G-Induced Loss of Consciousness Prediction Using a Support Vector Machine.

INTRODUCTION: Gravity-induced loss of consciousness (G-LOC) is a major threat to fighter pilots and may result in fatal accidents. The brain has a period of 5-6 s from the onset of high +Gz exposure, called the functional buffer period, during which transient ischemia is tolerated without loss of consciousness. We tried to establish a method for predicting G-LOC within the functional buffer period by using machine learning. We used a support vector machine (SVM), which is a popular classification algorithm in machine learning.METHODS: The subjects were 124 flight course students. We used a linear soft-margin SVM, a nonlinear SVM Gaussian kernel function (GSVM), and a polynomial kernel function, for each of which 10 classifiers were built every 0.5 s from the onset of high +Gz exposure (Classifiers 0.5-5.0) to predict G-LOC. Explanatory variables used for each SVM were age, height, weight, with/without anti-G suit, +Gz level, cerebral oxyhemoglobin concentration, and deoxyhemoglobin concentration.RESULTS: The performance of GSVM was better than that of other SVMs. The accuracy of each classifier of GSVM was as follows: Classifier 0.5, 58.1%; 1.0, 54.8%; 1.5, 57.3%; 2.0, 58.1%; 2.5, 64.5%; 3.0, 63.7%; 3.5, 65.3%; 4.0, 64.5%; 4.5, 64.5%; and 5.0, 64.5%.CONCLUSION: We could predict G-LOC with an accuracy rate of approximately 65% from 2.5 s after the onset of high +Gz exposure by using GSVM. Analysis of a larger number of cases and factors to enhance accuracy may be needed to apply those classifiers in centrifuge training and actual flight.Ohrui N, Iino Y, Kuramoto K, Kikukawa A, Okano K, Takada K, Tsujimoto T. G-induced loss of consciousness prediction using a support vector machine. Aerosp Med Hum Perform. 2024; 95(1):29-36.

Decadal electrocardiographic changes between age 40 and 50 in military pilots.

INTRODUCTION: Cardiovascular diseases can lead to sudden in-flight incapacitation and long-term disability in aircraft pilots. Electrocardiogram (ECG) has been widely used to screen for these diseases in routine aeromedical examinations. Several ECG changes such as complete left bundle-branch block (CLBBB) and left ventricular hypertrophy (LVH) have been associated with increased likelihood of underlying structural cardiac diseases in addition to the emergence of newly recognized cardiovascular diseases such as Brugada syndrome. Therefore, the purpose of this study was to analyze decadal ECG changes in aircraft pilots between 40 and 50 yr in order to make an appropriate evaluation of these ECG changes. METHODS: We analyzed the ECGs from the annual aeromedical examination of age 50 compared to those 40 yr of age in a total of 176 Japan Air Self-Defense Force pilots. RESULTS: With regard to decadal changes, we detected 34 new ECG changes (1 of sinus tachycardia, 8 sinus bradycardia, 1 atrial fibrillation, 2 premature atrial contraction, 1 premature ventricular contraction, 2 left axis deviation, 6 first-degree atrioventricular block, 1 CLBBB, 3 complete right bundle-branch block, 2 incomplete right bundle-branch block, 1 right ventricular conduction delay, and 6 LVH). Although the majority of them were concluded to be normal variants, the results of echocardiography in two hypertensive pilots without good control demonstrated abnormalities: one had mild hypertrophic nonobstructive cardiomyopathy and another had heart enlargement. CONCLUSION: Thus, this study recommends additional cardiovascular examinations, including echocardiography for hypertensive pilots with ECG changes.

Ear pain and its treatment in hypobaric chamber training in the Japan Air Self-Defense Force.

