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At least 829 records · Page 46Linked to original sources
PubMed2001

Concept of a Neck Protective Device (CNPD).

During impact or sudden acceleration, the cervical and thoracic region of the spine of operators of Habitable Mobile Vehicles (HMV) may be exposed to extensive trauma since "whiplash"-type motion typically leads to impairment of a cervical joint. Furthermore, the frequent necessity of supporting added mass above the shoulders (e.g., crash helmet, displays, oxygen mask) can magnify the moment of inertia of the head. This additional mass affects the biomechanics of a Helmet-Head-Neck System and determination of the tolerable magnitudes of acceleration which it can undergo. Even if the body of the operator is restrained by seat belts, such acceleration can arise in all three vectors (Gx, Gy, and Gz). The population at risk for injury due to such forces are individuals exposed to forces generated in racing cars, involved in automobile impacts or emergency landing of aircraft, in normal landing on carriers or in piloting of 5th generation fighter planes, and in other aspects of operator activity in HMV. Various methods of fixation of the head to prevent cervical injury are described in the literature: cervical collars, inflated thoracic defensive members, airbags, cervical supports, etc. However, all of these have some deficiencies related either to one-time availability or the restricted range of head motion which they produce. Widely used automatic retaining systems composed of belts with forced pull and airbags, while successful in other regards, do not adequately protect the head and neck of the operators who are chronically exposed to iterated percussion, and other acceleration forces under diverse extreme conditions.

Aerospace Medicine↗
PubMed2001

Dynamic strength capabilities of small-stature females to perform high-performance flight tasks.

BACKGROUND: Naval Air Warfare Center Aircraft Division investigated the abilities of small-stature females (< or = 120 lb.) to fly under G-stress using the Dynamic Flight Simulator (DFS) and its tactical fight/attack cockpit, displays and controls. The objective was to determine if these individuals possess sufficient upper-body muscular endurance to perform tasks required during fighter-pilot training, aerial combat maneuvers, and failure modes. METHODS: Five female subjects (four small-stature and one medium) participated. DFS tasks featured bombing runs, surface-to-air missile (SAM) avoidance, and single engine failure. Muscular exertion and fatigue (arm, shoulder, neck) were assessed using electromyography. RESULTS: During the most physically taxing simulation (SAM avoidance), flight performance did not significantly degrade over time. No statistically significant increase in muscular fatigue was found during the bombing simulation, though there was some evidence of degraded fine muscle control. Evidence of flexor and extensor muscular fatigue was associated with the single-engine-failure simulation. CONCLUSIONS: Within the scope of these tests, small-stature individuals demonstrated the strength and endurance to safely fly physically strenuous missions. However, a larger subject sample is necessary to increase the statistical power of the results.

Adult↗
PubMed2001

The effects of +Gz force on the bone mineral density of fighter pilots.

HYPOTHESIS: Bone is a metabolically active tissue which responds to high strain loading. The purpose of this study was to examine the bone response to high +Gz force loading generated during high performance flying. METHODS: The bone response to +Gz force loading was monitored in 10 high performance RAAF pilots and 10 gender-, age-, height-, weight-matched control subjects. The pilots were stationed at the RAAF base at Pearce, Western Australia, all completing the 1-yr flight training course. The pilots flew the Pilatus PC-9 aircraft, routinely sustaining between 2.0 and 6.0 +Gz. Bone mineral density (BMD) and bone mineral content (BMC) were measured at baseline and 12 mo, using the Hologic QDR 2000+ bone densitometer. RESULTS: After controlling for change in total body weight and fat mass, the pilots experienced a significant increase in BMD and BMC for thoracic spine, pelvis, and total body, in the magnitude of 11.0%, 4.9%, and 3.7%, respectively. However, no significant changes in bone mineral were observed in the pilots lumbar spine, arms or legs. The control group experienced a significant decrease in pelvic BMC, with no other bone mineral changes observed at any site. CONCLUSIONS: These findings suggest that site specific BMD is increased in response to high +Gz forces generated during high performance flying in a PC-9.

Adaptation, Physiological↗
PubMed2001

Protection to +12 Gz.

