Proceedings of a Workshop—in Brief

Emerging Science and Technology to Address Naval Undersea Medicine Needs

Proceedings of a Workshop—in Brief

On March 21, 2024, the National Academies of Sciences, Engineering, and Medicine hosted a virtual public workshop, sponsored by the Office of Naval Research (ONR), to examine emerging science and technology in undersea medicine to best meet the operational needs of the U.S. Navy.¹ Kenneth W. Kizer, workshop chair and distinguished professor emeritus at UC Davis, and former Navy undersea medical officer, opened the meeting and introduced Michael LaFiandra, division director, ONR Warfighter Protection and Applications, and Sandra Chapman, program officer, ONR Undersea Medicine and Performance.² LaFiandra emphasized that undersea medicine is a National Naval Responsibility. This designation indicates that the Navy is the lead research organization in this field, and is responsible for advancing an understanding of the effects of the undersea environment on warfighter physiology and performance, he continued. Given budget limitations, investments are strategically mapped to those that will offer the greatest possible improvements for the Navy in terms of priority capabilities and unmet needs, LaFiandra explained. The current focus areas, he continued, include decompression sickness³ (DCS), bioenergetics, oxygen toxicity, environmental hazards, and exposures to cold and contaminated water. Chapman noted that priority capabilities for manned diving operations may evolve as increasingly sophisticated undersea robotics are developed. The ultimate goal of the research portfolio, she said, is to enable “deeper, longer, safer, and cheaper” operations. In support of that mission, the workshop’s charge is to provide insights about what the Navy’s priority research areas should be in terms of “low-hanging fruit,” “blind spots,” and “leap-ahead technology,” concluded LaFiandra.

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DIVE MONITORING AND INJURY PREVENTION

Key Developments and Advances in Undersea Medicine Since 2000

In 2002, ONR commissioned the Undersea and Hyperbaric Medical Society (UHMS) to provide a comprehensive analysis of the Navy’s research and development program in undersea medicine. The findings and recommendations of the report, An Assessment of a National Naval Need for Undersea Biomedical Research, led to the field’s designation as a National Naval Responsibility. Simon Mitchell, diving physician and head of the Department of Anesthesiology, University of Auckland, discussed eight key developments in undersea medicine that have occurred in the 2 decades since the UHMS report.

1. Significant variability in levels of venous gas emboli (VGE, also known as bubbling),⁴ has been shown to occur even within the same diver repeating identical dives.⁵ When DCS did occur, it was almost exclusively in cases where VGE were elevated. This highlights the limitations of DCS prevention strategies that exclusively focus on optimizing decompression profiles and points to VGE as a target for DCS prevention strategies.
2. Inflammation likely plays a key role in the pathophysiology of DCS.
3. Personalized decompression remains an important research goal.⁶ Advising upcoming dives based on automated recordings of VGE from prior dives has emerged as a strategy, he said. However, because VGE variability across identical dives challenges the validity of that approach, Mitchell predicted that real-time dive monitoring needs to be explored further.
4. Use of exotic gas breathing mixtures is a promising area of research.
5. Multiple experimental preconditioning strategies to prevent DCS have been explored. Pre-dive physiological conditions may contribute to the within-diver variability in decompression stress across identical dives. This requires additional investigation, Mitchell postulated.
6. A new clinical care consensus guideline recommending not to recompress cases of mild DCS has been widely implemented. While prior best practice demanded recompression treatment at “virtually any cost,” the new guidelines are more flexible for persons with mild symptoms, Mitchell explained.
7. Rebreathers have been associated with mission-ending accidents in military diving. Many of these events are associated with hypoxia, hyperoxia, or hypercapnia. Mitchell emphasized the need for diver monitoring and warning systems.
8. Immersion pulmonary edema (IPE) is increasingly recognized as a problem in diving and immersed exercise. Steps toward understanding IPE’s pathophysiology and prevention should be pursued, he concluded.

Implications of High Within-Diver Variability in VGE Across Identical Dives

David Doolette, research physiologist, Navy Experimental Diving Unit (NEDU), elaborated on recent advances in understanding the pathophysiology of DCS, and considered implications for prevention. There is a limited ability to predict DCS risk based on dive profile, depth, duration, gas mixture, work rate, temperature, and other factors. Currently, a diver’s DCS risk for a given dive can be estimated using probabilistic decompression models. Adding more variables to these models will not necessarily improve their predictive power, he explained. Instead, he suggested that future research directions should develop a better understanding of the role of existing variables in the mechanisms of DCS. Where and how bubbles in the blood form is “frustratingly, something we still don’t know after hundreds of years,” he emphasized.

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Doolette also emphasized that, ideally, a decompression schedule should be tailored to an individual diver’s physiology. The fact that a diver is more susceptible on some days than others should be incorporated into the prevention plan, he said. He proposed that initial research into the causes of within diver-variability in DCS risk across dives should focus on “easily observed and modified physiological status” instead of biospecimen collection and analysis. He also urged researchers to study the strong correlation between VGE and DCS, as well as gas kinetics and bubble formation, instead of the secondary effects of those bubbles. The pivotal NEDU Deep Stops Trial,⁷ which he said could inform future research, found that deep compression stops resulted in more DCS incidents than shallow decompression stops. To identify which patterns of VGE result in efficient decompression and to develop interventions, he suggested submersible real-time VGE monitoring. Furthermore, he encouraged targeted data collection in the field (since new and large-scale laboratory trials are unlikely), which could be enabled by the development of a sensitive, specific marker for DCS and wearable physiological monitors.

