BACKGROUND: Persistent headward fluid shift and mechanical unloading cause neuro-ocular, cardiovascular, and musculoskeletal deconditioning during long-term spaceflight. Lower body negative pressure (LBNP) reintroduces footward fluid shift and mechanical loading.METHODS: We designed, built, and tested a wearable, mobile, and flexible LBNP device (GravitySuit) consisting of pressurized trousers with built-in shoes to support ground reaction forces (GRF) and a thoracic vest to distribute load to the entire axial length of the body. In eight healthy subjects we recorded GRF under the feet and over the shoulders (Tekscan) while assessing cardiovascular response (Nexfin) and footward fluid shift from internal jugular venous cross-sectional area (IJVa) using ultrasound (Terason).RESULTS: Relative to normal bodyweight (BW) when standing upright, increments of 10 mmHg LBNP from 0 to 40 mmHg while supine induced axial loading corresponding to 0%, 13 ± 3%, 41 ± 5%, 75 ± 11%, and 125 ± 22% BW, respectively. Furthermore, LBNP reduced IJVa from 1.12 ± 0.3 cm² to 0.67 ± 0.2, 0.50 ± 0.1, 0.35 ± 0.1, and 0.31 ± 0.1 cm², respectively. LBNP of 30 and 40 mmHg reduced cardiac stroke volume and increased heart rate while cardiac output and mean arterial pressure were unaffected. During 2 h of supine rest at 20 mmHg LBNP, temperature and humidity inside the suit were unchanged (23 ± 1°C; 47 ± 3%, respectively).DISCUSSION: The flexible GravitySuit at 20 mmHg LBNP comfortably induced mechanical loading and desired fluid displacement while maintaining the mobility of hips and knee joints. The GravitySuit may provide a feasible method to apply low-level, long-term LBNP without interfering with daily activity during spaceflight to provide an integrative countermeasure.Petersen LG, Hargens A, Bird EM, Ashari N, Saalfeld J, Petersen JCG. Mobile lower body negative pressure suit as an integrative countermeasure for spaceflight. Aerosp Med Hum Perform. 2019; 90(12):993–999.

INTRODUCTION: Designed as a more ecological measure of reaction times, the Perception-Action Coupling Task (PACT) has shown good reliability and within-subject stability. However, a lengthy testing period was required. Perceptual-motor judgments are known to be affected by proximity of the stimulus to the action boundary. The current study sought to determine the effects of action boundary proximity on PACT performance, and whether redundant levels of stimuli, eliciting similar responses, can be eliminated to shorten the PACT.METHODS: There were 9 men and 7 women who completed 4 testing sessions, consisting of 3 familiarization cycles and 6 testing cycles of the PACT. For the PACT, subjects made judgments on whether a series of balls presented on a tablet afford “posting” (can fit) through a series of apertures. There were 8 ratios of ball to aperture size (B-AR) presented, ranging from 0.2 to 1.8, with each ratio appearing 12 times (12 trials) per cycle. Reaction times and judgment accuracy were calculated, and averaged across all B-ARs. Ratios and individual trials within each B-AR were systematically eliminated. Variables were re-averaged, and intraclass correlation coefficients (ICC) and coefficients of variation (CV_TE) were calculated in an iterative manner.RESULTS: With elimination of the 0.2 and 1.8 B-ARs, the PACT showed good reliability (ICC = 0.81–0.99) and consistent within-subject stability (CV_TE = 2.2–14.7%). Reliability (ICC = 0.81–0.97) and stability (CV_TE = 2.6–15.6%) were unaffected with elimination of up to 8 trials from each B-AR.DISCUSSION: The shortened PACT resulted in an almost 50% reduction in total familiarization/testing time required, significantly increasing usability.Johnson CD, LaGoy AD, Pepping G-J, Eagle SR, Beethe AZ, Bower JL, Alfano CA, Simpson RJ, Connaboy C. Action boundary proximity effects on perceptual-motor judgments. Aerosp Med Hum Perform. 2019; 90(12):1000–1008.

