Showing papers in "Aviation, Space, and Environmental Medicine in 2009"

Kinetics and kinematics for translational motions in microgravity during parabolic flight.

Abstract: Introduction: Astronauts soaring through space modules with the grace of birds seems counterintuitive. How do they adapt to the weightless environment? Previous spaceflights have shown that astronauts in orbit adapt their motor strategies to each change in their gravitational environment. During adaptation, performance is degraded and can lead to mission-threatening injuries. If adaptation can occur before a mission, productivity during the mission might improve, minimizing risk. The goal is to combine kinetic and kinematic data to examine translational motions during microgravity adaptations. Methods: Experiments were performed during parabolic flights aboard NASA's C-9. Five subjects used their legs to push off from a sensor, landing on a target 3.96 m (13 ft) away. The sensor quantified the kinetics during contact, while four cameras recorded kinematics during push-off. Joint torques were calculated for a subset of traverses (N = 50) using the forces, moments, and joint angles. Results: During the 149 traverses, the average peak force exerted onto the sensor was 224.6 ± 74.6 N, with peak values ranging between 65.8―461.9 N. Two types of force profiles were observed, some having single, strong peaks (N = 64) and others having multiple, weaker peaks (N = 86). Conclusions: The force data were consistent with values recorded previously in sustained microgravity aboard Mir and the Space Shuttle. A training program for astronauts might be designed to encourage fine-control motions (i.e., multiple, weaker peaks) as these reduce the risk of injury and increase controllability. Additionally, a kinematic and kinetic sensor suite was successfully demonstrated in the weightless environment onboard the C-9 aircraft.

Fatigue countermeasures in aviation.

Abstract: Pilot fatigue is a significant problem in modern aviation operations, largely because of the unpredictable work hours, long duty periods, circadian disruptions, and insufficient sleep that are commonplace in both civilian and military flight operations. The full impact of fatigue is often underappreciated, but many of its deleterious effects have long been known. Compared to people who are well-rested, people who are sleep deprived think and move more slowly, make more mistakes, and have memory difficulties. These negative effects may and do lead to aviation errors and accidents. In the 1930s, flight time limitations, suggested layover durations, and aircrew sleep recommendations were developed in an attempt to mitigate aircrew fatigue. Unfortunately, there have been few changes to aircrew scheduling provisions and flight time limitations since the time they were first introduced, despite evidence that updates are needed. Although the scientific understanding of fatigue, sleep, shift work, and circadian physiology has advanced significantly over the past several decades, current regulations and industry practices have in large part failed to adequately incorporate the new knowledge. Thus, the problem of pilot fatigue has steadily increased along with fatigue-related concerns over air safety. Accident statistics, reports from pilots themselves, and operational flight studies all show that fatigue is a growing concern within aviation operations. This position paper reviews the relevant scientific literature, summarizes applicable U.S. civilian and military flight regulations, evaluates various in-flight and pre-/postflight fatigue countermeasures, and describes emerging technologies for detecting and countering fatigue. Following the discussion of each major issue, position statements address ways to deal with fatigue in specific contexts with the goal of using current scientific knowledge to update policy and provide tools and techniques for improving air safety.

Musculoskeletal injuries and minor trauma in space: incidence and injury mechanisms in U.S. astronauts.

Abstract: INTRODUCTION: Astronauts have sustained musculoskeletal injuries and minor trauma in space, but our knowledge of these injuries is based mainly on anecdotal reports. The purpose of our study was to catalog and analyze all in-flight musculoskeletal injuries occurring throughout the U.S. space program to date. METHODS: A database on in-flight musculoskeletal injuries among U.S. astronauts was generated from records at the Johnson Space Center. RESULTS: A total of 219 in-flight musculoskeletal injuries were identified, 198 occurring in men and 21 in women. Incidence over the course of the space program was 0.021 per flight day for men and 0.015 for women. Hand injuries represented the most common location of injuries, with abrasions and small lacerations representing common manifestations of these injuries. Crew activity in the spacecraft cabin such as translating between modules, aerobic and resistive exercise, and injuries caused by the extravehicular activity (EVA) suit components were the leading causes of musculoskeletal injuries. Exercise-related injuries accounted for an incidence of 0.003 per day and exercise is the most frequent source of injuries in astronauts living aboard the International Space Station (ISS). Interaction with EVA suit components accounted for an incidence of 0.26 injuries per EVA. DISCUSSION: Hand injuries were among the most common events occurring in U.S. astronauts during spaceflight. Identifying the incidence and mechanism of in-flight injuries will allow flight surgeons to quantify the amount of medical supplies needed in the design of next-generation spacecraft. Engineers can use in-flight injury data to further refine the EVA suit and vehicle components. Language: en

Skeletal Effects of Long-Duration Head-Down Bed Rest

Abstract: Introduction Skeletal unloading during spaceflight causes regional loss of bone mineral density (BMD), primarily in the spine and lower body regions. This loss of skeletal mass could adversely affect crew health during and after spaceflight and jeopardize mission success. Bed rest has long been used as a spaceflight analog to study the effects of disuse on many body systems, including the skeleton. This study was undertaken by the NASA Flight Analogs Project (FAP) to collect control data for upcoming countermeasure studies. Methods There were 13 subjects who participated in 42, 44, 49, 52, 60, or 90 d of continuous, head-down bed rest. DXA scans (dual-energy X-ray absorptiometry) were obtained before and after bed rest to measure changes in BMD of the whole body, lumbar spine, hip, heel, and wrist; the 90-d subjects were also scanned at the 60-d time point. Follow-up DXA scans were performed after 6 mo and 12 mo of reambulation to assess BMD recovery. Results BMD changes were consistent with earlier bed rest and spaceflight studies, with statistically significant losses averaging 1% per month in the hip, pelvis, and heel. Recovery data were also consistent with data obtained after spaceflight. Bone biomarker data are described, and support the findings of previous studies. Specifically, the process of normal bone remodeling is uncoupled: increased bone resorption with no concomitant change in bone formation. Conclusion The FAP appears to be a valid test bed for skeletal disuse studies, and should provide a useful research platform for evaluating countermeasures to spaceflight-induced bone loss.

