The purpose of this study was to investigate whether nausea or gastric dysrhythmia, including tachygastria, which was determined by electrogastrography (EGG), were observed during optokinetic motion sickness in healthy Japanese volunteers. Twelve volunteers (9 men and 3 women) participated in the study. The subjects were asked to sit in a chair with their heads positioned in the center of a drum whose inside had been painted with black and white stripes. After a 15 min resting period, the drum was rotated at a speed of 60 degree/sec for 15 min. The EGG was continuously recorded for a total of 45 min (15 min resting period, 15 min rotation period, and 15 min recovery period). The severity of nausea was evaluated with a visual analogue scale (VAS) before, immediately after, and 15 min after the cessation of drum rotation. Other motion sickness symptoms were evaluated by scores of subjective symptoms of motion sickness (SSMS). Of 12 subjects who completed the study, 10 complained of nausea immediately after cessation of drum rotation. The VAS score for nausea immediately after the drum rotation period and 15 min after cessation of the rotation was significantly higher than during the resting period. The EGG during the drum rotation period showed a decrease in normogastria, which was accompanied with an increase in tachygastria. We conclude that gastric tachyarrhythmia and nausea may be induced by viewing an optokinetic rotating drum in healthy Japanese subjects who may have a hypersusceptibility to vection-induced motion sickness. The gastric dysrhythmia obtained with EGG could be a useful observation to support the appearance of nausea induced by optokinetic motion sickness.

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Research investigating the relationship between physical training and trace mineral concentrations has focused primarily on athletes. Exercise alters mineral content; flight is a form of exercise; therefore, flight may elicit changes in mineral content. This study examined the effects of stressful flight aptitude tests on the trace minerals zinc and copper in urine. During flight aptitude tests, urine samples were obtained from 100 men. The zinc concentration decreased following flight. Furthermore, because +Gz acceleration is one of many stressors for an aviator in flight, the effects of +Gz acceleration on the trace minerals zinc, copper, and chromium in human serum and urine were also examined. Blood and urine samples were obtained from 7 men and 3 women, before and after +Gz acceleration. The serum zinc and copper concentrations decreased after +Gz acceleration. The urinary zinc and copper concentrations were not altered by +Gz acceleration. These findings suggest that the circulating levels of zinc and copper presumably change as they are transported to tissues requiring greater amounts due to the increased physiological work associated with flight stress, including +Gz acceleration.

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The purpose of the present study was to examine the effect of unilateral lower limb suspension (ULLS) deconditioning on oxygen uptake kinetics. Eight healthy males underwent ULLS for 20 days and performed a series of 6-min square-wave transitions from rest to 60-W single-leg cycling exercises just before and after ULLS. To characterize the kinetics of the oxygen uptake response, a single exponential model was applied to the data until the end of the fast component omitted the first 15 s of the on-transit using a nonlinear least-squares fitting procedure. The following results were found: (i) the time constant of oxygen uptake was unchanged before and after ULLS; (ii) although there was no significant difference in the baseline and the asymptotic amplitude of the fast component, the asymptote, i.e., the absolute asymptotic amplitude of the fast component (the sum of the baseline and the asymptotic amplitude), and the end exercise oxygen uptake were decreased after ULLS; (iii) the contribution of the slow component to the total response of oxygen uptake was unchanged at pre- and post-ULLS. In conclusion, the asymptote in the fast component and the end exercise oxygen uptake were decreased after 20-d ULLS, though the response speed and the amplitude of the slow component of oxygen uptake were not changed. It is suggested that deconditioning as a result of limb disuse affects oxygen uptake response.

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Changes in intracranial pressure (ICP) resulting from head-down tilt (HDT) were studied in rabbits, and a possible role of edema formation in the change of ICP was examined. Animals were anesthetized with pentobarbital sodium and artificially ventilated. ICP was continuously monitored through a catheter inserted into the subarachnoid space, It increased depending on the tilt angle and decreased when the tilt angle was reduced. ICP elevated from 4.6±0.7 mmHg (mean±standard error of the mean) at horizontal prone position to 13.7±1.0 mmHg immediately after the onset of 45° HDT and gradually reduced toward the pre-HDT baseline in the next 8h. ICP decreased below the pre-HDT baseline value immediately after returning to the horizontal prone position, and gradually increased toward the baseline during the 2h of recovery period. Histological examination (HE stain) demonstrated that exposure to 8h of HDT did not cause remarkable edema in either the gray matter or the white matter in rabbits. Water content and specific gravity of brain tissues both were increased in the HDT group in comparison with the control group. These results suggest that edema formation plays little role in the elevation of ICP during the acute phase of HDT in rabbits.