BACKGROUND: The U.S. Air Force has developed +Gz-protective equipment that will provide most pilots protection to +9 Gz with minimal-to-no straining. This equipment includes a pressure breathing system called COMBAT EDGE (CE), which is currently operational, and the Advanced Technology Anti-G Suit (ATAGS), which is not yet operational. For future high-performance aircraft design it is important to know the upper limit of various protective equipment and techniques. METHODS: Six subjects were randomly exposed to a 12-cell matrix composed of +Gz and the following combinations of protective equipment at three seat-back angles (13 degrees, 30 degrees and 55 degrees from the vertical): 1) the standard CSU-13B/P anti-G suit (STD); 2) the STD suit with CE; 3) the ATAGS; and 4) the ATAGS with CE. Relaxed, followed by straining +Gz tolerance was determined using 15-s rapid onset runs to a maximum of +12 Gz. A comprehensive battery of baseline and post-exposure medical surveillance studies was performed to evaluate the medical consequences of these high +Gz exposures. RESULTS: All 6 subjects were able to achieve +12 Gz with various combinations of +Gz-protective equipment, seat-back angle, and various amounts of straining, from none to maximum. When the data were collapsed over all protective equipment there was a significant (p < 0.05) seat effect. Relaxed tolerance to ROR increased with seat-back angle from 13 degrees to 30 degrees to 55 degrees. There was also a significant protective equipment effect when the data were collapsed over all seat-back angles. CONCLUSIONS: These data confirm that effortless protection to +9 Gz is available using ATAGS/CE with the 13 degree and 30 degree seat-back angle (F-15, F-16 and F-22) and to +10.5 Gz with a 55 degree seat-back angle. Moreover, with ATAGS/CE, and a moderate degree of straining, +12 Gz is definitely achievable at 55 degrees, even with reduced anti-G suit pressure at 55 degrees. With additional straining +12 GC is also achievable at the 13 degree and 30 degree seat-back angles.

Acceleration↗
PubMed2001

Effect of repeated +Gz exposures on energy metabolism and some ion contents in brain tissues of rats.

BACKGROUND: It has been demonstrated that during +Gz exposure cerebral blood flow is significantly reduced, resulting in brain ischemia. In pilots, such conditions could recur several times during centrifuge training and combat maneuvers and could possibly cause reversible change in brain energy metabolism. HYPOTHESIS: In rats there is an association between +10 Gz exposure and the decreased brain metabolism, as indicated by decreased adenosine triphosphate (ATP) and ATPase activity, and increased adenosine diphosphate (ADP) and lactate, etc. The aim of the present study was to examine the time course and recovery of brain energy metabolism, lactate, ATPase activity, Na+, K+, Ca2+ and water contents after three +10 Gz exposures in rats. METHODS: There were 64 male Sprague-Dawley rats that were restrained and placed on an animal centrifuge. They were divided into groups of 16. Control rats were exposed to +1 Gz and experimental rats were exposed to +10 Gz three times each for 3 min at 30-min intervals. After being euthanized, rat brains were removed 0 h, 1 h, or 6 h after the last centrifuge run. Brain samples were analyzed for energy metabolism, lactate, Na+-K+-ATPase activity, water and electrolytes contents. RESULTS: The cortical ATP content, Na+-K+-ATPase and lactate dehydrogenase (LDH) activities decreased significantly, whereas the cortical ADP, adenosine monophosphate (AMP) and lactate contents increased significantly 0 h after three +10 Gz exposures, as compared with those of control. The ATP, ADP, and AMP contents returned to their control levels 1 h after the +10 Gz exposures, however, lactate content, Na+-K+-ATPase and LDH activities delayed recovery 6 h after +10 Gz exposures. The cortical K+ content increased significantly 0 h and 1 h after +10 Gz exposures, and returned to the control level 6 h after +Gz exposures. Na+ and water contents increased significantly 1 h and 6 h after the +10 Gz exposures. There was no significant change in Ca2+ content after +Gz exposures. CONCLUSIONS: Three +10 Gz (3 min each) exposures were associated with transient depression of brain metabolism as indicated by a decrease in ATP, Na+-K+-ATPase activity, and an accumulation of lactate, and disturbance of ion homeostasis. It is suggested that a causal relationship might exist between repeated high +Gz exposures and brain metabolism.

Acceleration↗
PubMed2001

Relationship between arm pain and distension of arteries and veins caused by elevation of transmural pressure in local vascular segments.

