McCrory JL, Derr J, Cavanagh PR. Locomotion in simulated zero gravity: ground reaction forces. Aviat Space Environ Med 2004; 75:203–210. Background: Exercise is likely to be an important countermeasure to bone demineralization, which remains a concern for astronauts during long-duration spaceflight. However, loads on the feet during exercise with 1 G equivalent gravity replacement are not known. The purpose of this study was to compare ground reaction forces (GRFs) during overground and simulated zero gravity (0 G) locomotion. Hypothesis: It was hypothesized that sufficient gravity replacement loading could be applied to the subjects such that GRF profiles similar to those seen in 1 G would occur during locomotion in a zero-gravity locomotion simulator (ZLS). Methods: GRFs were measured during overground walking and running, and during locomotion in two restraint harness designs in the ZLS with an initial loading of 1 body weight. Load cells measured the gravity replacement load (GRL) in the ZLS. Joint angles at the hip and knee were also measured by goniometers. Results: Peak forces were greater in overground locomotion than in the ZLS; however, loading rates were greater in the ZLS running conditions than in overground running. The knee joint was more flexed at key times in the support phase during running in the ZLS compared with overground. Conclusions: Large loads and loading rates can be generated at the feet during simulated 0 G exercise although peak forces during running in the ZLS are less than overground running at the same speed. The refinement of the gravity replacement system to provide a constant 1 G load should be considered.

Nyquist PA, Dick EJ, Buttolph TB. Detection of leukocyte activation in pigs with neurologic decompression sickness. Aviat Space Environ Med 2004; 75:211–214. Background: In a porcine model of neurological decompression sickness (DCS), perivascular leukocyte activation was a consistent finding in biopsies of associated cutaneous DCS. This prompted examination of other organs for similar changes; multifocal leukocyte activation was found in the lungs (pneumonitis) and liver (hepatitis). Hypothesis: DCS in pigs induces leukocyte aggregation and activation in the liver and lungs. Methods: Male Yorkshire swine, trained to run on a modified treadmill, were compressed to 200 ft of seawater (fsw) in a dry, air-filled compression chamber. Decompression varied according to the profile under study. Results: In 106 pigs, evidence for association of leukocyte aggregation and activation with the clinical diagnosis of neurologic DCS was sought. The incidence of pneumonitis (20/68, 29% with DCS; 4/38, 10% without DCS) and hepatitis (23/68, 33% with DCS; 4/38, 10% without DCS) were strongly correlated with the incidence of neurologic DCS via Pearson Chi-squared analysis (p = 0.026 pneumonitis and p = 0.008 hepatitis). Additionally, Kruskal-Wallis rank analysis for numbers of organs involved and incidence of neurologic DCS showed a strong correlation between the increasing occurrence of neurologic DCS and the involvement of both the liver and lungs (p = 0.004). Conclusions: The results imply that, at least in pigs, DCS induces leukocyte aggregation and activation in the liver and lungs. These organs are not normally considered targets of DCS. Leukocyte aggregation in these organs may be related to their roles as highly perfused organs. Leukocyte aggregation may be a marker for DCS, providing further evidence for wider, systemic effects of DCS.

Blutt SE, Conner ME. Kinetics of rotavirus infection in mice are not altered in a ground-based model of spaceflight. Aviat Space Environ Med 2004; 75:215–219. Introduction: The effect of simulated spaceflight conditions using the hindlimb unloading model on mucosal immune responses has not been examined. Therefore, we determined whether clearance, protection, and the antibody responses to an enteric pathogen, rotavirus, were altered under simulated spaceflight conditions. Methods: Groups of mice were either restrained and hindlimb unloaded, restrained without hindlimb unloading, or housed under standard conditions for either 4 or 14 d prior to and an additional 10 d following inoculation with ECwt murine rotavirus. An additional group of mice previously infected with rotavirus was housed under the three conditions for either 4 or 14 d prior to a rotavirus challenge. Results: Hindlimb unloading of mice did not alter clearance of a primary rotavirus infection compared with controls nor were there differences in protection from rotavirus challenge 42 d later between the three groups, all housed under standard conditions. There were no differences in protection from rotavirus challenge in mice that were hindlimb unloaded during the challenge infection compared with controls. The generation of rotavirus-specific fecal antibodies, as measured by enzyme-linked immunosorbent assay (ELISA), was not significantly different between any of the groups following either primary or challenge rotavirus infection. However, serum rotavirus-specific IgG1 antibody was not induced in mice housed under normal conditions and challenged under hindlimb unloading conditions compared with controls. Discussion: These data are the first examination of the mucosal immune response to an enteric viral pathogen under simulated spaceflight conditions and indicate that rotavirus immunity was not impacted in this model.

