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.

Cerebral near-infrared spectroscopy to evaluate anti-G straining maneuvers in centrifuge training.

INTRODUCTION: Over the past decade, near-infrared spectroscopy (NIRS) has emerged as an easily manageable noninvasive method for the continuous monitoring of cerebral cortical oxygenation during +Gz exposure. NIRS is also used to evaluate pilot trainees' ability to adequately perform anti-G straining maneuvers in the course of centrifuge training. This study aimed to determine the general patterns and individual differences in NIRS recordings during +Gz exposure. METHODS: There were 22 healthy male cadets who participated in the study. The centrifuge training profiles included a gradual onset run (GOR, onset rate of 0.1 Gz x s(-1)) and short-term repeated exposures, with Gz levels from 4 to 7 Gz at an onset rate of 1.0 Gz x s(-1) (rapid onset run, ROR). Cortical tissue hemoglobin saturation (tissue oxygenation index, TOI) and changes in the concentration of oxygenated hemoglobin (O2Hb) were recorded from the right forehead during the period of Gz exposure. RESULTS: Most of the subjects successfully performed an anti-G straining maneuver and maintained or increased the cerebral oxygenation level during Gz exposure. In four subjects, however, oxygenation decline was observed at levels over 4 Gz, even though their anti-G systems were functioning. In contrast to the O2Hb response, TOI, which reflects intracranial oxygenation changes, was decreased during the anti-G straining maneuver at Gz onset or during the countdown to a ROR exposure. CONCLUSION: Although NIRS is an effective tool for monitoring anti-G straining maneuver performance, it should be carefully evaluated in terms of intracranial oxygenation results.

Monitoring of pre-frontal oxygen status in helicopter pilots using near-infrared spectrophotometers.

BACKGROUND: There are few in-flight studies of cognition-related cerebral oxygen status in helicopter pilots. METHODS: Four male helicopter pilots volunteered for nine sorties during visual flight in a BK117 and UH-60J. The pilots' pre-frontal oxy-hemoglobin (O2Hb) and deoxy-hemoglobin (HHb) concentration were continuously monitored from the right/left sections of the forehead using near-infrared spectrophotometers with a consideration of motion artifacts. RESULTS: The concentration of O2Hb progressively increased (13.98 micromol*L-1 as a maximum increased concentration) in both the right/left sections of the forehead from the basal level during the heightened cognitive demand of helicopter flight. There was comparatively little change (4.32 micromol*L-1 as a maximum increased concentration) in HHb concentration during measurement of helicopter flight. HHb changes were apparently not affected by a heightened cognitive demand of helicopter pilots. CONCLUSION: These results demonstrate that near-infrared spectroscopy, especially O2Hb measurements, provides a sensitive method for the monitoring of cognitive demand (maneuvers) in helicopter pilots.

A new evaluation method for +Gz tolerance with loratadine by using a near-infrared spectroscopy.

BACKGROUND: Loratadine (Claritin), an over-the-counter antihistamine in U.S. and UK, is acceptable for use without adverse side effects by aircrew with mild or moderate allergic or other situations requiring an antihistamine. Although +Gz (head to foot direction) tolerance testing for aircrew with loratadine has not been documented in the published literature, it is commonly accepted that loratadine dose not effect +Gz tolerance. The purpose of this study was to offer and validate a new evaluation method for +Gz tolerance testing with loratadine by using a near-infrared spectroscopy (NIRS). METHODS: A double-blind, placebo-controlled, randomized, crossover protocol was used to administer 10 mg of loratadine or placebo in nine healthy subjects. The subjects didn't wear anti-G suit. The +Gz exposure profiles consisted of, in series, a gradual onset ran (0.1 G.sec-1) to the subject's visual end-point (peripheral light loss) or loss of consciousness (GLOC), and rapid onset run (1.0 G.sec-1) to the subject's same end-point. In this study, G-level tolerance was defined as the +Gz level at visual end-point and/or at GLOC. As a subject's G-duration tolerance, we measured the total time (seconds) during rapid onset run. Otherwise, to confirm the effect of loratadine on +Gz tolerance, we measured the cerebral NIRS variables (hemoglobin concentration changes and tissue oxygenation index) as a new quantitative method for +Gz tolerance during a centrifuge experiments. RESULTS: No significant differences were observed in +Gz tolerance (+Gz level, duration time and NIRS variables) between subjects taking loratadine and placebo. CONCLUSION: Our results demonstrate that loratadine has no detectable effect on +Gz tolerance by using a new method with cerebral NIRS variables and the traditional method with +Gz level and duration time. This study represents the first use of a quantitative parameter such as cerebral NIRS variables to assess the effects of a drug on acceleration tolerance.

