Showing papers in "Aviation, Space, and Environmental Medicine in 1996"

Sources of situation awareness errors in aviation.

Abstract: BACKGROUND: Situation Awareness (SA) is a crucial factor in effective decision-making, especially in the dynamic flight environment. Consequently, an understanding of the types of SA errors that occur in this environment is beneficial. METHODS: This study uses reports from the Aviation Safety Reporting System (ASRS) database (accessed by the term "situational awareness") to investigate the types of SA errors that occur in aviation. The errors were classified into one of three major categories: Level 1 (failure to correctly perceive the information), Level 2 (failure to comprehend the situation), or Level 3 (failure to project the situation into the future). RESULTS: Of the errors identified, 76.3% were Level 1 SA errors, 20.3% were Level 2, and 3.4% were Level 3. Level 1 SA errors occurred when relevant data were not available, when data were hard to discriminate or detect, when a failure to monitor or observe data occurred, when presented information was misperceived, or when memory loss occurred. Level 2 SA errors involved a lack of or an incomplete mental model, the use of an incorrect mental model, over-reliance on default values, and miscellaneous other factors. Level 3 errors involved either an overprojection of current trends or miscellaneous other factors. CONCLUSIONS: These results give an indication of the types and frequency of SA errors that occur in aviation, with failure to monitor or observe available information forming the largest single category. Many other causal factors are also indicated, however, including vigilance, automation problems, and poor mental models. Language: en

Exertional heat illness in Marine Corps recruit training.

Abstract: BACKGROUND: Exertional heat illness (EHI) is a recurring problem in military training resulting in loss of manpower and training effectiveness. A scientific approach to this problem requires quantitative analysis of factors related to its occurrence. METHODS: Review of clinic and hospital records identified all cases of EHI occurring among 217,000 Marine Corps recruits (90% male, 80% age 18-20 yr) entering 12-week basic training at Parris Island, SC during 1982-1991. RESULTS: There were 1454 cases, 89% males and 11% females; 11% of male and no female cases were hospitalized. The majority (88%) of cases occurred during May-September, with a peak rate of 2% of recruits in summer. Most of the cases occurred during the cooler early morning hours when recruits performed strenuous exercise. During 0700-0900 hours the rate of heat casualties increased substantially as the Wet Bulb Globe Temperature Index (WBGT) increased, beginning at levels as low as 65 degrees F. EHI rates increased 26- and 39-fold at WBGT 75- < 80 degrees F (over baseline rates at < 65 degrees F) for immediate and prior day exposures, respectively. Exposure to WBGT of 80 + degrees F was infrequent (25%) among the early morning cases at the time of illness, while it was common (87%) on the day prior to illness, suggesting a lasting effect of heat exposure. CONCLUSIONS: Risk for EHI in military training increases markedly as WBGT levels rise above 65 degrees F; cases occur primarily with strenuous exercise (e.g., running); and heat stress exposure on prior days may be important.

Alcohol elimination and simulator performance of male and female aviators: a preliminary report

Abstract: OBJECTIVES: In this preliminary study of alcohol effects on aviators' flight simulator performance, we addressed some methodological issues regarding possible gender-related differences in response to alcohol. METHODS: Subjects were 11 male and 12 female general aviation pilots, ages 21-40. Subjects received 8 h of training before they were tested with alcohol. On the alcohol test day they were tested before drinking, while intoxicated (target BAC of 0.08%), and 8 h after drinking. RESULTS: The average, observed peak BAC readings for men and women were within 0.003% of each other. We observed faster disappearance rates for women such that women reached the FAA cutoff of 0.04% approximately 1 h before men, on average. Compared to predrink performance, there was a significant decrement in simulator performance during acute intoxication, but not 8 h after drinking. There were no significant gender differences in performance before or after drinking alcohol. Slower rates of alcohol elimination were associated with larger performance changes 8 h after drinking. This is the first report to our knowledge suggesting a possible relation between alcohol elimination rate and change in performance after drinking alcohol. CONCLUSIONS: A 12.5% dose reduction for women appears to be adequate for achieving comparable peak BAC's for male and female groups. Future studies using measures of circadian rhythmicity in conjunction with pharmacokinetic and performance measures could potentially shed light on differences in subjects' acute and delayed responses to alcohol. Language: en

Effect of standing or walking on physiological changes induced by head down bed rest: implications for spaceflight.

Abstract: Background/hypothesis To simulate exposure to microgravity and to determine the effectiveness of intermittent exposure to passive and active +1 Gz force (head-to-foot) in preventing head-down bed rest (HDBR) deconditioning, 4 d of 6 degrees HDBR were used. Methods Volunteers were 9 males, 30-50 yr, who performed periodic standing or controlled walking for 2 or 4 h.d-1 in 15-min bouts, one bout per hour, or remained in a continuous HDBR control condition (0 Gz). Results Standing 4 h (S4) completely prevented, and standing 2 h (S2) partially prevented, decreases in post-HDBR orthostatic tolerance (survival rates with 30 min of upright tilt at 60 degrees). Walking, both 2 h (W2) and 4 h (W4), and S4 attenuated decreases in peak oxygen uptake compared to 0 Gz. Compared to 0 Gz, both S4 and W4 attenuated plasma volume loss during HDBR. Urinary Ca2+ excretion increased over time with HDBR; the quadratic trend for urinary Ca2+, however, was attenuated with W2 and W4. Conclusions We concluded that various physiological systems benefit differentially from passive +1 Gz or activity in +1 Gz and, in addition to the duration of the stimulus, the number of exposures to postural stimuli may be an important moderating factor.