Preventing the Leading Causes of Military Dive Casualties with Emerging Technologies in Rebreathers

Arne Sieber, co-founder and chief executive officer of SEABEAR, and associate professor for biomedical engineering, Chalmers University of Technology, explored approaches to support diver safety at the intersection of dive physiology and dive equipment. He explained that the mouthpiece of a closed circuit rebreather provides O₂ and diluent gas, removes carbon dioxide (CO₂), and replenishes the circuit with O₂ from a supply tank. The control of the breathing gas is based on readings from O₂ sensors, which are known to be unreliable. He asserted that how well a rebreather works depends not only on the machine itself but also on how it is used, the diver, and the environment.

Sieber elaborated on the three hazards associated with rebreather diving that can lead to accidents or fatal outcomes:

1. Hypercapnia, where CO₂ levels in the inhaled gas are too high. Potential causes include malfunctions in rebreather components, such as the mouthpiece valves or scrubbers.
2. Hypoxia, where O₂ levels in the inhaled gas are too low. Potential causes include incorrect O₂ sensing or insufficient O₂ availability; and
3. Hyperoxia, where O₂ levels in the inhaled gas are too high. Potential causes include failures of the O₂ sensing system, an open O₂ injection, incorrect diluent gas, or too fast of a descent.

While the physiological parameters for hypoxia and hyperoxia can be measured by the rebreather, many of the physiological parameters for hypercapnia cannot. To address this critical gap and reduce diver workload and stress, he advocated for more ergonomic rebreather systems, streamlined rebreathers, intuitive user interfaces, wireless systems, and the elimination of bulky bailout valve mouthpieces. Specifically, he recommended:

• Improved O₂ sensors to monitor the rebreather, the diver, and the diver–rebreather system,
• Intelligent systems to create warning systems (with data processing, signal validation, system modeling, signal fusion, and artificial intelligence [AI]), and
• An easy-to-use interface.

Neurophysiological Monitoring for Diving Injuries

Xavier Vrijdag, diving medical researcher, University of Auckland, discussed approaches in neurophysiological monitoring to prevent common causes of dive injuries. He pointed out that although divers are exposed to extreme physiological changes that affect the brain (e.g., gas narcosis, hypoxia, hyperoxia, hypercapnia, high-pressure neurological syndrome, and hypothermia), their neurophysiology is not monitored during operations. Neuromonitoring techniques being explored include electroencephalogram (EEG), functional near-infrared spectroscopy, eye-tracking, electrodermal activity, physiological monitoring, and a combination of these modalities, but many of these are not yet functional during immersion.

Vrijdag explained that what’s needed is a monitoring and warning system with real-time data analysis. Ideally, the system would include:

• Robust data selection tools,

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• Complex analysis methodologies to detect small effects early, possibly with machine learning algorithms,
• A body area network to capture and analyze signals,
• Operator feedback via a user-friendly interface, and
• Wireless communication abilities.

He underscored the need to establish the limits of the safe environmental envelope in which a diver can continue operations, especially to prevent false alarms. Once a monitoring system is in place, he said, neuromodulation via electrical or magnetic stimulation could be deployed to protect the brain from the harmful effects of the underwater environment.

Discussant Responses

Following the presentations, Mitchell moderated a session in which three discussants shared expertise, offered reflections, and posed questions. Capt. Evan Colbert (U.S. Navy), Deputy Director for Navy diving, Undersea Warfare Division, Office of the Chief of Naval Operations, explained that the U.S. Navy and U.S. Marine Corps have approximately 8,000 qualified military divers across different task-specific specialties. As new or improved equipment is designed, he continued, developers must be careful not to unnecessarily increase the divers’ already high cognitive loads. Four questions should be considered before the Navy implements new technology, he said. These include:

1. Does the technology support the mission requirements?
2. Does it improve diver and dive supervisor decision making?
3. Is the human interface simple?
4. Is the technology rugged and reliable?

Richard E. Moon, professor of anesthesiology and medical director of the Hyperbaric Center, Duke University School of Medicine, wondered if more could be gained by looking at animal models of decompression. He also highlighted the conundrum that although higher levels of VGE are associated with more severe DCS, the link between microbubbles in the blood and DCS pathophysiology remain unclear, and asked, “Should we be working on detection of bubbles in tissues, maybe in the central nervous system, in the spinal cord, conceivably?” He encouraged continued research on IPE variability and susceptibility, and on diver-monitoring technology. Further, he suggested research into novel gas mixtures to breathe during dives as an area of “low-hanging fruit” for ONR.

Peter Lindholm, professor and Gurnee Endowed Chair of Hyperbaric and Diving Medicine Research, University of California, San Diego, remarked that an important area of study is to determine if susceptibility to swimming-induced pulmonary edema in otherwise healthy Navy trainees is a genetic issue, or one that can be addressed with adapted training.

Open Discussion

Mitchell invited all workshop participants to join the conversation with the session’s discussants and speakers. He championed Colbert’s request for systems that are “intuitive, understandable, easily interpreted and implemented, and rugged.” Sieber added that integrated monitoring systems with multimodal sensing is a “big opportunity” for the future.

Chapman asked about the effect of variations in respiratory health among divers. Doolette mentioned that respiratory gas exchange, blood flow changes, and bubble formation are key factors, while Lindholm referenced his ongoing study of free divers, where airway inflammation and postinfection residual lung damage could be affecting DCS risk. In response to a follow-up question from Chapman on integrating respiratory control techniques in diver training, Colbert suggested that further exploration might be of interest, if there was research to support it.

