INTRODUCTION: To flip a switch “down,” our motor system can normally rely on concordant visual, gravitational, and egocentric cues about the vertical. However, divers must sometimes perform this task while visual cues are limited and gravitational cues are misaligned with egocentric cues. Astronauts must also flip switches “down” in absence of gravitational cues. Our study evaluates this ability using a laboratory simulation.METHODS: The subjects were 24 healthy volunteers who were blindfolded, tilted into different angles of roll, and asked to silence an alarm by flipping a switch “down.” The switch was constructed such that it could be flipped in any direction in the subjects’ frontal plane.RESULTS: Two subjects deflected the switch in accordance with the direction of gravity, irrespective of their body orientation. Twenty subjects deflected it in accordance with their body orientation, irrespective of the direction of gravity. The remaining two persons could not be classified unequivocally. Notably, some egocentric responders deflected the rod consistently toward their feet, but others deflected it consistently toward other parts of their body.DISCUSSION: Since our findings disagree with perceptual studies where gravitational rather than egocentric cues predominated in the absence of vision, we posit that perception and action may access distinct internal representations of the vertical. On the practical side, our findings indicate that designers of spaceflight and underwater equipment should not rely on divers’ intuitive knowledge on how to flip a switch “down.”Bock O, Bury N. Flipping a switch “down” when not aligned with the gravitational vertical. Aerosp Med Hum Perform. 2016; 87(10):838–843.

BACKGROUND: A noninvasive method to monitor changes in intracranial pressure (ICP) is required for astronauts on long-duration spaceflight who are at risk of developing the Visual Impairment/Intracranial Pressure syndrome that has some, but not all of the features of idiopathic intracranial hypertension. We assessed the validity of distortion product otoacoustic emissions (DPOAEs) to detect changes in ICP.METHODS: Subjects were eight patients undergoing medically necessary diagnostic cerebrospinal fluid (CSF) infusion testing for hydrocephalus. DPOAE measurements were obtained with an FDA-approved system at baseline and six controlled ICP levels in ∼3 mmHg increments in random order, with a range from 10.8 ± 2.9 mmHg (SD) at baseline to 32.3 ± 4.1 mmHg (SD) at level 6.RESULTS: For f2 frequencies between 800 and 1700 Hz, when ICP was ≥ 12 mmHg above baseline ICP, DPOAE angles increased significantly and DPOAE magnitudes decreased significantly, but less robustly.DISCUSSION: Significant changes in DPOAE angle and magnitude are seen when ICP is ≥ 12 mmHg above a subject’s supine baseline ICP during CSF infusion testing. These results suggest that the changes in DPOAE angle and magnitude seen with change in ICP are physiologically based, and suggest that it should be possible to detect pathological ICP elevation using DPOAE measurements. To use DPOAE for noninvasive estimation of ICP during spaceflight will require baseline measurements in the head-up, supine, and head-down positions to obtain baseline DPOAE values at different ICP ranges.Williams MA, Malm J, Eklund A, Horton NJ, Voss SE. Distortion product otoacoustic emissions and intracranial pressure during CSF infusion testing. Aerosp Med Hum Perform. 2016; 87(10):844–851.

BACKGROUND: During hovering with a helicopter, an involuntary change in attitude (during brownout) results in reduced lifting force and a horizontal acceleration component. This movement pattern is difficult to perceive via the otolith organs. If the angular displacement occurs rapidly, it will, however, activate the semicircular canals. The major aim of this study was to establish to what extent pitch-plane angular displacements can be perceived based on canal information when there is no tilt stimulus to the otoliths.METHODS: In a helicopter, 9 nonpilots (N) and 8 helicopter pilots (P) underwent 5–6 pitch-forward displacements (magnitude 14–33°, angular velocity 2–7° · s⁻¹). In a swing-out gondola centrifuge, 9 N and 3 P were exposed to a similar canal-otolith conflict (acceleration, seated centripetally) with four displacements of 25° and two of 60°. The visually perceived eye level (VPEL) was continuously recorded using an adjustable luminous dot in darkness. For each helicopter dive and centrifuge run the gain was calculated as the ratio (VPEL deflection)/(displacement of helicopter or gondola).RESULTS: In the helicopter there was no difference between N (0.28 ± 0.13) and P (0.36 ± 0.22). In the centrifuge the gains were 0.34 ± 0.18° (25° displacements) and 0.30 ± 0.16° (60° displacements). Values obtained in the helicopter did not differ significantly from those in the centrifuge. There was a correlation between data obtained during the 25° and 60° displacements in the centrifuge.CONCLUSION: There was a pronounced underestimation of pitch angular displacements in a helicopter. The interindividual variability was considerable. Gains for perceived displacement were similar in helicopter and centrifuge.Tribukait A, Bergsten E, Eiken O. Pitch-plane angular displacement perception during helicopter flight and gondola centrifugation. Aerosp Med Hum Perform. 2016; 87(10):852–861.