BACKGROUND: Exposure to high +Gz forces may induce arm pain, which has been hypothesized to be caused by pressure-induced overdistension of local blood vessels. The purpose of the present investigation was to study the pressure-distension relation of veins and arteries in the human arm and the relation between arm pain and distension of local vessels. METHODS: Increased distending pressures (DP) in the vasculature of the arm were accomplished by placing the subject (n = 8) in a pressure chamber with one arm positioned through a port in the chamber door, and increasing chamber pressure to +180 mm Hg in a stepwise manner. Diameters in the brachial artery and in the brachial, radial and cephalic veins were measured by ultrasonography. Changes in forearm volume were estimated from measurement of tissue impedance. Perceived pain was rated using a 10-point scale. RESULTS: Arm pain increased with pressure to a maximum rating of 8.5 (= median; range: 4-10). Increasing DP from 30 to 180 mm Hg resulted in a steady increase (p < 0.05) in venous diameter which varied from 12 +/- 8% (mean +/- SD) in the brachial vein to 23 +/- 14% in the radial vein. Inthe brachial vein diameter increases were most pronounced at the sites of the venous valves. Arterial diameter was unchanged up to a DP of about 200 mm Hg (calculated as diastolic arterial pressure + applied chamber pressure), but then increased by 32 +/- 9% (p < 0.001). Forearm impedance dropped with increasing pressure (delta = 23 +/- 5%; p < 0.01); the rate of change was non-linear with a faster change at the highest DP which may indicate pressure distension of precapillary resistance vessels. CONCLUSIONS: Elevation of pressure in arm vessels to levels that may occur in pilots flying high-performance aircraft results in distension not only of veins but also of arteries and probably of smaller precapillary vessels. Therefore, and because these changes coincide with the development of severe arm pain, local overdistension of blood vessels remains a plausible cause of G-induced arm pain.

Adult↗
PubMed2001

Human tolerance to Gz acceleration loads generated in high-performance helicopters.

BACKGROUND: As the Gz capabilities of tactical helicopters increase, the risk to unprotected helicopter aircrew resulting from the physiologic response to transitions from -1 Gz (push) to +4.5 Gz (pull) loads needs to be addressed. METHODS: There were 9 volunteers who participated in a study conducted at the Veridian Operations Centrifuge Facility in Warminster, PA. A 1-h mission scenario consisting of nine helicopter maneuvers, based on inflight G measurements (push-pull mission, PPM), simulated both current (CM: -0.2 to +3.5 Gz) and projected future platform capabilities (FM: -1 Gz to +4.5 Gz). Additional scenarios were run in which push transitions were limited to +1 Gz (GM). Measurements included blood pressure (BP), heart rate (HR), loss of vision, and subjective fatigue. RESULTS: Visual decrements were minimal during CM while muscular tensing was required to avoid blackout during FM. Light loss typically occurred during the transition from -Gz to +Gz. Within the scope of these tests, subjects tolerated the range of Gz stresses associated with current U.S. Navy rotary wing platforms. When subjected to FM G-loads (typical of current U.S. Army high-performance platforms), cardiovascular stress significantly increased, Gz tolerance dropped as much as 1.2 G, and HR increased as much as 67 bpm. Cardiovascular changes were significantly greater during FM PPM relative to GM. Four subjects reported Almost-Loss of Consciousness (A-LOC) symptoms during FM. CONCLUSIONS: While G-stress experienced by aircrew generated by current helicopters does not appear to present a high risk, G-awareness training is recommended to reduce risks to aircrew exposed to G-loads generated by more aggressive helicopters. Future studies are required to determine the impact of longer mission times and dehydration.

Acceleration↗
PubMed2001

A mechanical model of cerebral circulation during sustained acceleration.