Physiological, psychophysical, and psychological responses of firefighters to firefighting training drills.

Abstract: This study was designed to describe the physiological, psychophysical, and psychological responses of firefighters to firefighting drills in a training structure containing live fires. Fifteen male firefighters, wearing standard turnout gear which resulted in full encapsulation, performed two firefighting tasks (advancing fire hose, chopping wood) while inside the training structure. Measurements of heart rate, tympanic membrane temperature, blood lactate, perceptions of respiration, mood, perceived exertion, and thermal sensation were obtained after 8 min of advancing fire hose, and again after 8 min of chopping. Heart rate and temperature increased significantly from baseline and from advancing hose to wood chopping, whereas blood lactate increased initially after advancing the hose and remained elevated at the end of the chopping task. At the completion of the test (both tasks), mean heart rate (182.3 b.min-1), temperature (40.1 degrees C, [104.1 degrees F]), and blood lactate (3.8 mMol) suggested that the firefighting tasks used in this study impose considerable physiological strain on firefighters. Psychophysical and psychological data mirrored the greater physiological strain following firefighting tasks performed in a hot environment while wearing full turnout gear. Language: en

Psychological reactions during polar expeditions and isolation in hyperbaric chambers.

Abstract: Background Psychological data from environments that are considered as analog to space was collected from 68 subjects; 18 in hyperbaric chambers, 16 in polar expeditions, and 34 on Arctic stations. The objective was to identify psychological reactions expected in different phases of spaceflights and examine personality variables associated with superior adaptation. Method Helmreich Personality Characteristic Inventory was administered before the isolation. Adaptation to the environment was assessed through a questionnaire once a week. Results Crews in hyperbaric chambers indicated a steady increase in coping over the isolation. Polar expeditions members reported high aggressiveness and anxiety in the first quarter and an increase in homesickness over time. A personality characterized by strong expressiveness and instrumentality ("the right stuff") predicted superior adaptation in hyperbaric chambers. Conclusion The data suggest that isolation in hyperbaric chambers and polar expeditions should be considered as models for different aspects of the space environment.

U.S. naval aviation mishaps, 1977-92: differences between single- and dual-piloted aircraft.

Abstract: The present study examined U.S. Naval aircraft mishap trends between January 1977 and December 1992 using all Class A, B, and C mishaps. Results of this investigation revealed that mishaps attributable to both human error and mechanical/environmental factors have declined steadily over the past 16 years, although mishaps attributed to human error have declined at a much slower rate. For those mishaps attributed to human error, differences were observed between single- and dual-piloted aircraft when phase-of-flight (takeoff, in-flight, landing) and time-of-day were evaluated. For single-piloted aircraft, in-flight mishaps constituted the highest proportion of mishaps during the day ( > 55%), while landing mishaps constituted the highest proportion of mishaps during the evening and night (43-65%). For dual-piloted aircraft, no consistent variation was evident for phase-of-flight and time-of-day. In-flight (approx. 55%) mishaps constituted the highest proportion of mishaps across all times of day, followed by landing (approx. 35%), and takeoff (approx. 10%) mishaps. These data support focused rather than global investigations of aviation mishaps.

Melatonin efficacy in aviation missions requiring rapid deployment and night operations

Abstract: Background The rapid deployment of Army aviation personnel across time zones, combined with missions beginning immediately upon arrival, results in desynchronization of physiological and cognitive performance rhythms. Implementation of effective countermeasures enhances safety, health, well-being, and mission completion. The naturally occurring hormone melatonin has been suggested as an effective counter measure for jet lag and shift lag because of its influence on the human circadian timing system and its hypnotic properties. Methods The efficacy of melatonin (10 mg) in maintaining stable sleep/wake cycles of Army aircrews was tested during a training mission involving rapid deployment to the Middle East and night operations. Cognitive performance was tested before and after travel; activity rhythms were recorded continuously for 13 d. Results Melatonin treatment advanced both bedtimes and rise times (2-3 h) and maintained sleep durations between 7-8 h. Placebo treatment was mostly associated with longer advances in rise times than bedtimes resulting in shorter sleep durations (5-7 h). Upon awakening, the melatonin group exhibited significantly fewer errors (mean: 7.45) than the placebo group (mean: 14.50) in a dual-task vigilance test. Conclusion Melatonin can be a useful treatment for the prevention of sleep disruptions and cognitive degradation, even in uncontrolled sleeping environments characteristic of military deployments.

Crewmember interactions during a MIR space station simulation.

