Kaber DB, Alexander AL, Stelzer EM, Kim S-H, Kaufmann K, Hsiang S. Perceived clutter in advanced cockpit displays: measurement and modeling with experienced pilots. Aviat Space Environ Med 2008; 79:1007–18.Introduction: Synthetic and enhanced vision systems (SVS and EVS) are being introduced into the cockpit to promote safety under workload conditions. Integration of existing iconic imagery with SVS and EVS displays may lead to perceptions of clutter. This research evaluated head-up display (HUD) features, including SVS, EVS, traffic collision avoidance system symbology, flight pathway (TUNNEL) guidance, and different primary flight display symbol sets, on pilot perceptions of clutter. A perceptual decomposition of the construct of clutter was also conducted. Method: During a simulated landing, 4 expert pilots viewed images of 16 HUD configurations. Pilots rated clutter for each image and the utility of pairs of terms for describing clutter. Results: Results revealed all HUD features and two-way interactions to be significant in perceived clutter. Ratings increased with additional features. The presence of EVS, TUNNEL, and an expanded symbol set contributed the most. Regression models were developed to predict the likelihood of clutter ratings based on pilot perceptions of display characteristics. Pairs of terms found to have the greatest use for describing clutter included “redundant/orthogonal,” “monochromatic/colorful,” “salient/not salient,” “safe/unsafe,” and “dense/sparse” (in that order). A factor analysis revealed underlying display qualities explaining ∼78% of variability in perceived clutter, including global density, feature similarity, feature clarity, and the dynamic nature of displays. These qualities corresponded with the display descriptor terms plus the terms “static/dynamic.” Discussion: The study provided information on the relationship of display features and pilot perceptions of clutter. We identified terminology pilots use to describe clutter and latent display variables that drive perceived clutter.

Joseph JA, Griffin MJ. Motion sickness: effect of changes in magnitude of combined lateral and roll oscillation. Aviat Space Environ Med 2008; 79:1019–27.Background: In tilting trains, low-frequency lateral and roll oscillation combine and can cause motion sickness. During a journey, passengers are exposed to motions of varying magnitudes, but the effect of a change in magnitude on motion sickness is not known. It was hypothesized that the rate of increase in motion sickness would be greater during exposure to a high-magnitude motion than during exposure to a low-magnitude motion and that there would be no difference in sickness between motions when the ‘motion sickness dose value’ was the same. Method: At intervals of at least 1 wk, 20 subjects were exposed to 4 conditions consisting of 0.1-Hz sinusoidal lateral oscillation with 50% roll compensation. Each condition had four successive 15-min periods of motion presented without a break (total duration 1 h). Each 15-min motion was either a high-magnitude motion (H) (±1.26 ms⁻² lateral oscillation with ±3.66° roll oscillation) or a low-magnitude motion (L) (±0.63 ms⁻² lateral oscillation with ±1.83° roll oscillation). The four conditions involved four different combinations of magnitude: 1) LLLL, 2) HHHH, 3) LHHL, and 4) HLHL. Subjects were seated in a rigid closed cabin and gave ratings of sickness at 1-min intervals. Results: Symptoms of motion sickness were experienced in 56 of the 80 sessions. The rate of increase in motion sickness was greater with the high-magnitude motion than with the low-magnitude motion. For the two variable conditions (i.e., LHHL and HLHL), there was no significant difference in accumulated illness ratings when the motion sickness dose values were the same (i.e., between 30 and 60 min of motion). Illness ratings decreased during periods of low-magnitude motion experienced after periods of high-magnitude motion and also after the cessation of all motion. Conclusions: With combined lateral and roll oscillation, the rate of increase in motion sickness is greater during periods of high-magnitude motion than during periods of low-magnitude motion. With motions having the same motion sickness dose value but different sequences of exposure, there were no significant differences in accumulated illness ratings at times when the motion sickness dose values were the same.