BACKGROUND: We have documented that ear pain is the most prevalent physiologic incident during hypobaric chamber training in the Japan Air Self-Defense Force. Ear pain may increase also in flight in the future because it is closely related to allergic rhinitis. Therefore, it is very important to know the characteristic of ear pain and the efficacy of its treatment. METHODS: The incidence of ear pain was calculated in each training profile from 1990 to 1998. Type III chamber flight records were further analyzed for the characteristics of ear pain: relationship with a trainee occupational category, time of occurrence of ear pain, and efficacy of treatment. RESULTS: Of 17,935 exposures, 740 trainees (4.1%) had ear pain. Of 7,047 trainees, 429 (6.1%) complained of ear pain especially in Type III, totaling 625 times. Fighter pilots and cargo pilots complained of ear pain one twelfth and one third the number of times, respectively, compared with passengers. Of the 625 episodes, 616 (98.6%) occurred during descent. Three kinds of treatment were administered until the pain was relieved in the following order: Valsalva maneuver, Politzer bag, and decompression. The efficacy rates were 35.8, 92.3, and 83.9%, respectively. Only 5 trainees (0.07%) could not complete training due to ear pain despite treatment. CONCLUSION: The combination treatment of Valsalva maneuver, Politzer bag, and decompression is very effective for relieving ear pain encountered during hypobaric chamber training. A health specialist needs to understand ear pain and its treatment in hypobaric environment such as aircraft.

Urinary catecholamine responses in F-15 pilots: evaluation of the stress induced by long-distance flights.

Included in the Cooperative Cope Thunder exercises from Japan to Alaska is one of the longest distance flight missions carried out by Japan Air-Self Defense Force F-15 pilots. The magnitude of the flight stress of these pilots is considered to be quite high. The purpose of this study was to evaluate the flight stress induced by the long-distance flights. The subjects were eight pilots who participated on a volunteer basis. Samples of urine were collected approximately 30 minutes before (preflight) and 20 minutes after (postflight) the flights. The ratios (post-:preflight) of noradrenaline levels were 1.20 +/- 0.09 (Japan-Alaska) and 1.32 +/- 0.12 (Alaska-Japan), and those of adrenaline were 4.03 +/- 1.06 and 3.68 +/- 0.98. These results strongly suggest that psychological stress during the long-distance flights is increased in the fighter pilots.

Expression of endothelin-1 in the brain and lung of rats exposed to permanent hypobaric hypoxia.

High-altitude hypoxia causes pulmonary hypertension in humans and animals. Endothelin-1 (ET-1) is a novel and long-lasting vasoconstrictor. However, no study has dealt with the effects of a hypobaric hypoxic environment (HHE) on ET-1 activity in the brain. We examined 134 male rats permanently exposed to the equivalent of 5500 m altitude for 1 to 8 weeks. In these HHE rats, the mean pulmonary arterial pressure was significantly raised. The level of ET-1 protein, measured by enzyme immunoassay, increased rapidly in the lungs on exposure to HHE, but decreased in the brain. The level of ET-1 mRNA, measured by semiquantitative RT-PCR, was raised at 1, 4, and 6 weeks' exposure in the lungs and at 4 or more weeks' exposure in 3 of 8 brain regions. By in situ hybridization and immunohistochemistry of brain sections, ET-1 mRNA and protein were detected in the endothelial cells, neurons, and astrocyte-like cells in control rats. In HHE rats, the immunoreactive intensity for ET-1 protein decreased rapidly with time in these cells within the brain, although a few weakly ET-1 protein-positive cells were detected until 8 weeks' exposure to HHE. Only a few weakly ET-1 mRNA-positive endothelial cells were detected in any HHE rats. Although the reactivity for ET-1 mRNA had decreased significantly in neurons and astrocyte-like cells at 1 and 2 weeks' exposure to HHE, it was again strong in both types of cells at 4 weeks' exposure to HHE. These results raise the possibility that during exposure to HHE, ET-1 production in the lung may play a role in the development of pulmonary hypertension, while a decrease in ET-1 production within the brain may help to protect neurons by preventing or limiting the constriction of cerebral microvessels during the hypoxia induced by HHE.

Peptic ulcer data from 4 years of endoscopy in 955 pilots of the Japan Air Self Defense Force.