Abstract: Background: Interpersonal problems may negatively affect crews on long-duration space missions. These problems stem from crewmember tension and its displacement to the outside monitoring personnel, and from disruptions in crew cohesion and unclear leadership roles. Hypotheses: We hypothesized that crew tension and dysphoria would transiently increase following stressful events and be greater in the second half of a mission; that cohesion would be less during the second half of a mission; that tension and dysphoria would be displaced to the outside monitoring personnel; and that high levels of leader support and control would produce high levels of cohesion. Methods: We tested these hypotheses during a 135-d Mir space station simulation study in Moscow. At weekly intervals, the three crewmembers completed items from two group climate questionnaires, a mood questionnaire, and a log of stressful events. Results: Contrary to expectations, there was significantly (p < 0.05) more total mood disturbance and tension during the first 9 wks than during the subsequent 10 wks of the simulation. Although levels of cohesion remained the same over time, cohesion scores dropped at a significantly greater rate during the last third of the seclusion. There was evidence for the displacement of tension and dysphoria to the outside monitoring personnel. There were significant correlations in the predicted direction between leader support and control and crew cohesion, as well as evidence of status leveling in the mission commander. Conclusions: Crewmember tension, cohesion, and leadership are important issues affecting people working in secluded environments, and they need to be studied further in space.

EGb 761 in control of acute mountain sickness and vascular reactivity to cold exposure.

Abstract: Method : We recruited 44 subjects to participate in a study of the preventive effect of Ginko biloba extract (EGb 761) on acute mountain sickness (AMS) and vasomotor changes of the extremities during a Himalayan expedition. After giving their written informed consent, the subjects were randomized to two groups. One group received 160 mg of EGb 761 per day in two divided doses and the other group received placebo. Assessment was based on the course of the Environmental Symptom Questionnaire (ESQ) score and the cold gradient measured by photoplethysmography. Results : The prophylactic efficacy of treatment with EGb 761 was clearly demonstrated in this study. In terms of factor 1 (AMS-Cerebral), no subject in the EGb 761 group developed acute mountain sickness versus 40.9% of subjects in the placebo group ; this difference was very significant (p ≤ 1.4 x 10 -3 ). In terms of factor 2 (AMS-Respiratory), 3 subjects (13.6%) in the EGb 761 group developed acute mountain sickness versus 18 (81.8%) in the placebo group ; this difference was very significant (p = 1.2 x 10 -5 ). Conclusion : Due to its multiple pharmacological actions, EGb 761 provides an interesting response to the prevention of mountain sickness for moderate altitude (5400 m) with gradual exposure. It also decreased vasomotor disorders of the extremities, as demonstrated by plethysmography (p < 10 -8 ) and a specific questionnaire (p < 10 -9 ).

Cancer incidence in United States Air Force aircrew, 1975-89.

Abstract: UNLABELLED We compared the cancer incidence of male United States Air Force (USAF) aircrew (342 cancers, 532,980.97 man-years) with non-flying Air Force officers (827 cancers, 1,084,370.08 man-years) between 1975-89. METHODS Incident cancer cases for both aviators and non-flying officers were obtained from USAF hospitalization records. Age-adjusted standardized incidence ratios (SIR's) were calculated for aircrew using data from the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) program. Aviator age-adjusted cancer rate ratios were also obtained using non-flying officers as an internal comparison group. RESULTS We observed statistically significant excesses of aircrew cancers for all sites, testis, and urinary bladder. All other aviator cancer classifications were not significantly different from the comparison cohort; most notably, cancers of the colon and rectum, skin (both malignant melanoma and non-epithelial), brain and nervous system, Hodgkin's Disease and leukemias. CONCLUSION Previous studies of commercial pilots that demonstrated excesses of these cancers may have been biased by the use of external comparison groups. We used an internal comparison population to reduce selection bias, information bias and confounding. From these data we detected notable excess aircrew cancer risk for cancers of the testis, urinary bladder, and all sites combined.

Lymphedema initiated by aircraft flights.

Abstract: Introduction : This study arose because a number of patients volunteered that flying had triggered, or worsened, their lymphedema. The nature of lymphedema is discussed, including the pre-lymphedematous latent-phase. In this phase the limb is clinically normal, but lymphostatic. There are many of the alterations found in clinical lymphedema involving blood vessels, tissues, lymphatics, and proteolytic cells. Since edema itself impairs many of the safety factors against edema (increased tissue hydrostatic pressure, dilution of proteins in tissue fluid, increased lymphatic transport, and increased proteolysis), any edema occurring in such a limb is likely to persist as chronic lymphedema. Method & Results: Questionnaires were sent to 1,020 patients with lymphedema ; 749 replied, with 531 answering a question about what triggered the condition. It was present from near birth in 41, but developed later in 490 (163 post-mastectomy lymphedemas, and 136 primary and 191 secondary leg lymphedemas). In 27 of the 490, it started during an aircraft flight (15 legs and 12 arms). In addition, flying caused existing lymphedema to permanently worsen in 23 arms and 44 legs in the 749 respondents. Some typical case histories are given. Conclusions : Because of its frequency in arms and legs, it is highly likely that this triggering, or worsening, of lymphedema is produced by lowered cabin pressure. Obstruction of veins and lymphatics, and reduced muscle pumping, may contribute to this in the legs. Using additional compression for existing lymphedema, or limbs at risk, would prevent this. If it occurs, it should be treated by additional compression, using inflated splints or pressure bandages.

Total sleep deprivation and the thyroid axis: effects of sleep and waking activity.

