During constant speed rotation of the body, head rotation about an axis other than the axis of rotation of the body (i.e., Coriolis stimulation) induces motion sickness. The position of the body relative to the center of rotation will influence the sickness caused by Coriolis stimulation; the direction of head movement will not affect the sickness caused by Coriolis stimulation. There were 24 seated subjects (12 male, 12 female) who made 30° pitch motions of the head every 30 s while rotating about a vertical axis at 10 r.p.m, on a turntable at two separate locations: a) at the center of rotation; and b) 0.75 m from the center of rotation. After each head movement the subjects gave ratings of motion illness. There was no significant difference between illness 0.75 m from the center of rotation and illness at the center of rotation, or between the illness ratings from male and female subjects. Moving the head up from the horizontal caused significantly fewer increases in ratings of motion illness than moving the head back down to the horizontal. Precise location of the body at the center of rotation is not critical during Coriolis stimulation, but the direction of head movement has a large effect on nausea. An influence of somatosensory information on sickness caused by Coriolis stimulation is suggested.Abstract
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Watt et al. (15) and Young et al. (17) have demonstrated that during prolonged microgravity, large errors can be made when pointing at memorized targets in the absence of vision. However, those experiments could not distinguish between errors caused by not knowing where the arm was pointed and errors caused by not knowing target location. The primary goal of this study was to determine the relative contribution of each of these potential sources of error. It was hypothesized that pointing errors would be greater than pre-flight controls if vision was continuously absent during testing, but not greater than pre-flight if vision was restricted only while pointing. Five subjects on Spacelab SLS-2 (Part A) pointed at targets while keeping their eyes closed continuously; (Part B) touched various body parts and estimated the position of their arms while the eyes remained closed; and (Part C) pointed at the same targets as in A but closed their eyes only while pointing. On the ground, if the eyes were closed only while pointing, pointing errors averaged 4.5° After several days m space, errors averaged 7.0° (p < 0.05). Again on the ground, if the eyes were closed continuously while pointing, an additional error of 4.0° was measured. However, after several days in space, the additional error was 10.5° (p < 0.0005). The results of this study suggest that the major problem encountered when pointing at memorized targets in microgravity is a lack of knowledge of target, not limb, position.Abstract
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Although intact vestibular function is indispensable to maintaining spatial orientation, no good screening tests of vestibular function are implemented in the aviation community. High frequency voluntary head rotation was selected as a vestibular stimulus to isolate the vestibulo-ocular reflex (VOR) from visual influence. A dynamic visual acuity test that incorporates voluntary head rotation was evaluated as a potential vestibular function screening tool: 27 normal subjects performed voluntary sinusoidal head rotation at frequencies from 0.7-4 Hz under 3 different visual conditions: visually-enhanced VOR, normal VOR, and visually suppressed VOR. Standardized Bailey-Lovie chart letters were presented on a computer monitor in front of the subject, who then was asked to read the letters while rotating his head horizontally. The electro-oculogram and dynamic visual acuity score were recorded and analyzed. There was no significant difference in gain or phase shift among 3 visual conditions in the frequency range 2.8-4 Hz. The dynamic visual acuity score shifted less than 0.3 log MAR at frequencies under 2.0 Hz. The dynamic visual acuity test at frequencies around 2 Hz can be recommended for evaluating vestibular function.Abstract