Combined pitch and roll and cybersickness in a virtual environment.

Abstract: BACKGROUND Stationary subjects who perceive visually induced illusions of self-motion, or vection, in virtual reality (VR) often experience cybersickness, the symptoms of which are similar to those experienced during motion sickness. An experiment was conducted to test the effects of single and dual-axis rotation of a virtual environment on cybersickness. It was predicted that VR displays which induced illusory dual-axis (as opposed to single-axis) self-rotations in stationary subjects would generate more sensory conflict and subsequently more cybersickness. METHODS There were 19 individuals (5 men, 14 women, mean age = 19.8 yr) who viewed the interior of a virtual cube that steadily rotated (at 60 degrees x s(-1)) about either the pitch axis or both the pitch and roll axes simultaneously. Subjects completed the Simulator Sickness Questionnaire (SSQ) before a trial and after 5 min of stimulus viewing. RESULTS Post-treatment total SSQ scores and subscores for nausea, oculomotor, and disorientation were significantly higher in the dual-axis condition. CONCLUSIONS These results support the hypothesis that a vection-inducing VR stimulus that rotates about two axes generates more cybersickness compared to aVR stimulus that rotates about only one. In the single-axis condition, sensory conflict and pseudo-Coriolis effects may have led to symptoms. However, in the dual-axis condition, not only was perceived self-motion more complex (two axes compared to one), the inducing stimulus was consistent with twice as much self-motion. Hence, the increased likelihood/magnitude of sensory conflict and pseudo-Coriolis effects may have subsequently resulted in a higher degree of cybersickness in the dual-axis condition.

Long-duration head-down bed rest: project overview, vital signs, and fluid balance.

Abstract: Introduction: Spaceflight has profound effects on the human body. Many of these effects can be induced with head-down bed rest, which has been a useful ground-based analog. With limited resources aboard the International Space Station for human research, the bed rest analog will be a primary platform on which countermeasures will be developed and tested for lunar and Mars mission scenarios. Methods: NASA Johnson Space Center, in conjunction with the University of Texas Medical Branch (UTMB), has created the NASA Flight Analogs Project (FAP), a research program with the overall objective of using head-down bed rest to evaluate, compare, and refine candidate countermeasures to spaceflight deconditioning. This paper serves as an overview and describes the standard conditions, the standard set of subject screening criteria, and the standard set of measurements for all FAP bed rest subjects. Results: Heart rate and diastolic pressures decreased transiently at the onset of bed rest. Fluid balance showed an early diuresis, which stabilized within 3 d. In this supplement, detailed results from multiple disciplines are presented in a series of reports. Discussion: The following reports describe multi-disciplinary results from the standard measurements by which the responses to bed rest will be assessed and by which countermeasures will be evaluated. The data presented in this overview are meant to serve as a context in which to view the data presented in the discipline specific manuscripts. The dietary support and behavioral health papers provide additional information regarding those aspects of implementing bed rest studies successfully.

Ventilated vest and tolerance for intermittent exercise in hot, dry conditions with military clothing

Abstract: Introduction: Recent research has focused on developing air-ventilated garments to improve evaporative cooling in military settings. This study assessed a ventilated vest (Vest) in hot (45°C), dry (10% RH) ambient conditions over 6 h of rest and exercise. It was hypothesized that the Vest would lower the thermal strain and increase the amount of exercise done by subjects. Methods: Eight healthy heat-acclimated men, wearing combat clothing, body armor, and a 19-kg load in webbing walked on a treadmill at 5 km · h−1 at a 2% incline until rectal temperature (Trec) reached 38.5°C. They then rested until Trec reached 38°C, at which point they recommenced walking. On one occasion the subjects wore a Vest, blowing ambient air around the torso. On the second occasion subjects did not wear the vest (NoVest). Exercise/rest ratio, Trec, skin temperature (Tsk), sweat responses, rating of perceived exertion (RPE), and thermal comfort (TC) were measured. Results: Subjects wearing the Vest exercised for significantly longer (18%; 11 min/h) as a percentage of total exposure time, stopped exercise significantly less often [Mean (SD); NoVest: 3 (2) stops; Vest: 1 (2) stops], and maintained significantly lower skin temperature under the body armor [Tchest: NoVest 37.55 (0.51)°C; Vest: 35.33 (1.00)°C; Tback: NoVest: 36.85 (0.83)°C; Vest: 35.84 (0.88)°C]. The Vest provided 28 W of cooling during exercise and 73 W when at rest as estimated by thermometry. Conclusion: A ventilated vest can provide cooling, and thereby reduce thermal strain and increase exercise done in dry environmental temperatures up to 45°C, without causing skin irritation and discomfort.

