Bock O, Weigelt C, Bloomberg JJ. Cognitive demand of human sensorimotor performance during an extended space mission: a dual-task study. Aviat Space Environ Med 2010; 81:819–24.Introduction: Two previous single-case studies found that the dual-task costs of manual tracking plus memory search increased during a space mission, and concluded that sensorimotor deficits during spaceflight may be related to cognitive overload. Since dual-task costs were insensitive to the difficulty of memory search, the authors argued that the overload may reflect stress-related problems of multitasking, rather than a scarcity of specific cognitive resources. Here we expand the available database and compare different types of concurrent task. Methods: Three subjects were repeatedly tested before, during, and after an extended mission on the International Space Station (ISS). They performed an unstable tracking task and four reaction-time tasks, both separately and concurrently. Inflight data could only be obtained during later parts of the mission. Results: The tracking error increased from pre- to in flight by a factor of about 2, both under single- and dual-task conditions. The dual-task costs with a reaction-time task requiring rhythm production was 2.4 times higher than with a reaction-time task requiring visuo-spatial transformations, and 8 times higher than with a regular choice reaction-time task. Conclusions: Long-term sensorimotor deficits during spaceflight may reflect not only stress, but also a scarcity of resources related to complex motor programming; possibly those resources are tied up by sensorimotor adaptation to the space environment.

Caruso JF, Coday MA, Taylor ST, Mason ML, Lutz BM, Ford JL, Kraemer WJ. Prediction of resultant testosterone concentrations from flywheel-based resistive exercise. Aviat Space Environ Med 2010; 81:825–32.Introduction: Numerous variables impact resultant testosterone concentrations (TC) that foretell the efficacy of workouts. Identifying variables may aid the development of in-flight exercise prescription. Methods: To identify variables that predict the variance in TC from flywheel ergometer exercise, 17 subjects did 3 workouts in a randomized order. Comprised of 10-repetition leg press sets, workouts entailed either: 1) 3 sets of both concentric and eccentric muscle actions (CE3), and concentric-only actions done for 2) three (CO3), or 3) six (CO6) sets. Venous plasma TC were collected before and at 1 and 30 min post-exercise. The last two collection points served as criterion measures. Body mass, delta blood lactate levels, peak angular velocity, average power, and total work from workouts were used to predict the variance in TC. Results: Predictor variables accounted for significant levels of variance at both 1 and 30 min post-exercise for both the CE3 and the concentric-only (CO3 and CO6 bouts combined) workouts using multivariate regression. Inclusion of eccentric variables (only collected from the CE3 bout; r² = 0.90) predicted nearly twice the variance than the concentric-only (r² = 0.54) workouts. Conclusions: Body mass and average power indices were the best predictors of the variance in post-workout TC. Since a flywheel-based device is used to abate in-flight muscle atrophy and strength losses, exercise prescriptions may wish to monitor these indices as they impacted post-workout TC to the greatest extent. Future research should assess why eccentric variables increased the amount of explained variance from flywheel ergometer workouts.

McClelland LE, Pilcher JJ, Moore DD. Oculomotor measures as predictors of performance during sleep deprivation. Aviat Space Environ Med 2010; 81:833–42.Introduction: Studies have indicated that working under sleep deprivation conditions results in deficits in performance on various tasks. Few studies, however, have attempted to find a measure for predicting performance changes under sleep deprivation conditions. The current study examined whether oculomotor measures could predict changes in performance under non-sleep deprivation and acute short-term sleep deprivation conditions. Methods: Oculomotor measures and performance were examined during five testing sessions in each study. In the non-sleep deprivation study (N = 23) the testing sessions took place during 2 consecutive days. The sleep deprivation study (N = 26) took place in an 18-h sustained operations period during the night of sleep deprivation. Results: Under non-sleep deprivation conditions, pupil diameter significantly predicted performance on grammatical reasoning (B = 0.360) and constriction latency significantly predicted performance on combined tasks (B = 0.182). Under sleep deprivation conditions, diameter, constriction latency, and saccadic velocity significantly predicted performance on a psychomotor vigilance task (B = −21.002, B = −23.126, B = −18.028, respectively). Overall, oculomotor measures better predicted performance changes under sleep deprivation conditions and better predicted performance decrements on vigilance-based tasks than cognitive tasks under acute sleep deprivation conditions. Discussion: The current research suggests saccadic velocity and pupil diameter may be the most useful predictors of performance under sleep deprivation conditions, perhaps because these measures are largely controlled by involuntary neural components that slow during sleep deprivation. These data support research suggesting that saccadic velocity and pupil diameter detect excessive sleepiness and predict performance decrements under sleep deprivation conditions using additional oculomotor measures and a non-sleep deprivation comparison group.

