G-induced Loss Of Consciousness Research Articles

Reduced G Tolerance Associated With Supplement Use

High G forces encountered in tactical military aviation and aerobatic flight produce a host of physiologic responses aimed at preserving cerebral perfusion. The military has instituted measures to augment the physiologic response in order to avoid G-induced loss of consciousness (G-LOC) because of its potential to cause a catastrophic mishap. The case presented here details a Naval Aviator who experienced reduced G tolerance over two successive flights with a temporal relationship of starting a new supplement. Two components of the supplement, coenzyme Q10 and niacin, are highlighted here for their hemodynamic effects. After stopping the supplement the aviator regained his normal G tolerance and had no further issues in flight. There are several factors that can reduce G tolerance and supplement use has to be considered here because of the potential for altering the normal physiological response to increased G force. Our discussion reviews the physiological effects of increased G force, the spectrum of signs of decompensation under the stress of G force, and the potential effects this supplement had on the normal physiological response to increased G force, thus reducing the aviator's G tolerance.

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.

New Method of Visual Disturbances Assessment in Pilots During Tests in the Polish Human Centrifuge

Visual disturbances are commonly accepted criteria for acceleration tolerance assessment. Researchers during centrifuge experiments use them as a safe criterion for cessation of acceleration exposure. Visual disturbances analysis is a non-invasive method of assessing retinal blood flow. Limitation of visual stimuli perception is a measure of physiological state of the experiment participants before hemodynamic changes, which reach a critical level manifested by G-induced loss of consciousness. Detection of these disturbances play an important role during the acceleration tolerance assessment. In this study, an attempt was made to answer the question on how many mistakes or incorrect reactions had to be identified to classify the ability of the pilot to fly on military jets. A new computer-aided research apparatus of our own design was used to assess visual disturbances, being a criterion of +Gz tolerance. In the center of monitor screen, a line of 3 light points was projected. During the centrifuge test, green lateral lights randomly changed their shapes from circles to squares while central light, being a point of vision fixation, remained unchanged. To assess its efficacy, 14 volunteers participated in the tests with various stimuli exposure. The authors aimed at selecting parameters of stimuli and exposure so that the division of reactions presented in the table would correspond with the score scale appropriate for our goals. Preliminary tests showed that appropriately selected light intensity of the exposed stimuli enables the use of test results to assess the number of erroneous reactions, and consequently the level of pilots' concentration during centrifuge tests. It has been found that the chosen luminance range of the projected light points is correct as it allows to evaluate the reactions, which should be considered erroneous. Additionally, prolongation of the correct reaction time to the mean value of about 400 ms facilitates better differentiation of results. Proper results evaluation, depending on the number of errors, lack of reactions or prolonged reactions made the assessment easier with computer-aided methods.

NIRS monitoring of pilots subjected to +Gz acceleration and G-induced loss of consciousness (G-LOC).

With the increasing maneuverability of modern aircraft, there is an increased frequency of pilots losing consciousness due to high +Gz acceleration. This phenomena is defined as "G-induced loss of consciousness" (G-LOC). We used an NIRS system of our design to monitor cerebral oxygenation changes of pilots subjected to high +Gz acceleration and G-LOC. During the +Gz pulse, delta HbO2, and delta TotalHb decreased, with lesser changes of delta Hb. The maximum decrease of delta HbO2 and delta TotalHb usually occurred at the onset of G-LOC. After G-LOC, delta HbO2 and delta TotalHb increased rapidly for the first few seconds, beginning the reactive hyperemic recovery phase. delta HbO2 and delta TotalHb peaked, and then began to decrease towards baseline. The subjects were unconscious for 3-10 seconds after the onset of G-LOC. Upon returning to consciousness, the subjects were disoriented for another 4-11 seconds. NIRS provides an additional means of studying physiological mechanisms leading to and recovery from G-LOC.

Vestibulo-Ocular Response of Human Subjects Seated in a Pivoting Support System During 3 Gz Centrifuge Stimulation

The vestibulo-ocular reflex (VOR) and spatial orientation perceptions were recorded in 15 subjects during 3 Gz centrifuge runs. These data were obtained to study two issues: (1) to gain insight into reports of asymmetrical disorientation and disturbance during acceleration and deceleration of centrifuge runs like those used to train pilots on the procedures to counteract G-induced loss of consciousness (G-LOC); (2) to study the effects of sustained vertical linear acceleration on the vestibular system. The centrifuge angular velocity profile consisted of a 19 s angular acceleration to 3 Gz that was sustained for 5 min during a period of constant angular velocity, and a 19 s deceleration to 1 Gz. The runs were repeated three times with the subject facing the motion and three times with the subject's back to the motion. The VOR and spatial orientation perceptions from the eight subjects who completed all six runs were analyzed. The total VOR response during acceleration and deceleration was composed of interacting angular (AVOR) and linear components (LVOR). Asymmetries in pitch orientation perception between centrifuge acceleration and decleration were not matched by asymmetries in the total VOR slow phase velocity. During the constant velocity high-G phase of the run, sustained up-beating LVOR (Lz nystagmus) was present in 14 of the 15 subjects. Significant individual differences in Lz nystagmus were found, but the maximum Lz response in our 15 subjects was probably of insufficient magnitude to degrade visual scan of cockpit instruments. Mean magnitudes ranged from 0 to 10 deg/s at 90 s from onset of centrifuge run.

Rat brain glucose and energy metabolites: effect of +Gz (head-to-foot inertial load) exposure in a small animal centrifuge.

