INTRODUCTION: The Hypobaric Decompression Sickness (DCS) Treatment Model links a decrease in computed bubble volume from increased pressure (P), increased oxygen (O₂) partial pressure, and passage of time during treatment to the probability of symptom resolution [P(SR)]. The decrease in offending volume is realized in two stages: 1) during compression via Boyles law; and 2) during subsequent dissolution of the gas phase via the oxygen window.METHODS: We established an empirical model for the P(SR) while accounting for multiple symptoms within subjects. The data consisted of 154 cases of hypobaric DCS symptoms with ancillary information from tests on 56 men and 18 women.RESULTS: Our best estimated model is P(SR) 1/(1exp((ln(P) 1.510 0.795 AMB 0.00308 Ts)/0.478)), where P is pressure difference (psid); AMB 1 if ambulation took place during part of the altitude exposure, otherwise AMB 0; and Ts is the elapsed time in minutes from the start of altitude exposure to recognition of a DCS symptom.DISCUSSION: Values of P as inputs to the model would be calculated from the Tissue Bubble Dynamics Model based on the effective treatment pressure: P P2 P1 | P1 V1/V2 P1, where V1 is the computed volume of a bubble at low pressure P1 and V2 is computed volume after a change to a higher pressure P2. If 100% ground-level oxygen was breathed in place of air, then V2 continues to decrease through time at P2 at a faster rate.Conkin J, Abercromby AFJ, Dervay JP, Feiveson AH, Gernhardt ML, Norcross JR, Ploutz-Snyder R, Wessel JH III. Hypobaric decompression sickness treatment model. Aerosp Med Hum Perform. 2015; 86(6):508517.

INTRODUCTION: The main aim of this study was to differentiate the magnitude of a pilot’s heart rate variability (HRV) when performing assisted and unassisted flights, as well as simple and complex flight tasks.METHODS: Cardiac monitoring in flights was carried out using a compact, mobile ECG recorder. A frequency analysis of the heart rate (HR) signal was performed to determine the ratio of low-frequency spectral power (LF) to high-frequency spectral power (HF).RESULTS: The LF/HF ratio observed in the zone (M = 1.047, SD = 0.059) was significantly different than the LF/HF calculated preflight (M = 0.877, SD = 0.043) and postflight (M = 0.793, SD = 0.037). There was no main effect of the flight type (unassisted zone flight vs. zone flight with an instructor) on the LF/HF parameter. However, greater psychophysiological load of a pilot was observed in the training zone flights when compared to simple circle flights (main effect of the flight type).CONCLUSIONS: As the LF/HF ratio turned out to be significantly higher in the zone than pre- and postflight, this parameter can be useful for predicting the risk of excessive stress and arousal of pilots during flights. Based on the LF/HF ratio we can also estimate difficulty level of flight tasks, because our research has shown higher values of this parameter in the training zone flights than in simple circle flights.Skibniewski FW, Dziuda Ł, Baran PM, Krej MK, Guzowski S, Piotrowski MA, Truszczyński OE. Preliminary results of the LF/HF ratio as an indicator for estimating difficulty level of flight tasks. Aerosp Med Hum Perform. 2015; 86(6):518–523.

PURPOSE: The objective of the study was to evaluate the effect of short-term, head-down bed rest (HDBR), with and without artificial gravity countermeasures, on splanchnic and lower limb vein properties.METHODS: Data were collected from 12 men before and after 5 d of continuous −6° HDBR without countermeasures (CON) and with two artificial gravity countermeasure protocols: 30-min continuous centrifugation (AG1), and 30-min intermittent centrifugation (AG2). Portal (PV), tibial (TibV), and gastrocnemius (GastV) veins were investigated by echography supine and after 30 min of head-up tilt.RESULTS: After HDBR, there was no change in PV, TibV, or GastV cross-sectional area at rest in any of the three conditions. In response to tilt, GastV and TibV area increased (168 ± 141% and 192 ± 124%, respectively) with no change in this response post-HDBR in any of the experimental conditions (P > 0.05). PV area decreased with tilt (−33 ± 13%) and was not different pre- to post-HDBR in the CON or AG1 conditions. However, there was a greater reduction in PV area in the AG2 group post-HDBR (−32 ± 10% pre, −49 ± 9% post-HDBR, P = 0.003).CONCLUSIONS: Calf veins were not significantly affected by 5 d of HDBR and did not appear to be negatively impacted by the artificial gravity countermeasures over this time period. In addition, the intermittent protocol resulted in better splanchnic vasoconstriction in response to head-up tilt, which may have contributed to a better maintenance of orthostatic tolerance post-HDBR.Provost RM, Zuj KA, Arbeille P. 5-day bed rest: portal and lower limb veins with and without artificial gravity countermeasures. Aerosp Med Hum Perform. 2015; 86(6):524–528.