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Research to date on the effect vehicle-ride exposure has on the development of cervical pathologies in mounted Warfighters is conflicting. The purpose of this study was to determine if the literature suggests a definite effect of vehicle-ride exposure on cervical pathology. Databases were searched using multiple combinations of select terms. Twelve studies meeting the inclusion criteria were included in the meta-analysis. The results of the meta-analysis revealed that overall vehicle-ride exposure was likely to increase cervical pathology (p=0.01, odds ratio=1.59, 95% CI=1.16−2.17). Using vehicle type as a moderator it was found that vehicle-ride exposure in ground-based vehicles (p=0.01, odds ratio=2.33, 95% CI=1.41−3.85) and fixed-wing aircraft (p=0.01, odds ratio =1.59, 95% CI=1.13−2.23) were likely to increase cervical pathology. Using operator/other personnel moderator it was found that in the populations tested, fighter pilots or fighter jet weapons systems operators were more likely to develop a cervical pathology (p<0.001, odds ratio=1.78, 95% CI=1.26−2.50). The available studies indicate an increase in cervical pathology for personnel exposed to ground-based vehicles and fixed-wing aircraft.

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In recent years, the measurement of cerebral oxygen status with near-infrared spectroscopy (NIRS) has been widely used to study for cortical activations and/or brain monitoring. The present paper provides an overview of the Aeromedical Laboratory research concerning NIRS measurements.

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Numerous studies have reported on biochemical responses of the Japan Air Self-Defense Force personnel to aviation stresses (e.g., ＋Gz, hypobaric hypoxia, vibrations, noise, temperature, long flight, flight task, etc.). The present paper provides an overview of the Aeromedical Laboratory research concerning biochemical responses to various aviation stresses.

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The mechanisms responsible for the morphological and metabolic adaptation of skeletal muscles to the removal of antigravity activity were investigated in rats. Significant atrophy relative to the levels before suspension was induced in ankle plantarflexsors, may be due to a reduced tension production caused by decreased muscle length and electromyogram activity. Growth failure was significant in ankle dorsiflexors, although these muscles did not atrophy. Forced muscle contraction through electrical stimulation at 1 or 100 Hz during hind limb suspension generally had detrimental effects. The percent contribution of water loss to the suspension-related change in weight was 85, 88, and 93% in soleus, plantaris, and extensor digitorum longus, respectively. The total levels of both β-hydroxyacyl CoA dehydrogenase (HAD) and lactate dehydrogenase (LDH) were less in the suspended muscles than in the controls, having high positive correlations with the total protein content. The specific activity of HAD, but not of LDH, of the suspended muscles was lower than in the controls (25–61%). These data suggest that the cause of muscle atrophy and changes in metabolic properties may be a decreased tension development, not necessarily the reduction of electrical or contractile activity. Further, it is clearly suggested that electrical stimulation of a muscle group with different composition of fiber phenotype at a certain pattern or frequency is not suitable for the countermeasure. It is also suggested that the major cause of the decreased muscle weight was loss of water, even though protein content was also lowered after suspension. Moreover, the data suggest that the HAD level was affected more than the total protein content and LDH.

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The purpose of the present study was to examine the effects of different types of personal cooling equipments (PCE) on the alleviation of heat strain during red pepper harvest simulated in a climatic chamber. The experiment consisted of eight conditions: 1) Control, 2) Neck cooling scarf A with a cooling area of 68 cm², 3) Neck cooling scarf B (cooling area 154 cm²), 4) Brimmed hat with a frozen gel pack, 5) Cooling vest (cooling area 606 cm²), 6) Hat+Neck Scarf B, 7) Hat+Vest, and 8) Hat+Neck Scarf B+Vest. Twelve subjects worked a red pepper harvest simulated in a climatic chamber of WBGT 33℃. The result showed that rectal temperature (T_re) was effectively maintained under 38℃ by wearing PCE. Mean skin temperature (T_sk) and heart rate (HR) became more stable through wearing PCE. When wearing the ‘Hat+Scarf B+Vest’, particularly, T_sk and HR quickly decreased to the comfort level during the mid-rest stage. We confirmed that the vest with a cooling area of only 3.3% body surface area (BSA) was effective in alleviating heat strain in a simulated harvest work. Furthermore, the heat strain of farm workers can be considerably eliminated by the combination of the cooling vest, a scarf, and a brimmed hat, with the total cooling area of 4.2% BSA.

