Helmet-mounted displays (HMDs) allow pilots to view aircraft instrument information while looking to the side, away from the aircraft centerline axis. In that situation, pilots may lose attitude awareness and thus develop spatial disorientation. A secondary concern is the possible effects of visual conflict between the apparent motion of traditional, nose-referenced flight symbology and the off-axis view of the outside world. Alternative symbologies will provide improved attitude awareness for HMDs when compared with the conventional inside-out symbology now used with head-up displays (HUDs), if the HUD symbology is used on a HMD. The 9 pilots were presented with 48 randomly arranged unusual attitude conditions on a Helmet-Mounted Display (HMD). The three symbologies included: 1) the inside-out representation now used with fixed HUDs, which features a moving horizon and pitch ladder; 2) an outside-in display depicting a moving aircraft relative to a fixed horizon; and 3) an inside-out novel symbology termed the ‘grapefruit’ display (GD). The background scene contained a mix of either a front view orientation or a side view one. Conditions were randomized within and across subjects. Subjective preferences were collected after the completion of all tasks. Analysis of variance repeated measures design revealed that stick input for the GD was significantly faster with fewer roll reversal errors than either of the other two. The time to recover to straight and level was significantly shorter for the front view orientation than the side view. Of the nine pilots, eight preferred the GD symbology as a method of presenting attitude information on the HMD. Results suggest the current HUD symbology is not the best way of displaying attitude information on the HMD. Given the conditions of this study, the best way of presenting the pilot with attitude information on the HMD is with the GD symbology.Abstract
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Primary hypertensives who are acutely exposed to hypoxic flypoxia show an enhanced reactivity of arterial chemoreceptors as well as an exaggerated response of the sympathetic nervous system. Since these phenomena could influence their ability to tolerate sustained hypoxic hypoxia, this study was performed to determine whether persons predisposed to hypertension have a normal tolerance of simulated high altitude. Subjects were 18 young men with a family history of hypertension (sons of hypertensives, SOHT) whose BP values were in the upper normal or borderline hypertensive range. Controls were 15 young men without parental hypertension (sons of normotensives, SONT) who had normal BP values. Each subject underwent both a control and an altitude experiment. The latter consisted of an 8-h exposure to hypobaric hypoxia (equivalent to 4200 m) while resting supine in an altitude chamber. Fluids were administered by mouth and by intravenous line to produce sustained diuresis. Variables measured included heart rate, BP, respiratory rate, O2 saturation, urine flow rate, and sodium excretion. All subjects tolerated the control experiment and all SONT also completed altitude exposure. However, 8 of 18 SOHT developed antidiuresis and had to leave the chamber early due to symptoms of mild acute mountain sickness. Compared with SONT, SOHT exhibited more stable cardiorespiratory parameters at altitude. The data support the hypothesis that borderline hypertensives have stronger cardiorespiratory responses to altitude than controls, a response that is compatible with higher excitability of their arterial chemoreceptors. However, their altitude tolerance is reduced even at rest, probably because of the renal effects of an exaggerated response in the sympathetic nervous system.Abstract
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Two current theories concerning the etiology of motion sickness (MS)--the eye movement hypothesis and sensory conflict theory—were evaluated under conditions that manipulated the degree of optokinetic nystagmus (OKN) and/or vection. Eye movement and perceptual responses were elicited with whole field stimulation in a vertically striped rotating drum and modulated with fixation and/or a restriction of the field of view (FOV). Measures of OKN, vection, and MS were recorded under the various conditions. Both visual field restriction and/or fixation diminished circular vection, OKN, and MS. Conditions involving both fixation and restricted FOV resulted in greater reductions in MS than did either restriction alone. These findings lend support to a multi-factor explanation of MS, involving both sensory conflict and eye movement.Abstract