Postural reflexes, balance control, and functional mobility with long-duration head-down bed rest.

Abstract: Introduction Spaceflight has functionally significant effects on sensorimotor behavior, but it is difficult to separate the effects of ascending somatosensory changes caused by postural muscle and plantar surface unloading from descending visual-vestibular neural changes. To differentiate somatosensory changes from graviceptor changes in post-spaceflight sensorimotor behavior, bed rest may serve as an exclusionary analog to spaceflight. Methods Four separate tests were used to measure changes in sensorimotor performance: 1) the monosynaptic stretch reflex (MSR); 2) the functional stretch reflex (FSR); 3) balance control parameters associated with computerized dynamic posturography (CDP); and 4) a functional mobility test (FMT). Results A mixed model regression analysis showed significant increases in median MSR start and peak latencies, while the median FSR latency showed no significant increase. Median MSR peak magnitude showed a significant increase during the middle bed rest period (19-60 d). There were no significant effects of bed rest on balance control, but some indication that dynamic head movements may affect posture after bed rest. Time to complete the course for the FMT increased significantly with bed rest. Discussion The four primary tests indicate that long-duration head-down bed rest, through unloading and modification of the body's support surface, serves as an exclusionary analog for sensorimotor responses to spaceflight. Furthermore, the data suggest that procedures designed to alleviate modifications to the sensory substrate serving the soles of the feet may provide a countermeasure to help maintain support afferentation of the postural muscles.

Cardiovascular adaptations to long-duration head-down bed rest.

Abstract: INTRODUCTION: Orthostatic hypotension is a serious risk for crewmembers returning from spaceflight. Numerous cardiovascular mechanisms have been proposed to account for this problem, including vascular and cardiac dysfunction, which we studied during bed rest. METHODS: Thirteen subjects were studied before and during bed rest. Statistical analysis was limited to the first 49-60 days of bed rest, and compared to pre-bed rest data. Ultrasound data were collected on vascular and cardiac structure and function. Tilt testing was conducted for 30 minutes or until presyncopal symptoms intervened. RESULTS: Plasma volume was significantly reduced by day 7 of bed rest. Flow-mediated dilation in the leg was significantly increased at bed rest day 49. Arterial responses to nitroglycerin differed in the arm and leg, but did not change as a result of bed rest. Intimal-medial thickness markedly decreased at bed rest days 21, 35 and 49. Several cardiac functional parameters including isovolumic relaxation time, ejection time and myocardial performance index were significantly increased (indicating a decrease in cardiac function) during bed rest. There was a trend for decreased orthostatic tolerance following 60 days of bed rest. DISCUSSION: These data suggest that 6 head-down tilt bed rest alters cardiovascular structure and function in a pattern similar to short duration spaceflight. Additionally, the vascular alterations are primarily seen in the lower body, while vessels of the upper body are unaffected. KEY WORDS: spaceflight, orthostatic intolerance, hypotension, fluid-shift, plasma volume

Compression garments as countermeasures to orthostatic intolerance.

Abstract: Introduction All astronauts experience some degree of orthostatic intolerance following spaceflight, ranging from tachycardia to orthostatic hypotension and syncope. The purpose of this study was to evaluate the ability of two compression garments, the National Aeronautics and Space Administration's inflatable antigravity suit (AGS) and the Russian Federal Space Agency's non-inflatable compression garment (Kentavr), to prevent hypovolemia-related orthostatic intolerance. Methods To mimic the plasma volume loss experienced by astronauts during spaceflight 19 healthy subjects received an intravenous dose of a diuretic, furosemide (0.5 mg x kg(-1)), and then consumed a low-salt diet for 36 h. Thereafter, subjects participated in a 15-min 80 degrees head-up tilt test wearing either the AGS (N = 9) or Kentavr (N = 10). Compression garments were used in the fashion recommended by the respective agencies, delivering approximately 78 mmHg and approximately 30 mmHg of compression in the AGS and Kentavr, respectively. Incidence of presyncope and hemodynamic responses during upright tilt were compared to a separate group of hypovolemic control subjects (N = 16). Results Subjects wearing the AGS or Kentavr completed the full 15 min of upright tilt without incidence of orthostatic hypotension or presyncope. In contrast, only 9 control subjects (56%) were able to complete the tilt test. In addition, both types of compression garments maintained systolic blood pressure and significantly reduced tilt-induced tachycardia and reductions in stroke volume. Conclusions Although both garments successfully countered hypovolemia-induced orthostatic intolerance, the Kentavr provided protection by using lower levels of compression. Determining the optimal compression level required for protection of intolerance may improve crewmember comfort and decrease restrictions on physical activities after spaceflight.