Dimenhydrinate effect on cerebral oxygen status and salivary chromogranin-A during cognitive tasks.

To investigate the effects of dimenhydrinate on cerebral oxygen status (COS; cerebral oxygenated hemoglobin concentration changes) and salivary chromogranin-A (CgA) during a cognitive test battery, a double-blind, placebo-controlled, randomized, crossover protocol was used to examine the effect of 50 mg of dimenhydrinate or placebo in 12 subjects. This test battery includes tests of both reaction time and fundamental cognitive ability and was used in the assessment of pilots. Poor cognitive performance was observed in the subjects taking dimenhydrinate. We used two-channel near-infrared spectroscopy to investigate the effects of dimenhydrinate on the COS. With the one exception of shifting attention task in the left forehead, no significant difference was found between dimenhydrinate and placebo during the tasks of the test battery. Under placebo treatment, on the other hand, CgA levels were significantly elevated during cognitive testing when compared with baseline. However, CgA levels were not significantly elevated above baseline following dimenhydrinate. The present study is one of the first to demonstrate that the first-generation antihistamine drugs altered the responses of salivary CgA during cognitive tasks. The changes in salivary CgA secretion, as a result of dimenhydrinate administration, may serve as a sensitive biomarker of a psychological status such as a drug-induced sedation during the performance of a cognitive test battery. Further studies, however, are required to examine the usefulness of this sensitive biomarker in investigation of psychological agents during cognitive tasks.

Effects of flight workload on urinary catecholamine responses in experienced military pilots.

This study investigated the flight responses induced by strenuous aerobatic demonstration flight and an air-to-air combat maneuvering flight in experienced pilots. Subjects were 54 military male pilots on a volunteer basis: 8 T-4 pilots (M= 35.8 yr., SD=4.9), 15 F-4 pilots (M=32.6 yr., SD=5.1), 13 F-15 pilots (M=33.8 yr., SD=1.0), and 18 F-2 pilots (M=33.7 yr., SD=3.9). Samples of urine were collected approximately 30 min. before and 20 min. after the flights. The postflight adrenaline in all pilots was significantly higher than at preflight, while a significant increase in noradrenaline at postflight was not observed. The post-/preflight ratio of adrenaline in all pilots was relatively similar and high. These findings might be regarded as a result of autonomic nervous system response to the flight workload of military pilots. Especially is increment in sympathetic activity considered to play an important part in psychological adaptation to flight.

Frontal cortical oxygenation changes during gravity-induced loss of consciousness in humans: a near-infrared spatially resolved spectroscopic study.

Gravity (G)-induced loss of consciousness (G-LOC), which is presumably caused by a reduction of cerebral blood flow resulting in a decreased oxygen supply to the brain, is a major threat to pilots of high-performance fighter aircraft. The application of cerebral near-infrared spectroscopy (NIRS) to monitor gravity-induced cerebral oxygenation debt has generated concern over potential sources of extracranial contamination. The recently developed NIR spatially resolved spectroscopy (SRS-NIRS) has been confirmed to provide frontal cortical tissue hemoglobin saturation [tissue oxygenation index (TOI)]. In this study, we monitored the TOI and the standard NIRS measured chromophore concentration changes of oxygenated hemoglobin and deoxygenated hemoglobin in 141 healthy male pilots during various levels of +G(z) (head-to-foot inertial forces) exposure to identify the differences between subjects who lose consciousness and those who do not during high +G(z) exposure. Subjects were exposed to seven centrifuge profiles, with +G(z) levels from 4 to 8 G(z) and an onset rate from 0.1 to 6.0 G(z)/s. The SRS-NIRS revealed an approximately 15% decrease in the TOI in G-LOC. The present study also demonstrated the TOI to be a useful variable to evaluate the effect of the anti-G protection system. However, there was no significant difference found between conditions with and without G-LOC in subjects with terminated G exposure. Further studies that elucidate the mechanism(s) behind the wide variety of individual differences may be needed for a method of G-LOC prediction to be effectively realized.