Abstract: Background: Circadian and sleep components modulate anterior pituitary release of thyrotropin (TSH), the chemical substance regulating the thyroid hormones, thyroxine (T 4 ), and triiodothyronine (T 3 ). The present study examined TSH, T 4 , and T 3 concentrations across the wake-sleep boundary time (2300-0130 hours) before, during, and after a 64-h sleep deprivation paradigm. Additionally, adrenocorticotropic hormone (ACTH) and cortisol were measured as an index of hypothalamic-pituitary-adrenal axis activation. Activity levels and ratings of effort required to perform cognitive tasks were also incorporated to evaluate physical and cognitive load, respectively, across the study period. Assessing the combined effects of activity and sleep deprivation on thyroid hormone economy is relevant to the relationship of high physical and/or cognitive performance demands during sleep deprivation inherent in extended military operations and space exploration. Method: There were 12 healthy subjects who were monitored during a 2-d baseline period, 3 d of total sleep deprivation, and 2 nights of recovery sleep. Serum samples were collected at 2300 hours and 0130 hours across the entire study period, and measured for TSH, T 4 , T 3 , and glucocorticoids. Results: Change scores evaluated at the wake-sleep boundary time demonstrated significant inhibitory effects of sleep on thyroid hormone measures. As expected, sleep deprivation was associated with elevated TSH. However, sleep deprivation also significantly increased circulating levels of T < at 2300 hours and T4 concentration change scores (2300-0130 hours). Glucocorticoid levels did not track thyroid hormone changes. Physical activity remained constant while subjective ratings of effort to perform cognitive tasks increased significantly during sleep deprivation. Conclusion: Compared to sleep deprivation studies under constant conditions reporting no change in peripheral T 4 and T 3 levels, the present study suggests activity level, including cognitive effort to perform, during total sleep deprivation may produce substantive changes in the thyroid axis.

Perception of the medical risk of spaceflight

Abstract: We conducted an opinion survey to improve the characterization of medical risk during spaceflight, using a questionnaire designed to elicit space medicine experts' perceptions of the probability, health effect, and mission impact of selected medical events occurring during spaceflight missions of 30-90 d. This questionnaire was directed toward those events about which little data currently exist, therefore medical events that have occurred during spaceflights with some frequency, such as space motion sickness, were excluded from the questionnaire. The questionnaire was mailed to 99 clinical and research professionals involved with NASA medical programs ; 65 responses were returned, of which 60 could be analyzed. The experts rated skin disorders as the most likely to occur, but which would have little effect on mission completion or astronaut health. Circulatory diseases were rated as having the lowest probability of occurrence, but the highest effect on the mission or on a crewmember's health. The results of this survey will be combined with data from analogous populations and existing astronaut health data to establish a data set to support decisions about allocation of health care resources.

Swimming behavior of fish during short periods of weightlessness

Abstract: Background : Birds and fish show tumbling and spinning movements when subjected to short periods of weightlessness during parabolic flight. The reason for this behavior is not clear. Hypothesis : The semicircular canal system is a rotation-detecting device ; however, it seems that linear accelerations have an influence, too. Microgravity induces rotatory sensations which leads to a compensatory behavior (e.g., rotatory movements). Methods : The swimming behavior of goldfish was studied with the fish in four different conditions : normal fish (group I) ; fish with one eye recently removed (group II) ; fish with both eyes recently removed (group III) ; and fish with both eyes removed 10 months previously (group IV). Further, a group of naturally blind (e.g., not surgically treated) cavefish (group V) were involved in the study also. All procedures conformed to the guiding principles as required in the Dutch Law on Care and Use of Animals. Results : Three main different patterns of abnormal swimming behavior could be observed : tumbling (pitch), corkscrew movements (pitch and roll), and spinning movements (roll). NF did not shown any special swimming pattern. One-eyed fish (group II) : mostly corkscrew movements (62%). Blind fish (group III) : a mixture of the three movements (17, 22 and 25%). Blind fish (group IV) : mostly spinning movements (20%). Cavefish (group V) : tumbling (21%), corkscrew movements (12%) and spinning movements (58%). Conclusion : Vision is the dominant cue, explaining the behavior of normal goldfish. When vision is absent, the fish relies on vestibular information with respect to orientation. The swimming behavior is presumably caused by an attempt to compensate rotatory illusions. As all movements were shown in the planes of the vertical canals, we conclude that these canals play a dominant role when fish are deprived from proper otolith information.

The effects of 600 mg of slow release caffeine on mood and alertness

Abstract: BACKGROUND Caffeine is the most widely used psychostimulant. PURPOSE This study evaluated the pharmacokinetics and effects of mood and alertness of a single oral administration of 600 mg of a slow release caffeine (SRC) on a large group of healthy subjects. METHOD In this double-blind, parallel-group study, 120 young adult males were randomly assigned to either a caffeine group (CG, n = 100) or a placebo group (PC, n = 20). After a normal sleep, each subject took 600 mg of a SRC or a placebo. Circulating caffeine was determined by salivary caffeine assays after acetylation phenotype categorization. Mood, alertness and nocturnal sleep were evaluated by visual analog scales (VAS). RESULTS This SRC was well tolerated probably due to its relative low plasmatic Cmax (10.37 micrograms.ml-1). Between CG and PG, there were no differences for alertness, contentedness and sleep quality of the night after treatment (N2) compared to the previous night (N1). VAS scores showed a decrease in calmness in the CG (p < 0.01). Sleep latency in N2 was significantly increased with caffeine (p < 0.01). Calmness, sleep onset latency, quality of sleep onset and overall rating of N2 compared to N1 were correlated with caffeine levels, which were only influenced by tobacco consumption. CONCLUSIONS Although a single oral dose of 600 mg of a SRC is well tolerated, further evaluation must be done on alertness and pharmacokinetics with fatigued subjects and with females using oral contraceptives.

