mask Fixed respiration rate: (c) Accuracy of simulation of chest motion only agent transport in IPE, that is, under-ensemble Variable respiration rate Additional small increase in based on level of physical accuracy of simulation of activity or exertion (O) agent transport in IPE and in IPE mask 3.3.11 Decontaminate with no Necessary to process multiple effect on next iteration tests of test (T) Â Decontaminate leaving Â â negligible agent residual defined by DA PAM 385-61 (O)
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 53 Cost Impact/ Near-term Disadvantages Comments Availability Feasibilitya Pneumatic or Positive or Potentially 2 actuated system negative pressure applicable that drives not specified in subsystem also respiratory flow requirements available from respiratory- mask testing companies Pneumatic or May be Used by 1 actuated system insignificant some current that simulates chest compared with mannequins motion limb-motion effects Preprogrammed Â â Potentially 1 control, variable- applicable speed motor subsystem also available from respiratory- mask testing companies Will probably Â â Â â 1 require time, effort, resources between tests Agent residue may Â â Â â 1 complicate some sensor readings continued
54 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Table 2.1 Continued Requirement Requirement Number Description Technical Benefit 3.3.13 System measure recording Test-data logging for analysis Nonrequirement issues: Physiologic integration Necessary for all requirements System integration to be met simultaneously Accurate modeling of skin, â anatomy to represent mask seals Packaging âÂ Cooling Â â a3 = high feasibility, 2 = medium feasibility (achievable with substantial effort), 1 = low feasibility (extremely difficult to achieve)
DESIGN CHALLENGE: SIMULATION OF HUMAN PHYSIOLOGY 55 Cost Impact/ Near-term Disadvantages Comments Availability Feasibilitya Additional â Available 3 power, storage from several requirements mannequin manufacturers â Significant design Â â 1 and development riskâcombined robotic-physiologic mannequins are not available, nor is approach evident â Not clear whether â 2 mask sealing has high priority; could be addressed with separate test Physical Technical challenge Â â 1 connections, such with no precedent as tubes and wires, in current state must fit within of art volume, thermal constraints Â â Overall integration Â â 1 of movement, physiology, thermal requirements is far greater challenge than separate elements