Hovis JK. Repeatability of the Holmes-Wright type A lantern color vision test. Aviat Space Environ Med 2008; 79:1028–33.Purpose: Recent studies showing a lack of internal consistency for the Holmes-Wright Type A Lantern (HWA) raise the issue as to whether the lantern test is repeatable. This study determines the HWA repeatability for several scoring criteria. Methods: There were 78 individuals with normal color vision (NCV) and 80 individuals with defective color vision (DCV) who were tested during two separate visits. Three runs of the test lights were always presented in dim room illumination. An additional dark-adapted run was presented during both visits for a subset of 61 subjects. Repeatability was evaluated for the following pass/fail criteria: the Joint Aviation Requirements, Farnsworth's criterion, the Commission Internationale de l'Éclairage criterion for the HWA, a perfect performance, and the 99^th and 100^th percentile scores of the NCV sample. Results: The NCV agreement for passing both sessions was high, with 96% having a perfect score at both sessions. The DCV agreement for passing both sessions was lower, ranging from 0.62 to 0.80. Criteria which stopped the test after a perfect performance on the first run had the lowest values. The DCV agreement for failing both sessions was high, ranging from 0.97 to 0.99. Conclusions: Stopping the test after a perfect performance on the first run should be abandoned. Presenting three runs of the nine test lights and allowing no more than two errors is repeatable, passes all the NCV, and minimizes the number of individuals who pass the lantern at the first session and fail at a later session.

Machado-Moreira CA, Caldwell JN, Mekjavic IB, Taylor NAS. Sweat secretion from palmar and dorsal surfaces of the hands during passive and active heating. Aviat Space Environ Med 2008; 79:1034–40.Introduction: It is generally accepted that the palmar (volar) and dorsal surfaces of human hands display different sudomotor responses to mental or thermal stimuli. We tested the hypothesis that, during thermal stimulation, secretion from the dorsal surfaces would always exceed that from the volar aspect of the hand. Methods: Sweat secretion from 10 hand sites and the forehead was examined (ventilated capsules) in 10 subjects during passive heating (climate chamber: 36°C, 60% relative humidity, water-perfusion suit: 40°C) immediately followed by incremental cycling to volitional fatigue. Results: This treatment significantly increased core temperature (39.3°C), heart rate (178 bpm), and sweat rate at all sites. Mean sweat secretion during exercise was greater at the forehead (2.90 mg · cm⁻² · min⁻¹; ± 0.19) than the hand (1.49 mg · cm⁻² · min⁻¹; ± 0.27). While no significant differences in sweating were observed among dorsal sites, a nonuniform secretion pattern was observed across the volar surface, with sweating at the palm being the lowest, and that from the volar aspect of the distal phalanges being equivalent to the dorsal hand. These differences became more evident as exercise progressed. Mean hand sweat rate during exercise was 41.7 ml · h⁻¹, with sweating from the palm accounting for only about 6% of sweat secretion. Conclusion: Sweat secretion from both the palmar and dorsal surfaces of the hand increases during exercise in the heat, although this occurs in a nonuniform fashion. It is possible that a greater sweat gland density on the fingers may account for variations across the volar surface. However, higher dorsal sweating with lower gland counts (high glandular flow) may be attributable to either larger sweat glands, or to a greater cholinergic sensitivity of these glands.

Powell D, Spencer MB, Holland D, Petrie KJ. Fatigue in two-pilot operations: implications for flight and duty time limitations. Aviat Space Environ Med 2008; 79:1047–50.Objectives: Two-pilot operations make up the majority of commercial flights. Fatigue is an important consideration in these operations as there is little opportunity for in-flight rest. We investigated the role of duty length, time of day, and whether one or two sectors were flown on reported fatigue at the top of descent in two-pilot regional operations. Methods: Pilots flying two-pilot operations ranging from 3-12 h completed Samn-Perelli fatigue ratings prior to descent at the end of each rostered duty over a 12-wk period. We collected 3023 usable ratings (72% of rostered duties) comprising 26% single and 74% double sector duties. Results: We found that time of day has a marked effect on the pattern of fatigue at the start of the duty and on the rate at which fatigue levels increased, with the highest levels in the window of circadian low (0200–0600). Fatigue also increased with the length of duty and was 0.56 higher at the end of a two-sector compared with a single-sector duty. Discussion: The results imply authorities should consider increasing existing limits for daytime duties and reducing those for nighttime two-pilot operations.

