Assessment of Sex-Dependent Medical Outcomes During Spaceflight.

Background: In this study sex-differences in medical outcomes during spaceflight are reviewed and probabilistic risk assessment (PRA) is used to assess the impact on spaceflight missions of varying lengths. Materials and Methods: We use PRA to simulate missions of 42 days, 6 months, and 2.5 years. We model medical outcomes using three crews: two men and two women, four women, or four men. Total medical events (TME), crew health index (CHI), probability (0-1) of medical evacuation (pEVAC), probability of loss of crew life (pLOCL), and influential medical conditions were determined. Results: No differences were seen in any metric for the 42-day mission. There were no differences seen for any mission length, in any crew, for TME, CHI, pLOCL, or environmental causes of pEVAC. Sex-dependent differences are seen for rates of nonemergent pEVAC during the 6 month and 2.5-year missions, where women have a higher pEVAC in the 182-day (0.0388 vs. 0.0354) and 2.5-year missions (0.350 vs. 0.228). These differences were driven by higher incidence of partially treated urinary tract infection (UTI). In the 2.5 year mission, with resupply of medical resources, the influence of UTI in women on pEVAC decreases (0.35-0.11). Conclusion: Although resupply is unlikely for deep space missions, modeled results suggest that sex-specific medical needs can be readily managed through preventive measures and inclusion of appropriate medical capabilities. Within its many limitations, PRA is a useful tool to estimate medical risks in unique environments where only expert opinion was previously available.

Estimating medical risk in human spaceflight.

NASA and commercial spaceflight companies will soon be retuning humans to the Moon and then eventually sending them on to Mars. These distant planetary destinations will pose new risks-in particular for the health of the astronaut crews. The bulk of the evidence characterizing human health and performance in spaceflight has come from missions in Low Earth Orbit. As missions last longer and travel farther from Earth, medical risk is expected to contribute an increasing proportion of total mission risk. To date, there have been no reliable estimates of how much. The Integrated Medical Model (IMM) is a Probabilistic Risk Assessment (PRA) Monte-Carlo simulation tool developed by NASA for medical risk assessment. This paper uses the IMM to provide an evidence-based, quantified medical risk estimate comparison across different spaceflight mission durations. We discuss model limitations and unimplemented capabilities providing insight into the complexity of medical risk estimation for human spaceflight. The results enable prioritization of medical needs in the context of other mission risks. These findings provide a reasonable bounding estimate for medical risk in missions to the Moon and Mars and hold value for risk managers and mission planners in performing cost-benefit trades for mission capability and research investments.

Back Pain in Outer Space.

Space travel has grown during the past 2 decades, and is expected to surge in the future with the establishment of an American Space Force, businesses specializing in commercial space travel, and National Aeronautics and Space Administration's planned sustained presence on the moon. Accompanying this rise, treating physicians are bracing for a concomitant increase in space-related medical problems, including back pain. Back pain is highly prevalent in astronauts and space travelers, with most cases being transient and self-limiting (space adaptation back pain). Pathophysiologic changes that affect the spine occur during space travel and may be attributed to microgravity, rapid acceleration and deceleration, and increased radiation. These include a loss of spinal curvature, spinal muscle atrophy, a higher rate of disc herniation, decreased proteoglycan and collagen content in intervertebral discs, and a reduction in bone density that may predispose people to vertebral endplate fractures. In this article, the authors discuss epidemiology, pathophysiology, prevention, treatment, and future research.

Probabilistic Risk Assessment of Prophylactic Surgery Before Extended-Duration Spaceflight.