BACKGROUND: High positive Gz may result in inadequate blood supply to the brain even if the central blood pressures are maintained at normal levels. We use a mechanical model to simulate the influence of sustained +Gz on cerebral circulation. METHODS: The model consists of ascending and descending tubes representing the extracranial arteries and veins, respectively, and a cranium in which the tubes are enclosed within water-filled rigid container to account for the skull and the cerebrospinal fluid. A thick-walled Tygon tube and a thin-walled surgical drain tube were used for the arteries and veins, respectively. The flow of water was driven by a pressure difference at the model ends, and the change in the gravitational vector was accomplished by tilting the model. RESULTS: The flow drops with an increasing tilt angle only if the descending arm collapses. However, when the pressures at the model ends are sufficiently elevated, the flow is restored to normal value. In the cranium model, the pressure in the water surrounding the tubes always stays close to the pressure in the surgical tubing. Consequently, the tubes in the container do not collapse. CONCLUSIONS: The principal effect of Gz on flow through the model occurs via changes in the resistance of the collapsed descending arm. As the pressures at the model ends are elevated, the descending arm opens and the flow increases. The pressure in the cranium model is dictated by the condition that the volume of the container has to remain constant.

Acceleration↗
PubMed2001

Accommodation of females in the high-G environment: the USAF Female Acceleration Tolerance Enhancement (FATE) Project.

BACKGROUND: In 1993, the U.S. Secretary of Defense opened combat aircraft assignments to women. To verify the adequacy of acceleration (+Gz) protection for female high-G aircrew, USAF investigators conducted fit tests of standard and developmental G-protective equipment and determined the effectiveness of a unique laboratory modification (AL Mod) of the standard (CSU-13B/P) anti-G suit during gender-comparative centrifuge evaluations. METHODS: Investigators determined relaxed +Gz tolerance and straining endurance to +4.5 to +7 Gz and +5 to +9 Gz simulated aerial combat maneuver (SACM) centrifuge profiles (4.5-7 SACM: 8 females and 10 males; and 5-9 SACM: 6 females and 8 males, respectively). Additionally, in the 5-9 SACM study, between and within gender SACM endurance differences were assessed before and after female subjects' use of the AL Mod. Ten female subjects also were fit tested in extended coverage, developmental G-protective equipment. RESULTS: There was no gender difference in 4.5-7 SACM endurance. Male 5-9 SACM endurance exceeded that of females in the unmodified CSU-13B/P (p < 0.05), but gender parity was achieved when females wore the AL Mod. Fit modifications of developmental G-protective equipment were not required, but smaller sizes of the standard CSU-13B/P and a developmental anti-G suit were indicated and developed. CONCLUSION: In properly fitted anti-G suits, gender parity in SACM endurance is achievable; however, full accommodation of female aircrew in the high-G environment will require the AL Mod and/or smaller sized anti-G suits.

Acceleration↗
PubMed1991

+Gx-tolerance in the final stage of space flights of various durations.

Study of acceleration tolerance at the final stage of orbital flights after exposure to weightlessness is an important element of medical support of space flights. The cosmonauts tolerance to accelerations has been analyzed during 38 space missions of 8- to 326-day duration. Tolerance to acceleration during descent in all cases was estimated as satisfactory. Acceleration tolerance during the final stage of orbital flights depended on flight duration, individual tolerance and use of countermeasures.

Acceleration↗
PubMed1993

The regulation of rat activity following exposure to hyperdynamic fields.

The microgravity of spaceflight and the hyperdynamic fields produced via centrifugation have allowed researchers to examine the effect of altered gravitational environments on the regulation of physiological systems. In previous studies, we have discussed the importance of homeostatic and circadian mechanisms for the regulation of physiological systems such as body temperature and heart rate. Rats exposed to a chronic 2G field exhibited lower mean daily body temperature and heart rate. The homeostatic component of regulation for body temperature and heart rate adapts to a new steady state after 5-6 days. However, the circadian rhythm of body temperature and heart rate became severely depressed and did not recover for approximately 7-10 days. The measurements of body temperature and heart rate suggest an adaptation of homeostatic and circadian regulatory mechanisms following 10 days exposure to 2G. However, an important function of physiological homeostasis is to respond to environmental stressors. An important question thus becomes whether the regulation of body temperature and heart rate has sufficiently recovered to respond to an environmental challenge separate from that of the hyperdynamic field. In this study, a high frequency light/dark cycle (LD 3:3) was provided for 24 hours as an environmental challenge to assess the recovery of homeostatic and circadian regulation. Previous studies have demonstrated that high frequency light dark cycles are highly effective for testing homeostatic and circadian components of physiological regulation in monkeys and rats. For example, the nocturnal rat exhibited a homeostatic increase in body temperature during the dark periods and a decrease during the light periods. In addition, the magnitude of the body temperature response exhibits a time of day variation demonstrating the effect on circadian regulation.