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This study investigates changes in intraocular pressure (IOP) in rabbits during head-down tilt (HDT), which is commonly used as an experimental model to simulate microgravity. IOP was measured by the needle insertion technique (IOP_NEEDLE) and Tono-pen tonometry (IOP_TONO-PEN). Although the absolute value of the IOP_TONO-PEN was significantly smaller than that of the IOP_NEEDLE, a significant correlation (r=0.99) was observed between them. A linear regression analysis yielded an equation as follows: IOP_TONO-PEN=0.67 IOP_NEEDLE−0.67. Both the IOP_NEEDLE and the IOP_TONO-PEN changed depending on the tilt angle. Tilting from horizontal (0°) to 75° head-down increased the IOP_NEEDLE and the IOP_TONO-PEN by 7.3±0.8 (mean±SEM) mmHg and 4.4±1.3mmHg. The IOP_NEEDLE elevated from 13.1±1.3 to 16.9±1.0mmHg immediately after the onset of 45° HDT and then gradually declined. The value of the IOP_NEEDLE during 8h of HDT was significantly higher than the value in the control animals, which were kept at the horizontal prone position throughout the experiment. Similar findings were observed in the IOP_TONO-PEN. These results suggest that the needle insertion technique and the Tono-pen tonometry are both useful for measuring IOP in rabbits.

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There are considerable individual differences in cognitive performance deficits resulting from extended work hours and shift work schedules. Recent progress in sleep and performance research has yielded new insights into the causes and consequences of these individual differences. Neurobiological processes of sleep/wake regulation underlie trait individual variability in vulnerability to performance impairment due to sleep loss. Trait vulnerability to sleep loss is observed in the laboratory and in the work environment, even in occupational settings where (self-)selection pressures are high. In general, individuals do not seem to accurately assess the magnitude of their own vulnerability. Methods for identifying workers who are most at risk of sleep loss-related errors and accidents would therefore be helpful to target fatigue countermeasure interventions at those needing them most. As yet, no reliable predictors of vulnerability to sleep loss have been identified, although candidate genetic predictors have been proposed. However, a Bayesian forecasting technique based on closed-loop feedback of measured performance has been developed for individualized prediction of future performance impairment during ongoing operations. Judiciously selecting or monitoring individuals in specific tasks or occupations, within legally and ethically acceptable boundaries, has the potential to improve operational performance and productivity, reduce errors and accidents, and save lives. Trait individual variability in responses to sleep loss represents a major complication in the application of one-size-fits-all hours of service regulations―favoring instead modern fatigue risk management strategies, because these allow flexibility to account for individual vulnerability or resilience to the performance consequences of extended work hours and shift work schedules.

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Changes in cerebral blood flow (CBF) and somatosensory-evoked potentials (SEPs) were studied in rabbits exposed to head-down tilt (HDT) at 45° and 75°. The animals were anesthetized with alpha chloralose and the lungs were artificially ventilated. CBF was continuously measured by laser Doppler flowmetry (LDF), and SEPs were recorded as responses of the cortex to median nerve stimulation. In the 45° HDT rabbits, CBF did not change significantly in the parietal cortex during 1 h of HDT. In contrast, in the 75° HDT rabbits, CBF did not change significantly within 5 min after the onset of HDT, but decreased gradually to 79% of the pre-HDT baseline value at the end of 1 h of HDT. The latency and amplitude of SEPs did not change significantly throughout the experiment in any group. These results suggest that CBF and SEPs do not change significantly during 1 h of 45° HDT and that 75° HDT disturbs the regulation of the cerebral circulation but does not affect cortical somatosensory response, at least for 1 h.