Pelvic blood pooling of men and women during lower body negative pressure.

Abstract: Introduction The objective of this study was to investigate possible gender differences in the hemodynamic responses of the lower body during lower body negative pressure (LBNP). Methods In this study, 17 women (mean age = 56 yrs) and 15 men (mean age = 55 yrs) underwent a 15 min exposure to -50 mm Hg LBNP. A Beckman (BR-100) Impedance Plethysmograph was used to measure each subject's leg and pelvic blood flow and pooling during the LBNP test. Results The women had an 83% greater increase in blood volume in the pelvic region than men as a result of the LBNP exposure. Women and men had similar increases in leg blood volume as a result of the 15 min exposure to -50 mm Hg. There was no significant gender difference in the decreased amount of blood flow to the leg or pelvic regions by the end of -50 mm Hg LBNP. Conclusions These results demonstrate that women have greater blood pooling in the pelvic region compared to men when exposed to -50 mm Hg LBNP. These results should be considered when designing life-support equipment for men and women pilots and astronauts, especially the designing of anti-G and Space Shuttle re-entry garments.

Mental workload in heat: toward a framework for analyses of stress states.

Abstract: BACKGROUND: Effects of stress on performance are often interpreted by recourse to the arousal theory, which accounts for performance effects only in relation to the level of nervous system activity. This omits voluntary control that may be exerted in moderating stress effects. The present work elaborates on two control processes (viz., strategies and effort exertion) from the standpoint of the theory of mental workload, which was assessed in two experiments as a function of task demand and heat stress. Task demand was varied by increasing the complexity of decision rules and by presenting feedback indicating efficiency of task-strategies. HYPOTHESES: As decision rules are made more complex, task demand increases, causing longer reaction time (RT) and higher workload. Feedback improves performance by affecting strategies and effort exertion. Heat's effect on performance is related to the generated thermophysiological state and degree of effort exerted to maintain efficiency. METHOD: Performance and workload were measured in a decision-making task as a function of complexity of decision rules and feedback in 22 degrees C and 40 degrees C temperature conditions. Workload was measured by secondary task RT (STRT), subjective rating of effort (SRE), and heart rate (HR). Core temperature (Tc) was monitored continuously. RESULTS: Primary task RT (PTRT), STRT, SRE, and HR increased as complexity of decision rules increased. Feedback decreased PTRT, and increased STRT, SRE, and HR. In heat, a higher Tc was associated with a shorter PTRT and a longer STRT. CONCLUSIONS: A substantial part of variation in adaptation to demand was accounted for by control processes that involved higher cognitive functions. Language: en

Human performance during exposure to toluene

Abstract: Purpose: The purpose of this research was to examine the effects of inhalation of toluene on respiratory function and neuropsychological performance of humans. Methods: We exposed six healthy adults to 100 ppm toluene or air (control) for 6 h, in a double-blind, randomized fashion, with exposures separated by at least 14 d and including 30 min of exercise at a level that quadrupled minute ventilation. Blood and exhaled air toluene levels were measured before, during, immediately, and 1 and 2 h post-exposure. Lung function was measured before and immediately after exposure. Three repetitions of two computerized neuropsychological tests were performed, including a brief standard neuropsychological battery (ANAM) and a 1-h complex performance test (SYNWORK). Statistical analysis of the psychological data was conducted as a repeated measures ANOVA. Findings: Following exercise, the mean blood and exhaled air toluene levels averaged 1.5 μg and 28 ppm, respectively. Lung function was unchanged post-exposure. on the SYNWORK test, the Composite score obtained over time during toluene exposure was lower than that during room air (F = 29.20, p = 0.005), with the score from the final hour reduced by 10%. On standard neuropsychological tests, latency but not accuracy proved the sensitive measure for five of the seven subtests presented. Conclusions: Performance of complex tests and response time to simple brief tests can be disrupted by toluene inhalation at 100 ppm. Differences in performance between air and toluene conditions were greatest after exercise, indicating that physical activity may enhance the response to volatile organic solvents.

The initial signs and symptoms of altitude decompression sickness.