Karen Van Hoesen, professor of emergency medicine and co-director of the San Diego Center of Excellence in Diving, University of California, San Diego, asked whether an individual’s overall inflammatory state influences bubbling. Mitchell remarked that some inflammatory processes could be a precursor to bubble formation, and research is ongoing to investigate this further. Moon explained that, while expanding bubbles disturb normal physiological processes, the tremendous range of clinical abnormalities observed in DCS could be mediated by the body’s “host response” to that external insult, and this might explain the variability.

SUBMARINE MEDICINE

Changes in Submarine Operations Since 2000

Rick Panlilio, deputy director for Plans, Policy, and International Engagement, Commander Submarine Force Atlantic, defined a submarine as “a system of systems that operates for extended periods in a remote, harsh, and austere environment that largely precludes outside assistance for physical contingencies.” To bolster the reliability of submarine systems, the undersea medical community is responsible for screening trainees, and maintaining the health of active and retired crewmembers. “From a health and physiologic perspective,” he continued, “our operations have remained largely the same.” However, recent advances in undersea medicine have improved the performance and reliability of humans in that system. He suggested reviewing long-term trend data to determine the effects of these advances on unplanned losses, disrupted deployments or missions, and medical evacuations.

Panlilio emphasized that the most significant change to the crew system is the inclusion of women on submarines, remarking that the widening of the talent pool “has been a very, very positive change for the submarine force.” Another significant change, he continued, is the shift from an 18-hour watch cycle to a 24-hour watch cycle. More time between each watch improves sleep patterns and alertness. Elimination of smoking, embedded mental health care, nutrition and fitness training to improve resilience, and an “allowed materials list” also support healthier crews. He encouraged a focus on health and human performance for the submarine force in combat conditions, particularly for extended combat operations and responses to combat casualties.

Building Physiology-Based Models for Predicting Performance Impairment

Jeffrey Bolkhovsky, research physiologist, Naval Submarine Medical Research Laboratory (NSMRL), provided an overview of his work using noninvasive monitoring to predict performance decrement caused by fatigue. His team collects physiological measurements (such as pulse variability, blood volume changes, and blink rate) using facial tracking, eye tracking, electrodermal activity, and cardiovascular system monitoring. Using machine learning (ML), these metrics can be leveraged to predict changes in cognitive performance, which can then be used to make recommendations to crew managers about watch schedules. Bolkhovsky’s team, with the support of multiple collaborators, developed an Optimized Watch-standing and Logistics (OWL) Tool, a software package that takes these data to provide personalized performance predictions for submariners, and detect unexpected deviations in schedules. The integration of non-invasive wearables with an analytics tool, like OWL, can provide watch managers with data-driven recommendations about who should be shifted, rotated, or rested—thus improving crew performance. Future steps include developing a larger dataset with more operational predictions, mapping fatigue scores to specific duties, and providing analytics in real-time.

Human Factors for Extended Manned Submarine Operations

Capt. Michael Daigle (U.S. Navy), Future Attack Submarine Requirements, Office of the Chief of Naval Operations, emphasized that health, readiness, and performance are priorities for extended manned submarine operations, especially because crews are small and specialized, and submerged operations can exceed a month without sunlight or fresh air.

Daigle underscored that continued research is needed to address several key challenges.

1. First, mental health is an issue for all ranks and experience levels. This is especially the case for young and new personnel, those dealing with deaths of loved ones, and those dealing with relationship issues when deployed and communication with family and friends is limited. He urged the continued provision of mentoring and coping tools.
2. Second, in a sedentary environment, nutrition issues can cause weight problems, high cholesterol, and high blood pressure. Balancing the need for healthy food with the need for enjoyable food that boosts morale is difficult, as is prioritizing fitness amidst the limited facilities available on submarines.
3. Third, he said that screening is paramount even as recruiting challenges increase because confidence in crew health and well-being before deployment is critical. He added that mixed-gender crew interactions are particularly important.

4. Fourth, infectious disease prevention and management is also vital, with the potential to use lessons learned during the COVID-19 pandemic.
5. Fifth, he noted, although the change to a 24-hour watch cycle has made significant improvements, fatigue remains an issue as crew members continue to experience sleep disruptions.

He also suggested:

• Customized wearables to monitor and manage daily stress, health, fitness, and performance,
• Location tracking inside the cabin during casualty conditions,
• Future submarine design for mixed-gender crews,
• Fitness and nutrition-related improvements,
• Crew protection in combat shock environments, and
• Continued support of crew resilience.

Lessons Learned from Analog Contexts and Lunar Mission Planning

Robert Sanders, flight surgeon and program medical officer of the Extravehicular Activity and Human Surface Mobility Program, National Aeronautics and Space Administration (NASA), described how some of the challenges of lunar mission planning are similar to those of submarine operations. For example, astronauts leaving the International Space Station (ISS) to conduct spacewalks experience decompression stress under conditions that are comparable to divers leaving a submarine. The ISS official mitigation strategy against decompression stress is O₂ pre-breathing, which lowers the nitrogen levels in the body before the spacewalk. However, this approach is time consuming and is not efficient for a lunar mission. He emphasized NASA’s need to determine an acceptable level of risk for DCS for its astronauts; NASA learned that if the risk level is high enough, medical outcomes like DCS, are not considered as “failures,” but are accepted as statistical likelihoods that should be anticipated. To wit, NASA uses mathematical models to plan for its operations, considering the health risk and the operational risk of DCS as independent entities—the latter of which can result in an unacceptable loss of mission objectives and resources.