Cognitive Function and Mood During Acute Cold Stress After Extended Military Training and Recovery

Abstract: Introduction Acute cold stress is often accompanied by exposure to other adverse factors, such as sleep loss, under-nutrition, and psychological stress that singly and together may affect cognitive function. Methods The effect of moderate cold stress on cognitive function was investigated in 15 male volunteers exposed to cold air (10 degrees C) for 4 h after they had completed an intense, 61-d regimen (U.S. Army Ranger training). The single cohort of volunteers was tested on three separate occasions: (1) immediately after completing Ranger training; (2) 2 d later when they had partially recovered from training; (3) 108 d later after full recovery. Documented training stressors included limited sleep (approximately 4 h sleep/night), caloric deficit (approximately 850 kcal x d(-1), intense physical activity, and psychological stress. Results Baseline rectal temperature fell significantly due to training alone (from 36.6 degrees C +/- 0.1 to 36.3 degrees C +/- 0.1) and was lower still with acute cold exposure (35.9 degrees C +/- 0.2). Cognitive function was affected by training alone, as indicated by significant decreases in vigilance, four-choice reaction time, pattern recognition, symbol-digit substitution, word-list learning, grammatical reasoning, and mood prior to exposure to acute cold stress. Mood states were also adversely affected, including tension, depression, anger, fatigue, confusion, and vigor. Acute cold exposure itself significantly degraded vigilance, overall mood, and increased tension. Discussion Chronic multifactorial stress impaired cognitive function and mood; the addition of moderate, acute cold stress further degraded vigilance and mood. When such circumstances occur, such as during disasters or military operations, measures to prevent adverse cognitive and physiological outcomes are recommended.

Nutritional status assessment before, during, and after long-duration head-down bed rest.

Abstract: Introduction: Bed rest is a valuable ground-based model for many of the physiological changes that are associated with spaceflight. Nutritional changes during and after 60 or 90 d of head-down bed rest were evaluated. Methods: A total of 13 subjects (8 men, 5 women; ages 26― 54 yr) participated in either 60 or 90 d of bed rest. Blood and urine were collected twice before bed rest and about once per month during bed rest. Samples were stored frozen and batch analyzed. Data were analyzed using repeated-measures analysis of variance. Results: During bed rest, markers of bone resorption (such as N-telopeptide excretion, P < 0.001) increased and serum concentration of parathyroid hormone decreased (P < 0.001). Also, oxidative damage markers such as superoxide dismutase increased (P < 0.05), and after 90 d of bed rest, total antioxidant capacity decreased (P < 0.05). During bed rest, iron status indices showed patterns of increased iron stores with a decreased concentration oftransferrin receptors (P < 0.01). Discussion: These changes are similar to some of those observed during spaceflight, and further document the utility of bed rest as a model of spaceflight.

Executive functions and the ability to sustain vigilance during sleep loss.

Abstract: Introduction There is considerable individual variability in the ability to sustain performance during sleep loss Preliminary evidence suggests that individuals with higher trait-like activation/functioning of the prefrontal cortex may be less vulnerable to fatigue Methods We tested this hypothesis in a sample of 54 healthy volunteers who were assessed bi-hourly on a variant of the Psychomotor Vigilance Test during 41 h of sleep deprivation A subset of these subjects, representing the top and bottom 25% of the sample based on their ability to sustain vigilance performance during sleep deprivation, were compared with respect to baseline neurocognitive abilities Results The sleep deprivation Resistant group (N = 13) scored significantly higher than the sleep deprivation Vulnerable (N = 13) group on all three baseline tasks assessing prefrontal executive function abilities (letter fluency, Stroop Color-Word test, Color Trails Form 2), whereas no differences were found on non-executive function tasks Similarly, groups showed no differences on demographic variables including age, education, hand preference, morningness-eveningness preference, global intellectual ability, or pre-study sleep history Discussion Findings are consistent with the hypothesis that greater prefrontal/executive functioning may be protective against the adverse effects of sleep deprivation and suggest that baseline executive function testing may prove useful for prediction of resilience during sleep loss

Immune status, latent viral reactivation, and stress during long-duration head-down bed rest.

Abstract: Introduction As logistical access for space research becomes more limited and NASA prepares for exploration-class missions, ground-based spaceflight analogs will increase in importance for biomedical countermeasures development. A monitoring of immune parameters was performed during the NASA Flight Analogs Project bed rest study (without countermeasure); to establish 'control' data against which future studies (with countermeasure) will be evaluated. Some of the countermeasures planned to be evaluated in future studies may impact immune function. Methods The immune assessment consisted of: leukocyte subset distribution, early T cell activation, intracellular cytokine profiles, latent viral reactivation, virus specific T cell levels and function, stress hormone levels, and a behavioral assessment using stress questionnaires. Results In general, subjects did not display altered peripheral leukocyte subsets, constitutive immune activation, altered T cell function, or significant latent viral reactivation (EBV, VZV). Levels of constitutively activated T cells (CD8+/CD69+) and virus-specific T cells (CMV and EBV) decreased during the study. Cortisol levels (plasma and saliva) did not vary significantly during 90-d bed rest. Conclusions These data demonstrate the absence of significant immune system alteration and physiological stress during 90-d bed rest, and establish control data against which future studies (including countermeasures) may be compared.