Introduction. Prophylactic surgery before spaceflight may eliminate the risk of appendicitis and cholecystitis in astronauts on deep space missions. However, even minimally invasive surgery increases the risk of small bowel obstruction (SBO). Probabilistic risk assessment (PRA) is a method that can be used to estimate the benefits and risks of prophylactic surgery. Methods. Risks of appendicitis and cholecystitis during a 2.5-year Mars mission are compared to the risk of SBO after laparoscopic removal of the appendix, gallbladder, or both. A PRA model using Monte Carlo methodology was used to forecast the risks. Results. Prophylactic appendectomy and cholecystectomy combined, conferred an increased probability of medical evacuation (pEVAC) due to SBO as compared to the no surgery group. A slightly higher probability for the loss of crew life (pLOCL) was found in the no surgery group when compared to the cases in which either prophylactic appendectomy alone, or appendectomy plus cholecystectomy are performed. Discussion. The need for medical evacuation can be viewed as a potential risk for death in the context of a space mission where evacuation is not possible. Because of the higher pEVAC due to SBO and relatively small benefit in the reduction of pLOCL in the prophylactic surgery groups, this analysis does not support the prophylactic removal of appendix and/or gallbladder for spaceflight. Future advances in surgical or medical technique or mission medical capabilities may change these results. This work demonstrates the utility of PRA in providing quantitative answers to "what if" questions where limited information is available.

Quantification of Medical Risk on the International Space Station Using the Integrated Medical Model.

INTRODUCTION: The Integrated Medical Model (IMM) is a quantified, evidence-based decision support tool developed by National Aeronautics and Space Administration (NASA) to assist in the assessment of the medical risk of human spaceflight missions. The IMM utilizes a probabilistic risk assessment (PRA) approach to simulate potential in-flight medical events and resultant health and mission outcomes.METHODS: The IMM has been utilized to estimate the medical risk associated with International Space Station (ISS) missions. The IMM outputs that have been most informative to the ISS program are the probabilities of evacuation (pEVAC) and loss of crew life (pLOCL). These outputs are incorporated into a continuously maintained ISS PRA model so that its quantification of total ISS mission risk includes the medical risk.RESULTS: Results of this analysis revealed that the forecasted risk values of pEVAC and pLOCL due to medical events were improved by using the IMM with the ISS PRA model instead of using data from prior sources in which these values were underestimated.DISCUSSION: The IMM provides an evidence-based PRA approach to directly communicate and integrate medical risk with other ISS risks. A comparison of IMM outputs of pEVAC and pLOCL to empirical spaceflight data and analog population data revealed that IMM outputs were comparable with actual experience. With appropriate outcome context, these findings increase subject matter expert confidence in the accuracy of IMM risk estimates. IMM outputs provide quantifiable objective estimates of medical risk that can be used to inform mission risk assessments and to optimize crew health.Walton ME, Kerstman EL. Quantification of medical risk on the International Space Station using the Integrated Medical Model. Aerosp Med Hum Perform. 2020; 91(4):332-342.

Blood transfusion for deep space exploration.

BACKGROUND: Astronauts on exploration missions may be at risk for traumatic injury and medical conditions that lead to life threatening hemorrhage. Resuscitation protocols are limited by the austere conditions of spaceflight. Solutions may be found in low-resource terrestrial settings. The existing literature on alternative blood product administration and walking blood banks was evaluated for applicability to spaceflight. STUDY DESIGN AND METHODS: A literature review was done using PubMed and Google Scholar. References were crosschecked for additional publications not identified using the initial search terms. Twenty-seven articles were identified, including three controlled trials, six retrospective cohort analyses, 15 reviews, one case report, and two experimental studies. RESULTS: Solutions to blood transfusion in austere settings include lyophilized blood products, hemoglobin-based oxygen carriers (HBOCs), and fresh whole blood. Many of these products are investigational. Protocols for walking blood banks include methods for screening and activating donors, transfusion, and monitoring for adverse reactions. Microgravity and mission limitations create additional challenges for transfusion, including baseline physiologic changes, difficulty reconstituting lyophilized products, risk of air emboli during transfusion, equipment constraints, and limited evacuation and surgical options. CONCLUSION: Medical planning for space exploration should consider the possibility of acute blood loss. A model for "floating" blood banks based on terrestrial walking blood bank protocols from austere environments is presented, with suggestions for future development. Constraints on volume, mass, storage, and crew, present challenges to blood transfusion in space and must be weighed against the benefits of expanding medical capabilities.