Qiang Y, Rebok GW, Baker SP, Li G. Hearing deficit in a birth cohort of U.S. male commuter air carrier and air taxi pilots. Aviat Space Environ Med 2008; 79:1051–5.Purpose: Long-term exposure to multiple risk factors in aviation may place pilots at excess risk of developing hearing deficits. We examined the incidence and risk factors for hearing deficit in a birth cohort of male commuter and air taxi pilots. Methods: The subjects (N = 3019), who were 45-54 yr of age and held Class I medical certificates in 1987, were followed up from 1987 to 1997 through the medical certification system of the Federal Aviation Administration (FAA). In this study, hearing deficit refers to the FAA pathology code 220 (defective hearing, deafness, not elsewhere classified). Poisson regression modeling based on generalized estimation equations was used to assess the associations between pilot characteristics and the risk of developing hearing deficit. Results: The 10-yr follow-up accumulated a total of 20,671 person-years and 574 incident cases of hearing deficit, yielding an incidence rate of 27.8 per 1000 person-years. Compared with age 45-49 yr, the risk of developing hearing deficit at age 50-54 yr, 55-59 yr, and 60-64 yr increased by 12% [adjusted relative risk (RR) 1.12, 95% confidence interval (CI) 0.98-1.30], 34% (RR 1.34, 95% CI 1.13-1.59), and 79% (RR 1.79, 95% CI 1.20-2.67), respectively. Conclusions: Hearing deficit is prevalent among commuter air carrier and air taxi pilots and the risk of hearing deficit increases progressively with pilot age. Effective programs for preventing excess hearing loss in the pilot population are warranted.

Droma Y, Ota M, Hanaoka M, Katsuyama Y, Basnyat B, Neupane P, Arjyal A, Pandit A, Sharma D, Ito M, Kubo K. Two hypoxia sensor genes and their association with symptoms of acute mountain sickness in Sherpas. Aviat Space Environ Med 2008; 79:1056–60.Introduction: Hypoxia-inducible factor (HIF) and von Hippel-Lindau tumor suppressor protein (VHL) are hypoxia sensors that control cellular responses to hypoxia. Although many Sherpas live at high altitudes for their entire lives, some of them manifest symptoms of acute mountain sickness (AMS) during mountaineering at extremely high altitudes. We hypothesize that the two hypoxia sensor genes might associate with the occurrence of AMS symptoms in Sherpas at extremely high altitude. Methods: In a village at an altitude of 3440 m, 104 Sherpas who had mountaineered at extremely high altitudes (over 5000 m) were divided into two groups: Sherpas with (N = 45) and without (N = 59) histories of AMS symptoms. The rs11549465 SNP in the HIF-1α gene (HIF1A) and the rs28940298, rs779805, rs779808, rs1678607, and 1149A > G SNPs in the VHL gene (VHL) were identified in the two Sherpa groups using PCR following RFLP. Results: There were no significant differences in either the genotype distributions or the allele frequencies of the HIF1A and VHL genetic variants between the two Sherpa groups. Conclusion: These genetic variants of HIF1A and VHL are not associated with AMS symptoms that occur in Sherpas at extremely high altitudes. It seems unlikely that HIF1A and VHL are associated with hypoxic sensing sensitivity in Sherpas.