Abstract: BACKGROUND: With the potential for higher aircraft and cabin altitudes, the way in which altitude decompression sickness (DCS) presents continues to be of interest. The majority of previous papers on the symptomatology of DCS are retrospective reviews of patients treated hours or days post-exposure. The initial presentation while still at altitude is the form of DCS that aircrew must be able to recognize in order to respond correctly. This paper reports the initial manifestations of DCS that occurred during a series of prospective hypobaric chamber studies. These studies had been specifically designed to investigate DCS. METHODS: This paper presents a prospective analysis of DCS symptoms from 447 subjects, recorded over an 11-yr period at the Armstrong Laboratory (AL), and is an attempt to provide an accurate representation of the initial presentation of altitude DCS. RESULTS: Of the 447 cases, 83.2% had musculoskeletal involvement, 2.7% had chokes, 2.2% skin manifestations, 10.8% paresthesia, and 0.5% frank neurological features. CONCLUSIONS: The most common presenting feature was musculoskeletal, with knee pain predominating (occurring in 70% of these cases). A very low incidence of neurological features was seen in the AL database, which was in contrast to data from many other sources. Reasons for this difference may include the use of preoxygenation and the policy of prompt recompression upon symptom development at AL. There is also the possibility that individuals in the training and operational environments are more likely to report frank neurological involvement than other forms of DCS. Language: en

Effects of hypovolemia and posture on responses to the Valsalva maneuver.

Abstract: Introduction: We tested the hypotheses that hypovolemia would result in attenuated elevation in blood pressure, greater baroreflex-mediated tachycardia, and reduced capacity for vasoconstriction during a Valsalva maneuver (VM). Methods: Heart rate (HR) and mean arterial pressure (MAP) were measured beat-by-beat before strain, during a 15-s VM strain at 30 mmHg expiratory pressure, and post-strain. Eight subjects performed three VM trials in each of three postures (supine, sitting, and standing) under two experimental conditions (normovolemic and hypovolemic). Hypovolemia was acutely induced by a bolus injection of 30 mg furosemide. Each experimental condition was conducted on a different day, separated by one week. delta MAP was used in analyses of phase I, late phase II (an indicator of vasoconstriction) and phase III of VM. The ratio delta HR/delta MAP, an index of nonspecific baroreflex control of HR, was used in analysis of early phase II and phase IV of the VM. Results: Compared to normovolemia, hypovolemia resulted in 12% lower plasma volume (p = 0.0001). delta MAP for both phase I and phase III of the VM differed between postures (p = 0.0132 and p = 0.0003, respectively) and was lower in the hypovolemic condition than in the normovolemic condition for phase I in the standing posture (-5 mmHg, p = 0.0385). Conclusions: HR and blood pressure responses to alterations in intrathoracic pressure are affected by fluid redistribution (posture change), but not by circulating blood volume. Therefore, our results did not support our hypothesis that hypovolemia would result in attenuated elevation in blood pressure, greater baroreflex-mediated tachycardia, and reduced capacity for vasoconstriction during a Valsalva maneuver. However, moderate hypovolemia can be specifically predicted by the phase I response to a VM performed in the standing posture.

Neurological decompression illness in swine

Abstract: Background : A porcine model of neurological decompression illness (DCI) and its treatment is described. Methods : Pigs (wt. 16-22 kg) underwent a simulated dive to 200 feet of seawater (fsw) (612.6 kPa) for 24 min, then decompressed at 60 fsw/min -1 (183 kPa.min -1 ). Pigs that developed neurological DCI were sedated with diazepam, then treated by recompression on U.S. Navy Treatment Table 6. Functional outcome was assessed by treadmill running. At necropsy 24 h postdive, carcass density was measured by underwater weighing, and tissue samples including heart, spinal cord, and brain were taken for histopathological examination. Results : Neurological DCI occurred in 73% of control animals and developed within 2-7 min in 50% of cases. Affected pigs had significantly earlier onset of skin DCI than unaffected pigs (means : 9.52 min vs. 17.9 min, p < 0.001). Only 16.4% of pigs made a full functional recovery after recompression treatment. Outcome at 24 h was not improved in 20 pigs randomized to receive adjunctive lidocaine infusion compared to 20 pigs that received saline alone. Following necropsy, 77% of cases had petechial hemorrhages grossly visible in the spinal cord. Multifocal, microscopic hemorrhages, predominantly of spinal cord white matter, were found in 86.6% of DCI cases. Neither weight, density, nor genetic predisposition were found to influence DCI risk. Conclusions : The model is analogous to severe, early-onset, neurological DCI in humans and allows prospective evaluation of risk reduction and treatment stratagems for this form of DCI. Many applied and basic science issues relevant to diving medicine may also be studied using the model, and adaptation to study hypobaric DCI and other clinical applications of hyperbaric oxygen is feasible.

Ground Reaction Forces During Locomotion in Simulated Microgravity

Abstract: Significant losses in bone density and mineral, primarily in the lower extremities have been reported following exposure to weightlessness. Recent investigations suggest that mechanical influences such as bone deformation and strain rate may be critically important in stimulating new bone formation. It was hypothesized that velocity, cadence and harness design would significantly affect lower limb impact forces during treadmill exercise in simulated zero gravity (0G). A ground-based hypogravity simulator was used to investigate which factors affect limb loading during tethered treadmill exercise. A fractional factorial design was used and 12 subjects were studied. The results showed that running on active and passive treadmills in the simulator with a tethering force close to the maximum comfortable level produced similar magnitudes for the peak ground reaction force. It was also found that these maximum forces were significantly lower than those obtained during overground trials, even when the speeds of locomotion in the simulator were 66 % greater than those in 1 G. Cadence had no effect on any of the response variables. The maximum rate of force application (DFDT-Max) was similar for overground running and exercise in simulated 0G, provided that the "weightless subjects ran on a motorized treadmill. These findings have implications for the use of treadmill exercise as a countermeasure for hypokinetic osteoporosis. As the relationship between mechanical factors and osteogenesis becomes better understood, results from human experiments in 0G simulators will help to design in-flight exercise programs that are more closely targeted to generate appropriate mechanical stimuli.