BACKGROUND: Hypoxia-induced elevation in pulmonary artery pressure during air travel may contribute to the worldwide burden of in-flight medical emergencies. The pulmonary artery pressure response may be greater in older passengers, who are more likely to require flight diversion due to a medical event. Understanding these effects may ultimately improve the safety of air travel.METHODS: We studied 16 healthy volunteers, consisting of a younger group (aged < 25 yr) and an older group (aged > 60 yr). Using a hypobaric chamber, subjects undertook a 2-h simulated flight at the maximum cabin pressure altitude for commercial airline flights (8000 ft; 2438 m). Higher and lower altitudes within the aeromedical range were also explored. Systolic pulmonary artery pressure (sPAP) was assessed by Doppler echocardiography.RESULTS: There was a progressive increase in sPAP which appeared to be biphasic, with a small initial increase and a larger subsequent rise. Overall, sPAP increased by 5 ± 1 mmHg from baseline to 35 ± 1 mmHg at 8000 ft, an increase of 18%. The sPAP response to 8000 ft was greater in the older group than the younger group.CONCLUSIONS: This study confirms that pulmonary artery pressure increases during simulated air travel, and provides preliminary evidence that this response is greater in older people. Advancing age may increase in-flight susceptibility to adverse pulmonary vascular responses in passengers, aircrew, and aeromedical patients.Turner BE, Hodkinson PD, Timperley AC, Smith TG. Pulmonary artery pressure response to simulated air travel in a hypobaric chamber. Aerosp Med Hum Perform. 2015; 86(6):529–534.

INTRODUCTION: The dose-effect relationships between different levels of hypergravity (> +1.0 G_z) and steady-state hemodynamic parameters have been reported in several studies. However, little has been reported on the dose-effect relationship between hypergravity levels and estimates of autonomic circulatory regulation, such as heart rate variability, arterial pressure variability, and spontaneous cardiac baroreflex sensitivity. We investigated dose-effect relationships between hypergravity levels from +1.0 G_z to +2.0 G_z (0.5 G_z) and autonomic circulatory regulation to test our hypothesis that autonomic circulatory regulation has a linear relationship with hypergravity levels.METHODS: Using a short-arm human centrifuge, 10 healthy seated men were subjected to +1.0 G_z, +1.5 G_z, and +2.0 G_z hypergravity. We evaluated steady-state hemodynamic parameters and autonomic circulatory regulation indices. Heart rate variability, arterial pressure variability, and spontaneous cardiac baroreflex sensitivity between arterial pressure and R-R interval variabilities were assessed by spectral analysis, sequence analysis, and transfer function analysis.RESULTS: Steady-state heart rate, stroke volume, and sequence slope (indicating spontaneous cardiac baroreflex sensitivity in response to rapid changes in arterial pressure) showed linear correlations with increases in gravity (from +1.0 G_z to +2.0 G_z). On the other hand, steady-state cardiac output, steady-state systolic arterial pressure, and low-frequency power of diastolic arterial pressure (indicating peripheral vasomotor sympathetic activity) remained unchanged with gravity increases.CONCLUSION: Contrary to our hypothesis, the present study suggested that autonomic circulatory regulations show complex changes with hypergravity levels. Spontaneous cardiac baroreflex sensitivity reduces in a dose-dependent manner from +1.0 G_z to +2.0 G_z, whereas peripheral vasomotor sympathetic activity seems to be maintained.Ueda K, Ogawa Y, Yanagida R, Aoki K, Iwasaki K. Dose-effect relationship between mild levels of hypergravity and autonomic circulatory regulation. Aerosp Med Hum Perform. 2015; 86(6):535540.

