Gravity induced loss of consciousness

BACKGROUND: The push-pull maneuver (PPM) can lead to loss of consciousness in pilots of high-performance aircraft. Modeling of the physical and physiological aspects of this phenomenon should allow improved countermeasures. METHODS: A structurally based mechanistic computer model was developed to incorporate dynamic carotid baroreflex responses and detailed modeling of vessel segments for different anatomic regions. The model was used to predict the effect of the PPM on cardiovascular responses and the protection afforded by extended coverage anti-G suits (ECGS) and neck pressure...

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The status of a system under development for detection of gravity-induced loss of consciousness (G-LOC) and subsequent recovery is presented. The physiological factors under investigation for use in the loss-of-consciousness monitoring system (LOCOMS) effort are eye blink rate, head slumping, head-level arterial pulsations, and spectral shift in EEG frequency. Also being studied for inclusion in the LOCOMS are a means of detecting the presence/quality of the anti-G straining maneuver and anti-G suit functions, and a system for voice-synthesized query for interrogating the pilot prior to intervention in aircraft control...

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)]...

The gravitational stress encountered by pilots of high-performance aircraft can cause dramatic shifts in blood volume and circulatory pressure, thus placing the cardiovascular system under significant stress, sometimes resulting in loss of consciousness due to cerebral under-perfusion. Since pilots experience both increased and decreased gravitational stress in high-risk environments, it is important not only to examine the cardiovascular effects of altered gravitational exposure, but also to create effective countermeasures that will increase pilot safety...

INTRODUCTION: Prevalence of G-induced loss of consciousness (G-LOC) in the United Kingdom Royal Air Force (RAF) was found to be 19.3% in 1987. With the introduction of the Typhoon, a fourth generation aircraft, the prevalence of G-LOC has been re-assessed to determine the effectiveness of current G tolerance training. METHOD: A survey was sent to 4018 RAF aircrew, irrespective of their current role. Information was requested on G-LOC, role and aircraft type, experience, and attitudes toward G-LOC prevention...

OBJECTIVES: We examine the time course of performance recovery from gravity-induced loss of consciousness (GLOC) and evaluate the utility of exposing participants to repeated bouts of GLOC in promoting recovery time. BACKGROUND: A substantial number of accidents among fighter pilots have resulted from episodes of GLOC. U.S. Air Force doctrine holds that when pilots experience GLOC, impairment lasts for 24 s, in which there are 12 s of complete unconsciousness and 12 s of confusion...

INTRODUCTION: Only one previous study has assessed almost loss of consciousness (A-LOC) in operational fighter pilots, reporting an incidence rate of 14%. Research also indicates that 8-13% of pilots have experienced G-induced loss of consciousness (G-LOC). A-LOC can be as insidious as G-LOC due to the associated altered state of awareness and relative incapacitation time, making it a significant risk factor in the high +Gz environment. Royal Australian Air Force (RAAF) pilots currently fly the F/A-18 and Hawk 127, producing +Gz accelerations up to +7...

The aim of the present experiment was to study the influence of +Gz acceleration (head-to-foot inertial forces) onset on cerebral oxygenation changes (cerebral oxy- and deoxy-hemoglobin) and cerebral blood volume (CBV) in order to evaluate the role of cerebral hypoxemia and ischemia in the appearance of +Gz-induced loss of consciousness (G-LOC). We used five rhesus monkeys which were equipped with near infrared spectroscopy optodes fixed onto the parietooccipital cranial bone. G-LOC (isoelectric electrocorticogram) was detected with silver balls electrodes in contact with the dura matter...

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This article is a contribution to the workshop on "Operational Requirements in the Prevention of G-Induced Loss of Consciousness (G-LOC) in High Performance Aircraft"; it focuses on the "operational" side of the requirements to prevent G-LOC. There are two types of requirements for prevention of G-LOC; a) pre-G-LOC detection devices that monitor physiologic changes of the pilot before G-LOC occurs, and b) the more generic personal G protection systems that increase G tolerance. Recently there have been major advances in G-protection research and development (R&D) systems (soon to become operational) that significantly improve G-level and G-duration tolerances...