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Current space suits are rigid, gas-pressurized shells that protect astronauts from the vacuum of space. A tight elastic garment or mechanical-counter-pressure (MCP) suit generates pressure by compression and may have several advantages over current space suit technology. In this study, we investigated local microcirculatory effects produced with and without a prototype MCP glove. The right hand of eight normal volunteers was studied at normal ambient pressure and during exposure to -50, -100 and -150 mm Hg with and without the MCP glove. Measurements included the pressure against the hand, skin microvascular flow, temperature on the dorsum of the hand, and middle finger girth. Without the glove, skin microvascular flow and finger girth significantly increased with negative pressure, and the skin temperature decreased compared with the control condition. The MCP glove generated approximately 200 mm Hg at the skin surface; all all measured values remained at control levels during exposure to negative pressure. Without the glove, skin microvascular flow and finger girth increased with negative pressure, probably due to a blood shift toward the hand. The elastic compression of the material of the MCP glove generated pressure on the hand similar to that in current gas-pressurized space suit gloves. The MCP glove prevented the apparent blood shift and thus maintained baseline values of the measured variables despite exposure of the hand to negative pressure.Abstract
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Previous studies have revealed that modafinil elevates resting core temperature during periods of sustained wakefulness. The purpos of this study was to examine the effects of modafinil on core temperature during rest and exercise throughout 40 h of sustained wakefulness in a warm environment. Ten males performed a drug session (three 100 mg doses per day) and a placebo session that involved a control day, 40 h of sustained wakefulness, and a recovery sleep. For 38 h of the sustained wakefulness, subjects were exposed to 30°C with 50% relative humidity. During the afternoon of both days of wakefulness and during the early morning of the second day, subjects performed 2 h of exercise at 60% Vo2max while exposed to the warm environment. The data revealed that rectal temperature (Tre) was elevated at rest 0.15-0.2°C following modafinil ingestion throughout the periodof sustained wakefulness. This increase in body temperature at rest was due to an increase in heat production during the first day of wakefulness followed by a lower evaporative heat loss during the second day. During exercise, an inconsistent effect of the drug on Tre was observed throughout the 38-h period. On the first afternoon, the impact of modafinil on Tre was no longer evident after 20 min of exercise. In contrast, during the early morning and afternoon of the second day, the effects of the drug on Tre at rest remained during exercise. For seven subjects who had Tre data for 80 min during all exercise periods, Tre during the placebo session was 38.9, 38.4, and 38.7°C after 80 min of exercise for periods one, two and three, respectively, whereas the corresponding values during the modafinil session were 38.8, 38.7, and 38.9°C With a greater cumulative dose of the drug, Tre remained elevated throughout the exercise period to an extent similar to the increase observed under resting conditions when compared with the placebo condition.Abstract
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Previous isolation studies have shown increased 24-h urine volumes and body weight gains in subjects. This project examined those and other physiological variables in relationship to sleep motor activity, subjective sleep quality, mood, and complaints during confinement. Six male and two female subjects lived for 7 d in the National Space Development Agency of Japan's isolation chamber, which simulates the interior of the Japanese Experiment Module. Each 24-h period included 6 h of sleep, 3 meals, and 20 min of exercise. Each morning, subjects completed Sleep Sensation and Complaint Index questionnaires. Catecholamine and creatinine excretion, urine volume, and body weight were measured on the 2 d before and 2 d after confinement, and sleep motor activity was measured during confinement. Confinement produced no significant change in body weight, urine volume, or questionnaire results. In contrast, epinephrine, norepinephrine, and sleep motor activity exhibited significant differences during confinement (p < 0.05). Higher nocturnal norepinephrine excretion correlated with higher sleep motor activity. The 24-h epinephrine values were slightly higher than normal throughout the experiment, but lower than for subjects working under time-stress. High sympathetic activity (as indicated by norepinephrine) may have interfered with sleep.Abstract
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The NDRI (noradrenalin-dopamine re-uptake inhibitor) bupropion SR (sustained-release) is marketed as Wellbutrin® for treatment of depression or Zyban® as a smoking cessation aid. There has been considerable interest in the possibility of returning aircrew to restricted flying duties once stabilized on bupropion SR after resolution of depressive symptoms, or while taking bupropion SR for smoking cessation. This study was undertaken to determine whether bupropion SR affects psychomotor performance. There were 24 subjects (18 men and 6 women) who were assessed for psychomotor performance during placebo and bupropion SR treatment, in a double-blind cross-over in counter-balanced order. Each treatment arm lasted 5 wk. The daily bupropion SR dose was 150 mg during week 1, and 300 mg during weeks to 2 to 5. Subjects completed a drug side-effect questionnaire and were tested on two psychomotor test batteries once per week during each of the placebo and drug arms. There was no significant Impact of bupropion SR on serial reaction time, logical reasoning, serial subtraction, or multitask performance. With respect to drug side effects there was a main effect of drug on “number of awakenings” (p < 0.048), “difficulty returning to sleep” (p < 0.004), and “dry mouth” (p < 0.049). There was no impact of bupropion SR on dizziness. While we found some of the expected side effects due to bupropion SR, there was no effect on psychomotor performance. These findings support the possibility of returning aircrew to restricted flight duties (e.g., in non-fast jet aircraft) under close observation once stabilized on bupropion SR.Abstract