Hyperventilation in response to progressive reduction in central blood volume to near syncope

Abstract: Introduction: There is little evidence to support the usefulness in monitoring respiration during casualty triage and transport as an early indicator of hemorrhage severity and trauma patient outcome. We, therefore, tested the hypothesis that hyperventilation can be elicited by progressive reductions in central blood volume independent of metabolic stimuli. Methods: Progressive central hypovolemia was induced in 10 healthy subjects (5 men, 5 women) by applying lower body negative pressure (LBNP). The LBNP protocol consisted of a 5-min controlled rest period (0% LBNP) followed by progressive 5-min chamber decompressions until the onset of hemodynamic decompensation (LBNP max ). During each LBNP stage, total minute ventilation volume (V E ), tidal volume (V T ), respiratory rate, oxygen uptake (Vo 2 ), end-tidal CO 2 (E T co 2 ), arterial oxygen saturation (S p o 2 ), and venous blood pH and lactate were measured. Results: Compared with baseline, Vo 2 , S p o 2 , Po 2 , Pco 2 , pH, and lactate were unaltered throughout LBNP. V E was unaltered through 80% of LBNP tolerance, but increased by 54% during LBNP max as a result primari.ly of elevated V T , while E T co 2 was reduced. Conclusions: Increased V E at LBNP max combined with reduced E T co 2 in the absence of changes in blood and systemic metabolic stimuli support the hypothesis that severe reductions in central blood volume drive hyperventilation. The endogenous "respiratory pump" may be a protective strategy to optimize cardiac filling in conditions of central hypovolemic hypotension, but its late appearance indicates that respiratory parameters may not be useful as a clinical metric for early prediction of patient outcome during hemorrhage.

Fatigue in pilots of remotely piloted aircraft before and after shift work adjustment.

Abstract: Background: Remotely piloted aircraft (RPA) with long endurance allow near-continuous operations, necessitating the implementation of shift work for crewmembers to provide the necessary manning of ground control stations. Shift work has a well-known association with fatigue, degraded work performance, and an increased risk for errors and accidents. This study presents the results of a follow-up survey of a particular population of shift-working RPA crewmembers 1 yr after modification of their shift work schedule. Methods: A cross-sectional survey of 66 RPA crewmembers was conducted using a collection of validated fatigue scales. This data was compared to survey data collected a year prior from the same population and from a reference group of non-shift-working aircrew. Shift system features and individual and situational differences associated with fatigue were explored. Additionally, several alternative types of shift schedules were assessed through modeling and simulation. Results: The study found no significant reduction in reported fatigue despite prior modifications to the shift work schedule to increase opportunities for recovery. Months shift working, sleep quality, and disturbances in family and social activities were associated with overall fatigue scores. Approximately half of those surveyed met criteria for occupationally significant fatigue. Months shift working, use of on-duty napping, and fatigue scores were predictive of those with occupationally significant fatigue. Modeling of feasible variants of the current shift work schedule failed to reveal a significantly improved alternative schedule. Conclusions: Collectively, the results demonstrate a persistent problem with chronic fatigue in this study population, likely reflective of continued inadequate opportunities for recovery and restorative sleep.

Cold-water dousing with ice massage to treat exertional heat stroke: a case series.

Abstract: INTRODUCTION We sought to determine the rate of cooling via a novel water ice therapy (WIT) as an alternative to cold-water immersion for the acute treatment of exertional heat stroke (EHS). METHODS Observations were made at the 2004-2008 Marine Corps Marathons (mean +/- SD: 16.3 +/- 4.9 degrees C dry bulb, 32 +/- 6% RH). Nine (seven men, two women) EHS patients (33 +/- 6 yr of age; 268 +/- 54 min average race time for six who finished) were observed during on-site treatment. Patients were treated while lying supine on a porous stretcher resting on a tub filled with cold water (approximately 10-12 degrees C). Medical personnel monitored T(re), doused the patient with water and massaged major muscle groups with ice bags until T(re) decreased to 38.9 degrees C. Patients were not immersed in water. Serial T(re) and time were used to calculate cooling rates. RESULTS Final T(re) (39.12 +/- 0.63 degrees C) was significantly lower than initial T(re) (41.43 +/- 0.71 degrees C, P < 0.05). Cooling rates were 0.13 +/- 0.04 degrees C min(-1). The decrease in T(re) for the initial 6 min of WIT (0.38 +/- 0.13 degrees C) was significantly less than for the subsequent 6-min time period (1.31 +/- 0.34 degrees C, P < 0.001). Cooling rates for these time periods were significantly different (0.06 +/- 0.02 degrees C x min(-1) and 0.22 +/- 0.06 degrees C x min(-1), respectively, P < 0.05). Initial T(re) was not correlated with overall cooling rate (r = 0.434, P = 0.244), or total cooling time required (17 +/- 4 min; r = 0.207, P = 0.593). Survival rate was 100%. CONCLUSION WIT provided cooling rates that were 70% as effective as those published for cold-water immersion with 8 degrees C water (0.19 degrees C x min(-1)) and resulted in 100% patient survival.

Confinement and sleep deprivation effects on propensity to take risks

Abstract: INTRODUCTION: The impact of confinement and sleep deprivation on risk-taking propensity is a key issue in crew management. We investigated both confinement and gender effects on risk propensity and performance during up to 36 h of extended wakefulness. METHOD: We studied 4 groups of 3 men and 3 women [N = 24, mean age (+/- SD) = 32.9 +/- 5.8 yr] for 10 consecutive days: a 7-d confined period (CONF) or a 7-d baseline (BASE) condition preceding one control night of normal sleep, one night of sleep deprivation, and one recovery night in the laboratory. Risk propensity (EVAR scale) and simple reaction time task (SRTT) performances were monitored every 2.25 h (0930-1945) during CONF and every 2.11 h (0930-0745) during the sleep deprivation condition. RESULTS: Overall risk propensity during extended wakefulness showed a variation in both conditions with two diurnal peaks separated by a nocturnal minima. After the confinement period, no second peak was found. Number of lapses (reaction time > 500 ms) on the SRTT varied daily in both conditions. In the normal sleep schedule, subjects increased their level of impulsiveness between the first day and the end of confinement (P Language: en

Bed rest and cognition: effects on executive functioning and reaction time.

