Acceptable Limits for n-Hexane in Spacecraft Atmospheres

INTRODUCTION:The Spacecraft Maximum Allowable Concentrations (SMACs) for C2-C9 alkanes set by NASA in 2008 under the guidance and approval of the National Research Council specifically excluded SMACs for n-hexane. Unlike other C2-C9 alkanes, n-hexane can cause polyneuropathy after metabolism in humans or rodents and so requires more stringent SMACs than the other members of this group do. This document reviews the relevant published studies of n-hexane toxicity to develop exposure duration-specific SMACs for n-hexane of 200 ppm for 1 hour, 30 ppm for 24 hours, and 2.4 ppm for 7 days, 30 days, 180 days, and 1000 days.Garcia HD. Acceptable limits for n-hexane in spacecraft atmospheres. Aerosp Med Hum Perform. 2021; 92(12):956–961.

Aeromedical Decision Making for Military Aircrew with Graves’ Disease

BACKGROUND: Graves’ Disease (GD) is a common cause of hyperthyroidism. Although definitive treatment with radioactive iodine (RAI) is preferred for military aircrew, there are cultural and individual differences in receptivity toward RAI, and clinical guidelines that recommend antithyroid drugs (ATD) as the first line therapy. We examined a case series of Republic of Singapore Air Force (RSAF) aviators with GD treated with ATD and the impact of their condition on aeromedical disposition.CASE SERIES: All RSAF aircrew diagnosed with GD and treated with ATD over a 15-yr period were retrospectively identified and analyzed to determine the impact on their fitness for flying duties. The mean age of the 13 aircrew was 33 ± 7.1 yr (range, 25–47 yr), with 11 (84.6%) being males. There were 10 (76.9%) who had ATD as the only treatment while 3 (23.1%) were initially treated with ATD but subsequently underwent RAI or surgery. Of the 10 treated with only ATD, 3 (30.0%) were returned to restricted flying, 6 (60.0%) were returned to unrestricted flying, and 1 (10.0%) is still undergoing ATD titration. There were 10 (76.9%) aircrew who were returned to some form of flying duties while on low doses of ATD.DISCUSSION: This case series suggests that ATD is a viable treatment modality in the aeromedical management of military aviators with GD and it is possible to return military aircrew on a stable maintenance dose of ATD to flying duties. A framework is proposed to support the aeromedical decision-making process for military aircrew in the treatment of GD.Loh EH-T, Soh FW, See B, Tan BBC. Aeromedical decision making for military aircrew with Graves’ disease. Aerosp Med Hum Perform. 2021; 92(12):980–986.

Excessive Daytime Sleepiness and Associated Factors in Military Search and Rescue Personnel

BACKGROUND: Abnormal excessive daytime sleepiness (EDS) has been reported worldwide, but too little is known about EDS and its determinants in Search and Rescue (SAR) populations. We aimed to determine the prevalence of abnormal EDS and contributing factors among Royal Norwegian Air Force (RNoAF) SAR helicopter personnel.METHODS: In this cross-sectional study, a total of N = 175 RNoAF SAR personnel completed an electronic survey including socio-demographic and lifestyle questions. The Epworth Sleepiness Scale (ESS) was used as both a continuous and categorical outcome variable to measure EDS.RESULTS: Abnormal EDS defined by ESS was found in 41% of the participants in this study. We observed no associations between socio-demographic and lifestyle factors and abnormal EDS in this study. DISCUSSION: There is a high prevalence of abnormal EDS in the current RNoAF SAR population. Despite this elevated level of fatigue, we did not find that the socio-demographic and lifestyle factors assessed in this study were associated with abnormal EDS in RNoAF SAR helicopter personnel. Also unusually, the study cohort did not demonstrate higher scores in factors found to change ESS scores in similar study populations (e.g., caffeine use, tobacco use, exercise level). Further research is required to investigate other factors (organizational, operational) that may be associated with abnormal EDS in this and other SAR populations.Akter R, Larose TL, Sandvik J, Fonne V, Meland A, Wagstaff AS. Excessive daytime sleepiness and associated factors in military search and rescue personnel. Aerosp Med Hum Perform. 2021; 92(12):975–979.