BACKGROUND: Portable noninvasive Heart Rate Complexity (HRC) and Compensatory Reserve Measurement (CRM) monitors have been developed to triage supine combat casualties. Neither monitor has been tested in upright individuals during physical exercise. This study tests the hypothesis that exercise evokes proportional changes in HRC and CRM.METHODS: Two instruments monitored volunteers (9 civilian and 11 soldiers) from the Army Trauma Training Department (ATTD) before, during, and following physical exercise. One recorded heart rate (HR, bpm), cardiac output (CO, L · min⁻¹), heart rate variability (HRV, root mean square of successive differences, ms), and HRC (Sample Entropy, unitless). The other recorded HR, pulse oximetry (S_po₂, %), and CRM (%).RESULTS: Baseline HR, CO, HRV, HRC, and CRM averaged 72 ± 1 bpm, 5.6 ± 1.2 L · min⁻¹, 48 ± 24 ms, 1.9 ± 0.5, and 85 ± 10% in seated individuals. Exercise evoked peak HR and CO at > 200% of baseline, while HRC and CRM were simultaneously decreased to minimums that were ≤ 50% of baseline (all P < 0.001). HRV changes were variable and unreliable. S_po₂ remained consistently above 95%. During a 60 min recovery, HR and CRM returned to baseline on parallel tracks (t^1/2=11 ± 8 and 18 ± 14 min), whereas HRC recovery was slower than either CRM or HR (t^1/2=40 ± 18 min, both P < 0.05).DISCUSSION: Exercise evoked qualitatively similar changes in CRM and HRC. CRM recovered incrementally faster than HRC, suggesting that vasodilation, muscle pump, and respiration compensate faster than cardiac autonomic control in young, healthy volunteers. Both HRC and CRM appear to provide reliable, objective, and noninvasive metrics of human performance in upright exercising individuals.Mulder MB, Eidelson SA, Buzzelli MD, Gross KR, Batchinsky AI, Convertino VA, Schulman CI, Namias N, Proctor KG. Exercise-induced changes in compensatory reserve and heart rate complexity. Aerosp Med Hum Perform. 2019; 90(12):1009–1015.

BACKGROUND: Hemorrhage and traumatic brain injury can be lethal if left unattended. The transportation of severely wounded combat casualties from the battlefield to higher level of care via aeromedical evacuation (AE) may result in unintended complications. This could become a serious concern at the time of evacuation of mass casualties or for prolonged field care scenarios with limited resources.METHODS: Following instrumentation (t1), anesthetized Sprague-Dawley rats were injured or not [75-kPa blast and 30% estimated blood-volume controlled hemorrhage] (t2). After 15 min, all rats were resuscitated with saline. During the simulated 3-h evacuation, 8000 ft (2440 m) vs. sea-level heart rate, temperature, and oxygenation (S_po₂) were continuously recorded. One group of rats was euthanized immediately after evacuation (t3) and another after a 72-h recovery period (t4). Hematology and metabolic levels were measured at t1, t2, t3, and t4.RESULTS: Survival was 100% in control-uninjured animals, 83% in injured animals under normobaria, and significantly reduced to 50% under hypobaria. This AE setting resulted in significantly lower hemodynamics, thermoregulation, and oxygenation parameters in the animals under hypobaria than those under normobaria. The initial lower mean arterial pressure (MAP) with the reduced oxygen level before AE were critical factors for the survival of injured animals. We observed a general increase of white blood cells and platelet ability to aggregate at t4 in all experimental groups.CONCLUSION: Physiological parameters were affected during aeromedical evacuation in all groups. This was worsened for injured animals with MAP less than 60 mmHg associated with low S_po₂ in a simulated aeromedical evacuation. This represented a high risk of mortality for severely polytraumatized animals.Arnaud F, Pappas G, Maudlin-Jeronimo E, Goforth C. Simulated aeromedical evacuation in a polytrauma rat model. Aerosp Med Hum Perform. 2019; 90(12):1016–1025.