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Hypothesis: This study tested the hypothesis that respiratory muscle fatigue occurs during a simulated air combat maneuver (SACM) centrifuge profile. Methods:Six subjects (four males, two females) were exposed to a SACM consisting of alternating +4 Gz to +7 Gz plateaus until volitional fatigue. Electrical activities of the diaphragm, scalene, intercostal and external oblique muscles were monitored along with esophageal pressure and ventilation. Results:SACM times averaged 358 ± 115 s. The mean frequency of the electromyographic signal of the diaphragm and scalenes during inspiration, and the intercostals during the static expiratory portion of the anti-G straining maneuver (AGSM), decreased significantly (p < 0.05) over the course of the SACM by about 9%, 10% and 4%, respectively, indicating muscle fatigue. Esophageal pressure (PES) during the straining portion of the AGSM decreased significantly from 72 ± 20 to 66 + 21 mmHg (mean ± SD). Ventilation increased significantly both at +4 Gz and +7 Gz (32 ± 16 L.min 1 to 56 - 19 L.min − at +4 Gz and 27 · 5 to 35 + 9 L.min -− at +7 Gz) over time. PES during a maximal AGSM at +1.4 Gz (baseline) was decreased post- vs. pre-SACM (p = 0.0575). PES exerted during a maximal static inspiratory maneuver at residual lung volume was not changed after the SACM. Inspiratory work increased significantly during the SACM. The elastance of the respiratory system did not change during the SACM, but itwas significantly increased when tested after the SACM. Conclusion:Increased inspiratory work, decreased pressure generation during a maximal AGSM and EMG frequency shifts suggest respiratory muscle fatigue coincides with the termination of SACM.Abstract
The physiological responses of a group of nine subjects exercising at a metabolic rate of 510 W in a new low burden chemical protective ensemble, the Chemical/Biological Combat Suit (CBCS), have been determined under a warm, humid climatic condition, 30− and 60% relative humidity. The CBCS was significantly superior to a current NBC overgarment (MK4) in terms of induced physiological strain. Furthermore, there was no statistically significant difference between the normal combat uniform (DPCU) and the CBCS worn as a combat uniform (CS), without hood, mask and gloves, in terms of increase in rectal temperature and increase in heart rate. The major limitation on performance in the fully encapsulated CBCS was imposed by the combination of mask, permeable hood and impermeable gloves. It was concluded that there would be a mgnificant improvement in soldier performance in the CBCS rather than in the current MK4 overgarment and that there would be no detriment to soldier performance when wearing the CS uniform in times of chemical threat.Abstract
Identification of stresses of mixed-gender squadrons, attention to the psychological concerns of pilots in combat, and recognition of the difficulties of balancing a career and family are important in today's United States Air Force (USAF). What qualities are desirable in male and female pilots in combat situations, how do men and women view their career and family goals, and how do men and women work together in day-to-day squadron activities versus deployment and combat situations? A semi-structured clinical interview sought information about personal/family health, squadron relationships, and career/deployment stresses. The interview covered the effect of grounding for more than 30 d, motivation to fly, health decrements due to aircraft design, teamwork difficulties and blocks to success, career demands, combat and prisoner of war (POW) concerns, stress and coping styles, flying goals, and family/health concerns. There were 114 (64 male and 50 female) pilots who participated in the study. The majority of male pilots interviewed asserted that they would be more protective of a woman in combat than a man and were concerned about their reaction to a female POW. Many women were concerned about being used to exploit men in a POW camp. The majority of pilots believed women were well integrated into their squadrons. Those interviewed reported that the squadron members with the most difficulty dealing with women were older males, including enlisted crew and some commanders. The information gained from this study will assist the USAF in understanding and coping with the psychological stresses associated with combat, deployment, and mixed-gender squadrons.Abstract
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Operational fighter squadrons frequently find themselves deployed to semi-isolated stations in the Arctic. This paper discusses the major issues necessary for fhght surgeon consideration. In particular, the areas of pre-deployment planning, preparing for the worst, routine operations, and post deployment actions are discussed. A recent month-long deployment of a 12-ship squadron of F18s with support elements from Bagotvdle, Canada, to Evenes, Norway, is examined. A proposed kit list to support a similar deployment to a semi-isolated station is provided.Abstract
