Abstract

Six Swedish Air Force pilots and two Armstrong Laboratory subjects volunteered for this study to determine whether reduced pressure in extended coverage anti-G trousers (ECT), in combination with positive pressure breathing for G protection, affected +Gz tolerance. Group mean gradual onset run (GOR) time for the low pressure Khedule (0.8 psig · G^-1) was significantly different from the other two conditions (1.1, 1.5 psig · G^-1)---84.1, 9S.6, and 94.1 s, respectively. Group mean simulated aerial combat maneuver (SACM) times statistically differed between the low and middle pressure rates compared to the highest pressure scheclule--147.6, 164.8 and 232.3 s, respectively. SACM heart rate (HR) responses for the +9 Gz plateaus were not statistically different among conditions. However, +5 Gz HR’s were lower for the highest pressure condition. Similarities were identified between the middle and high pressurization conditions for GOR. However, reducing pressure in the ECT during SACM exposures was not supported by these data.

Abstract

The effect of exercise and LBNP countermeasures on the cardiovascular deconditioning response have been evaluated by the study of heart rate variability during progressive LBNP tests before, during (day 15), and after 28 d continuous 6° head-down tilt bed rest. Twelve healthy men (age 27-42 years) were studied in two groups. Six were assigned to a countermeasure regime (CM) consisting of strenuous short-term resistance exercise once per day, 6 days per week from day 7 to day 28, combined with lower body negative pressure (LBNP, -28 mm Hg) for 15 min on days 16, 18, 20, and 22-28. Results were compared with data from six subjects, matched on the basis of maximum oxygen uptake, who received no countermeasures (No-CM). The main effects of bed rest were seen in reductions in RR-interval, and in total spectral power. The results of spectral analysis showed a significant reduction in an index of parasympathetic activity with a nonsignificant increase in a sympathetic indicator. The fractal component of heart rate variability was reduced also, suggesting a change in cardiovascular control mechanisms. Although there were significant differences between CM and No-CM for a number of variables, there were no bed rest by countermeasure interaction effects in the statistical analysis. These results suggested that this particular series of countermeasures was ineffective in preventing at least certain changes indicative of cardiovascular deconditioning with 28 d head-down tilt bed rest.

Abstract

The neuromuscular characteristics of the triceps surae muscle were investigated during the various types of stretch-shortening cycle (SSC muscle loading. The analysis concentrated on the preactivation and the contact phases of SSC. Muscle leading was changed unconventionally by artificially changing the condition of the gravity in drop jumps. This was accomplished by using a special lifting block system where the gravity could be modified to control leading and unloading effects of the triceps surae muscle. The normal gravity condition showed an advantage over the other gravity drop jump conditions for the measured parameters. The same tendency could be seen in the activation characteristics of the investigated muscles in the preactivation and eccentric phases. Further, the preactivation EMG was related to the eccentric peak angular velocity of the ankle joint. The correlation coefficients were 0.37 (p < 0.05) and 0.48 (p < 0.01) for the gastrocnemius and the seleus muscles, respectively. All the results emphasized considerable adaptation of the neuromuscular system to the normal gravity condition. However, the overall control of landing may also depend on the vestibular and visual inputs, which might modify even the earlier learned central programs.

Abstract

The purpose of this study was to document the amount and rate of muscular fatigue during alternating levels of isometric contraction similar to that found during the Simulated Aerial Combat Maneuver (SACM). In addition, the time needed to recover from such an exercise was examined. Twenty malesbetween the ages of 22 and 35 years performed an isometric contraction of their right quadriceps muscle at alternating levels of tension (20 and 50% maximum voluntary contraction) until exhaustion. The time at each contraction level was 10 s. After each exhaustive exercise bout, subjects were assigned to one of six recovery intervals (10, 20, 40, 60, 120, and 240 min) followed by a repeat of the exhaustive exercise. All subjects were tested under each of the six recovery intervals. Results showed that the amplitude (RMS) of the myoelectric signal increased while the frequency content of the signal (MPF) decreased over the course of the fatiguing activity. Endurance time (ET) was found to be significantly (p < 0.05) recovered (90.96%) within 60 rain after stopping the exercise. Although MPF returned to its prefatigue value within 10 min of rest, the RMS value had still not recovered after 4 h.

Abstract

This study investigated burnout in air traffic controllers (ATC´s). There were 109 Italian ATC´s who filled out the Rome Burnout Inventory, a new tool for burnout assessment, during breaks in the working environment. The questionnaire assessed: 1) emotional-mental exhaustion (EME);2) physical exhaustion (PE); 3) social support by components of the social network; 4) work-and nonwork-related stressors; 5) self-reported psychosomatic and psychiatric disorders. Our data show that the burnout syndrome is closely and positively related to age, years spent in air traffic control, professional dissatisfaction, and to work stressers, but not to nonwork stressors. In our sample, burnout was negatively correlated with social support provided by friends and family.