BACKGROUND: The treatment of peptic ulcer disease has undergone profound changes due to the recognition of Helicobacter pylori as a causative factor. A survey of medical records was made to determine the prevalence of peptic ulcer among pilots of the Japan Air Self Defense Force (JASDF) and to decide on a possible change in JASDF medical policy toward an ulcer-treatment regime involving therapy to eradicate Helicobacter pylori. METHODS: The subjects were 955 male pilots, age 40 or older. Between 1996 and 1999, they underwent gastrointestinal endoscopy 2.47 times on average. Annual ulcer rates and recurrence rates were obtained from the endoscopic file data. Smoking habits and use of NSAIDs were also assessed as important risk factors for peptic ulcer. RESULTS: The detection rate of open ulcer for each year was 2.3-3.1% in the stomach and 1.9-4.4% in the duodenum. For ulcers including scarring, the corresponding figures were 7.3-9.5% and 12.7-19.9%. The recurrence rate from S1 scars in the duodenum was 34%, significantly higher than that from S2 scars (7%) (p < 0.0005). There was no significant difference in recurrence rate between S1 scars and S2 scars in the stomach. There was a significant association between gastric ulcer and smoking (p < 0.0005). None of the pilots took long-term NSAID medications. CONCLUSIONS: Peptic ulcer occurs more frequently in the JASDF pilots than in the general population. S1 scarring in the duodenum, as well as open ulcers in either stomach or duodenum, are candidates for Helicobacter pylori eradication therapy if the bacterium is detected. Other types of scars are also candidates for this therapy when pilots have symptoms related to infection with Helicobacter pylori.

Long-term disability among aviators in Japan Air Self-Defense Force: analysis of 260 cases.

BACKGROUND: As part of a study of the risks associated with aviator incapacitation, we identified the diseases that caused long-term disability (LTD) among aviators in the Japan Air Self-Defense Force (JASDF), and then assessed the magnitude of the problem that each group of diseases represented with regard to the safety of flight. METHODS: Case-notes for JASDF aviators who stopped work for more than 3 mo during 1980-2002 were identified from all files kept at the Medical Evaluation Section of the Aeromedical Laboratory. The case-notes were divided into four age groups and analyzed by diagnostic category or injury. RESULTS: We identified 260 aviators with LTD, including 217 active-duty pilots and 43 navigators with flying status. Of those, 59 cases (22.7%) had permanent disability for flight. About 75% of LTD cases could be attributed to five diagnostic categories: neoplasms, nervous system and sense organs, circulatory system, digestive system, and musculoskeletal system. Peaks in LTD were found in the 20-29 and 40-49 age-groups. In the younger group, 78.2% of the patients were students, of whom 23 were found to have a disability associated with a preexisting medical condition which was not detected in the initial screening process for pilots. In the 20-29 yr age-group, the most common reason for LTD was the nervous system and sense organs, while in the 40-49 yr age-group it was the circulatory system. CONCLUSION: Reduction in the frequency of LTD might be accomplished by improving the medical screening process for applicants and emphasizing the prevention of circulatory diseases during a pilot's career.

Physiological incidents during 39 years of hypobaric chamber training in Japan.

BACKGROUND: Hypobaric chamber training for military aircrew is very important for flight safety. Since we began hypobaric training in our laboratory in 1960, some trainees have suffered physiological incidents. This study will characterize the physiological incidents during hypobaric chamber training at the Japan Air Self-Defense Force (JASDF). METHODS: All available training records from 1960-1998 were reviewed and the frequency of physiological incidents counted and analyzed. RESULTS: There were 29,677 trainees and 58,454 exposures. Overall frequency of physiological incidents was 6.3%. Physiological incidents included ear pain, paranasal sinus pain, abdominal pain, hypoxia, hyperventilation, joint pain, and toothache. Decompression sickness (DCS-I, simple joint pain only) was rare. In cases of DCS-I, joint pain was easily relieved with controlled descent. During the last three decades, overall prevalence of physiological incidents has gradually increased from 5.3 to approximately 6.1% before 1991, to 6.8-9.9% after 1991. However, prevalence rate showed no change through out the period when ear pain was factored out. The increase in prevalence was entirely due to an increased frequency of ear pain: 3.6 to approximately 4.6% before 1991, and 5.4 to approximately 7.2% after 1991. CONCLUSIONS: DCS has not been a problem in the JASDF hypobaric chamber training experience. The majority of physiological incidents during hypobaric chamber training in JASDF have been ear pain, a minor but frequent obstacle to hypobaric training. The exact cause of the observed increase in frequency of Eustachian tube dysfunction currently remains unclear.

Statin inhibits hypoxia-induced endothelin-1 via accelerated degradation of HIF-1α in vascular smooth muscle cells.