The effect of hyperbaric hyperoxia on the pharmacokinetics of caffeine was investigated in human volunteers. Some 600 ml of coffee were administered to 2 volunteers and blood samples were serially collected for 24 h. The volunteers entered a hyperbaric chamber 2.5 h following coffee ingestion for a total period of 110 min (0.25 MPa, alternating 100% O2-breathing for 20 min and air breathing for 5 min). The concentrations of caffeine in serum was determined by high pressure liquid chromatography. The caffeine amount ingested was determined by analyzing an aliquot of the coffee beverage. Data were analyzed assuming hnear kinetics and an open one-compartment model. Effects of hyper-baric hyperoxia on caffeine disposition were investigated using a runs test. Moreover, a one-population t-test was applied to residuals, separately for data from the matial normobaric period, the hyperbaric period and the terminal normobaric period. Pharmacokinetic parameters were similar to established literature data on caffeine [Volunteer 1 : maximal concentration (Cmax: 6.13 mg. L-1 at Tmax: 55 min, half-time of elimination (T1/2:180 min, total clearance (CI): 3.41 ml·min-1·kg-1; volume of distribution (Vd: 0.88 L·kg-1; Volunteer 2: Cmax: 6.23 mg·L-1, Tmax: 94 min, T1/2: 283 min, CI: 1.90 ml·min-1·kg-1, Vd: 0.77 L·kg-1]. The runs test as well as the analysis of residuals gave no evidence for alterations of caffeine disposition by hyperoxia (p > 0.05). The pharmacokinetics of caffeine do not seem to be influenced in a clinically relevant way in humans during a stay for 110 min at 0.25 MPa, alternating 100% O2 and air breathing.Abstract
Muscular diseases including the dystrophies and myopathies are often incompatible with a variety of occupations including aviation and military duty. Many of these diseases present early in life, are readily diagnosable, and are therefore rare in the aviation community because of pre-screening and selection. Some forms, however, may not present until adulthood during an established aviation career. Furthermore, although initial presentations may be subtle and insidious, the potential occupational and aeromedical ramifications of these diseases can be profound. The following report describes the case of a subjectively a symptomatic career military aviation officer who presented with an unusual gait, and was subsequently determined to have one of the late-presenting muscle disease variants: Anterior Compartment Distal Myopathy. The patient's presentation and progression, diagnostic evaluation, prognosis, aero-medical risk and disposition, and issues of occupational and aeromedical significance are discussed.Abstract
Doppler-detectable microbubbles (DMB) are frequently, used to evaluate altitude decompression stress. However, the role of DMB in the therapy of decompression sickness (DCS) has not been examined. The ability of Doppler to detect microbubbles during decompression (Doppler test) may be used in the diagnosis of DCS, and to aid clinical decisions about treatment options for DCS. We examined the data on DMB and symptoms from NASA Database on DCS (n = 516). The accuracy of Doppler test was obtained from the Receiver Operating Characteristic (ROC) for DMB (grades I through IV), and efficacy was obtained by calculating predictive or post-test probabilities. Threshold analysis was used to obtain the probabilities for testing and/or treatment decisions. The Doppler test was useful for both screening and confirming DCS, when different criteria (grade I for screening; grade IV for confirming) were used for a positive test. Calculation of predictive values and threshold analysis showed that: 1) early recompression was the therapy of choice when post-test probability of disease was >0.25 in individuals with non-specific pain at altitude, and early recompression with 100% oxygen for 2 h at site level was optimal therapy when this probability was >0.33; 2) hyper-baric therapy was optimal when post-test probability was >0.04 in individuals with uncertain symptoms post-flight. The Doppler test was of greater utility in excluding DCS than confirming its presence, and was useful in making therapeutic decisions on DCS when confronted with non-specific symptoms at altitude.Abstract
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Pilot studies are presently being carried out to determine the efficacy of raising the oxygen concentration in the room air of commercial and scientific facilities at altitudes of 4000-5500 m. This is a remarkably effective way of relieving hypoxia. For example, oxygen enrichment by only 5% (i.e., raising the oxygen concentration from 21 to 26%) reduces the equivalent altitude by 1500 m. However, concern has been expressed about the possibility of fire hazard. In this article, existing data from various sources have been analyzed to determine the burning rate of materials such as paper and cotton clothing at various altitudes when the Po2 in the air is increased to 110 mmHg to give an equivalent altitude of 3000 m. The analysis shows that in spite of the.increase in oxygen concentration, the burning rate is much less than at sea level, primarily because the Po2 is so much lower even with oxygen enrichment.Abstract