Price MJ, Mather MI. Comparison of lower- vs. upper-body cooling during arm exercise in hot conditions. Aviat Space Environ Med 2004; 75:220–226. Introduction: Studies examining cooling strategies and exercise have generally employed lower-body exercise despite the fact that arm exercise is an important mode for many industrial tasks and disabled populations. The aim of this study was to determine the effects of two cooling strategies during arm exercise in the heat. Methods: There were eight male subjects (mean ± SD age 24.5 ± 4.0 yr, weight 81.0 ± 7.8 kg, upper-body [V-dot]O₂peak 3.13 ± 0.50 L · min⁻¹) who volunteered for this study. Subjects undertook arm crank exercise for 30 min (50% [V-dot]O₂peak) in a hot environment (40.2 ± 0.4°C, 38.7 ± 7.4% RH) on three occasions (no cooling control, CON; lower-body cooling, LC; upper-body cooling, UC). Results: No differences were observed between trials for oxygen consumption, respiratory exchange rate (RER), or blood lactate. Heart rate (HR) was greatest during CON (151 ± 11 bpm) when compared with UC and LC (148 ± 16 and 138 ± 13 bpm; p < 0.05). Mean skin temperature was warmer during CON (36.3 ± 0.5°C) when compared with UC (31.2 ± 1.4°C, p < 0.05), which was warmer than during LC (28.5 ± 1.3°C, p < 0.05). No differences were observed for rectal or aural temperatures between trials. At the end of exercise, heat storage was hyperthermic (3.04 ± 0.68 J · g⁻¹), thermoneutral (0.18 ± 1.21 J · g⁻¹), and hypothermic (−2.37 ± 0.81 J · g⁻¹) during CON, UC, and LC, respectively (p < 0.05). Perceived exertion was lowest during LC and greatest during CON (p < 0.05). Conclusions: The results of this study suggest that cooling the lower body during arm exercise in hot conditions is more effective in reducing physiological and thermal strain than cooling the upper body.

Miller KE, Muth ER. Efficacy of acupressure and acustimulation bands for the prevention of motion sickness. Aviat Space Environ Med 2004; 75:227–234. Introduction: The purpose of this study was to examine whether acupressure and acustimulation prevent motion sickness, taking into consideration whether or not the acupressure and acustimulation are administered properly. These techniques claim to reduce nausea through stimulation of the P6/Neiguan acupuncture point by applying acupressure or electrical acustimulation. Methods: The Acuband™ and ReliefBand® were used to administer acupressure and acustimulation, respectively. There were 77 subjects who were assigned to 1 of 5 conditions: Acuband™ trained or untrained; ReliefBand® trained or untrained; or placebo. Subjects were exposed to a 20-min baseline and a maximum of 20 min of optokinetic drum rotation. Untrained subjects read the device directions, used it as they deemed appropriate, and completed a usability analysis following drum exposure. Trained subjects read the device directions and were trained to use the device appropriately prior to drum exposure. Symptoms and gastric myoelectric activity were monitored during baseline and rotation. Results: In all conditions, symptoms of motion sickness and gastric tachyarrhythmia increased, and 3 cpm gastric myoelectric activity decreased, during drum exposure. The only difference found between conditions was a potential delay in symptom onset for the ReliefBand® compared with the Acuband™. While the Acuband™ was found difficult to use (0 untrained subjects used it correctly) and only a few minor usability issues were identified for the ReliefBand®, usability had no impact on efficacy. Discussion: Neither band nor placebo prevented the development of motion sickness, regardless of whether the bands were used correctly or incorrectly.