Yu Y, Yank JR, Villard S, Stoffregen TA. Postural activity and visual vigilance performance during rough seas. Aviat Space Environ Med 2010; 81:843–9.Background: Motion of a ship at sea often challenges crew performance. In previous studies, the influence of rough weather on stance at sea has been evaluated in terms of the likelihood of staggers or falls. Few studies have evaluated the influence of sea state on visual performance. Effects of rough seas on visual vigilance performance, subjective mental workload, and the kinematics of postural control have not been demonstrated. Method: Crewmembers of the R/V Thomas G. Thompson stood on a force plate, from which we obtained data on the center of pressure (COP). We varied stance width (the distance between the feet in side-by-side stance; 5 cm, 17 cm, and 30 cm) and the difficulty of visual vigilance tasks (Easy vs. Hard). Separately, we evaluated subjects’ self-selected foot positioning. Results: Visual performance was better on the Easy task (mean d’ = 4.20) than on the Hard task (mean d’ = 3.57). Overall vigilance performance (mean d’ = 3.88) was worse than when the same subjects were tested under mild sea states (mean d’ = 4.11). Subjective mental workload (mean = 28.0) was greater than under mild sea states (mean = 19.9). Relative to mild sea states the variability of postural activity was greater and its predictability was reduced. In addition, postural dynamics were influenced by controlled variations in stance width. Conclusions: Rough seas affect visual vigilance performance and postural activity, but do not eliminate the effects of vigilance task difficulty or stance width that have been found in mild seas.

Hermes EDA, Webb TS, Wells TS. Aircraft type and other risk factors for spinal disorders: data from 19,673 military cockpit aircrew. Aviat Space Environ Med 2010; 81:850–6.Introduction: Many assume that exposure to flight in high-performance aircraft (HPA) or rotary wing aircraft (RWA) increases the risk of spinal disorders compared to other fixed wing aircraft (FWA). However, this association has yet to be confirmed. This study explores the relationship between flight in different aircraft and the development of lumbar and cervical spine disorders. Methods: The flight records of 19,673 U.S. Air Force (USAF) cockpit aircrew officers were examined for entries with a spinal disorder diagnosis in an existing aircrew health information database. Univariate and multivariate analyses were employed to examine the association between aircraft type, other variables, and spinal disorders. Results: In stratified analysis of HPA and FWA, but not RWA categories, statistically significant unadjusted associations were observed between flight hours and cervical [HPA: odds ratio (OR) = 2.80, FWA: OR = 4.73] and lumbar disorders (HPA: OR = 2.46, FWA: OR = 3.01). After adjustment for birth year in a stratified multivariate analysis, these associations were no longer statistically significant. In all three aircraft types, statistically significant adjusted associations were observed between older birth year category and both cervical (HPA: OR = 3.82, FWA: OR = 5.88) and lumbar disorders (HPA: OR = 4.16, RWA: OR = 2.96, FWA: OR = 2.39). Discussion: The risk produced by exposure to HPA, RWA, or FWA as measured by flight hours may be overshadowed by that produced by birth year, which was the strongest predictor for spinal disorders in this study. Future endeavors should more closely examine the association between age and accrual of flight hours in various aircraft types in order to accurately direct preventive measures.

Singh B, Cable GG, Hampson GV, Pascoe GD, Corbett M, Smith A. Hypoxia awareness training for aircrew: a comparison of two techniques. Aviat Space Environ Med 2010; 81:857–63.Introduction: Major hazards associated with hypoxia awareness training are the risks of decompression sickness, barotrauma, and loss of consciousness. An alternate method has been developed which combines exposure to a simulated altitude of 10,000 ft (3048 m) with breathing of a gas mixture containing 10% oxygen and 90% nitrogen. The paradigm, called Combined Altitude and Depleted Oxygen (CADO), places the subjects at a physiological altitude of 25,000 ft (7620 m) and provides demonstration of symptoms of hypoxia and the effects of pressure change. CADO is theoretically safer than traditional training at a simulated altitude of 25,000 ft (7620 m) due to a much lower risk of decompression sickness (DCS) and has greater fidelity of training for fast jet aircrew (mask-on hypoxia). This study was conducted to validate CADO by comparing it with hypobaric hypoxia. Methods: There were 43 subjects who were exposed to two regimens of hypoxia training: hypobaric hypoxia (HH) at a simulated altitude of 25,000 ft (7620 m) and CADO. Subjective, physiological, and performance data of the subjects were collected, analyzed, and compared. Results: There were no significant differences in the frequency and severity of the 24 commonly reported symptoms, or in the physiological response, between the two types of hypoxia exposure. Conclusions: CADO is similar to HH in terms of the type and severity of symptoms experienced by subjects, and appears to be an effective, useful, and safe tool for hypoxia training.