Sanders also discussed DCS mitigation strategies via approaches that modulate changes in cabin atmosphere: the O₂ in the cabin could be increased, which benefits the operator but increases risks of fire; or the pressure could be lowered to reduce the level of nitrogen, which lowers O₂ and creates a risk for hypoxia. NASA has found that 34 percent O₂ at 8.2 pounds per square inch is a level that humans can tolerate well, while also decreasing the level of decompression stress and requiring only a short O₂ pre-breathe before a spacewalk. NASA also learned that facilitating communication and cooperative controls between vendors is critical to realizing effective engineering solutions, such as these. He also emphasized the importance of organizational policies for DCS prevention and mitigation that are clear and reasonable. In closing, he reiterated that although their missions may differ, NASA and the Navy can learn from each other, and he championed government and industry collaborations to address key questions.

Discussant Responses

Following the presentations, David Fothergill, scientific director at NSMRL moderated a session in which four discussants offered perspectives and posed questions about how the issues raised intersect with priority research areas in subdomains of submarine medicine. Michael Goodson, research biologist, Air Force Research Laboratory, explained that although everyone has a different microbiome,⁸ within each person the microbiome stays the same during deployment. Furthermore, each person’s microbiome before deployment correlates with performance, cognition, and mood during deployment. He asked whether evidence demonstrates that people who are healthier before deployment have better performance during deployment. Panlilio and Daigle noted that submarines with a “command culture of health” tend to have crews who perform better under pressure and return in better physical condition. In response to a follow-up question from Fothergill, Daigle said that the effects of pre-deployment operations vary by submarine type and that maintaining good health on a shorter operational cycle or on a larger submarine with exercise facilities is

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easier. Sanders explained that NASA treats fitness as a risk with a set of requirements, and trainers educate and empower crews throughout missions.

Justin Handy, research psychologist, NSMRL, noted that his team dedicates significant resources to screening, assessment, and readiness during training, but extending this work to be available to submariners as part of ongoing mental health maintenance programs is challenging. He asked how to measure whether solutions for health promotion and monitoring are successful, as well as whether strategies exist to identify people at risk and intervene before a medical evacuation situation would arise. Panlilio responded that work is underway to develop leading indicators of the success of new crew members. Bolkhovsky commented that if a low level of risk for fatigue is maintained and tools are developed for the submarine community to use, positive feedback on the effectiveness of these tools could be an indicator of success. Sanders introduced NASA’s multipronged approach for health maintenance, comprising a fitness team, doctors, a behavioral health team, a food laboratory, and microbiome researchers.

Dominica Hernandez, research psychologist, NSMRL, said that because the applicant pool for divers and submariners is so small, workforce development should be prioritized over workforce selection, and she inquired about efforts to help sailors develop psychological coping mechanisms. Panlilio noted that embedded mental health onshore helps prevent psychological unplanned losses. In response to a question from Hernandez about efforts to maintain cardiometabolic health, Daigle pointed out that personal choice is key, but leaders have to prioritize it—for example, with fitness sessions and rewards involving the entire crew. Sanders added that individualization of exercise plans is key.

Manik Anand, mechanical engineer, Carderock Naval Surface Warfare Center, asked about capabilities in the “clean sheet design” (a completely new design that does not rely on existing designs or parent models) of the next-generation attack submarine. Daigle encouraged a focus on more detailed requirements, especially concepts for mixed-gender crews that include standards for berthing. Anand posed a question about the use of wearables to mitigate and respond to submarine distress scenarios. Bolkhovsky indicated that wearables could facilitate triage, and further research on physiological signals from an injured person would help determine who needs care first. In response to a question from Anand about medical training for NASA’s crews, Sanders explained that some missions have a crew medical officer with 40-hour first aid training and others have a physician, but no requirement exists beyond the former.

Open Discussion

Fothergill invited all workshop participants to join the conversation with the session’s discussants and speakers. Chapman asked about the consequences of hypoxia and whether cognitive effects have been studied. Fothergill replied that the Submarine Atmosphere Control Manual provides minimum and maximum levels of O₂ and CO₂. The O₂ levels are usually not at a point at which a person would be able to measure cognitive changes, but higher levels of CO₂ may have an effect. Sanders said measurable effects of CO₂ have been observed by NASA even in chronic low-level exposures, and hypoxia research related to cognitive function is underway. Daigle urged the medical community to study anything that could hinder or improve the performance of sailors in any phase of operation.

Given the potential for infectious disease to affect readiness and performance, Fothergill posed a question about screening for asymptomatic individuals who could put the crew at risk if deployed. Bolkhovsky said that facial tracking, eye tracking, heart rate variability, modulations in vocal patterns, and electrodermal activity could be used alongside AI and machine learning to predict (nearly) asymptomatic carriers. Fothergill also expressed concern about low vitamin D levels in submariners, given their lack of sunlight and diet changes, which can correlate with weight gain, metabolic syndrome, type 2 diabetes, bone health issues, cancer, and inflammation. He wondered if submariners’ vitamin D levels should be tested regularly or if other mitigation strategies should be considered. Sanders championed NASA’s successful use of high-dose vitamin D supplements for some of its astronauts, as well as its strategies for engineering food that is low in weight and mass, while remaining healthy and enjoyable.