Shi S-J, South DA, Meck JV. Fludrocortisone does not prevent orthostatic hypotension in astronauts after spaceflight. Aviat Space Environ Med 2004; 75:235–239. Background: During stand/tilt tests after spaceflight, 20% of astronauts experience orthostatic hypotension and presyncope. Spaceflightinduced hypovolemia is a contributing factor. Fludrocortisone, a synthetic mineralocorticoid, has been shown to increase plasma volume and orthostatic tolerance in Earth-bound patients. The efficacy of fludrocortisone as a treatment for postflight hypovolemia and orthostatic hypotension in astronauts has not been studied. Our purpose was to test the hypothesis that astronauts who ingest fludrocortisone prior to landing would have less loss of plasma volume and greater orthostatic tolerance than astronauts who do not ingest fludrocortisone. Methods: There were 25 male astronauts who were randomized into 2 groups: placebo (n = 18) and fludrocortisone (n = 7), and participated in stand tests 10 d before launch and 2–4 h after landing. Subjects took either 0.3 mg fludrocortisone or placebo orally 7 h prior to landing. Supine plasma and red cell volumes, supine and standing HR, arterial pressure, aortic outflow, and plasma norepinephrine and epinephrine were measured. Results: On landing day, 2 of 18 in the placebo group and 1 of 7 in the fludrocortisone group became presyncopal (χ² = 0.015, p = 0.90). Plasma volumes were significantly decreased after flight in the placebo group, but not in the fludrocortisone group. During postflight stand tests, standing plasma norepinephrine was significantly less in the fludrocortisone group compared with the placebo group. Conclusions: Treatment with a single dose of fludrocortisone results in protection of plasma volume but no protection of orthostatic tolerance. Fludrocortisone is not recommended as a countermeasure for spaceflight-induced orthostatic intolerance.

Owen G, Turley H, Casey A. The role of blood glucose availability and fatigue in the development of cognitive impairment during combat training. Aviat Space Environ Med 2004; 75:240–246. Introduction: The aim of this study was to determine whether inadequate nutrition would produce a reduction in the blood glucose concentration and impair cognitive function. Methods: Energy intake, blood glucose, and cognitive function were measured in 18 male subjects during a 4-d military field exercise. Baseline measures of fasting blood glucose, body mass, cognitive function, and mood were taken before the start of combat training. Measurements of blood glucose, cognition, and well-being were then repeated during every subsequent 24 h period. Activity levels were monitored continuously using wrist-worn activity monitors. Results: Subjects experienced an increase in symptoms relating to hypoglycemia after 24 h in the field (p < 0.01), vigor decreased (p < 0.001), and fatigue increased (p < 0.001). After 48 h, subjects reported feelings of depression (p < 0.05), anger (p < 0.01), and confusion (p < 0.001). Delayed memory recall was significantly impaired after 48 h (p < 0.05), and there was a decrease in vigilance (p < 0.01). Between 48 and 72 h, there was a decrease in immediate memory recall (p < 0.05). Delayed memory recall and vigilance remained impaired, but did not deteriorate further. When subjects were extracted from the field after 96 h, nude BM had decreased by 2% (p < 0.05). Conclusion: Although it was possible to reproduce the symptoms and cognitive impairment associated with hypoglycemia, there was no change in blood glucose concentration throughout the 4-d period. The impairment in cognitive function is likely to have been the result of significant sleep deprivation.

Smith SD. Cockpit seat and pilot helmet vibration during flight operations on aircraft carriers. Aviat Space Environ Med 2004; 75:247–254. Introduction: Human vibration exposure data relative to military tactical and strategic aircraft operations are required for assessing the potential health risks and performance consequences when using helmet-mounted equipment. The objective of this study was to characterize cockpit seat and pilot helmet vibration in a jet aircraft during aircraft carrier flight operations. Methods: The Remote Vibration Environment Recorder (REVER) was used to measure triaxial accelerations at the seat base, seat pan, seat back, and helmet in the F/A-18C (Hornet) jet aircraft. Data were collected during flight operations on 2 aircraft carriers for a total of 11 catapult launches (CATs), 9 touch-and-goes (TGs), and 4 arrested landings (TRAPs). Helmet pitch acceleration and displacement were estimated from the helmet translational acceleration data. Results: Of particular interest was the substantial low frequency seat and helmet vibration observed during the catapult launch. During the stroke period, seat and helmet vertical (Z) accelerations reached 6 and 8 g peak-to-peak, respectively, and occurred in the frequency range of 3–3.5 Hz. The associated helmet pitch reached peak-to-peak displacements ranging between 9° and 18°. Discussion: The large helmet rotations may be associated with helmet slippage that can cause partial or complete loss of the projected image on a helmet-mounted display (HMD) (vignetting). This is highly undesirable when using the HMD as the primary flight reference. The aircraft operational vibration can be regenerated in the laboratory for investigating this specific concern. The goal is to develop helmet-mounted equipment design guidelines that consider hostile vibratory environments.