A probabilistic model of hypobaric decompression sickness based on 66 chamber tests

Abstract: One consequence of the NASA tissue ratio (TR) model is that calculated probability of decompression sickness [P(DCS)] is constant in tests at different ambient pressures so long as the ratio of P1 N 2 to P2 is the same in each test ; P1N 2 is N 2 pressure in the 360 minute half-time compartment, and P2 is ambient pressure after decompression. We test the hypothesis that constant P(DCS) is better described by TRs that decrease as P2 decreases. Data were from 66 NASA and USAF hypobaric chamber tests resulting in 211 cases of DCS in 1075 exposures. The response variable was presence or absence of DCS while at P2. Explanatory variables were P1N 2 , P2, exercise at P2, (yes or no), time to DCS (failure time), and time to end of test in those without DCS (censored time). Probability models were fitted using techniques from survival analysis. The log likelihood for the two parameter log logistic survival model was -846 with only failure and censored times, -801 when TR [P1N 2 /P2] plus exercise were added, and -663 when modified TR [(((P1 N 2 + C1)/P2)-1) c2 ) plus exercise were added, where c1 and c2 are fitted parameters in the five parameter model. Constant P(DCS) was better described by TRs that decrease as P2 decreases ; a conclusion supported by additional empirical observations, and bubble growth models that are independent of DCS data. Exercise increased the P(DCS) at P2. As a description of decompression dose, the modified TR was superior to TR over a wider range of experimental conditions.

Muscle strain during aerial combat maneuvering exercise.

Abstract: BACKGROUND: Little is known about the in-flight muscular strain of fighter pilots. HYPOTHESIS: The purpose of this study was to measure fighter pilots' mean and peak muscular strain during aerial combat maneuvering exercises. The results obtained were compared against existing ergonomic recommendations. METHODS: Six pilots volunteered to serve as test subjects. Their mean age (+/- SD) was 28.5 +/- 5 yr, height 181 +/- 7 cm, and weight 75 +/- 10 kg. They performed one-to-one dog-fight exercises in the morning and in the afternoon. During the flights, the pilots' electromyographic activity (EMC) was measured from the thigh, abdomen, back, and lateral neck. The mean and peak muscular strain for each muscle was calculated as the percentage of maximal voluntary contraction (%MVC). RESULTS: The results showed that the mean muscular strain was 5.2-19.8% MVC, the strain in the lateral neck being the highest. Peak muscular strain (over 50% MVC) occurred almost only during the encounters and usually in the lateral neck. Other muscles were subjected to fewer peak strain episodes; most of these occurred in the back. At least one peak strain episode exceeding 100% MVC was recorded for every muscle studied. The highest peak strain 257% MVC, was measured in the lateral neck. This peak strain episode caused an injury to the lateral neck area, and the flight mission was discontinued. CONCLUSIONS: The mean muscular strain measured in this study was rather low. However, the strain occurring in the lateral neck and the back exceeds the ergonomic recommendations for static work. Especially in the lateral neck, and to some extent in the back, peak strain occurs frequently, in a magnitude that is well above the maximal voluntary contraction; in these areas, the peak strain presents a potential risk of injury and negative health effects. The level and frequent occurrence of peak strain episodes means that fighter pilots' muscular strength and muscular endurance, especially in the neck and shoulder area, are subjected to demands clearly higher than those of the average population. Language: en

Exercise-enhanced preoxygenation increases protection from decompression sickness.

Abstract: Introduction: Prevention of decompression sickness (DCS) during exposure to altitude equivalents of 30,000 ft (9144 m) requires extensive denitrogenation. In preparation for extravehicular activity (EVA), present NASA policy is to denitrogenate using a 10.2 psia staged decompression of the entire shuttle for at least 12 h, including 100 min of preoxygenation (breathing 100% oxygen at 14.7 psia prior to decompression), before decompression to the 4.3 psia (30,000 ft; 9144 m) suit pressure. This staged decompression provides the same or better protection from DCS as a 3.5- or 4-h preoxygenation used on earlier Shuttle EVA's. For high altitude reconnaissance flights at similar cockpit altitudes, a 1-h preoxygenation is currently required. Methods: We have investigated the use of a 1-h and a 15-min preoxygenation period, each beginning with 10 min of dual-cycle ergometry performed at 75% of each subject's peak oxygen consumption (Vo 2 peak) to enhance preoxygenation efficiency by increasing perfusion and ventilation. Male subjects accomplished a 1-h preoxygenation with exercise, a 15-min preoxygenation with exercise, or a 1-h resting preoxygenation before exposure to 4.3 psia for 4 h while performing light to moderate exercise. Results: Incidence of DCS following the 1-h preoxygenation with exercise (42%; n = 26) was significantly less than that following the 1-h resting preoxygenation (77%; n = 26). Incidence and onset of DCS following the 15-min preoxygenation with exercise (64%; n = 22) was not significantly different from the incidence following the 1-h resting control. Conclusion: Preoxygenation with exercise has been shown to provide significantly improved DCS protection when compared with resting preoxygenation.