Salivary chromogranin-A as a marker of psychological stress during a cognitive test battery in humans.

The purpose of the present study was to evaluate the salivary Chromogranin-A (CgA) response to the psychological stress induced by a cognitive test battery. The subjects were 14 healthy volunteers administered the cognitive test battery CogScreen Aeromedical Edition (CogScreen-AE). CogScreen-AE is a test of reaction time and fundamental cognitive ability in the assessment of aeroplane pilots. The subjects were given five batteries of the test (1st approximately 5th) on separate days with 2 week intervals. Saliva samples were collected at 20 min before the test (BASE), immediately before the test (PRE), in the middle of the test (MID), and 5 min after the test (POS) for each subject. The concentration of CgA was determined by enzyme-linked immunosorbent assay. ANOVA revealed a significant by time interaction (BASE, PRE, MID and POS) without a significant effect of battery interaction (1st, 2nd, 3rd, 4th and 5th). The CgA concentration increased at PRE (2.46 +/- 0.24 pmol.mg protein- 1) from BASE (1.19 +/- 0.10 pmol.mg protein- 1). CgA level remained increased in the MID (2.90 +/- 0.26 pmol.mg protein- 1) and remained high in the POS samples (2.81 +/- 0.23 pmol.mg protein- 1). Salivary CgA remained at basal levels during a control study over the same time course without exposure to CogScreen-AE. The changes in salivary CgA secretion as a result of exposure to a cognitive task may indicate psychological stress in humans.

Cerebral oxygenation monitor during head-up and -down tilt using near-infrared spatially resolved spectroscopy.

Reflectance near-infrared spectroscopy (NIRS) has become a suitable and easily manageable method to monitor cerebral oxygenation changes in presyncopal and syncopal symptoms caused by postural changing or standing. A new clinical tissue oxygenation monitor has been recently developed which measures absolute tissue haemoglobin saturation (Tissue Oxygenation Index, TOI) utilizing spatially resolved spectroscopy (SRS). The present study examined the effects of postural changes on cerebral oxygenation as reflected in SRS-NIRS findings. Cerebral oxyhaemoglobin (O2Hb), deoxyhaemoglobin (HHb), and the TOI were recorded from both sides of the forehead in five healthy male subjects (age range, 28-40 years) during 90 degrees head-up tilt (HUT) and -6 degrees head-down tilt (HDT). Three series of measurements were carried out on separate days. O2Hb was decreased during HUT. TOI was significantly lower in HUT than in the supine position (SUP). There was no significant change in TOI during HDT. A significant session effect was observed in the left forehead TOI during SUP, but not in the right. SRS-NIRS measurements confirmed sub-clinical alterations of cortical oxygenation during HUT. NIRS data from the left side of the forehead, which may vary with cognitive or emotional activation, were more variable than those from the right side.

Changes in urinary zinc and copper with strenuous physical exercise.