Abstract: INTRODUCTION: Executive functions are high-order aspects of cognition heavily dependent upon the prefrontal cortex. Both prefrontal cortex activity and executive function task performance are enhanced by participation in aerobic physical activity, suggesting that a lack of such activity during the bed rest model of prolonged weightlessness might induce executive function deficits. METHODS: Twenty-four healthy males (ages 21-45 yr) undertook 60 d of head-down bed rest (-6 degrees) for the 2nd Berlin Bed Rest Study (BBR2-2). Three executive function tasks (Iowa Gambling Task, working memory, and flanker) and a reaction time task were administered before, during, and after bed rest. RESULTS: Iowa Gambling Task scores were significantly worse during bed rest (1.7 +/- 6.9) than in other sessions (24.3 +/- 7.8). Effects on working memory and flanker task performance were less obvious, requiring practice effects to be considered. Reaction time was significantly slower after bed rest (569 +/- 42 ms) than in earlier tests (529 +/- 45 ms). There was also significantly less intrasubject variability in reaction time after bed rest, consistent with more efficient executive functioning at this stage. DISCUSSION: Our results provide some evidence for a detrimental effect of bed rest on executive functioning. Whether this stems from a lack of aerobic physical activity and/or changes in the prefrontal cortex remains to be determined. Cognitive effects of bed rest could have implications for the planned human exploration of Mars, and for medical and lifestyle conditions with inadequate levels of aerobic physical activity.

Whole-body vibration effects on bone mineral density in women with or without resistance training.

Abstract: INTRODUCTION Whole-body vibration exposure may translate into improved bone mass in young adult women. The primary focus of this study was to examine the effects of graded whole-body vibration or vibration exposure plus resistance training on bone mineral density (BMD), hematological measures for bone remodeling, and exercise metabolism in young women. METHODS There were 51 healthy active women [mean (SD) age, 21.02 (3.39) yr; height, 165.66 (6.73) cm; body mass 66.54 (13.39) kg] who participated in the intervention. Subjects were randomly assigned to whole-body vibration (WBV), whole-body vibration plus resistance training (WBV+RT), or control (CONT) groups for 16 wk. RESULTS A repeated-measure ANOVA found no significant (P < 0.05) group differences in BMD at the completion of 16 wk. A significant within group change was apparent for the WBV (2.7% femoral neck) and WBV+RT (femoral neck 1.9%; vertebra 0.98%). WBV and WBV+RT experienced a significant (P < 0.05) 60% and 58% increase in adiponectin, 48% and 30% in transforming growth factor-beta1, and 17% and 34% in nitric oxide with an accompanying 50% and 36% decrease in osteopontin, 19% and 34% in interleukin-1beta, and 38% and 39% in tumor necrosis factor-alpha. CONCLUSIONS The results indicate graded whole-body vibration exposure may be effective in improving BMD by increasing bone deposition while also decreasing bone resorption. Whole-body vibration may also provide an efficient stratagem for young women to achieve peak bone mass and help stave off osteoporosis later in life and provide a novel form of physical training.

Animal studies of the subgravity state during rocket flight

Abstract: I N T H E I R D I S C U S S I O N of man under gravity free conditions, Gauer and Haber G were the first to suggest that subgravity might lead to interesting physiological effects. They did not anticipate direct disturbances of respiration and of the circulation. However, they thought that the conflict between normal visual observations and the changed impulses from the labyrinth and proprioceptive apparatus might eventually lead to disturbances in performance and even to motion sickness. At the time the), proposed this, no practical means for producing the weightless state was available. Subsequently, Haber and Habeff pointed out that this condition could be briefly reproduced by an aircraft or rocket which followed a ballistic trajectory. I f the vehicle follows a course in which the horizontal velocity is constant and a downward acceleration exactly equaling the earth's gravity is developed, then no support is provided to objects within it and they become essentially weightless. Throughout the period that a high altitude research rocket coasts to its Presented at the Twenty-third Annual Meeting of the Aero Medical Association, Washington, D. C., March 17-19, 1952. This paper should be read in conjunction with those appearing in the Space Medicine Section in the August issue. Unfortunately, it was received too late to include with the other papers.

Cultural differences in crewmembers and mission control personnel during two space station programs.

Abstract: Cultural differences among crewmembers and mission control personnel can affect long-duration space missions. We examine three cultural contrasts: national (American vs. Russian); occupational (crewmembers vs. mission control personnel); and organizational [Mir space station vs. International Space Station (ISS)]. Methods: The Mir sample included 5 American astronauts, 8 Russian cosmonauts, and 42 American and 16 Russian mission control personnel. The ISS sample included 8 astronauts, 9 cosmonauts, and 108 American and 20 Russian mission control personnel. Subjects responded to mood and group cli-mate questions on a weekly basis. The ISS sample also completed a culture and language questionnaire. Results: Crewmembers had higher scores on cultural sophistication than mission control personnel, espe-cially American mission control. Cultural sophistication was not related to mood or social climate. Russian subjects reported greater language fl exibility than Americans. Crewmembers reported better mood states than mission control, but both were in the healthy range. There were several Russian-American differences in social climate, with the most robust being higher work pressure among Americans. Russian-American social climate differences were also found in analyses of crew only. Analyses showed Mir-ISS differences in social climate among crew but not in the full sample. Discussion: We found evidence for national, oc-cupational, and organizational cultural differences. The fi ndings from the Mir space station were essentially replicated on the ISS. Alterations to the ISS to make it a more user-friendly environment have still not re-solved the issue of high levels of work pressure among the American crew. Keywords:

Whole-body vibration effects on bone before and after hind-limb unloading in rats.