Campbell JS, Ruiz MA, Moore JL. Five-factor model facets characteristics of non-aeronautically adaptable military aviators. Aviat Space Environ Med 2010; 81:864–8.Background: The present study revisited a large sample of clinically referred military aviators, previously evaluated across factors of the Five Factor Model of personality (FFM), to determine whether identified facet differences were consistent with U.S. Navy guidelines for evaluating aeronautical adaptability. Methods: Clinically evaluated U.S. Naval aviators and flight officers (N = 954) disposed as either aeronautically adaptable (AA) or not aeronautically adaptable (NAA) were compared with respect to their facet level scores on the NEO Personality Inventory (NEO PI-R). Additional analyses were conducted to control for NAA status attributable to physical as opposed to psychological standards and for student versus designated aviator/flight officer experience levels. Results: NAA aviators and flight officers, when compared to their AA counterparts, evidenced significant and substantive effect size differences on facets measuring negative emotionality, interpersonal effectiveness, and goal-orientation. Conclusion: FFM facet differences between AA and NAA officers were only partially consistent with U.S. Navy guidelines; expected facet differences related to compliance, deliberation, actions, and excitement-seeking/impulsivity were not observed.

Thomas RS, Wright ST, Clark PJ, Thompson WT, Gooch JM. Optical filter effects on night vision goggle acuity and preservation of dark adaptation. Aviat Space Environ Med 2010; 81:869–72.Introduction: The high output of night vision goggles (NVGs) can cause a loss of dark adaptation, resulting in suboptimal unaided vision. Optical filters have been designed to mitigate this problem by changing the overall output characteristics of the NVGs. Methods: Several aspects of visual performance related to NVG use were studied in a repeated measures design, filters versus no filters. NVG acuity was assessed using a 25% contrast chart, while preservation of dark adaptation after NVG use was measured with a scotopic sensitivity tester (SST) and a low luminance acuity chart. Testing was accomplished at two light levels, roughly corresponding to starlight and quarter moon conditions. Results: Use of the filters resulted in a statistically significant loss of acuity of about a 1/2 line (approximately 2.5 letters) at both light levels. The second part of the study identified a 47% improvement in preservation of dark adaptation under simulated starlight conditions and a 31% improvement under simulated quarter moon conditions with filter use; however, only the starlight finding was statistically significant. No significant differences in performance were seen with the low luminance chart. Discussion: Despite a small loss of visual acuity with filter use, the improvement in retention of dark adaptation may be beneficial in certain operational environments. Aviators, airmen, and commanders should evaluate how the potential for slightly poorer visual acuity and improved recovery of dark adapted vision relates to their mission specific requirements prior to implementing use of NVG filters.

Morgagni F, Autore A, Landolfi A, Torchia F, Ciniglio Appiani G. Altitude chamber related adverse effects among 1241 airmen. Aviat Space Environ Med 2010; 81:873–7.Introduction: Altitude chambers are used for training aircrews, but incidents have been reported, including decompression sickness (DCS) and barotrauma. To minimize chamber-related adverse effects we implemented a set of measures, including altitude restriction and a pre-chamber clinical selection (PCS) of subjects before exposure. Methods: We reviewed our records regarding 1254 individuals who were trained from 2003 to 2009. After the first 3 subjects, the maximum altitude of the highest training profile was limited to 43,000 ft (13,106.4 m) instead of 45,000 ft (13,716 m) and, after the first 327 subjects, a clinical evaluation of each trainee was performed by an otolaryngologist before altitude exposure. The evaluation included otoscopy and tympanometry, and subjects with abnormal results were not cleared for altitude exposure. Subjects were grouped by having undergone the highest profile before (3 subjects) or after altitude restriction (8 subjects) and received clinical selection (PCS group, 927 subjects) or not (control group, 327 subjects). Results: We recorded 32 total adverse effects (overall incidence 2.6%), 21 in the PCS group (2.3%) and 11 in the control group (3.4%). The difference between groups was not significant. Adverse effects included 19 cases of acute barotitis (1.5%), 1 case of DCS (0.08%), and 4 cases of syncope (0.3%). The incidence of barotitis was 1.1% in the PCS group and 2.7% in the control group. The altitude restriction was ineffective in preventing both barotrauma and DCS. Conclusions: The incidence of adverse effects in our subjects was low and pre-chamber clinical selection appeared to be effective in reducing the risk of barotitis.