The ability to tolerate +Gz radial acceleration depends primarily on the maintenance of sufficient head level arterial pressure and cerebral blood flow to prevent the occurrence of blackout and G-induced loss of consciousness (G-LOC). Because of the hydrostatic effect on the heart-to-head blood column during +Gz acceleration, if exposures to higher +Gz levels are to be tolerated, either the column must be shortened or arterial pressure at heart level must be elevated. This paper is an overview of the effect and concomitant side effects of positive pressure breathing (PBG) as a means to increase arterial pressure at the heart, and, indirectly, at the cerebral level...

BACKGROUND: Ground-based research has investigated the loss of cognitive function in the extreme conditions of G-induced loss of consciousness, however, little is known about pilots' abilities to maintain cognitive performance throughout prolonged conscious exposure in the high-G environment. The effects of fatigue and G layoff on performance during exposure to high G are mostly unknown for the female population. METHODS: This research was conducted on the centrifuge Dynamic Environment Simulator...

BACKGROUND: There is a need for evaluation of new G protection equipment. HYPOTHESIS: There is no difference between the two anti-G ensembles on affecting subjects' ability to tolerate multiple simulated aerial combat sorties. METHODS: There were 15 subjects wearing the standard CSU-13 B/P anti-G ensemble (STD) or COMBAT EDGE/ATAGS (CE/ATAGS) ensemble who were exposed to 3 centrifuge-based simulated air combat sorties during a 2-h period. Each sortie consisted of four different G-profiles: 1) a gradual onset profile; 2) simulated air combat maneuver consisting of +4...

A major physical limitation affecting pilots is G-force (+Gz, head-to-foot inertial load) induced loss of consciousness. Previous studies have shown that +Gz produces qualitatively similar effects on human and rat EEG activity. The present study sought to quantitatively correlate changes in rat EEG activity with increasing +Gz levels. A frontal-parietal differential electrode recorded rat EEG data during +Gz exposures (30 s) ranging from +0.5 to +25.0 Gz. Acceleration levels < or = +10 Gz had little effect on EEG activity...

INTRODUCTION: The anti-G straining maneuver (AGSM) is still an important part of pilot protection for G-induced loss of consciousness. The specific requirements for and the effects of breathing systems on the performance of the AGSM are essential elements to designing compatible breathing systems. METHODS: Subject pools of 27 and 34 naval aviators were recruited and used to measure the inhalatory and exhalatory flow requirements for the AGSM and the breathing system effects of mask cavity pressure during AGSM performance on the Naval Air Warfare Center Dynamic Flight Simulator at acceleration levels up to 8 Gz...

Gravity-induced loss of consciousness (G-LOC) is known to have occurred in pilots since the early 1920's. Most of the research in this area has shown that G-LOC occurs due to a decrease in cerebral blood pressure and a concomitant reduction in brain perfusion. Since a reduction in cerebral blood flow can cause transient hypoxia, it is important to study the cerebral metabolism during high +Gz exposure. One component of these studies should include measurements of substrate availability and degradative products...

During acceleration (+Gz) training in the human centrifuge, the anti-G suit (AGS) is usually deflated as acceleration decreases upon termination of the exposure, regardless of the reason for termination, including +Gz-induced loss of consciousness (G-LOC). This is when the trainee most needs the support provided by the AGS. A method to reduce the time of incapacitation resulting from G-LOC was evaluated. The standard CSU15-P suit worn by 30 aircrew while undergoing +Gz tolerance training was inflated to 10 psi immediately upon G-LOC (GS group)...

It has been suggested there is a relationship between acceleration-induced loss of consciousness (G-LOC) and head/body position. A two-part investigation was conducted to determine whether head and body position affects acceleration tolerance. A retrospective analysis of high-G training data (N = 1,914) compared G-LOC occurrence during straight-ahead exposure to a "check-6" exposure [10 s at +9 Gz; 6 G/s onset rate; G-suit inflated; anti-G straining maneuver (AGSM) performed]. A prospective study (N = 12) was conducted with acceleration exposures using light loss criteria with subjects in straight-ahead, above, over-the-right shoulder, or over-the-left shoulder positions...

Air combat maneuver acceleration (G) profiles with onset/offset patterns that occur faster than the response characteristics of the human cardiovascular system may lead to regulatory instability and, ultimately, acceleration-induced loss of consciousness (G-LOC) incidents. We have developed an acute animal model that simulates the hemodynamic situations seen under acceleration to study the effects of complex G environments on individual reflexogenic areas. This preparation allowed us to individually isolate the effects of high gravity on venous return and cardiac preload, arterial baroreflexes and splanchnic capacity...