The PE construct seemed to be unreliable in detecting physical burnout in Italian ATC´s Using analysis of variance, subjects with self-reported psychosomatic disorders did not show higher levels of EME scores. Further, EME was positively correlated with self-perceived psychological distress(anxiety, depression and impulse discontrol), but not with physician-ratod psychopathology, as revealed by psychoactive drug intake. We suggest that burnout is a construct independent from clinical anxiety or depression.

Abstract

Pastural central may reflect the pilotʹs ability to deal successfully with the stresses of spatial orientation. In this study, we hypathesized that fighter pilots would have better performance on the ʺtetra-axiametric posture testʺ than would helicopter pilots (less rigorously selected) and candidates for flight training. We tested 28 fighter pilots, 23 helicopter pilots and 43 candidates by tetra-axiametric posturegraphy. Fighter pilots were found on the level position to have significantly more compensatory anterior-posterior sway (moving anterior-posterior rather than laterally, p = 0.02) and required less movements to maintain balance (p = 0.02) than did candidates. Helicopter pilots had intermediate values. In stressed positions, fighter pilots demonstrated relatively more slow movements (p = 0.018) than did the candidates, which may be related to increased labyrinth control, in the stressed positions, helicopter pilots had postural profiles similar to the candidates. We conclude that there are significant differences in postural control as tested by tetra-axiametric posturography between fighter pilots, helicopter pilots, and candidates for flight training. This could be due to either innate ability, which could be used in the selection process, or to training. A prospective study is planned in order to determine if posturography can predict a candidateʹs ability to complete flight training.

Abstract

Helmet-mountod displays under development for rotary- and fixed-wing aircraft will allow the user to switch electronically between forward-looking infrared (FLIR) and night vision goggle (NVG) sensors. These sensor transitions potentially involve large changes in display luminance which could transiently impair visual resolution and performance. The purpose of this study was to identify the display luminances which produce a transient reduction in vision when switching from a higher luminance (i.e., FLIR) to a lower luminance (i.e., NVG) display. A letter recognition task was used to assess the effect of luminance adaptation on visual resolution in five subjects. A significant reduction in letter recognition was observed in the first second after switching from simulated FLIR to simulated NVGʹs when the FLIR luminance was ≥10 fL. By varying letter size, contrast, and exposuro time, the magnitude and duration of visual loss after switching from a bright (49.2 fL) FLIR display were determined. The visual loss lasted up to 4 s, and included a 2᙭ reduction in visual acuity, and a 3᙭ reduction in contrast sensitivity, large differences in sensor display luminance should be avoided to maintain high levels of visual performance and aviation safety. Design features or training may be necessary to achieve a proper balance between FLIR and NVG luminances which optimize performance and safety without sacrificing the quality of the sensor image.

Abstract

Two cases are presented of Canadian Forces pilots who experienced inflight bredycardia during 15 s of -1 Gz acceleration. The bradycardia was characterized by rapid cardio-deceleration, stable bradycardia, then cardio-acceleration during recovery following the -Gz exposure that was slower than the cardio-deceleration. Vagally mediated bradycarclla in humans subjected to -Gz acceleration stress has been previously documented in laboratory studies. This bradycardla may be operationally significant since it signifies the presence of other physiological effects that predispose aviators to reduced subsequent +Gz tolerance. Research to investigate the implications of reduced +Gt tolerance following -Gz acceleration is warranted.

Abstract

Retinal vein occlusions are primarily a disease of the elderly, frequently with permanent visual abnormalities. However, both branch and central retinal vein occlusions occur rarely in young individuals. Reported hera are a series of retinal vein occlusions in USAF aviators. Seven cases were identified from records of the USAF Armstrong Laboratory Aeramedical Consultation Service from 1976-91. Four cases of central retinal vein occlusions and three cases of branch occlusions are summarized. Initial visual acuity ranged from 20/15 to 20/400. All seven aviators recovered 20/15 vision and returned to flying status. Hyperlipidemia was found in four of the seven aviators, and hypertension was diagnosed in two aviators. Included is a discussion of current concepts in the natural history, associated systemic conditions, treatment options, and aeramedical implications of retinal vein occlusions.

Abstract

To develop an amplification system for physiologic chest sounds during air medical transport in let helicopters, we compared frequency spectra of physiologic chest sounds and Allison C-28 equipped jet helicopter noise. We found that the frequency spectrum of physiologic chest sounds is contained entirely within that of jet rotorcraft noise. Attempts to amplify physiologic chest sounds or to filter let rotercraft noise will invariably fall to improve perception of chest sounds. Future research must focus on assessment of actual movement of the chest and of each hemithorax, as well as on carbon dioxide production, as indicators of adequate ventilation and proper endotracheal tube position.