Naumann FL, Grant MC, Dhaliwal SS. Changes in cervical spine bone mineral density in response to flight training. Aviat Space Environ Med 2004; 75:255–259. Background: High magnitude loads and unusual loading regimes are two important determinants for increasing bone mass. Past research demonstrated that positive Gz-induced loading, providing high loads in an unaccustomed manner, had an osteogenic effect on bone. Another determinant of bone mass is that the bone response to loading is site specific. This study sought to further investigate the site specific bone response to loading, examining the cervical spine response, the site suspected of experiencing the greatest loading, to high performance flight. Methods: Bone mineral density (BMD) and bone mineral content (BMC) was monitored in 9 RAAF trainee fighter pilots completing an 8-mo flight training course on a PC-9 and 10 age-height-weight-matched controls. Results: At completion of the course, the pilots had a significant increase in cervical spine BMD and total body BMC. No significant changes were found for the control group. Conclusions: This study demonstrated that the physical environment associated with flight training may have contributed to a significant increase in cervical spine bone mass in the trainee PC-9 pilots. The increase in bone mass was possibly a response to the strain generated by the daily wearing of helmet and mask assembly under the influence of positive sustained accelerative forces.

Mitchell SJ, Evans AD. Flight safety and medical incapacitation risk of airline pilots. Aviat Space Environ Med 2004; 75:260–268. Background: This paper examines the use of quantitative incapacitation risk assessment for aeromedical decision-making in determining the medical fitness of multicrew airline pilots, and estimates the effect on flight safety should medical standards be relaxed. The use of the “1% rule” for setting limits for aircrew incapacitation risk is re-examined. Human failure (medical incapacitation) is compared with acceptable failure rates in another safety-critical system, the aircraft engines. Methods: The expected number of cardiovascular incapacitations occurring in flight was modeled by applying an age-related cardiovascular incapacitation risk to the pilot population. The effect on flight safety of relaxing the maximum acceptable incapacitation risk on estimated incapacitation rates in two-pilot operations was also modeled, taking into account a likely increase in the number of pilots who would be allowed to continue to fly with a known medical condition. Results: The model overestimates cardiovascular incapacitation risk and, therefore, provides a cautious estimate. If the maximum acceptable cardiovascular risk is increased, the model predicts a disproportionately small increase in the number of such incapacitations in flight. Conclusions: The evidence suggests that the incapacitation risk limits used by some states, particularly for cardiovascular disease, may be too restrictive when compared with other aircraft systems, and may adversely affect flight safety if experienced pilots are retired on overly stringent medical grounds. States using the 1% rule should consider relaxing the maximum acceptable sudden incapacitation risk to 2% per year.

Yildiz S, Ay H, Günay A, Yaygili S, Aktaş Ş. Submarine escape from depths of 30 and 60 feet: 41,183 training ascents without serious injury. Aviat Space Environ Med 2004; 75:269–271. Introduction: In the case of a submerged, disabled submarine, survivors may be forced to escape by entering the water and ascending rapidly to the surface. The large pressure changes involved may produce pulmonary barotrauma, arterial gas embolism, or barotrauma. To assess the likelihood of such injuries, we retrospectively evaluated medical problems due to submarine escape training among military personnel. Methods: We evaluated 41,183 controlled ascents performed over the past 21 yr in the escape training tank at Gölcük-Kocaeli, Turkey. Each trainee performed two free ascents from 30 ft and two hooded ascents from 60 ft. Before participating, candidates were screened by physical examination, spirometry, and chest X-rays; ear examinations for barotrauma were made after ascents. If a trainee failed to exhale properly during ascent, an instructor aborted the ascent and took him to a bell or side recess of the tank. Results: No record of pulmonary barotrauma or other major complications were found. Middle-ear barotrauma was observed following 1,643 of the ascents (4.1%), with rupture of the tympanic membrane in 35 cases. Discussion: Submarine escape ascents can be safely performed provided that subjects are medically screened and well trained.