Abstract: Skeletal unloading during spacefl ight leads to bone loss. Following long-duration fl ight, such loss may be very slow or im-possible to fully recover. Therefore, it is important to seek countermea-sures to prevent the loss. Methods: We studied the effects on bone of whole-body vibration (WBV) with variable parameters (10 – 60 Hz and 0.1 – 1 g) using hind-limb unloading (HLU) in the rat as a model for mi-crogravity. The bone mineral densities (BMD) of the femur, tibia, and lumbar spines were measured and the mechanical properties of the fe-mur were determined by mechanical testing. Serum alkaline phospha-tase (ALP) and pyridinoline (PYD) levels were analyzed. Results: After 28 d of HLU, WBV reduced the losses of BMD in the femur and tibia from 18.8 to 10.1% and from 16.7 to 7.1%, respectively, and prevented the loss in stiffness of the femur after HLU. However, WBV had no effect on the lumbar spine. ALP levels were suppressed by HLU and maintained by WBV (28.3% increase). There was no signifi cant difference in PYD among groups. In the recovery period following HLU, there were no sig-nifi cant effects of WBV on BMD, and the elastic modulus of femur re-turned to normal. Discussion and Conclusions:

Functional assessment of the cervical spine in F-16 pilots with and without neck pain

Abstract: Introduction: Spinal symptoms in fighter pilots are a serious aeromedical problem. The most common neck complaints are muscular pain and strain. The aim of the current study was to determine possible differences in the cervical range of motion (CROM), neck position sense, and neck muscle strength between pilots with and without neck pain. Methods: There were 90 male F-I 6 pilots who volunteered, of which 17 had experienced bilateral neck pain. A standardized questionnaire was used to collect personal information. The maximum isometric neck flexion/extension and lateral flexion strength, the neck position sense, and the cervical range of motion were measured. Results: There were no significant differences between healthy pilots and those with neck pain concerning neck Muscle strength and neck position sense. The neck pain group had a limited CROM in the sagittal plane (130 degrees; CI: 116 degrees-144 degrees) and in the transversal plane (155 degrees; CI: 140 degrees-170 degrees) compared to the healthy pilots. Discussion: In the current study we screened for different motor skills so that deficits Could be detected and retraining programs could be implemented when necessary. According to our results, individual retraining programs might reduce neck pain and therefore a well-instructed training program to maintain a proper active CROM should be implemented. Future Studies should investigate the effectiveness of this kind of program.

Pre-dive vibration effect on bubble formation after a 30-m dive requiring a decompression stop.

Abstract: The preconditioning of divers to reduce post-dive decompression sickness (DCS) has gained increased interest in diving medical research over the last few years. The beneficial effects of physical exercise, oxygen breathing, hyperbaric exposure, heat exposure, hyperhydration, or nitroglycerin administration before the dive are only a few examples of ongoing research. In this work, we investigated the effects of pre-dive whole-body vibration on post-dive bubble formation.

Off-vertical axis rotation of the visual field and nauseogenicity

Abstract: BACKGROUND: Off-vertical axis rotation (OVAR) causes motion sickness which increases with angle of tilt and is most provocative around 0.2 Hz. The aim was to determine the tilt angle and frequency characteristics for visual OVAR, which is also known to be nauseogenic. METHODS: A computerized scene, as seen by a pilot at moderate altitude, rotated at different frequencies about an axis which could tilt as during OVAR. A concurrent visual detection task controlled attention. Exposures were for 10 min or until nausea developed. There were four experiments: Frequency tuning-visual motion at 0.05, 0.2, and 0.8 Hz, all at 18 degrees tilt of the axis of rotation (N = 14); gross visual tilt tuning-visual motion at 0, 45, and 90 degrees of tilt at 0.2 Hz (N = 12); fine visual tilt tuning -- 18, 36, 54, and 72 degrees tilts at 0.2 Hz (N = 24); and whole-body tilt of the participant at 0, 45, and 90 degrees, viewing rotation about a vertical axis at 0.2 Hz (N = 12). RESULTS: Nauseogenicity was significantly greater at 0.2 Hz than at lower or higher frequencies. Visual tilts 18 degrees to circa 45 degrees were significantly more nauseogenic. No differences were found between whole-body tilts. CONCLUSIONS: Nauseogenicity of visual OVAR peaks around 0.2 Hz, and increases with stimulus strength up to circa 45 degrees tilt, similar to real motion. With higher tilt angles, decreasing nauseogenicity suggests that the visual impact is partially quarantined because the motion would appear patently absurd and not a sensory conflict. Whole-body tilt may have failed to modulate nauseogenicity because of overriding somatosensory cues to Earth vertical.