Abstract

Pilotsʹ sensations of orientation while pushing over (bunting) are inconsistent. We flew 13 aircrew or naive subjects individually in a Hawk or Hunter jet training aircraft. With sun visor down and eyes closed, each was asked to report what the aircraft was doing. After unaccelerated level flight for 30 s, the aircraft was accelerated in level flight from 200 to 250 kts at +0.15 to +0.25 Gx, and gently pulled into a stable 250-kt, 3000 ft/min climb. After 30 s, it was pushed to -1 G during 3 s. Minus 1 G was then held for a further 3 s. Of 30 maneuvers, 14 produced sensations of inversion in 9 of 13 subjects. Two subjects reported feet-up rotation to the inverted; one felt a rotation of indeterminate direction; five felt sudden inversion. This illusion was experienced by 3/3 naive non-pilots, 6/8 pilots, and 0/2 test pilots. We conclude that the ʺinversion illusionʺ exists, and that the postulated sensation of backward rotation is often not perceived.

Abstract

Night vision goggles (NVGʹs) have widespread use in military and civilian environments. NVGʹs amplify ambient illumination making performance possible when there is insufficient illumination for normal vision. While visual performance through NVGʹs is commonly assessed by measuring threshold functions such as visual acuity, few attempts have been made to assess vision through NVGʹs at suprathreshold levels of stimulation. Such information would be useful to better understand vision through NVGʹs across a range of stimulus conditions. In this study visual evoked potentials (VEPʹs) were used to evaluate vision through NVGʹs across a range of stimulus contrasts. The amplitude and latencyof the VEP varied linearly with log contrast. A comparison of VEPʹs recorded with and without NVGʹs was used to estimate contrast attenuation through the device. VEPʹs offer an objective, electrophysiological tool to assess visual performance through NVGʹs at both threshold and suprathreshold levels of visual stimulation.

Abstract

Sixteen U.S. Army aviators, who were given training on focus adjustment technique with aviator night vision goggles (NVG), showed an improvement in visual acuity with focus adjustment compared to a fixed infinity focus control. The long-term effect of focus adjustment on vision was not measured; however, adjustment accuracy was found to be generally within acceptable limits based on computer modeling and available physiologic data. Fixed focus eyepieces that are set to a low minus power may partially compensate for instrument myopia, but they may not optimize visual acuity to the extent that adjustable focus eyepieces do. Eyepiece adjustment proficiency with present night vision devices can be improved through training that emphasizes focusing to the least passible minus dioptric power. Future night vision displays can minimize focus misadjustment by providing a tactile zero marking, a limited dioptric adjustment range, and a focusing knob capable of finer adjustment than is available with current NVG’s.

Abstract

A compact device for the collection of alveolar air (breath) from humans aboard spacecraft was developed. The system uses silicone one-way valves that operate independent of gravity, and provide minimal backpressure. Small charcoal filters clean ambient air used for inhalation. The device provided good recoveries of organic compounds at the 20 ng/L level, with generally low carryover of these compounds to a blank sample following a sample at exposure to 100 ng/L. When water accumulated in the system, this carryover increased for highly water soluble compounds. The new device was used in parallel with a larger, previously developed alveolar air sampler that requires gravity for proper operation; comparable results were obtained with the two units. The device measures 47 x 34 x 11.4 cm and weighs approximately 3.2 kg. Sufficient space is available within the case to accommodate a number of sample collection options.

Abstract

The Armstrong Laboratory and its predecessors have conductod responsible animal research in support of USAF operations for nearly three decades. The use of animal models is essential in research that requires a complex living system, but would be too hazardous to humans. The Laboratory also has aggressively pursued alternatives to the use of animals and improved methods in conducting animal research. Thus far, fewer animals are used currently in some areas of research. Since the human is the focus for Armstrong Laboratory research, human test subjects are used as frequently as possible. As improved noninvasive physiologic monitoring methods become available, humans will be used more extensively.

Abstract

A robustly healthy aviator experienced a sudden focal impairment in cerebral function from which he rapidly recovered in a manner consistent with the entity known as ʺspectacular shrinking deficit syndrome.ʺ Although brain imaging studies revealed a ʺlacunarʺ type lesion involving the caudato nucleus, the clinical picture was much more suggestive of a cardiogenic embolic event. Transthoracic echocardiography was required to demonstrate the probable cause of the stroke (an atrial septal defect). Following surgical repair of the atrial septal defect, the aviator was recommended for waiver to resume duties involving ariatian as pilot in command.