Fuel Planning Errors in General Aviation from 2015 to 2020

BACKGROUND: Planning, whether preflight or in-flight, is a cause of accident that is presumably almost entirely preventable. Planning skills on the part of the pilot should assist in avoiding dangerous situations with regards to light conditions, weather, fuel shortage, and/or improper weight and balance. Fuel planning is noted as especially unnecessary, as fuel planning is not considered a complex skill but part of proper flight preparation and in-flight planning.METHODS: A total of 196 accident reports from 2015 until 2020 were extracted from the NTSB online database in which the probable cause included either preflight or in-flight planning as a cause attributed to the pilot. Of those accidents, the majority (N = 131, 67%) were attributed to fuel planning and were further analyzed.RESULTS: Fuel-planning related accidents were significantly less often fatal compared to all planning-related accidents and all fuel-related accidents. The majority of fuel planning accidents resulted in fuel exhaustion. Additionally, the cause attributed to the accidents was frequently the skill-based error of “fuel planning (pilot)” and the crew resource management issue of “fuel-fluid level”. Specific information regarding the pilot’s fuel plan was only available in 52 (40%) of the accident reports.CONCLUSIONS: The frequency of fuel-related planning accidents suggests that this aspect of pilotage is underestimated and requires more attention both in training and in standard operating procedures. In particular, more detailed information regarding the pilot’s fuel plan is necessary in order to determine which step in the process most frequently results in an accident.Kalagher H. Fuel planning errors in general aviation from 2015 to 2020. Aerosp Med Hum Perform. 2021; 92(12):970–974.

Sleep Disorders Among Commercial Airline Pilots

BACKGROUND: Over the next 20 yr, international market expansion will necessitate the production of new commercial airplanes and the recruitment of additional crewmembers and technicians. Research has proven that fatigue and lack of sleep are risk factors for impaired cognitive performance and human error. Pilots frequently report fatigue to their employers, which may be related to sleep disturbance. Airline pilots, in particular, often experience circadian desynchronization and other types of sleep disorders. Shift workers have been observed to be at higher risk of fatigue that affects their performance and alertness. In Saudi Arabia, sleep disorders among airline pilots are understudied and underreported. The primary objective of this study was to screen for and determine the risk of sleep disorders, fatigue, and depression among pilots.METHODS: A cross-sectional epidemiological study with national commercial pilots was conducted from March 2019 to March 2020 using validated questionnaires to screen for the risk of sleep disorders, fatigue, and depression.RESULTS: In total, 344 pilots participated in the study. Half the sample was at risk for insomnia and fatigue. Older and more experienced pilots were less likely to suffer impaired sleep quality, insomnia, sleepiness, fatigue, and depression. In total, 59 (17.2%) pilots were at high risk for sleep apnea.CONCLUSION: The current study found that pilots were at risk of developing sleep disorders. A more robust and objective assessment is warranted for screening.Alzehairi A, Alhejaili F, Wali S, Al Qassas I, Balkhyour M, Pandi-Perumal SR. Sleep disorders among commercial airline pilots. Aerosp Med Hum Perform. 2021; 92(12):937–944.

Grounding of Pilots: Medical Reasons and Recommendations for Prevention

BACKGROUND: This article presents the results of an EASA-commissioned study aimed at analyzing the medical causes of grounding of a broad European pilot population and recommending measures to reduce the risk of in-flight incapacitation in commercial air transport pilots.METHOD: European National Aviation Authorities (NAAs) were requested to provide data concerning the total number of pilots that were examined, their age and license category, number of unfit pilots, and the medical causes of each case of grounding. Diagnoses were classified according to the format and definitions laid down in Commission Regulation (EU) No. 1178/2011 Part Med.RESULTS: Analyzed were 82,435 cases assessed by 6 NAAs. Of these cases, 2.1% were assessed as unfit to fly. Frequent causes for grounding a pilot were cardiovascular (19%), psychiatric (11%), neurological (10%), and psychological (9%). Cardiovascular conditions were the most frequent cause for grounding in the older age groups, with 21% in the age 51–60 cohort, 28% in the age 61–65 cohort, and 48% in those beyond 65 yr. Psychiatric and psychological diagnoses were most frequent in the age 20–40 cohort.DISCUSSION: Cardiovascular conditions were the most frequent cause for grounding. Cardiovascular diseases (CVD) are associated with modifiable risk factors. Tackling these risk factors gives aeromedical examiners the opportunity to improve the health of pilots and reduce CVD-related flight safety risks by reducing the number of pilots at risk of in-flight incapacitation. The mandatory periodical medical examination of pilots provides an excellent framework for risk prevention and follow-up of preventive measures.Simons R, Maire R, Van Drongelen A, Valk P. Grounding of pilots: medical reasons and recommendations for prevention. Aerosp Med Hum Perform. 2021; 92(12):950–955.