BACKGROUND: Current attempts to culturally tailor human factors training in aviation segregates cultural identities based on geopolitical, passport nationality, and is therefore poorly suited for (adult) ‘Third Culture Kids’ (TCKs) whose cross-cultural upbringing has led to the development of multicultural individual identities that do not reflect their passport nationalities. In this study, respondents’ self-categorization of personal cultural identity, as opposed to passport nationality, was used to determine whether there were cultural differences in airline pilots’ behaviors.METHOD: A survey with items imported from established scales was distributed to pilots of an international airline to measure pilots’ work values, flight management attitudes, and cultural dimensions, with respondents segregated into Western, TCK, or Asian cultural groups.RESULTS: TCKs shared similar work values with Westerners, were similarly individualistic, had comparable preference for shallow command gradients, were similarly pragmatic in self-evaluation of performance under stress, and both had lower dependency and preference for rules and procedures. TCKs scored in the middle between Westerners and Asians in automation preference attitudes, and on the cultural dimensions of power distance and uncertainty avoidance. TCKs did not share any similarities with Asians at all.DISCUSSION: The results show that TCKs were neither assimilated into a mainstream culture, nor culturally “middle of the pack” as may be expected from their “East meets West” backgrounds. Having identified TCK pilots’ unique values, attitudes, and dimensions, practical implications include changing training design to better suit TCKs’ cultural characteristics and the adaptation of airline management to cater for TCKs’ work values.Chan WT-K, Harris D. Third-culture kid pilots and multi-cultural identity effects on pilots’ attitudes. Aerosp Med Hum Perform. 2019; 90(12):1026–1033.

INTRODUCTION: The Statement of Demonstrated Ability (SODA) is a type of U.S. aeromedical waiver used for disqualifying conditions that are not expected to change. About 21,000 (2%) U.S. pilots possess a SODA waiver.METHODS: We matched all pilot medical exams from the FAA’s medical certification database from 2002 through 2011 to their respective accidents in the National Transportation Safety Board accident database. The association of SODA waivers and SODA conditions with the odds of an accident were explored using logistic regression techniques.RESULTS: For 3^rd class flight exams, the presence of a SODA waiver was not associated with the odds of an accident. For the 1^st and 2^nd class exams, the accident odds ratio (OR = 1.45) was statistically significant. Crop dusting operations accounted for 17 of the 40 accidents where SODAs were present and returned a significant accident OR = 1.68. SODAs were not associated with the odds of accidents during other commercial operations. Six SODA conditions (amputation, internal eye, external eye, visual fields, bone and joint, and miscellaneous) were also found to have elevated ORs but were based on very small accident counts. NTSB investigators and the authors reviewed all accidents and none thought the SODA condition to be contributory.DISCUSSION: SODA waivers were not associated with increased accident odds except for crop dusting operations. Six specific SODA conditions also had elevated odds of an accident, but there was no evidence they contributed to the accidents. Overall, U.S. pilots with SODA waivers appear to have a satisfactory safety record.Mills WD, Davis JT. U.S. Statement of Demonstrated Ability aeromedical waivers. Aerosp Med Hum Perform. 2019; 90(12):1034–1040.

INTRODUCTION: Effects of breathing gas with elevated oxygen partial pressure (Po₂) and/or elevated inspired oxygen fraction (F_Io₂) at sea level or higher is discussed. High F_Io₂ is associated with absorption problems in the lungs, middle ear, and paranasal sinuses, particularly if F_Io₂ > 80% and small airways, Eustachian tubes, or sinus passages are blocked. Absorption becomes faster as cabin altitude increases. Pulmonary oxygen toxicity and direct oxidative injuries, related to elevated Po₂, are improbable in flight; no pulmonary oxygen toxicity has been found when Po₂ < 55 kPa [418 Torr; 100% O₂ higher than 15,000 ft (4570 m)]. Symptoms with Po₂ of 75 kPa [520 Torr; 100% O₂ at 10,000 ft (3050 m)] were reported after 24 h and the earliest signs at Po₂ of 100 kPa (760 Torr, 100% O₂ at sea level) occurred after 6 h. However, treatment for decompression sickness entails a risk of pulmonary oxygen toxicity. Elevated Po₂ also constricts blood vessels, changes blood pressure control, and reduces the response to low blood sugar. With healthy lungs, gas transport and oxygen delivery are not improved by increasing Po₂. Near zero humidity of the breathing gas in which oxygen is delivered may predispose susceptible individuals to bronchoconstriction.Shykoff BE, Lee RL. Risks from breathing elevated oxygen. Aerosp Med Hum Perform. 2019; 90(12):1041–1049.