Hamilton DR, Sargsyan AE, Kirkpatrick AW, Nicolaou S, Campbell M, Dawson DL, Melton SL, Beck G, Guess T, Rasbury J, Dulchavsky SA. Sonographic detection of pneumothorax and hemothorax in microgravity. Aviat Space Environ Med 2004; 75:272–277. Introduction: An intrathoracic injury may be disastrous to a crewmember aboard the International Space Station (ISS) if the diagnosis is missed or delayed. Symptomatic or clinically suspicious thoracic trauma is treated as a surgical emergency on Earth, usually with immediate stabilization and rapid transport to a facility that is able to deliver the appropriate medical care. A similar approach is planned for the ISS; however, an unnecessary evacuation would cause a significant mission impact and an exorbitant expense. Hypothesis: The use of ultrasound imaging for the detection of pneumothorax and hemothorax in microgravity is both possible and practical. Methods: Sonography was performed on anesthetized pigs in a ground-based laboratory (n = 4) and microgravity conditions (0 G) during parabolic flight (n = 4). Aliquots of air (50–500 ml) or saline (10–200 ml) were introduced into the pleural space to simulate pneumothorax and hemothorax, respectively. Results: The presence of “lung sliding” excluded pnemothorax. In microgravity, a loss of “lung sliding” was noted simultaneously in the anterior and posterior sonographic windows after 100 ml of air was introduced into the chest, indicating pneumothorax. The presence of the fluid layer in simulated hemothorax was noted in the anterior and posterior sonographic windows after 50 ml of fluid was injected into the pleural space. During the microgravity phase, the intrapleural fluid rapidly redistributed so that it could be detected using either anterior or posterior sonographic windows. Conclusion: Modest to severe pneumothorax and hemothorax can be diagnosed using ultrasound in microgravity.

Rayman RB, Zanick D, Korsgard T. Resources for inflight medical care. Aviat Space Environ Med 2004; 75:278–280.With the anticipated growth of air travel, inflight illness and injury are expected to increase as well. This is because more elderly people and people with preexisting disease are taking to the air. Although inflight medical events and deaths are uncommon, physician passengers are occasionally called upon to render care. Resources for the physician may include emergency medical kits, automatic external defibrillators (AEDs), ECG monitors, portable oxygen bottles, and first-aid kits. Most airlines provide around-the-clock air-to-ground radio consultation either with their own medical department personnel or contracted medical consultants. Furthermore, some flight attendants are trained in cardiopulmonary resuscitation, first-aid, and operation of AEDs. This paper describes those inflight resources available to a physician who is called upon to treat an ill or injured passenger. In a broader sense, it is also providing advice to physicians who administer inflight medical care. The Aviation Medical Assistance Act of 1998 (“Good Samaritan act”) is also discussed.

Grossman A, Barenboim E, Azaria B, Sherer Y, Goldstein L. The maintenance of wakefulness test as a predictor of alertness in aircrew members with idiopathic hypersomnia. Aviat Space Environ Med 2004; 75:281–283.Aviators are required to maintain a high level of alertness during their missions. Two conditions that may disrupt this alertness are fatigue and hypersomnia. Fatigue is a physiological state, while hypersomnia is a pathologic state, also termed excessive daytime sleepiness (EDS), which is manifested by the tendency to fall asleep in inappropriate places or situations, such as during flight or driving. Hypersomnolence may be diagnosed by subjective measurements, such as the Epworth sleepiness scale, but the diagnosis is established by two objective tests: the Multiple Sleep Latency Test (MSLT) and the Maintenance of Wakefulness Test (MWT). The first consists of four 20-min sessions used to determine the time it takes the patient to fall asleep when given the opportunity and is considered positive when the sleep latency time is shorter than 5 min, although some authors use 8 min as the cut-off for the diagnosis. The Maintenance of Wakefulness Test (MWT) consists of four 40-min sessions during which the patient attempts to maintain wakefulness while seated in a dark, quiet room during the day. Herein we report 2 cases of aviators who were returned to flying duty despite a pathologic MSLT. These aviators were waivered based on a normal MWT and safety history obtained from their commanders.

Beyer RW, Daily PO. Renal artery dissection associated with Gz acceleration. Aviat Space Environ Med 2004; 75:284–287.A 55-yr-old male presented with flank pain and nausea minutes after intensive aerobatic flight maneuvers. An initial diagnosis of acute appendicitis was made. Computed axial tomography and renal arteriography showed a right kidney with two renal arteries, a right upper pole infarction, and a dissection in the upper renal artery which had a more vertical trajectory than the usual main renal artery. No signs of diseases known to be associated with renal artery dissection were present. The patient recovered without residual hypertension. Heavy positive G loads may have potential to cause renal arterial injury, particularly when renal vascular anatomical variations exist. The postulated mechanism is similar to fall injuries in which the subjects landed on their feet, with inertia causing caudal renal dislodgement and stretch of the renal vessels.