BACKGROUND: Air rescue trainees in the Japan Air Self Defense Force participate in a curriculum that includes 24 wk of strenuous physical training. The trace minerals zinc and copper are directly involved in many physiologic processes that are altered by physical exercise of this sort. It has also been demonstrated that urinary excretion of catecholamines (adrenaline and noradrenaline) increases during both mental work and physical exercise. HYPOTHESIS: Air rescue trainees will exhibit changes in trace mineral excretion and catecholamine levels that vary with the type of training undertaken. METHODS: The levels of urinary zinc (Zn), copper (Cu), noradrenaline (NAd), and adrenaline (Ad) were determined in 11 air rescue trainees before and after daily training sessions for consecutive 3- or 4-d periods during four phases of the curriculum, as follows: control (Cont), classroom instruction without physical exercise; preliminary (Prelim), daily exercise sessions for increased physical strength; basic (Basic), a combination of lectures and demanding physical exercise; and simulated mountain rescue (Sim). RESULTS: The mean urinary concentrations of Zn and Cu increased significantly after sessions with physical exercise (Prelim, Basic, and Sim), but remained unchanged for Cont. The NAd levels also increased significantly after training with physical exercise. In contrast, Ad levels increased significantly after sessions in all phases, both with and without physical exercise. CONCLUSIONS: The urinary levels of Zn, Cu, NAd, and Ad rose with strenuous exertion, whereas only Ad responded to both physical and mental tasking.

Pilot cerebral oxygen status during air-to-air combat maneuvering.

BACKGROUND: Successful monitoring of in-flight cerebral oxygen status (COS; cerebral hemoglobin concentration changes and oxygenation changes under dynamic flight conditions) was recently achieved using near-infrared spectroscopy (NIRS). In this study, we examined the effects of air-to-air combat maneuvering on COS. METHOD: Six F-15 fighter pilots performed 2-vs.-1 air-to-air combat one to three times in each of eight sorties. We took continuous measurements of the pilots' in-flight COS using a commercial NIRS system. We measured the direct effects of G-forces on COS as evidenced by relative concentrations of oxy- and deoxy-hemoglobin. RESULTS: With respect to the G-levels reached during air combat maneuvering (Gz range of -0.4 to + 9.5), oxyhemoglobin concentration (O2Hb) and tissue oxygenation index (TOI, the ratio of oxygenated to total tissue hemoglobin) decreased with increasing G-forces during aerial combat maneuver (ACM). Maximum changes in relative O2Hb ranged from -4.2 to -26 micromol x L(-1). Subjects' experience as measured by total fighter time was an independent determinant of the magnitude of decrease in relative oxygenation. CONCLUSIONS: 1. Pilots' COS declined with dynamic G-forces experienced under aerial combat conditions. 2. Fighter pilots with more flying hours maintained a higher cerebral oxygen level at the same level of G-forces than pilots with less flying time. 3. NIRS technology in the form of the NIRO-300G has matured for continuous monitoring of in-flight cerebral oxygen status under vigorous field conditions.

Effect of muscle tensing on cerebral oxygen status during sustained high +Gz.

BACKGROUND: Successful monitoring of oxyhemoglobin during +Gz exposure was recently achieved using near-infrared spectroscopy (NIRS). To assess the effects of muscle tensing on sustained +Gz tolerance, we measured muscle activity and cerebral oxygen status (COS) during anti-G straining maneuvers at sustained high +Gz. METHOD: We exposed 21 male pilots wearing CSU-13/P anti-G suit to two different centrifuge profiles: 1) short-term repeated exposure (5 to 20 s) at 4, 5, 6, 5.5, or 7 Gz; 2) sustained exposure to a + 7Gz plateau for 30 s. During the Gz exposures, surface electromyographic (EMG) measurements were taken from the vastus medialis (VM) and rectus abdominis (RA) muscles. At the same time, the COS was recorded from the left forehead area using a commercial NIRS system. Mean muscular tensing for each muscle was calculated as a percentage of maximal voluntary contraction (% MVC). RESULTS: Oxyhemoglobin (O2Hb) and total hemoglobin (sum of O2Hb and deoxyhemoglobin) were decreased during both short-term and sustained +Gz exposure. RA muscle tensing was positively correlated with changes in the concentration of O2Hb during sustained + 7Gz exposure (r = 0.540, p < 0.05). RA tensing ranged from 6.2 to 36.8%MVC, and O2Hb ranged from -41.3 to -7.28 micromol x L(-1) during the exposures. No significant correlation was observed between VM tensing and O2Hb. CONCLUSION: NIRS measurements confirmed that a muscle straining maneuver increases G tolerance. Higher RA muscle tensing helps preserve brain blood volume during sustained high +Gz.