Animals↗
PubMed1993

Circulatory filling pressures during transient microgravity induced by parabolic flight.

Theoretical concepts hold that blood in the gravity-dependent portion of the body would relocate to more cephalad compartments under microgravity conditions. The result is an increase in blood volume in the thoracic and cardiac chambers. This increase in central volume shift should result in an increase in central atrial filling pressures. However, experimental data has been somewhat contradictory and nonconclusive to date. Early investigations of peripheral venous pressure and estimates of central venous pressure (CVP) from these data did not show an increase in CVP in the microgravity condition. However, CVP recorded in human volunteers during the parabolic flight by Norsk revealed an increase in CVP during the microgravity state. On the June 1991 STS 40 shuttle mission, a payload specialist wore a fluid line that recorded CVP during the first few hours of orbital insertion. These data revealed decreased CVP. When this CVP catheter was tested during parabolic flight in four subjects, two subjects had increased CVP recordings and two other subjects had decreased CVP measurements. In April 1991, our laboratory performed parabolic flight studies in several chronic-instrumented baboon subjects. It was again noted that centrally recorded right atrial pressure varied with exposure to microgravity, some animals having an increase and others having a decrease. Thus, data presently available has demonstrated a variable response in the mechanism not clearly defined. In April 1992, we determined a test hypothesis relating the possible mechanism of these variable pressure responses to venous pressure-volume relationships.

Animals↗
PubMed1992

Centrifuges: their development and use in gravitational biology.

The nature of centrifuges and their use in biological research are reviewed historically. Centrifuges are particularly important to research in gravitational biology because the inertial (centrifugal) forces developed by motion can be combined with gravitation to produce gravitational fields other than Earth gravity. In orbiting satellites centrifuges can provide an on-board 1 g environment. A similarity of results from the orbiting and ground-based 1 g controls will provide an essential assurance that the biological responses to the spacecraft environment are the result of changes in the gravitational field. The relationship of biological responses to gravitational fields greater or less than Earth gravity is considered. However, at present there is insufficient equivalent information to decide whether there is or is not a proportionality of response to fields stronger or weaker than Earth gravity.

Acceleration↗
PubMed1991

Oriented movement of statoliths studied in a reduced gravitational field during parabolic flights of rockets.

During five rocket flights (TEXUS 18, 19, 21, 23 and 25), experiments were performed to investigate the behaviour of statoliths in rhizoids of the green alga Charo globularia Thuill. and in statocytes of cress (Lepidium sativum L.) roots, when the gravitational field changed to approx. l0(-4) g (i.e. microgravity) during the parabolic flight (lasting for 301-390 s) of the rockets. The position of statoliths was only slightly influenced by the conditions during launch, e.g. vibration, acceleration and rotation of the rocket. Within approx. 6 min of microgravity conditions the shape of the statolith complex in the rhizoids changed from a transversely oriented lens into a longitudinally oriented spindle. The center of the statolith complex moved approx. 14 micrometers and 3.6 micrometers in rhizoids and root statocytes, respectively, in the opposite direction to the originally acting gravity vector. The kinetics of statolith displacement in rhizoids demonstrate that the velocity was nearly constant under microgravity whereas it decreased remarkably after inversion of rhizoids on Earth. It can be concluded that on Earth the position of statoliths in both rhizoids and root statocytes depends on the balance of two forces, i.e. the gravitational force and the counteracting force mediated by microfilaments.

Actin Cytoskeleton↗
PubMed1988

Gravitational effects on mammalian cells.

In this paper we present first the results of our most recent investigations on gravitational effects on the activation of human lymphocytes: by immunoenzymatic staining and by using concanavalin A (Con A) coated to red blood cells (RBC) we demonstrate that the increase of activation measured at 10xg is due to a simultaneous activation of T- and B-lymphocytes whereas at 1xg only T-cells are stimulated. Conversely, activation of T-cells by chemical modification of the membrane with sodium periodate is depressed at 10xg. Secondly, experiments performed in the centrifuge as well as in the clinostat with Friend, K-562, and hybridoma cells show that each cell line develops its own adaptation reaction to gravitational stress.

B-Lymphocytes↗