Background: The prevalence of low back pain (LBP) for astronauts in space (68%) is higher than the 1-mo prevalence for the general population on Earth (39%). It is unclear whether differences occur between healthy subjects and astronauts with a history of LBP. Knowledge of this issue is important to assess whether a history of LBP could have an operational impact.Methods: We evaluated LBP prospectively during short duration spaceflight (15 d; N = 20) and compared this with similar data collected during two bed rest studies (N = 40). Astronauts completed a questionnaire 5–10 d preflight, during each flight day, and 5–10 d postflight.Results: All astronauts with a history of LBP also developed LBP in flight. These astronauts reported a significantly longer duration of LBP and a different pain location. LBP was most often experienced in the central area of the lower back during spaceflight with an incidence of 70% and a mean pain level of 3 (on a scale of 0–10). Pain resolved within 10 d of flight. No neurological signs were present. The most frequently reported countermeasure was assuming a “knees to chest (fetal tuck) position” combined with stretching. Greater LBP intensity was reported in spaceflight than bed rest with a trend indicating a greater number of days of pain during spaceflight.Discussion: The current study represents a prospective study of LBP in spaceflight. The results indicate that LBP is self-limiting in spaceflight and should not pose an operational risk. Prior LBP on Earth appears to be a risk factor for LBP in spaceflight.Pool-Goudzwaard AL, Belavý DL, Hides JA, Richardson CA, Snijders CJ. Low back pain in microgravity and bed rest studies. Aerosp Med Hum Perform. 2015; 86(6):541–547.

BACKGROUND: Future space exploration, such as a mission to Mars, will require space crews to live and work in extreme environments unlike those of previous space missions. Extreme conditions such as prolonged confinement, isolation, and expected communication time delays will require that crews have a higher level of interpersonal compatibility and be able to work autonomously, adapting to unforeseen challenges in order to ensure mission success. Team composition, or the configuration of member attributes, is an important consideration for maximizing crewmember well-being and team performance.METHODS: We conducted an extensive search to find articles about team composition in long-distance space exploration (LDSE)-analogue environments, including a search of databases, specific relevant journals, and by contacting authors who publish in the area.RESULTS: We review the team composition research conducted in analogue environments in terms of two paths through which team composition is likely to be related to LDSE mission success, namely by 1) affecting social integration, and 2) the team processes and emergent states related to team task completion.DISCUSSION: Suggestions for future research are summarized as: 1) the need to identify ways to foster unit-level social integration within diverse crews; 2) the missed opportunity to use team composition variables as a way to improve team processes, emergent states, and task completion; and 3) the importance of disentangling the effect of specific team composition variables to determine the traits (e.g., personality, values) that are associated with particular risks (e.g., subgrouping) to performance.Bell ST, Brown SG, Abben DR, Outland NB. Team composition issues for future space exploration: a review and directions for future research. Aerosp Med Hum Perform. 2015; 86(6):548–556.

INTRODUCTION: Although once a widely speculated about and largely theoretical topic, spaceflight-induced intracranial hypertension has gained acceptance as a distinct clinical phenomenon, yet the underlying physiological mechanisms are still poorly understood. In the past, many terms were used to describe the symptoms of malaise, nausea, vomiting, and vertigo, though longer duration spaceflights have increased the prevalence of overlapping symptoms of headache and visual disturbance. Spaceflight-induced visual pathology is thought to be a manifestation of increased intracranial pressure (ICP) because of its similar presentation to cases of known intracranial hypertension on Earth as well as the documentation of increased ICP by lumbar puncture in symptomatic astronauts upon return to gravity. The most likely mechanisms of spaceflight-induced increased ICP include a cephalad shift of body fluids, venous outflow obstruction, blood-brain barrier breakdown, and disruption to CSF flow. The relative contribution of increased ICP to the symptoms experienced during spaceflight is currently unknown, though other factors recently posited to contribute include local effects on ocular structures, individual differences in metabolism, and the vasodilator effects of carbon dioxide. This review article attempts to consolidate the literature regarding spaceflight-induced intracranial hypertension and distinguish it from other pathologies with similar symptomatology. It discusses the proposed physiological causes and the pathological manifestations of increased ICP in the spaceflight environment and provides considerations for future long-term space travel. In the future, it will be critical to develop countermeasures so that astronauts can participate at their peak potential and return safely to Earth.Michael AP, Marshall-Bowman K. Spaceflight-induced intracranial hypertension. Aerosp Med Hum Perform. 2015; 86(6):557–562.