AIMS: Endothelin-1 (ET-1) contributes to the pathogenesis of cardiovascular diseases with multiple properties such as vasoconstriction. Human ET-1 gene expression is up-regulated by the transcription factor hypoxia-inducible factor-1 (HIF-1) through hypoxia response element (HRE). Although previous studies suggested that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) alter HIF-1-related gene expression, it remained unclear whether statins modulate HIF-1-mediated ET-1 expression. Therefore, we investigated the effect of fluvastatin on hypoxia-induced human ET-1 expression in vascular smooth muscle cells (VSMC). METHODS AND RESULTS: Hypoxia (1% O(2)), compared with the normoxic condition (21% O(2)), significantly induced the expression of preproET-1 mRNA, ET-1 protein, and ET-1 secretion in VSMC. Hypoxia induced a 2.3-fold increase in HRE-dependent ET-1 reporter gene activation. Under concentrations of 1 µmol/L or greater, fluvastatin attenuated the hypoxia-induced ET-1 gene expression through the accelerated ubiquitin/proteasome-dependent degradation of HIF-1α, thus consequently attenuating HIF-1α binding to the HRE of the ET-1 gene. These inhibitory effects of fluvastatin were cancelled by concomitant treatment with mevalonate, farnesyl pyrophosphate, or geranylgeranyl pyrophosphate, but not squalene. CONCLUSION: The present study suggests that fluvastatin attenuates HIF-1-dependent ET-1 gene expression in conjunction with the stimulation of HIF-1α ubiquitin/proteasome-dependent degradation via isoprenoid-dependent mechanisms.

Allergic rhinitis and ear pain in flight.

BACKGROUND: Ear pain is the most common physiologic incident in hypobaric chamber training in the Japan Air Self-Defense Force, and the incidence of ear pain has been gradually increasing. There has been a concomitant increase in the incidence of allergic rhinitis in Japan. We hypothesized that the increased incidence of ear pain may be due to the increased incidence of eustachian tube dysfunction associated with allergic rhinitis. OBJECTIVE: To explore whether there is an association between allergic rhinitis and ear pain experienced in hypobaric chamber training. METHODS: We examined 9 years of training records and noted whether there was a seasonal influence on the occurrence of ear pain in 7047 trainees. In addition, we studied the prevalence of allergic rhinitis among trainees during a representative training year using a questionnaire method, noting association between allergic rhinitis and the occurrence of ear pain. RESULTS: Comprehensive review of training records showed 429 (6.1%) of 7047 trainees complained of ear pain. Ear pain occurred more often in spring than the other 3 seasons. The questionnaire data showed 202 (23.0%) of 878 trainees had allergic rhinitis. Trainees with allergic rhinitis complained of ear pain more often in the spring than trainees without allergic rhinitis. CONCLUSIONS: Active allergic rhinitis is closely associated with the occurrence of ear pain in hypobaric chamber training. A similar phenomenon might occur in an actual flight. Special attention should be paid to not only common cold but also allergic rhinitis in both hypobaric chamber training and actual flights.

Expressions of adrenomedullin mRNA and protein in rats with hypobaric hypoxia-induced pulmonary hypertension.

Experimental pulmonary hypertension induced in a hypobaric hypoxic environment (HHE) is characterized by structural remodeling of the heart and pulmonary arteries. Adrenomedullin (AM) has diuretic, natriuretic, and hypotensive effects. To study the possible effects of HHE on the AM synthesis system, 150 male Wistar rats were housed in a chamber at the equivalent of a 5,500-m altitude level for 21 days. After 14 days of exposure to HHE, pulmonary arterial pressure (PAP) was significantly increased (compared with control rats). The plasma AM protein level was significantly increased on day 21 of exposure to HHE. In the right ventricle (RV), right atrium, and left atrium of the heart, the expressions of AM mRNA and protein were increased in the middle to late phase (5-21 days) of HHE, whereas in the brain and lung they were increased much earlier (0.5-5 days). In situ hybridization and immunohistochemistry showed AM mRNA and protein staining to be more intense in the RV in animals in the middle to late phase of HHE exposure than in the controls. During HHE, these changes in AM synthesis, which occurred strongly in the RV, occurred alongside the increase in PAP. Conceivably, AM may play a role in modulating pulmonary hypertension in HHE.