BACKGROUND: In-flight cardiac arrest (IFCA) is a relatively rare but challenging event. Outcomes and prognostic factors are not entirely understood for victims of IFCAs in commercial aviation.METHODS: This was a retrospective cohort study of airline passengers who experienced IFCA. Demographic and operational variables were studied to identify association in a multivariate logistic regression model with the outcome of survival-to-hospital. In-flight medical emergencies were processed by a ground-based medical center. Subsequent comparisons were made between reported shockable-rhythm (RSR) and reported non-shockable-rhythm (RNSR) groups. Logistic regression was also used to identify predictors for shock advised and flight diversions using a case control study design. Significant predictors for survival-to-hospital were RSR and remaining flight time to destination.RESULTS: The percentage of RSR cases was 24.6%. The survival to hospital admission was 22.7% (22/97) for passengers in RSR compared with 2.4% (7/297) in the RNSR group. The adjusted odds ratio for survival-to-hospital for the RSR group compared to the RNSR group was 13.6 (5.5–33.5). The model showed odds for survival to hospital decreased with longer scheduled remaining flight duration with adjusted OR = 0.701 (0.535–0.920) per hour increase. No correlation between diversions and survival for RSR cases was found.CONCLUSIONS: Survival-to-hospital from IFCAs is best when an RSR is present. The percentage of RSR cases was lower than in other out-of-hospital cardiac arrest (OHCA) settings, which suggests delayed discovery. Flight diversions did not significantly affect resuscitation outcome. We emphasize good quality cardio-pulmonary resuscitation (CPR) and early defibrillation as key factors for IFCA survival.Alves PM, DeJohn CA, Ricaurte EM, Mills WD. Prognostic factors for outcomes of in-flight sudden cardiac arrest on commercial airlines. Aerosp Med Hum Perform. 2016; 87(10):862–868.

BACKGROUND: This study examined whether subjective measurements of in-flight sleep could be a reliable alternative to actigraphic measurements for monitoring pilot fatigue in a large-scale survey.METHODS: Pilots (3-pilot crews) completed a 1-page survey on outbound and inbound long-haul flights crossing 1–7 time zones (N = 586 surveys) between 53 city pairs with 1-d layovers. Across each flight, pilots documented flight start and end times, break times, and in-flight sleep duration and quality if they attempted sleep. They also rated their fatigue (Samn-Perelli Crew Status Check) and sleepiness (Karolinska Sleepiness Scale) at top of descent (TOD). Mixed model ANCOVA was used to identify independent factors associated with sleep duration, quality, and TOD measures. Domicile time was used as a surrogate measure of circadian phase.RESULTS: Sleep duration increased by 10.2 min for every 1-h increase in flight duration. Sleep duration and quality varied by break start time, with significantly more sleep obtained during breaks starting between (domicile) 22:00–01:59 and 02:00–05:59 compared to earlier breaks. Pilots were more fatigued and sleepy at TOD on flights arriving between 02:00–05:59 and 06:00–09:59 domicile time compared to other flights. With every 1-h increase in sleep duration, sleepiness ratings at TOD decreased by 0.6 points and fatigue ratings decreased by 0.4 points.DISCUSSION: The present findings are consistent with previous actigraphic studies, suggesting that self-reported sleep duration is a reliable alternative to actigraphic sleep in this type of study, with use of validated measures, sufficiently large sample sizes, and where fatigue risk is expected to be low.van den Berg MJ, Wu LJ, Gander PH. Subjective measurements of in-flight sleep, circadian variation, and their relationship with fatigue. Aerosp Med Hum Perform. 2016; 87(10):869–875.