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Ejection from a fighter aircraft can expose the pilot to extreme cold and windy conditions. Knowledge of the effects of such conditions on thermal responses and performance of the pilot is scarce. It is expected that the temperature of bare skin and fingers may decrease to the level where health and/or performance are hampered. Seven fighter pilots performed a simulated parachute descent (SPD) at ambient temperature (Ta) of -35°C and wind velocity of 10 m ° s-1. The 8-min SPD was followed by a 60-min cold exposure (CE) at Ta of -20°C. Flight garments with or without immersion suit were used. During SPD the subjects performed basic survival tasks. Rectal and skin temperatures were measured and manual performance was tested. Thermal responses did not significantly differ between the clothing ensembles. Mean skin temperature was 28°C and 27°C at the end of SPD and CE, respectively. The cheek temperature was 9°C (range 3.2-13.8°C at the end of SPD. Finger skin temperature was 7°C and 9° at the end of SP and CE, respectivefy. The subjects could perform the defined tasks during SPD while manual performance was slightly impaired during CE. Subjects could tolerate the 8-min SPD and the following CE in the studied conditions without a loss of vital performance in basic survival actions. However, the risk of frostbite on the uncovered skin area as well as numbness of the fingers may jeopardize pilots’ health and performance during parachuting.Abstract
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Female pilots now fly many types of aircraft including military fighters capable of maneuvers that produce high, sustained acceleration in the +Gz axis. Although women have participated as subjects in various centrifuge studies, little is known about the acceleration tolerance of female pilots. Between April 1995 and December 1997, 17 female pilot trainees were studied at the Institute of Aerospace Medicine, Bangalore, India. The subjects were 23.2 ± 1.4 yr old and led physically active lives. Their relaxed +Gz tolerance (defined as peripheral light loss) were tested using the High G and Disorientation Demonstrator. The protocol included a series of rapid onset runs (RORs) to tolerance followed by a single gradual onset run (GOR) to tolerance. The mean ROR tolerance was 4.2 ±0.4 G. The mean GOR tolerance was 5.2 ± 0.6 G. Three of the subjects were unable to complete the GOR due to severe nausea. Two women reported breast discomfort at levels of 3.5 G and beyond. No other problems were reported. The acceleration tolerances for the female pilot trainees were comparable to those for male pilots previously studied in our laboratory.Abstract
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Approximately 54% of civilian pilots rely on ophthalmic lenses to correct defective vision in order to maintain a valid airman medical certificate. This report reviews aviation accidents and incidents where the use or misuse of ophthalmic devices was considered to have been a contributing factor in the mishap. The NTSB's Aviation Accident/Incident Database and the FAA's Incident Data System were queried for terms related to ophthalmic devices. All reports were reviewed to determine whether an ophthalmic device was a factor in the mishap and then stratified based on the type of ophthalmic correction involved. Additionally, the Aviation Safety Reporting System (ASRS), which allows aviation personnel to report actual or perceived safetyrelated problems was similarly queried and reviewed. The NTSB and FAA databases included 19 mishaps with contributing factors such as lost and/or broken eyeglasses, problems with sunglasses, incompatibility with personal protective breathing equipment, adaptation difficulties, or inappropriate ophthalmic prescriptions and contact lenses. Aviation personnel voluntarily submitted 26 ASRS reports describing operational problems involving ophthalmic devices that adversely affected aviation safety. Ophthalmic devices used by pilots have contributed to aviation accidents and incidents. The review and reporting of these events provides important information that can be used to educate flight crewmembers, Aviation Medical Examiners, and eyecare practitioners about the potential hazards of using inappropriate ophthalmic devices. Recommendations in this report may assist pilots in avoiding similar hazardous situations and enhance aviation safety.Abstract