Aviation-Related Injury Morbidity and Mortality: Data from U.S. Health Information Systems

Abstract: INTRODUCTION: Information about injuries sustained by survivors of airplane crashes is scant, although some information is available on fatal aviation-related injuries. Objectives of this study were to explore the patterns of aviation-related injuries admitted to U.S. hospitals and relate them to aviation deaths in the same period. METHODS: The Healthcare Cost and Utilization Project (HCUP) Nationwide Inpatient Sample (NIS) contains information for approximately 20% of all hospital admissions in the United States each year. We identified patients in the HCUP NIS who were hospitalized during 2000-2005 for aviation-related injuries based on the International Classification of Diseases, 9th Revision, codes E840-E844. Injury patterns were also examined in relation to information from multiple-cause-of-death public-use data files 2000-2005. RESULTS: Nationally, an estimated 6080 patients in 6 yr, or 1013 admissions annually (95% confidence interval 894-1133), were hospitalized for aviation-related injuries, based on 1246 patients in the sample. The average hospital stay was 6.3 d and 2% died in hospital. Occupants of non-commercial aircraft accounted for 32% of patients, parachutists for 29%; occupants of commercial aircraft and of unpowered aircraft each constituted 11%. Lower-limb fracture was the most common injury in each category, constituting 27% of the total, followed by head injury (11%), open wound (10%), upper extremity fracture, and internal injury (9%). Among fatalities, head injury (38%) was most prominent. An average of 753 deaths occurred annually; for each death there were 1.3 hospitalizations. CONCLUSIONS: Aviation-related injuries result in approximately 1000 hospitalizations each year in the United States, with an in-hospital mortality rate of 2%. The most common injury sustained by aviation crash survivors is lower-limb fracture. Language: en

Simulator sickness in a helicopter flight training school.

Abstract: Introduction Simulator sickness (SS) is a common problem during flight training and can affect both instructor pilots (IP) and student pilots (SP). This study was conducted in response to complaints about a high incidence of SS associated with use of new simulators for rotary-wing aircraft. Methods The problem was evaluated using the Simulator Sickness Questionnaire (SSQ) to collect data on 73 IP and 129 SP who used the new simulators. Based on analysis of these data, operator comments, and a search of the literature, we recommended limiting simulator flights to 2 h, removing unusual or unnatural maneuvers, turning off the sidescreens to reduce the field-of-view, avoiding use of improperly calibrated simulators until repaired, and stressing proper rest and health discipline among the pilots. The success of these measures was evaluated 1 yr later by collecting SSQ data on 25 IP and 50 SP. Results There was a main effect of time, in that after the recommendations were implemented, there was a significant reduction in nausea, oculomotor, and total SSQ scores from the pre-study to the post-study. There was also a main effect of experience, as IP reported significantly greater SS than SP for the same scores. Discussion Implementation of the recommendations reduced SS in the new simulators at the cost of limiting session duration and shutting down some simulator features. Although the optimal solution to the SS problem lies in addressing SS during a simulator's design stage, these recommendations can be used as interim solutions to reduce SS.

Dietary support of long-duration head-down bed rest.

Abstract: Introduction: Dietary control and nutrient intake are critical aspects of any metabolic study, but this is especially true in the case of bed rest studies. We sought to define nutritional requirements, develop menus, and implement them during long-duration head-down bed rest studies. Methods: The dietary goals were to provide 100% of subjects' nutrient requirements and to maintain subjects' bodyweight to within 3% of their weight on the third day of head-down bed rest. The research dietitian and metabolic kitchen staff are an important part of the multidisciplinary team required to implement a bed rest study. Results: We report herein the planning steps and nutrient intake results from 13 subjects. We also provide insight into some of the dietary challenges that arise during long-duration bed rest studies. Discussion: Regardless of the overall objective of the bed rest study to be performed, nutrition must be carefully planned, implemented, and monitored to prevent results from being compromised.

Menstrual suppression using oral contraceptives: survey of deployed female aviation personnel.

Abstract: INTRODUCTION: Increasing numbers of women perform aviation duties in the combat flight environment. Oral contraceptive pills (OCPs) afford numerous health and operational benefits including prevention of anemia and suddenly incapacitating conditions as well as menstrual suppression when taken continuously. Until now the use of OCPs in the combat flight environment has not been examined. METHODS: An anonymous voluntary questionnaire was distributed to 62 female U.S. Army aviation personnel who had recently deployed in support of combat flight operations to characterize continuous OCP use and perceived barriers to this practice as well as to determine associations with menstrual burden. RESULTS: There were 81% (N=50) of the women who had personal experiences using OCPs and 93% (N=58) were aware that continuous use can suppress menstruation. For deployment 66% (N=41) desired menstrual suppression yet only 33% (N=20) reported any OCP use. Even fewer (15%; N=10) reported using continuously. Of the women who did not use OCPs continuously 35% had insufficient knowledge about OCPs and 44% of women reported difficulty in remembering to take a daily pill. Continuous OCP users were more compliant (P = 0.019) reported less spotting (P = 0.007) and fewer unexpected menstrual cycles (P = 0.03) than conventional OCP users. A trend toward reduced cramping was noted (P = 0.064). Most women (60%) desired standardized entry-level education about menstrual suppression through OCPs. CONCLUSIONS: The use of continuous OCPs is low in deployed women with aviation-related duties yet a majority desires menstrual suppression. Continuous OCP use in this setting is associated with significantly improved compliance and significant reductions in specific menstrual burdens. Entry-level education is desirable and may reduce barriers to continuous OCP use by addressing risks side effects and daily pill adherence strategies. Flight surgeons should provide further education and consider continuous OCP dosing in the austere environment of combat flight.