BACKGROUND: In the last 10 yr, the number of ultra-haul flights—defined as flights greater than 12 h of flying time—has increased. While the medical complications of these flights are well-known, the underlying cellular effects are less clear. The primary objective of this study was to test the effects of extended mild hypobaric hypoxia on overall well-being and skeletal muscle morphology and macrophage populations.METHODS: A total of 22 male C57BL/6 mice were assigned to a normobaric (NB) or hypobaric (HB) chamber for 14–17 h. Overall mouse well-being and the general morphology and resident macrophage number in hindlimb muscles were compared between the two pressure conditions.RESULTS: During mild hypobaric hypoxia, the mice behaved normally and no changes were observed in general muscle morphology. Regarding resident macrophages, the mean antigen area of CD206 in the hindlimb muscles, lateral gastrocnemius (LG, 33.8 ± 2.0 vs. 35.3 ± 1.6), medial gastrocnemius (MG, 32.4 ± 1.6 vs. 32.6 ± 1.5), and quadriceps femoris (QF, 36.3 ± 1.2 vs. 34.3 ± 1.1) were similar between NB and HB conditions, and the number of CD68-positive cells in the LG and QF were similar between the two conditions. Significantly fewer CD206-positive cells were counted in the LG muscle under the HB condition.CONCLUSION: Our findings indicate that extended exposure to mild hypobaric hypoxia, similar to that of an ultra-long-haul flight, does not adversely affect healthy skeletal muscle.Zhang L, Soulakova J, St. Pierre Schneider B. Mild hypobaric hypoxia effects on murine skeletal muscle morphology and macrophages and well-being. Aerosp Med Hum Perform. 2019; 90(12):1050–1054.

BACKGROUND: This study aimed to investigate the relationships among ACTN-3, body composition, fitness, and +G_z tolerance for senior cadet training development and their safe task performance.METHODS: The subjects were all senior cadets (N = 68) at the Korea Air Force Academy. All cadets are required to pass a physical fitness test (3-km running, sit-ups, push-ups) and body composition test on a semiannual basis. Isokinetic muscle function (strength and endurance), +G_z test (+6 G_z ⋅ 30 s⁻¹), and target gene (ACTN-3) were analyzed.RESULTS: The effects of body composition and physical fitness along with the relationship of the ACTN-3 genotype to the +6 G_z test results were determined. Consequently, no significant difference was found concerning the effect of ACTN-3 on the +6 G_z test result, body composition, and physical fitness; however, body fat (%) and isokinetic muscle strength (peak torque right leg extension and left leg flexion) showed significance between the pass and failure groups in the +G_z test.DISCUSSION: The cadets of the Korea Air Force Academy showed dominant fast genetic expression type based on their ACTN-3 genotype [RR and RX (N = 51, 75%) > XX (N = 17, 25%)]. Body fat (%) and isokinetic muscle strength (PT R EX, L FL) can be more effective predictors in the +6 G_z test for cadet training. Another speculation is that more RR- and RX-type-oriented training can promote cadets’ G_z tolerance from the isokinetic factors such as high peak torque and low fatigue index.Shin S, Jee H. ACTN-3 genotype, body composition, fitness, and +G_z tolerance in senior cadets. Aerosp Med Hum Perform. 2019; 90(12):1055–1060.

BACKGROUND: Little consensus exists on the best practices for post-acute care of patients who suffer splenic injury but retain functional splenic tissue. Moreover, no published guidance or case reports exist for managing pilots in this demographic, making the flight surgeon’s task particularly difficulty as he/she attempts to apply the best available evidence for a patient population exposed to unique occupational hazards.CASE REPORT: We describe the case of an F-16 pilot who suffered a spontaneous splenic rupture due to infectious mononucleosis and required splenic artery embolization for hemodynamic stabilization. Despite the salvage of a significant portion of his spleen, the pilot was managed as an asplenic patient due to concern that: 1) splenic artery embolization compromised the function of his spleen; and 2) his status as a military aviator placed him at increased risk of infection due to frequent travel. He received appropriate vaccinations for an asplenic patient, fever precautions, and amoxicillin-clavulanic acid for immediate use if he developed fever. After discussion with the Aeromedical Consult Service, who felt the aviator had minimal risk of a poor outcome, he was returned to flying status. Since returning to flying status he has logged over 15 h of flight time, routinely experiencing 8–9 +G_z without difficulty.DISCUSSION: This case provides a successful approach to the management of pilots of high-performance aircraft who suffer splenic injury but retain functional splenic tissue, and provides precedent for safely returning these patients to flying status following recovery.Tanael M, Saul S. Navigating the management of an F-16 pilot following spontaneous splenic rupture. Aerosp Med Hum Perform. 2019; 90(12):1061–1063.

Searson-Norris L. You’re the flight surgeon: renal cell carcinoma. Aerosp Med Hum Perform. 2019; 90(12):1064–1068.