A unique small animal centrifuge with on-line physiological monitoring and brain tissue collection (in < 1 s) capability was used to investigate the effect of increasing +Gz levels, exposure duration, number of exposures, and time course of metabolic changes in the rat brain. To determine the +Gz tolerance, rats were exposed to +7.5 to 25 Gz (30 s each) and EEG was monitored. G-induced loss of consciousness (G-LOC) defined as isoelectric EEG (I-EEG) occurred only at +22.5 and 25 Gz within 14.5 +/- 3 s. To study the effect of increasing +Gz levels on metabolism, rats were exposed to either 0.5 (control) or +7.5 to 25 Gz (30 s each), and brains were collected 1 min postcentrifugation by freeze fixation. A significant increase in lactate (> or = +7.5 Gz) and a decrease in glucose, creatine phosphate (Cr-P), and ATP levels were observed at +15 Gz and higher. The effect of exposure duration was investigated by exposing the rats to +22.5 Gz for 15-60 s. Brain lactate levels increased six-fold while glucose decreased (75%) following the 60-s exposure. The level of Cr-P and ATP decreased significantly after the 15- and 30-s exposures with no further changes at longer +Gz exposures. For time course studies, brains were collected both during (5-35 s) and after (1-15 min) a +25 Gz exposure. A significant decrease in Cr-P occurred within 5 s, but changes in glucose, ATP, and lactate required 15 s. All metabolites returned to control levels within 3 min, except lactate and adenosine, which required 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)

A Ten-Year Overview of USAF F-16 Mishap Attributes from 1980–89

The F-16 Falcon jet fighter is a marvel of engineering. Having been in operational United States Air Force service since approximately 1980, this fly-by-wire aircraft can climb vertically, sustain a 9-G turn without the loss of airspeed, and fly greater than the speed of sound. With such capabilities, this aircraft was originally designed and conceived of as a daylight air-to-air “dog-fighting” pilot's dream. As time has passed, the F-16 aircraft has been tasked with carrying out much more diverse missions than only day air-to-air combat. The aircraft and highly-trained pilots that fly it now accomplish additional missions such as day and night ground attack. An examination of ten years of USAF Safety Center accident data revealed that the F-16 aircraft had 59 Class A operational mishaps during this period. This was the highest number for any single-seat fighter-attack aircraft, and second only to the Aggressor's “Red Flag” F-5 per 100,000 hours of flight time (Class A Accident Rates: F-16 2.86 v. F-5 4.76). Incidentally, about 73% of the Royal Netherlands Air Force pilots reported that they were more susceptible to spatial disorientation and loss of situation awareness in the F-16 compared to other fighter aircraft that they had flown. After 11 years of operational experience, 21 of 210 of the Netherlands' F-16 aircraft were destroyed. A detailed examination of the USAF database revealed that a host of human factors issues are pertinent to the F-16 such as the loss of situation awareness, spatial disorientation, G-induced loss of consciousness, etc.; all of which contributed heavily to the accident rates cited for this aircraft. Additionally, cockpit design issues relatable to man-machine interfacing present human factors challenges to the pilot as well depending upon the mission scenario. The majority (53%) of F-16 accidents occurred during low-level or maneuvering flight. About 20% of the F-16 mishaps happened during the takeoff or landing phase of operations. Over 60% of the accidents were deemed by investigating officers to have “channelized attention” as a definite contributor to the mishap rate. Other human factors issues such as task oversaturation, distraction, and a variety of spatial disorientation problems contributed to many of the accidents also. Cockpit improvements, research, better training/awareness programs and Ground Collision Avoidance Devices (GCAS/PARS) are all suggested as methods to reduce future F-16 Falcon accident rates.

Changes in some biochemical and physiological indexes after hypergravitation.

The purpose of this study was to assess the G-tolerance and G-induced changes in plasma renin activity (PRA), serum cortisol, testosterone, thyroid hormones and blood concentrations of serotonin and histamine. Experiments were performed on 26 student pilots aged 22.7 +/- 0.7 years using simulated aerial combat manoeuvres (SACM) in a centrifuge with radius 7.5 m. G-tolerance was assessed by loss of vision criteria, G-induced loss of consciousness and significant disturbances in heart rhythm. PRA, cortisol, testosterone and thyroid hormones were measured by radioimmunoassay, serotonin and histamine by spectrofluorimetric methods 24 hours before and 5 min after SACM. The statistical significance of hypergravitation and G-tolerance were determined by ANOVA. We found a significant increase in PRA (p = 0.001) and thyroxine concentration (p = 0.005) after hypergravitation loads. It is known that these changes are indicative for cardiovascular adaptation and enhancement of energy mobilization. Histamine levels differed significantly by G-tolerance (p = 0.031), while serotonin concentrations changed by hypergravitation (p = 0.004). Significant dependence on hypergravitation x G-tolerance was found for serotonin values (p = 0.024). Studying G-induced hormonal changes can reveal individual peculiarities in G-tolerance, a limiting factor for the exploitation of high performance aircraft.

Loss-of-Consciousness&amp;Spatial Disorientation Auto-Recovery System

A G-induced loss-of-consciousness (GLOC) and spatial disorientation auto-recovery system has been developed and tested on the Advanced Fighter Technology Integration (AFTI)/F-16 aircraft. The pilot controls the operation of this system by entering an MSL altitude and manually arming the system. Engagement conditions of the auto-recovery maneuver are controlled by aircraft speed, altitude, attitude, and the set recovery altitude and do not depend upon any determination of pilot physiological condition. Initiation of the recovery maneuver is preceded by visual and aural warnings which continue until the pilot resumes control. The pilot always has the capability to override or disengage the autorecovery maneuver. This system, as developed on the AFTI/F-16, is directly and quickly applicable to other analog or digital flight control systems such as found in the F-16 or F-18. This system provides the pilot protection from ground collision in most air-to-air training environments.