Neuropathic pain.

Neuropathic pain is a clinical entity that presents unique diagnostic and therapeutic challenges. This chapter addresses the classification, epidemiology, pathophysiology, diagnosis, and treatment of neuropathic pain syndrome. Neuropathic pain can be distinguished from nociceptive pain based on clinical signs and symptoms. Although neuropathic pain presents a significant burden to individuals and society, a more accurate assessment of resource utilization, costs, and impairments associated with neuropathic pain would facilitate appropriate planning of healthcare policies. The underlying pathophysiology of neuropathic pain is not well defined. Several theories regarding the mechanism of neuropathic pain have been proposed, including central and peripheral nervous system sensitization, deafferentation, neurogenic inflammation, and the wind up theory. Neuropathic pain is a clinical diagnosis and requires a systematic approach to assessment, including a detailed history, physical examination, and appropriate diagnostic testing. The mainstay of treatment for neuropathic pain is pharmacological, including the use of antidepressants, antiepileptics, topical anesthetics, and opioids. Nonpharmacological treatments include psychological approaches, physical therapy, interventional therapy, spinal cord stimulation, and surgical procedures. Neuropathic pain is difficult to treat, but a combination of therapies may be more effective than monotherapy. Clinical practice guidelines provide an evidence-based approach to the treatment of neuropathic pain.

NASA's human system risk management approach and its applicability to commercial spaceflight.

As planning continues for commercial spaceflight, attention is turned to NASA to assess whether its human system risk management approach can be applied to mitigate the risks associated with commercial suborbital and orbital flights. NASA uses a variety of methods to assess the risks to the human system based on their likelihood and consequences. In this article, we review these methods and categorize the risks in the system as "definite," "possible," or "least" concern for commercial spaceflight. As with career astronauts, these risks will be primarily mitigated by screening and environmental control. Despite its focus on long-duration exploration missions, NASA's human system risk management approach can serve as a preliminary knowledge base to help medical planners prepare for commercial spaceflights.

Space adaptation back pain: a retrospective study.

INTRODUCTION: Back pain is frequently reported by astronauts during the early phase of spaceflight as they adapt to microgravity. The epidemiology of space adaptation back pain has not been well defined. This study aims to develop a case definition of space adaptation back pain, determine its incidence, and assess the effectiveness of available treatments. METHODS: Medical records from the Mercury, Apollo, Apollo-Soyuz Test Project (ASTP), Skylab, Mir, International Space Station (ISS), and Shuttle programs were reviewed. All episodes of in-flight back pain that met the criteria for space adaptation back pain were recorded. Pain characteristics, including intensity, location, and duration of the pain, were noted. The effectiveness of specific treatments was also recorded. RESULTS: The incidence of space adaptation back pain among astronauts was determined to be 52% (382/728). Most of the affected astronauts reported mild pain (86%). Moderate pain was reported by 11% of the affected astronauts and severe pain was reported by 3% of the affected astronauts. The most effective treatments were fetal positioning (91%) and the use of analgesic medications and exercise (primarily treadmill and cycle ergometer), which were both 85% effective. DISCUSSION: This retrospective study examines the epidemiology of space adaptation back pain. Space adaptation back pain is usually mild and self-limited. However, there is a risk of functional impairment and mission impact in cases of moderate or severe pain that do not respond to currently available treatments. Therefore, the development of preventive measures and more effective treatments should be pursued.

Medical monitoring during the NASA Artificial Gravity-Bed Rest Pilot Study.

The NASA artificial gravity-bed rest pilot study (AGPS) was designed to investigate the efficacy of daily exposure to a +Gz acceleration gradient for counteracting the physiologic decrements induced by prolonged bed rest. Test subjects were continuously monitored by a physician for signs and symptoms of pre-syncope, motion sickness, and arrhythmias while on the centrifuge. In this article, we have summarized the medical monitoring observations that were made during the AGPS and included an assessment of the relative usefulness of the information provided by the various monitoring tools in making a decision to terminate a centrifuge spin.