BACKGROUND: Barotrauma is a frequent problem in aviation medicine. Eustachian tube dysfunction plays a critical role in the pathogenesis of barotrauma. Function of the Eustachian tube can be indirectly assessed by multifrequency tympanometry, which provides valuable information about the resistance and permeability of the middle ear in a wide frequency range. The aim of this study was to research whether multifrequency tympanometry could be used for assessing middle ear impairments in pilots.METHODS: There were 140 pilots and pilot candidates between the ages of 20–55 with normal otoscopic examination who were evaluated by audiological test batteries. Body mass index values, flight hours, audiometric pure tone thresholds, tympanometry and multifrequency tympanometry test results were noted.RESULTS: There was statistically significant decrease in the multifrequency tympanometry measurements of the left and right ears of the pilots with 200–3000 flight hours compared to pilot candidates, and similarly, the pilots with 3000–10,000 flight hours compared to pilot candidates.DISCUSSION: Multifrequency tympanometry values changed between pilot candidates and pilots. However, the values of multifrequency tympanometry did not change due to flight hours. This test battery should not be used for follow up of pilots in the clinic.Tuncer MM, Babakurban ST, Aydin E. Middle ear resonance frequency in pilots and pilot candidates. Aerosp Med Hum Perform. 2016; 87(10):876–881.

INTRODUCTION: Anxiety may present challenges for commercial spaceflight operations, as little is known regarding the psychological effects of spaceflight on laypersons. A recent investigation evaluated measures of anxiety during centrifuge-simulated suborbital commercial spaceflight, highlighting the potential for severe anxiousness to interrupt spaceflight operations.METHODS: To pave the way for future research, an extensive literature review identified existing knowledge that may contribute to formation of interventions for anxiety in commercial spaceflight. Useful literature was identified regarding anxiety from a variety of fields, including centrifugation, fear of flying, motion sickness, and military operations.RESULTS: Fear of flying is the most extensively studied area, with some supportive evidence from centrifugation studies. Virtual reality exposure (VRE) is as effective as actual training flight exposure (or analog exposure) in mitigation of flight-related anxiety. The addition of other modalities, such as cognitive behavioral therapy or biofeedback, to VRE improves desensitization compared to VRE alone. Motion sickness-susceptible individuals demonstrate higher trait anxiety than nonsusceptible individuals; for this reason, motion sickness susceptibility questionnaires may be useful measures to identify at-risk individuals. Some military studies indicate that psychiatric history and personality classification may have predictive value in future research. Medication countermeasures consisting of benzodiazepines may quell in-flight anxiety, but do not likely improve anxiety on repeat exposure.DISCUSSION: The scarce available literature addressing anxiety in unique environments indicates that training/repeated exposure may mitigate anxiety. Anxiety and personality indices may be helpful screening tools, while pharmaceuticals may be useful countermeasures when needed.Mulcahy RA, Blue RS, Vardiman JL, Castleberry TL, Vanderploeg JM. Screening and mitigation of layperson anxiety in aerospace environments. Aerosp Med Hum Perform. 2016; 87(10):882–889.

BACKGROUND: This study is intended to identify efficacy, evolving applications, best practices, and challenges of spatial disorientation (SD) training in flight simulators for rotor wing pilots.METHODS: Queries of a UK Ministry of Defense research database and Pub Med were undertaken using the search terms ‘spatial disorientation,’ ‘rotor wing,’ and ‘flight simulator.’ Efficacy, evolving applications, best practices, and challenges of SD simulation for rotor wing pilots were also ascertained through discussion with subject matter experts and industrial partners. Expert opinions were solicited at the aeromedical physiologist, aeromedical psychologist, instructor pilot, aeromedical examiner, and corporate executive levels.RESULTS: Peer review literature search yielded 129 articles, with 5 relevant to the use of flight simulators for the spatial disorientation training of rotor wing pilots. Efficacy of such training was measured subjectively and objectively. A preponderance of anecdotal reports endorse the benefits of rotor wing simulator SD training, with a small trial substantiating performance improvement. Advancing technologies enable novel training applications. The mobile nature of flight students and concurrent anticollision technologies can make long-range assessment of SD training efficacy challenging. Costs of advanced technologies could limit the extent to which the most advanced simulators can be employed across the rotor wing community.DISCUSSION: Evidence suggests the excellent training value of rotor wing simulators for SD training. Objective data from further research, particularly with regards to evolving technologies, may justify further usage of advanced simulator platforms for SD training and research.Powell-Dunford N, Bushby A, Leland RA. Spatial disorientation training in the rotor wing flight simulator. Aerosp Med Hum Perform. 2016; 87(10):890–893.