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Since late 1990s, a new hypoxia training device using mixed gas delivered through trainee’s oxygen mask has been developed in the United States Navy. This “Reduced Oxygen Breathing Device (ROBD)”has been evaluated in many research projects and has been introduced to military aircrews training as an alternative method to traditional hypobaric hypoxia training in several countries. The purpose of this article is to review the ROBD focusing on physiological differences between normobaric and hypobaric condition. The ROBD has been reported to induce almost same physiological responses, symptoms and cognitive impairment as the hypobaric induced hypoxia. Rapid decompression familiarization, which is only produced by hypobaric chamber training, is one of the issues to consider before introducing the ROBD to aircrews training. We also summarized the ROBD training protocols combined with a flight simulator for military aircrews.

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Gravity-induced loss of consciousness (G-LOC) is a major threat to fighter pilots and may result in fatal accidents. High +Gz (head-to-foot direction) acceleration force induces cerebral blood loss and results in gray-out, black out, and G-LOC. Countermeasures to avoid G-LOC include anti-G strain maneuver, anti-G suits, and pressure breathing for G, etc. They effectively decrease G-LOC incident, but have not eradicated it. Objective detection of G-LOC related symptoms is the prerequisite. In spite of many G-protective measures, G-LOC monitoring system has yet to be developed. Technologies for non-contact monitoring or motion capture have ventured into health care market. Real time physiological sensing for heart rate, body temperature, respiratory rate, etc, is used to medical, health care, physical fitness and sports area. Those advanced technologies might have potential for future G-LOC monitoring. This article reviews current status and future of countermeasures for G-LOC, and related technologies.

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Earlier studies showed that exposure to microgravity caused cephalad fluid shift, increased capillary pressure in the head, and produced facial edema and nasal congestion. In the present study, edema formation in the brain was investigated in rabbits exposed to simulated microgravity, head-down tilt (HDT), by measuring water content and histological examinations. Water content in the brain tissues of rabbits exposed to 2 and 8 days of HDT did not increase significantly compared with that of control animals. Neither vital staining using Evans blue nor immunohistochemical examination demonstrated extravasation of plasma constituents in the brain tissues of the HDT rabbits. Although marked congestion was noted in the brain, hematoxylin and eosin staining did not show edematous changes, such as distension of the perivascular and pericellular spaces and vacuolar appearance, in the tissues obtained from HDT rabbits. Transmission electron microscopy revealed that tight junctions of the capillary endothelium were intact in the HDT rabbits. These results suggest that either HDT up to 8 days does not cause brain edema in rabbits or it induces only a slight brain edema which is hard to be demonstrated by measurement of water content or histological examinations.

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Researches into the relationship between the physical quantity of vibration and the subjectively perceived quantity become important in designs for the vibration environment. Subjective experimental methods to obtain the relationship between the physical quantity of vibration and the subjectively perceived quantity are different depending on the design objectives which consider the human sense of vibration characteristic. In this review, the following are outlined: (i) fundamental methods for obtaining the design objectives for vibration environments; (ii) reported findings on the physical quantity of vibration environments and the human characteristics of sense vibration; and (iii) problems with and limits of the ISO 2631-1 standard, which defines the subjective response of the ride comfort in public transportation. Finally, the directions of research into the subjective experimental methods for obtaining design objectives in the vibration environment considering of the human characteristics of sense vibration are described.

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Background A link between venous thromboembolism (VTE) and air travel has been recently discussed, so the present study aimed to clarify the characteristics of acute pulmonary thromboembolism (PTE) associated with air travel in Japan. Methods and Results The study group comprised 36 patients with acute PTE associated with air travel. Patients' characteristics, clinical risk factors for VTE and coagulation abnormalities were investigated, and compared with a group of PTE not associated with travel. Of the 36 cases, 30 cases were female, 34 were over 40 years of age and all had flown more than 6 h. Two-thirds of all cases did not leave their seats during the flight. Of the patients, 44% had no clinical risk factors for VTE or coagulation abnormalities. Idiopathic PTE (ie, PTE without clinical risk factors or coagulation abnormalities) was significantly more common in the air travel group. Conclusion Acute PTE associated with air travel in Japan is common in elderly women and may occur without any clinical risk factors for VTE or coagulation abnormalities. Remaining seated throughout the flight increases the risk. (Circ J 2005; 69: 1297 - 1301)

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