BACKGROUND: Pilots of fixed wing commercial aircraft face numerous occupational hazards. Low back pain is among the most common and costly workplace injury, though relatively little is known about causes of back injuries among pilots. The awkward lifting and twisting maneuvers in the flight deck to position flight bags has not been described as a cause of occupational back injury among pilots.METHODS: A case series of low back injuries among pilots was identified and described by a retrospective review of charts at an airport-based clinic. Circumstances of occupational back injury, initial direct medical costs, treatment, and work status following evaluation were described.RESULTS: Over a 6-yr period, 37 occupational low back injuries among 35 pilots were evaluated and treated. Of these, 24 (65%) involved flight bags. Only 27% of pilots with flight bag-associated injuries were returned to work after initial evaluation; medications with sedating properties were frequently required for treatment. Injuries due to slips, trips, and falls, typically in jet bridges or associated with hotel shuttles, were common among pilots with back injuries not related to flight bags.CONCLUSIONS: The majority of occupational low back injuries seen among pilots in an airport based clinic were attributable to use of flight bags. Substituting electronic flight bags for traditional flight bags could contribute to back injury prevention among pilots.Kanumuri VSR, Zautke JL, Dorevitch S. Flight bags as a cause of back injuries among commercial pilots. Aerosp Med Hum Perform. 2015; 86(6):563–566.

BACKGROUND: Assessment of the influence of personality and decision processes on the performance of two-person expedition teams has application for the composition of small teams for planetary exploration and potentially responding to off-nominal situations.CASE REPORT: We studied a two-man Special Forces team with a goal of reaching the North Pole in the shortest amount of time. Both subjects had high scores on measures of leadership/dominance, fearlessness, and achievement, and low scores on harm avoidance (high risk-taking). Differences were noted on scales measuring empathy, agreeableness, extraversion, emotional regulation, and callousness. Individual differences in the primacy of personal values of tradition vs. pleasure-seeking were evident.DISCUSSION: High dominance traits of both team members, incompatibility in other characteristics and values, and minimal pretraining had a significant impact on the decision to abort the trek because of severe frostbite suffered by one subject. Implications for dyads exploring the Mars surface are discussed.Leon GR, Venables NC. Fearless temperament and overconfidence in an unsuccessful special forces polar expedition. Aerosp Med Hum Perform. 2015; 86(6):567–570.

INTRODUCTION: Medical Guidelines for Airline Travel provide information that enables healthcare providers to properly advise patients who plan to travel by air. Although there are no publicly available databases providing information on the number of in-flight medical emergencies, the few studies published in the literature indicate that they are uncommon. Minor illnesses such as near-fainting, dizziness, and hyperventilation occur more frequently. However, serious illnesses, such as seizures and myocardial infarction, also occur. In-flight deaths are also rare.Thibeault C, Evans AD. AsMA medical guidelines for air travel: Reported in-flight medical events and death. Aerosp Med Hum Perform. 2015; 86(6):571.

INTRODUCTION: Medical Guidelines for Airline Travel provide information that enables healthcare providers to properly advise patients who plan to travel by air. All airlines are required to provide first aid training for cabin crew, and the crew are responsible for managing any in-flight medical events. There are also regulatory requirements for the carriage of first aid and medical kits. AsMA has developed recommendations for first aid kits, emergency medical kits, and universal precaution kits.Thibeault C, Evans AD, Pettyjohn FS, Alves PM. AsMA medical guidelines for air travel: In-flight medical care. Aerosp Med Hum Perform. 2015; 86(6):572–573.

Tontz RC. You're the flight surgeon: complex regional pain syndrome. Aerosp Med Hum Perform. 2015; 86(6):574–577.

Mulagha EH. You’re the flight surgeon: cholelithiasis. Aerosp Med Hum Perform. 2015; 86(6):577–580.