Kizer asked about the value of peer counseling for submariners and intimated that this may be a fruitful area of research based on other experiences within the military and with veterans. Bolkhovsky noted that his team is considering requirements for a version of an app, originally designed for astronauts, to provide self-guided cognitive behavioral therapy. Kizer also observed that the Department of Veterans Affair is increasingly using virtual reality (VR) and similar immersive technologies for therapy and training, and Bolkhovsky commented that researchers are studying how VR could be used for high-cost submarine equipment training. Maguire added that VR could be used to guide treatment. Kizer suggested that VR may be an area of “low-hanging fruit” for ONR-sponsored research. Goodson inquired as to whether commanding officers would be willing to test the efficacy of interventions targeting the microbiome, such as probiotics to promote gut health, during deployment. Daigle suggested that anything deemed safe that would improve operator performance could be considered. However, convincing the crew and Congress is difficult. Panlilio added that the messaging about the science is critical.

WOMEN OPERATORS

Van Hoesen moderated a roundtable discussion on the challenges and opportunities to explore sex-specific physiological responses to diving and to the submarine environment. She noted that women comprise 17 percent of the military, but research on specific operational risks for women has thus far been inadequate, which affects recruitment, retention, and readiness.

Frauke Tillmans, research director, Divers Alert Network, described evidence of physiological and pathological differences between the sexes in terms of reproduction and fertility, drug response, respiratory injury, immunity, and susceptibility to DCS. However, these studies should be revisited, she noted, as most of these data looking at sex-differences are from chamber dives and high-altitude dives, which are “not completely comparable” to water immersion. Meanwhile, she continued, there is evidence to suggest that, though decompression stress elicits comparable levels of VGE in male and female divers, women have a higher prevalence of DCS. “So we really do not know enough to say if a female diver can dive as deep and long and safe as their male counterpart,” said Tillmans, “because we do not understand a lot of the physiology.” She added, “That is a conundrum that we haven’t addressed and I think we do need to address.” As such, she noted the need for large-scale multinational field research looking at the health impacts on female divers.

Linda Hughes, statistician, NSMRL, explained that Navy women have concerns about CO₂ levels, radiation, vitamin D, bone density issues, and air contamination. Risk assessment studies on these issues were conducted in only male subjects prior to gender integration of the submarine force. Whether long-term effects exist for women remains unknown. A recent study revealed that women had a higher rate of injury during pressurized submarine escape training. Most of these injuries were due to arterial gas embolisms and pulmonary barotrauma. Further research is needed to help understand why. Ongoing work is underway to conduct longitudinal studies investigating the health impacts of the submarine atmosphere in women. She expressed her hope for a voluntary crew registry to track women “cradle to grave,” in part to understand and address why enlisted women retire from service earlier in their careers than men.

Brian Maguire, senior epidemiologist, Leidos, asserted that because the military will likely have more women in the future, now is the time to tackle questions of risks for women. Men and women in the military experience different levels of risk, and these risks can be predicted and prevented, he said. In a recent study,⁹ he and his team found that the incidence of mental disorders was lower for enlisted women than for enlisted men. However, the rate of cases in the ICD-9 diagnostic category for “symptoms, signs, and ill-defined conditions” was the same. However, for all the other eight diagnostic categories studied (e.g., injuries, neoplasms), the rates were higher for women than for men. For respiratory diseases in particular, the rate was almost double for women, which raises questions about why the risks appear to differ. In conversations with divers, Maguire and Hughes have learned that many divers avoid reporting health conditions to avoid being separated from their teams. He emphasized the value of researchers building relation-

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ships with women operators and gathering their feedback to better understand and target areas of need.

Open Discussion

Van Hoesen invited all workshop participants to join the conversation with the session’s speakers and encouraged discussion about the data needed to explore risks for women. Tillmans expressed her support for a diver registry. Maguire added that data from medical records, personnel files, and dive logs are available, but more real-time interactive data would help identify and address risks. Hughes pointed out that administrative databases designed for billing and human resources do not contain baseline measurements. Maguire acknowledged the challenges of collecting reliable data, as International Classification of Disease codes often are inaccurate in the military. William Johnson, consultant, WMJ Associates, LLC, proposed the creation of a data strategy using AI tools, an undertaking that needs leadership to collaborate with diverse stakeholders across multiple disciplines. Maguire agreed that to answer critical questions about the long-term health outcomes for Navy women, a better system is needed to collect and format data sources. Every $1 invested in risk prevention and health improvement research leads to a $3 return on investment, Maguire noted. Healthy operators serve longer, take shorter breaks away from service, and are less likely to become an unplanned loss from the workforce, he emphasized.

David Fothergill, scientific director, NSMRL, highlighted an opportunity to secure funding in light of a 2024 presidential executive order to strengthen women’s health research. Given the long periods of time that submarine crews are exposed to contaminated air, he asked if the submarine atmosphere limits that developed before women were onboard are safe for mixed gender personnel, and whether submarine atmosphere and submariner health databases could be used to answer this question. Hughes indicated that data from the Submarine Atmosphere Health Assessment Program (SAHAP) could be useful. Kizer asked how ONR’s Undersea Medicine program might prioritize its funding with regard to dive safety in women. Tillmans pointed to individual variations in monthly hormonal fluctuations as “something that should be on the radar,” and referred to studies from the 1990s which suggested that the position in the menstrual cycle and oral contraceptive use could be contributing risk factors for DCS. “Confirming what has been done before would be a really, really good way to start,” Tillmans concluded. Maguire noted that one of the biggest findings from his research is the large disparity in respiratory disease incidence. “The rate was almost twice as high for women as compared to men,” he said, adding, “We really need to have more research to develop the questions and priorities.” He pointed to better medical records, surveys, interviews, focus groups, and a diver registry as key enablers of progress. Hughes cautioned against “reinventing the wheel” to create a diver registry, as the current system could simply be modified. Tillmans added that the Divers Alert Network has a similar database, and she encouraged the expansion of data collection and data mining efforts across communities. Van Hoesen remarked that funded research should include equal numbers of men and women.