Oculometric Feature Changes During Acute Hypoxia in a Simulated High-Altitude Airdrop Scenario

BACKGROUND: Severe acute hypoxia results in a rapid deterioration of cognitive functioning and thus poses a risk for human operations in high altitude environments. This study aimed at investigating the effects of oxygen system failure during a high-altitude high-opening (HAHO) parachute jump scenario from 30,000 ft (9144 m) on human physiology and cognitive performance using a noncontact eye-tracking task.METHODS: Nine healthy male volunteers (ages 27–48) were recruited from the Norwegian Special Operations Commandos. Eye-tracking data were collected to derive information on cognitive performance in the context of rapid dynamic changes in pressure altitude while performing a modified King-Devick test. The baseline data was collected at 8000 ft (2438 m) while breathing 100% oxygen during decompression. For every test, the corresponding arterial blood gas analysis was performed.RESULTS: The study subjects endured severe hypoxia, which resulted in significant prolongations of fixation time (range: 284.1–245.6 ms) until 23,397 ft (131 m) and fixation size (range: 34.6–32.4 mm) until 25,389 ft (7739 m) as compared to the baseline (217.6 ± 17.8 ms and 27.2 ± 4.5 mm, respectively). The increase in the saccadic movement and decrease in the saccadic velocity was observed until 28,998 ft and 27,360 ft (8839 and 8339 m), respectively.DISCUSSION: This is the first study to investigate cognitive performance from measured oculometric variables during severe hypobaric hypoxia in a simulated high-altitude airdrop mission scenario. The measurement of altered oculometric variables under hypoxic conditions represents a potential avenue to study altered cognitive performance using noncontact sensors that can derive information and serve to provide the individual with a warning from impending incapacitation.Pradhan GN, Ottestad W, Meland A, Kåsin JI, Høiseth LØ, Cevette MJ, Stepanek J. Oculometric feature changes during acute hypoxia in a simulated high-altitude airdrop scenario. Aerosp Med Hum Perform. 2021; 92(12):928–936.

Persistent and Emergent Clinical Sequelae of Mild COVID-19

BACKGROUND: Knowledge of the clinical course and consequences of COVID-19 initially evolved in the context of severe presentations and among those with comorbidities. However, understanding the outcomes of milder infections in healthy individuals is important for safe return-to-duty in extreme environments or to occupations requiring significant fitness. We reviewed the literature to characterize the nature and timing of persistent and emergent clinical sequelae in milder COVID-19 cases to facilitate development of post-COVID-19 screening and surveillance protocols.METHODS: We searched databases including EMBASE, MEDLINE, Cochrane COVID-19 study register, gray literature, clinical trial registries, and relevant health and disease prevention sources for publications from 2019 to February 18th, 2021, documenting COVID-19 sequelae. Articles were included if the COVID-19 severity was mild and there were no, or only minor, pre-existing comorbidities. Persistent and emergent sequelae were then stratified based on time since diagnosis.RESULTS: Among those with mild COVID-19, sequelae were shown to emerge or persist for months following presumed recovery. Among those with no comorbidities, cardiac, hematological, and respiratory sequelae emerged after 1-2 mo, and primarily cardiac abnormalities persisted at ≥ 3 mo. Among those with minor comorbidities, persistent respiratory abnormalities, fatigue, dyspnea, and headache were common, and mental health symptoms emerged by 1-2 mo postinfection.DISCUSSION: After presumed recovery from mild COVID-19, a range of symptoms can persist and later emerge. Whether these are new or previously unrecognized is unclear. Under-recognized COVID-19 sequelae may increase the risk of subtle or sudden incapacitation and have implications for return-to-work (RTW) screening and surveillance for safety-critical roles.Tucci V, Saary J. Persistent and emergent clinical sequelae of mild COVID-19. Aerosp Med Hum Perform. 2021; 92(12):962–969.