Ebbatson M, Harris D, Huddlestone J, Sears R. Combining control input with flight path data to evaluate pilot performance in transport aircraft. Aviat Space Environ Med 2008; 79:1061–4.Introduction: When deriving an objective assessment of piloting performance from flight data records, it is common to employ metrics which purely evaluate errors in flight path parameters. The adequacy of pilot performance is evaluated from the flight path of the aircraft. However, in large jet transport aircraft these measures may be insensitive and require supplementing with frequency-based measures of control input parameters. Method: Flight path and control input data were collected from pilots undertaking a jet transport aircraft conversion course during a series of symmetric and asymmetric approaches in a flight simulator. The flight path data were analyzed for deviations around the optimum flight path while flying an instrument landing approach. Manipulation of the flight controls was subject to analysis using a series of power spectral density measures. Results: The flight path metrics showed no significant differences in performance between the symmetric and asymmetric approaches. However, control input frequency domain measures revealed that the pilots employed highly different control strategies in the pitch and yaw axes. Conclusion: The results demonstrate that to evaluate pilot performance fully in large aircraft, it is necessary to employ performance metrics targeted at both the outer control loop (flight path) and the inner control loop (flight control) parameters in parallel, evaluating both the product and process of a pilot's performance.

Kirkpatrick AW, Doarn CR, Campbell MR, Barnes SL, Broderick TJ. Manual suturing quality at acceleration levels equivalent to spaceflight and a lunar base. Aviat Space Environ Med 2008; 79:1065–6.Introduction: Cutaneous wounds, either from injuries or as a result of surgical incisions, are a likely possibility that future space medicine specialists will need to address. While there has been some prior study of manual suturing in microgravity (0 G), there has been no study of manual suturing in reduced gravity consistent with that of the Moon. Methods: Six separate operators with varying degrees of surgical experience (four trained surgeons, and two non-surgeons) attempted to manually suture wound phantoms during the reduced gravity phases of parabolic flight simulating either 0 G or lunar gravity (0.16 G). Each operator subjectively evaluated the difficulty and relative speed in performing the same task in different environments, serving as their own internal control. There were 20-s periods of 1 G that were carefully timed for each surgeon to compare to the approximately 20 s available for each parabola of either 0 G or 0.16 G. Results: Six periods of 1 G were used as controls to perform manual suturing of the phantoms. There were 51 parabolas of 0 G and 67 parabolas of 0.16 G performed by the six operators. As judged subjectively by the operators themselves and by group inspection of the sutured phantoms, there was no qualitative difference in the adequacy of wound closure as judged by suture placement accuracy and wound coaptation. There was consensus, though, that suturing in microgravity was significantly slower, as has been noted in more complex surgical studies. Discussion: The technical aspects of wound management during exploration-class missions in prolonged microgravity or lunar missions with reduced gravity (0.16 G) will likely not present challenges beyond those faced in addressing the tremendous logistical and training obstacles to providing experienced and equipped surgeons onboard such a mission.

Low R, Teoh T, Loh A, Ooi A. Vertebral fracture in a pilot during centrifuge training: finding of osteopenia. Aviat Space Environ Med 2008; 79:1067–70.We report on a case of an F-16 pilot who suffered a compression fracture of the L5 vertebral body during centrifuge training. The pilot sustained the injury during a rapid onset to 6 G run. He was subsequently diagnosed to have osteopenia with a bone mineral density T-score of −1.95. This report discusses the medical and operational management of the pilot with this rare condition. The pilot has since returned to flying duties, albeit in a transport platform.

Kayar SR. On beginning a second century of decompression sickness research: where are we and what comes next? Aviat Space Environ Med 2008; 79:1071–2.It is just 100 years since the publication of J. S. Haldane's groundbreaking work on the prevention of decompression sickness (DCS). While we still do not know the exact mechanisms that underlie DCS, probabilistic modeling now allows good estimation of risk for a given set of conditions, although reduction of risk to zero remains impractical. Unfortunately, individual monitoring for intravascular bubbles has not proven a good predictor of symptomatic DCS. Current research aims to identify underlying biological factors that, once understood, may allow development of preventive measures and treatment that go beyond recompression. With one or more drugs to combat DCS, we should be able to eliminate the residual risk, extend dive profiles beyond current limits, and rescue people who have exceeded the limits and taken a hit.