PERFORMANCE

Perspectives on Undersea Medicine for Operator Performance Needs

John Florian, scientific director, Navy Experimental Diving Unit, provided a brief overview of human performance challenges in undersea and hyperbaric environments. Due to time constraints, the session included four focused areas: operator needs, neurocognitive effects, thermal protection, and oxygen toxicity. He emphasized, however, that topics such as readiness and recovery, nutrition, sleep quantity and quality, whole body oxygen toxicity, resistive effort, hypercapnia, physiological monitoring, human-machine teaming, etc. require further research. While some of these topics may be broad (e.g., nutrition, sleep, fatigue, physiological monitoring, etc.) and may glean insight from work in other environments, all require specific research in the diving and hyperbaric environment to provide required capabilities for the military. Florian also noted research that shows the detrimental effects of long-duration hyperoxic dives on cardiovascular and muscular performance. More research is required to determine countermeasures or mitigations strategies to support diving capabilities.

Capt. David Regis (U.S. Navy, ret.), undersea medical officer, Supervisor of Diving and Salvage, and program manager, Deep Submergence Biomedical Development Program, NAVSEA, provided insights into the challeng-

ing conditions faced by Navy warfighters in the undersea theater of operations. He explained that Navy divers’ jobs have high risk—for example, de-fusing mines, doing reconnaissance, interacting with hostile forces on land, and working with dangerous machinery under water. Conditions while performing these tasks can be treacherous, including contaminated water (e.g., toxic chemicals, infectious microbes); cold, hot, or murky water; heavy gear; water that damages equipment; and unknowns that often cause deviations in plans and could increase risk of harm to the diver. However, he emphasized that the “commute” may be even riskier than the actual tasks. The Navy warfighter has so much to contemplate while completing missions, Regis reflected, including monitoring time, depth, position, breathing gas, the environment, cognitive impairment, DCS, seizures, drowning, physical injury, cold or heat injury, mission failure, and death. He emphasized that while Navy divers “aren’t afraid to suffer,” they would prefer to suffer far less. He asserted that solutions to meet operators’ needs should ultimately maximize value—safety, performance, efficiency, readiness, and longevity—and minimize burden—bulk, intrusiveness, weight, distractibility, and complexity.

Neurocognitive Effects

Lt. Cdr. Jennifer Jewell (U.S. Navy), research psychologist, director of Biomedical Research, and cognitive domain lead for Preservation of the Force and Family, Naval Special Warfare Command, highlighted the need for neurocognitive R&D at depth to optimize readiness and maximize performance during and after dives. She described several limitations related to this research, including data collection. A major constraint to understanding neurocognitive function is that limited technology is available to measure cognitive function while diving; current technology has a limit of 10–20 feet under water in a test pool environment. Other limitations with current technology include the need for the diver to pause operations to complete a tablet-based assessment, which increases cognitive load to the diver—an issue that is undesirable during both operations and research.

She noted that technology that would allow the study of neurocognitive function passively instead would be beneficial (e.g., via eye tracking); for example, measuring cognitive performance while divers engage in different stages of operations (tasks that vary within and between dive communities) without requiring active diver involvement in the data collection is critical. She made it clear that “We don’t know enough to know what we don’t know” because findings from the dry environment do not replicate to the submerged environment, and many different dive profiles, lengths, and operations exist; putting all of that into a question about neurocognitive functioning cannot be done without technological capabilities for the operational diving space.

Thermal Protection

David Hostler, director of the Center for Research and Education in Special Environments and the Emergency Responder Human Performance Lab, University of Buffalo, emphasized the importance of R&D to neutralize the effects of ocean temperature on warfighter performance. He noted that thermal strain and hydration affect almost all aspects of diving performance. If immersion occurs in warm water, thermal strain causes the diver to sweat without benefit; if immersion occurs in cold water, peripheral tissue vasoconstriction forces additional blood volume into the thorax, magnifying fluid loss.

Hostler described a 2007 study conducted by NEDU that revealed that DCS was lowest with a cold descent and a warm ascent.¹⁰ Furthermore, the highest proportion of low-level VGE occurred in these cold descent, warm ascent dives. This study showed a direct relationship between thermal strain and DCS risk, suggesting that decompression stress can be reduced by manipulating body temperature to limit on-gassing and encourage controlled off-gassing.

He also noted that when a diver returns to land, a rapid redistribution of body water occurs, and the diver can suffer rapid hypohydration, which is difficult to address with rehydration alone. He indicated that controlling thermal strain could partially control hydration status; for example, manipulating skin temperature prevents both sweating and vasoconstriction, and controlling skin temperature can offset metabolic heat in warm conditions and supplement body heat in cold conditions.