Prevalence of decompression sickness among U-2 pilots.

Abstract: BACKGROUND: Though it is rarely reported, decompression sickness (DCS) is an expected risk for U-2 aviators. The potential for chronic sequelae of untreated DCS in this population has never been addressed. METHODS: After conducting a preliminary survey at an active-duty U-2 squadron, a cohort of 416 U-2 pilots (active-duty and retired) were mailed two sequential anonymous surveys to assess demographic data, career prevalence of DCS symptoms, and overall health status with an emphasis on chronic musculoskeletal problems. RESULTS: The response rate for each mail-in survey was over 60%. During their career, 75.5% of pilots experienced DCS symptoms such as joint pain, skin manifestations, and/or various neurological problems. Symptoms generally started during flight and resolved upon descent. Many pilots voluntarily increased their oxygen prebreathing time, or inflated the pressure suit during flight to prevent or treat symptoms. At some point in their career 12.7% of those experiencing symptoms either altered the flight profile or aborted a mission as a result. The association of past DCS with current arthritic problems was not statistically significant. CONCLUSIONS: The career prevalence of DCS symptoms in U-2 pilots is higher than previously reported, and these symptoms sometimes affect mission completion. We found no evidence that chronic musculoskeletal sequelae (e.g., arthritis or dysbaric osteonecrosis) are causally associated with DCS in this population. Language: en

Evidence of sensory conflict and recovery in carp exposed to prolonged weightlessness.

Abstract: Background : Evidence in support of the sensory conflict hypothesis for space motion sickness (SMS) is still needed. Hypothesis : We hypothesized that sensory conflict and recovery processes should be demonstrated in intact fish during initial days of microgravity exposure, as a disturbance and restoration of the dorsal light response (DLR ; a functional model of visual-graviceptor interaction), respectively. We also expected that this would be true in an otolith-removed fish if it had been fully compensated for dysfunction before the exposure. Methods : The DLR of carp (Cyprinus carpio) was examined intermittently during the 8-d mission of Spacelab-J. Two carp, normal and labyrinthectomized (LB), made the flight. Results : In the normal carp, the DLR was unstable for the first 3 d inflight but gradually recovered thereafter. The recovery was characterized by gradual restoration of the DLR tilt speed. The LB fish whose otoliths had been removed 2 mo before the flight maintained DLR at the first inflight test session (22 h after launch), but DLR was disrupted at 2 d as in normal fish. The recovery process could not be evaluated in this fish, because the EEG cable which was attached to the fish for supplementary study became tightly twisted and thus immobilized the fish for the remainder of the experiment. Conclusion : These findings provided additional evidence in fish for sensory-motor disorder and readjustment during the early phase of microgravity, thus supporting the sensory conflict hypothesis for SMS.

Using outdoor exercise to decrease jet lag in airline crewmembers.

Abstract: The effects of outdoor exercise on urinary excretion of the 17-hydroxycorticosteroids (17-OHCS), catecholamine rhythm, and sleep-wake patterns in cockpit crewmembers were investigated before, during and after jet travel between Tokyo and Los Angeles (8-h time difference). On the day following arrival at Los Angeles (day 3) 5 crewmembers exercised outdoors for about 5 h (exercise group, aged 47.2 +/- 6.8 yr), and 5 others volunteered to remain in their rooms and go shopping after the flight (control group, aged 47.4 +/- 1.5 yr). The timing of the acrophase of the 17-OHCS rhythm and sleep-wake patterns showed similar patterns of advance in the two groups on the day of arrival in Los Angeles (day 2) compared with that at baseline (B) in Tokyo. In the exercise group, the acrophase of the 17-OHCS rhythm tended to be delayed on day 3, and then phase-advanced on the day following outdoor exercise (day 4). The timing of acrophase of the 17-OHCS rhythm and sleep-wake patterns showed gradual delay on days 3-4 in the control group, and a significant difference (p < 0.01) was observed between the groups for the acrophase of 17-OHCS rhythm on day 4. These results suggest that outdoor exercise has some effects in hastening the resynchronization to a new environment of the circadian rhythm of the urinary 17-OHCS excretion.

Grasping of virtual objects in changed gravity.

Abstract: Background: Little is known about the effects of changed gravity on the execution of grasping movements, even though such movements play an important role in normal motor behavior of humans. Hypothesis: The formation of an adequate grip aperture is impaired in changed gravity. Method: During parabolic flight, five subjects grasped mirror-viewed virtual targets with their thumb and index finger. From their video-taped responses, we determined grip aperture as the distance between the two fingertips. Results: In changed gravity, the final grip aperture was about 15% smaller than in normal gravity, and the peak grip aperture was about 30% less modulated by target size. Both findings were similar in hyper-G and in micro-G. Conclusions: We conclude that (virtual) grasping in changed gravity is affected by a deterioration of visual and/or proprioceptive signals, or by the increased computational burden of controlling movements in unusual force environments.