Stemper BD, Baisden JL, Yoganandan N, Pintar FA, Paskoff GR, Shender BS. Determination of normative neck muscle morphometry using upright MRI with comparison to supine data. Aviat Space Environ Med 2010; 81:878–82.Background: Neck muscles are important in the static and dynamic stability of the head-neck complex. Deep neck muscles act to maintain upright posture and superficial muscles are responsible for gross movements. Previous studies have quantified neck muscle geometry using traditional supine magnetic resonance imaging (MRI). However, supine orientation removes the vertical load on the cervical spine from the head-neck complex and changes the relative orientation of the spine and neck muscles. Therefore, the purpose of this study was to demonstrate the feasibility of upright MRI to obtain neck muscle morphometric data on a spinal level-by-level basis for subjects in upright seated positions. Methods: Upright MRI scans were obtained of the neck region for six younger male volunteers in neutral and flexed positions. Planar images were oriented parallel to the intervertebral disc space at each level. Cross-sectional area (CSA) and orientation of neck muscles were quantified at four spinal levels. Results: Area and position of all four muscles were significantly dependent upon spinal level. Average CSA of the sternocleidomastoid, longus colli, levator scapulae, and trapezius muscles in neutral position were 512, 113, 281, and 174 mm². Head-neck position significantly affected area and position of the sternocleidomastoid and position of posterior neck muscles. Discussion: Comparison of neck muscle areas from the present study to a previous study incorporating supine MRI demonstrated differing trends between anterior and posterior neck muscles that may be attributable to upright orientation of volunteers and planar image orientation in the present study. Differences between supine and upright MRI identified in the present study may warrant incorporation of this technique in future spinal imaging studies.

Stenger MB, Brown AK, Lee SMC, Locke JP, Platts SH. Gradient compression garments as a countermeasure to post-spaceflight orthostatic intolerance. Aviat Space Environ Med 2010; 81:883–7.Introduction: Post-spaceflight orthostatic intolerance affects ~30% of short-duration and 80% of long-duration crewmembers. While the current NASA antigravity suit is effective during Space Shuttle re-entry, it is not designed to be worn postflight and has several drawbacks. The purpose of this study was to evaluate the use of commercially available, thigh-high, gradient compression garments to prevent post-spaceflight orthostatic intolerance. Methods: Before spaceflight, five male Shuttle astronauts were fitted for compression garments. Postflight stand time, blood pressure, heart rate, stroke volume, cardiac output, and peripheral resistance during 10-min, 80° head-up tilt test within 4 h of landing in these astronauts were retrospectively compared to a group of nine male astronauts not wearing the compression garments. Results: On landing day, three of nine non-countermeasure astronauts developed presyncopal symptoms and could not complete the test, while no countermeasure subjects became presyncopal. Compared to the non-countermeasure subjects, the countermeasure subjects had higher systolic blood pressure (116 ± 3 vs. 134 ± 2 mmHg), stroke volume (42 ± 5 vs. 57 ± 6 ml), and cardiac output (3.1 ± 0.3 vs. 4.6 ± 0.4 L). Heart rate was not different between groups. Conclusions: In this small pilot study, the rate of presyncope in the non-countermeasure group was similar to that reported previously in subjects without a compression garment. In contrast, thigh-high graded compression garments mitigated the symptoms of orthostatic intolerance by improving stroke volume, cardiac output, and systolic blood pressure responses to standing.

Rivalland G, Mitchell SJ, van Schalkwyk JM. Pulmonary barotrauma and cerebral arterial gas embolism during hyperbaric oxygen therapy. Aviat Space Environ Med 2010; 81:888–90.Hyperbaric oxygen therapy (HBOT) is used to treat a variety of disorders. It is a safe treatment modality, but rare catastrophic complications may occur. In this case report, we describe the occurrence of irreversible spastic quadriparesis in a patient who suffered a cerebral arterial gas embolism (CAGE) during decompression from HBOT. The patient had a history of respiratory disease and was subsequently found to have bullous changes in the left lung, which almost certainly predisposed to this rare event. We discuss appropriate pretreatment screening to prevent such events and highlight the paradox that HBOT, the cause of the CAGE, is also the treatment of choice.

Gerathewohl SJ. Comparative studies on animals and human subjects in the gravity-free state. J Aviat Med 1954; 25:412–9.