Additionally, controlling skin temperature could greatly reduce the incidence of DCS. He posited that the Diver

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Thermal Protection System (DTPS) designed 20 years ago to hold the body temperature at a designated point needs to be re-envisioned. A next-generation DTPS for all types of diving could have an automated feedback system that integrates knowledge of the effect of thermal strain; AI and high-speed computing could enable fast-responding algorithms to incorporate water temperature and individual diver physiology and integrate those signals in real-time VGE monitors.

Central Nervous System (CNS) and Pulmonary Oxygen Toxicity

Aaron Hall, research physiologist, Naval Medical Research Center, noted that the benefits of O₂ used while diving are offset by the risk for CNS and pulmonary oxygen toxicity. He indicated that CNS oxygen toxicity primarily manifests as a seizure. He described significant developments in research on CNS oxygen toxicity prevention, including that nitric oxide plays a key role in its pathophysiology and that human studies are underway at Duke University. Elaborating on the latter, he said that probabilistic modeling is hampered by the day-to-day variability of risk of exposure. Studies have found that electrodermal activity is a potential signal, and EEG is also being explored as a prediction tool. Furthermore, with additional research support, biomarkers to predict CNS oxygen toxicity risk for a given dive on a given day could be identified. Initial animal research suggests that traditional anti-epileptics could prevent seizures, and in human research, nutritional ketosis showed modest efficacy; an upcoming study will use exogenous ketone esters to reduce or delay the onset of CNS oxygen toxicity symptoms.

Hall explained that pulmonary oxygen toxicity is a progressive disorder associated with shallower, longer-duration dives. Tracheobronchitis commonly arises during diving and recompression, pulmonary function decreases, and symptoms become intolerable before entering the exudative phase (pulmonary edema) and the proliferative phase (pulmonary fibrosis). Prevention is centered on limiting O₂ exposure. He mentioned that the Unit Pulmonary Toxic Dose (UPTD) tool enables prediction of pulmonary oxygen toxicity onset; however, it is modeled around decrements in vital capacity instead of symptom onset, which is what limits operations. Significant developments in research on pulmonary oxygen toxicity, for which nitric oxide is a key player, include operational risk models for symptoms, which he said could provide better prediction than the UPTD model.

Current research efforts focus on individual pre-dive risk via measurements of exhaled breath condensate and volatile organic compounds as well as exhaled nitric oxide to provide a noninvasive source of biomarkers for prediction of pulmonary oxygen toxicity for prolonged oxygen dives. Animal research has revealed that the parasympathetic nervous system is involved in pulmonary oxygen toxicity and that exudative phase countermeasures exist.

Open Discussion

Moderator John Florian, scientific director, NEDU, invited all workshop participants to join the conversation with the session’s speakers. He inquired about the current state of toxic chemical detection in contaminated water. Regis replied that real-time detection with off-the-shelf technology is an active project in development. Identifying biologic threats in the water is easier, while strategies for detecting toxic chemicals remain difficult and resource intensive. In response to a question about protective gear and temperature, Regis indicated that when the water is too hot, protective gear can slash viable time in the water down to minutes, owing to risk of heat stroke and exhaustion.

Florian asked about active versus passive neurocognitive assessment and wondered when a test for operational purposes would be available. Lieutenant Commander Jewell explained that active assessments target distinct cognitive functions that affect behavior at a point in time in a controlled research environment. Although these assessments provide valuable information, she said that actual cognitive function during operational tasks cannot be determined without disrupting operations and, thus, skewing results. More passive assessments would be useful but are expensive and require technical equipment. If other variables are directly associated with neurocognitive decline, she noted an opportunity to detect neurocognitive decline through more physiological measurements.

She said that developing a useful test for operational purposes likely will take at least 5 years. Few people work on neurocognitive advancement in submerged diving, despite its opportunity for safety improvements. In response to a question from Florian about new NSMRL

capabilities, Handy said that they have worked with off-the-shelf underwater-capable tablets, which are not optimal for neurocognitive testing, so they are developing a prototype based on testing millisecond-resolution reaction time to evaluate neurocognitive function under water.

WORKSHOP REFLECTIONS

Kizer moderated a final panel discussion on workshop themes, unexplored opportunities, and funding priorities for undersea medicine research. Chapman reiterated that medical threats to divers and submariners deserve more attention; the undersea workforce will continue to be limited if key research questions are not examined. Although robots could acquire tactical abilities, she cautioned against envisioning a future that does not include manned undersea operations. She added that gender representation will continue to be a focus of proposal considerations and research experimental design and expressed her support of a robust data collection framework to capture all demographics for performance and health outcomes.

Colbert emphasized that this workshop should help create a more cohesive narrative about how undersea medicine research best supports the fleet, which is critical to securing funding. Generally speaking, across the diving community and its diverse stakeholders with unique priorities, the desire to dive deeper, longer, and more safely is a consistent theme. As such, any research that aims to address these priorities should be an enduring focus. Additionally, there is growing interest in research related to the risks that have traditionally been underexplored, such as diving in contaminated water. With a finite budget bandwidth, he proposed research in three areas: (1) identification of hazards and protection while diving in contaminated water; (2) temperature moderation while wearing contaminated water protective equipment; and (3) disabled submarine scenarios, particularly involving escape and rescue.

Capt. Timothy Oliver (U.S. Navy, ret.), executive director, Naval Submarine League, suggested pursuing research in the following three areas: (1) prevention of suicide and self-harm, including by screening aimed at identifying submariner and diver candidates who may benefit from intervention and by developing indicators to identify those who would not be likely to succeed in isolated and arduous work environments; (2) optimization of the operator–machine interface to enhance performance; and (3) understanding how the submarine environment impacts health and performance in women.