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The value of the electroencephalogram (EEG) as a screening tool in aviation medicine is subject to debate. We evaluated the use of periodic repetition of the EEG—after an initial EEG screening—in healthy, fully-licensed pilots to identify risk factors for fatal air crashes. In a nested case-control study, we compared the EEG patterns of 33 pilots who died in military aviation accidents from 1990 to 2001 with the recordings of 66 controls. Cases and controls were matched for potentially confounding factors such as age, military membership, type of aircraft, and aeronautical experience. Both groups presented normal EEGs. EEG findings in cases and controls did not differ; nonspecific EEG abnormalities did not occur more frequently in those pilots who crashed. After an initial EEG screening, periodic repetition of the EEG is not a useful means to detect risk for fatal air crashes.Abstract
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The USAF devotes great financial and medical assets to the identification and evaluation of USAF aircrew who have been grounded from flying duties for medical conditions thought to be dangerous to the flying mission or personal safety. The purpose of this study is to update the literature and to demonstrate that USAF efforts during the past 19 yr have improved our ability to retain experienced aviators. The USAF waiver file was reviewed to quantify the number of USAF pilots and navigators receiving permanent medical disqualifications from flying duties during 1995-1999. We identified 157 cases, which were stratified by age group and sex. The number of disqualifications increased incrementally by age group. The most common diagnoses resulting in permanent disqualification were coronary artery disease, hypertension, back pain and disk abnormalities, migraine headaches, diabetes mellitus, and substance/alcohol abuse. These results are very similar to those reported in a 1984 USAF study and other studies of aviation populations. The rate of permanent flying disqualifications in this study was equal to 0.18% per year compared to 4.1% per year in 1984. This decrease in the rate of disqualifications could be due to modification of USAF standards, utilization of clinical management groups, better screening of applicants, new technology or therapies, and effective preventive medicine efforts throughout the Air Force.Abstract
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This report describes a case of central serous retinopathy (CSR) in the right eye of a commercial air transport pilot, which resulted in a permanent reduction in visual acuity and the loss of his license. The previously fit and well pilot developed sudden loss of central vision, which resolved spontaneously. He then went on to experience recurrent episodes of fluctuating visual acuity (down to 6/60)and visual dysfunction in the right eye. His left eye remained unaffected. Eventually his condition stabilized, and he was left with a permanent reduction in right visual acuity (6/36) with intact peripheral visual fields and a completely normal left eye. After a period of grounding of 12 mo, he sought to have his license reinstated. He was considered to be a functionally monocular pilot, and as such was granted a conditional Class 1 medical category. The aeromedical disposition of this pilot and the issues involved in determining the fitness to fly of pilots with permanent visual defects arising from CSR are discussed.Abstract
Sinus barotrauma, secondary to mucosal disturbances, is a common finding within the aviation community. Multiple etiologies have allled to mucosal inflammation and thickening with potential obstruction of the sinus osteomeatal complex, especially during the barometric changes of flight. Obstruction can, therefore, lead to problems with sinus pressure equilibration with atmospheric pressure, and can lead to barosinusitis. We present a case of a U.S. Air Force Command Pilot with acute left sinus barotrauma during descent while flyinga T-37 aircraft, along with a brief review of the pathophysiologic processes involved during barotrauma. An inflammatory polyp within his sinus was identified by plain radiography, confirmed with computed tomography, and subsequently excised. The patient had complete resolution and clearance to fly after an uneventful 4-wk convalescence and altitude chamber flight. This is the first case of sinus barotrauma secondary to an inflammatory maxillary sinus polyp, confirmed by histologic diagnosis, reported in the aeromedical literature.Abstract
It now appears likely that commercial entities will carry paying passengers on suborbital spaceflights in this decade. The stresses of spaceflight, the effects of microgravity, and the limited capability for medicalcare onboard make it advisable to develop a system of medical clearance for such space tourists. The Aerospace Medical Association, therefore, organized a Space Passenger Task Force whose first report on medical guidelines was published in 2001. That report consisted of a list of conditions that would disqualify potential passengers for relatively long orbital flights. The Task Force reconvened in 2002 to focus on less stringent medical screening appropriate for short duration suborbital flights. It was assumed that such commercial flights would involve: 1) small spacecraft carrying 4-6 passengers; 2) a cabin maintained at sea-level “shirt-sleeve” condition; 3) maximum accelerations of 2.0-4.5 G; 4) about 30 min in microgravity. The Task Force addressed specific medical problems, including space motion sickness, pregnancy, and medical conditions involving the risk of sudden incapacitation. The Task Force concluded that a medical history should be taken from potential passengers with individualized follow-up that focuses on areas of concern.Abstract