BACKGROUND: Elevated ambient Pco₂ in the International Space Station (ISS) has been cited as a potential contributor to the vision impairment intracranial pressure syndrome (VIIP), a significant health risk for astronauts during long-duration space missions. The elevation in ambient Pco₂ is rather modest and normal respiratory compensation could minimize the impact on arterial Pco₂.METHODS: In nine male astronauts, breaths measured prior to a rebreathing maneuver were examined to assess inspired and end-tidal Pco₂ during upright seated preflight and in-flight conditions.RESULTS: Inspired Pco₂ increased from preflight baseline (0.6 ± 0.1 mmHg) to in flight (3.8 ± 0.4 mmHg). End-tidal Pco₂ also increased from preflight baseline (36.0 ± 3.2 mmHg) to in flight (42.1 ± 3.7 mmHg). The difference between end-tidal Pco₂ comparing in flight to preflight (6.1 ± 1.6 mmHg) was greater than the difference between inspired Pco₂ comparing preflight to in flight (3.3 ± 0.5 mmHg).DISCUSSION: The greater increase in end-tidal vs. inspired Pco₂ might reflect alveolar hypoventilation due to differences in ventilatory control with spaceflight. These data suggest that further studies should focus on arterial Pco₂ and acid-base balance to determine if CO₂ dilates cerebral and retinal vessels and might contribute to the incidence of VIIP in astronauts.Hughson RL, Yee NJ, Greaves DK. Elevated end-tidal Pco₂ during long-duration spaceflight. Aerosp Med Hum Perform. 2016; 87(10):894–897.

BACKGROUND: High altitude retinopathy (HAR) includes a number of diseases related to high altitude such as acute mountain sickness (AMS), high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). High altitude retinopathy is mainly characterized by retinal hemorrhages, usually sparing the macular region, a condition specifically known as high altitude retinal hemorrhages (HARH). The pathogenesis of HARH is unclear. Many studies show that lack of oxygen causes an inadequate autoregulation of retinal circulation, causing vascular incompetence. Other retinal changes described in HAR have been reported, such as optical disk edema, optic disc hyperemia, cotton wool exudates, venous occlusions, and macular edema.CASE REPORT: In this paper we present a case of an aviator who developed a unilateral maculopathy through subhyaloid lipid accumulation on a climb to the top of Mt. Everest. The clinical findings are suggestive of an apparent case of temporary altitude-induced visual disruption maybe by the same presumable pathogenesis of HARH. Right eye visual loss was perceived at 5150 m when he was trying to take a photograph 40 d into the expedition.DISCUSSION: The maculopathy developed by this patient adds to the discussion on the pathogenesis of HARH, especially the aspect of this maculopathy and its complete resolution. It seems that autoregulation failure could lead to exudation and lipid deposits in the foveal area. Although macular damage is not a common signal in HARH, checking visual acuity during high altitude expeditions remains an important procedure to avoid late diagnosis as unilateral blindness may not be detected early.Rosas Petrocinio R, Gomes ED. Lipid subhyaloid maculopathy and exposure to high altitude. Aerosp Med Hum Perform. 2016; 87(10):898–900.

BACKGROUND: Central serous chorioretinopathy (CSC) is usually a self-limiting condition; however, there is potential for recurrence and permanent visual defects. Aviation demands perfect vision to minimize risk to pilots and aircraft. Consequently, this ailment disqualifies pilots and pilots to be.CASE REPORT: A fully trained fighter pilot with 1260 h in fighter airframes has been contending with central serous chorioretinopathy in the right eye over the course of 3 yr. The condition was diagnosed after the member presented with visual disturbances. His course was followed with multiple treatment modalities: watchful waiting, micropulse laser, and rifampin. His disease responded well with rifampin, but was ultimately stopped secondary to elevated liver enzymes. Micropulse laser failed to resolve subretinal fluid. Ultimately the pilot is left with a chronic area of CSC without visual defects and faces career termination.DISCUSSION: Uncompromised vision is inherently crucial in aerospace careers, especially that of a fighter pilot. With persistent CSC resistant to treatment, there is a risk for progression to permanent visual disturbances and/or defects. Safety concerns of authority figures overseeing pilots and aircraft are warranted. However, the concern could be mitigated in air frames that require two pilots. Another factor partially responsible for ending his career is the fear of G force affecting his prognosis. The author is not aware of any other studies illuminating the effects or consideration of excess G force on subretinal fluid in CSC. This is an area that requires further study.Dietrich KC. Fighter pilot with recurrent central serous chorioretinopathy. Aerosp Med Hum Perform. 2016; 87(10):901–905.

Lenz CR, Shields JL, Morgan AO. You’re the flight surgeon: an unusual case of ground-level F-15 decompression illness. Aerosp Med Hum Perform. 2016; 87(10):906–909.