John Marsack (U.S. Navy Chief Petty Officer and special operations operator, ret.), founder and managing partner, Legion Undersea Services, emphasized that divers should “take responsibility to make sure he or she is in the best possible condition to allow for the mission to go correctly.” This includes commitment to exercise and healthy eating, with doing so not only enhancing performance, but also reducing risks of DCS and oxygen toxicity. He pointed to additional research into the optimization of exercise routines and diet for performance as, “where we can get the most bang for our buck.”

Jim Bagian, former astronaut and professor of engineering practice and executive director of the Center for Risk Analysis Informed Decision Engineering, University of Michigan, said that funding should be prioritized based on the goal, human and financial resources, and the schedule. He suggested using existing research on common issues from other disciplines (e.g., fatigue) instead of spending limited funds conducting duplicate research. He noted that this would enable a focus on research specifically on undersea medicine, including in the following three areas: (1) rebreathing tools that alert the diver of a “go/no-go” situation and provide real-world data to researchers, (2) technologies such as EEGs to understand performance, and (3) communication with operators to understand what they need and why, so as to invest appropriately.

Virginie Papadopoulou, research assistant professor, University of North Carolina at Chapel Hill, suggested collaborating across specialities to create new interdisciplinary knowledge and maintain a robust research community. She prioritized the need to “attract, train, and retain” by developing outreach efforts to interest science, technology, engineering, and mathematics students in the field; emphasizing access to open source databases that enable innovation; creating multidisciplinary training that would allow work in academia, government, or industry; and creating exchange programs, which could improve

cross-disciplinary communication skills and help students develop a network of peer support.

Peter Witucki, president, Undersea and Hyperbaric Medical Society (UHMS); emergency medicine physician, University of California, San Diego; and diving medical officer, U.S. Naval Reserves, explained that UHMS offers courses for physicians and technicians and supports fellowships. He welcomed guidance for planning scientific meetings and extended UHMS’s assistance in providing resources and connecting people to support ONR’s needs.

Kizer suggested exploring the overlap of DCS and diffuse inflammation, analogous to the role of fine and ultra-fine particulate matter dispersed throughout the body from wildfire smoke. He also reiterated his support for a curated registry of women divers, as well as for VR in therapy and training.

Johnson emphasized the importance of leveraging operator input, engaging the broader undersea medicine community beyond DoD, and thinking outside the box. William Hoeft, fellow, Undersea Strategy, Systems Planning & Analysis, Inc., made the point that federal funding for naval undersea medicine is very limited. He offered his opinion that, although the U.S., writ large, has historically high levels of resources, the budget allocation to ONR underscores the difficulty of prioritizing funding for this research need. Kizer closed the meeting by emphasizing the urgency in tackling the issues raised during the workshop, guided by the best science to help the Navy prepare the warfighter for the next regional or global conflict.

DISCLAIMER This Proceedings of a Workshop—in Brief was prepared by Linda Casola and Chanel Matney as a factual summary of what occurred at the workshop. The statements made are those of the rapporteurs or individual workshop participants and do not necessarily represent the views of all workshop participants; the planning committee; or the National Academies of Sciences, Engineering, and Medicine.

*The National Academies of Sciences, Engineering, and Medicine’s planning committees are solely responsible for organizing the workshop, identifying topics, and choosing speakers. The responsibility for the published Proceedings of a Workshop—in Brief rests with the institution. Planning committee: Kenneth W. Kizer (Chair), Stanford University; Olujimi Ajijola, University of California, Los Angeles; Serena Auñón-Chancellor, Louisiana State University; John P. Florian, Navy Experimental Diving Unit; David Fothergill, Naval Submarine Medical Research Laboratory; William Hoeft, Jr., Systems Planning & Analysis, Inc.; William Johnson, WMJ Associates, Inc.; Simon Mitchell, University of Auckland; Virginie Papadopoulou, University of North Carolina at Chapel Hill; David Regis, Naval Sea Systems Command; and Karen Van Hoesen, University of California, San Diego.

REVIEWERS To ensure that it meets institutional standards for quality and objectivity, this Proceedings of a Workshop—in Brief was reviewed by James Chimiak, Chief Medical Officer, Divers Alert Network; John P. Florian, Scientific Director, Naval Submarine Medical Research Laboratory (NSMRL); and Dawn Kernagis, Director of Scientific Research, DEEP. Leslie Sim, the Report Review Officer for the Health and Medicine Division at the National Academies of Sciences, Engineering, and Medicine, served as the review coordinator.

SPONSOR This workshop was supported by a contract between the National Academy of Sciences and the Office of Naval Research. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.

STAFF Chanel Matney, Program Officer and Workshop Director; George Coyle, Senior Program Officer; Rebecca English, Senior Program Officer; Ashley Pitt, Senior Program Assistant; Clare Stroud, Senior Director, Board on Health Sciences Policy; and Ellen Chou, Director, Naval Studies Board.

For additional information regarding the workshop, visit https://www.nationalacademies.org/our-work/emerging-science-and-technology-to-address-naval-undersea-medicine-needs-a-workshop.

SUGGESTED CITATION National Academies of Sciences, Engineering, and Medicine. 2024. Emerging science and technology to address naval undersea medicine needs: Proceedings of a workshop—in Brief. Washington, DC: The National Academies Press. https://doi.org/10.17226/27878.

Health and Medicine Division Copyright 2024 by the National Academy of Sciences. All rights reserved.