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At least 1,153 records · Page 64Linked to original sources
PubMed2005

Tilt-table testing as a predictor of + GZ tolerance.

BACKGROUND: G-tolerance assessment is an essential element of both military pilot and pilot candidate evaluation. AIMS: Attempt at prediction of individual relaxed + Gz tolerance on the basis of head-up tilt (HUT) testing. SETTINGS AND DESIGN: In two stages, 20 healthy men at the mean age 21.5 years took part in this study. The first stage, a 45 min, HUT test was performed using the Westminster protocol. During the second stage each underwent a centrifuge evaluation in response to gradual onset rate profiles. METHODS AND MATERIAL: In each subject, heart rate (HR) and blood pressure (BP) before and at 2, 15 and 45 min of the tilt-test were recorded. The gravity-load centrifuge (GOR) studies were carried out [following the standard GOR programme, at 0.1 G%divide;s rate of gravity load increase until the gravity load tolerance limit (loss of peripheral vision) was reached]. STATISTICAL ANALYSIS USED: Relationships between variables were explored using Kendall's tau-B correlation coefficient. The critical P-level was one-tailed 0.05. RESULTS: In four of 20 subjects (20%), vasovagal syncope occurred during the tilt test. G-level tolerance of this group (of +Gz accelerations) lay in the range from +4 to +8.1 Gz, (+5.72 ? 0.86 Gz average) and was comparable to the group without syncope. Loss of consciousness did not occur in any subjects during the centrifuge test. No statistically significant correlation was observed between HR and BP during tilt test and tolerance to +Gz accelerations. CONCLUSIONS: The result of tilt testing, carried out according to the Westminster protocol, was not useful in predicting individual tolerance to +Gz gravity loads.

Adult↗
PubMedDate not supplied

[Evaluation of +Gz tolerance following simulation of 8-hr flight].

Tolerance of +Gz (head-pelvis) centrifugation of pilots was evaluated following simulation of a long flight on single-seat fighter. The experiment involved 5 test-subjects who were exposed to +Gz before and after simulated 8-hr flight with a growth gradient of 0.1 u/s without anti-g suits and muscles relaxed; in addition, limiting tolerance of intricate profile +Gz loads of 2.0 to 9.0 units with a growth gradient of 1.0 u/s of test-subjects in anti-g suits (AGS) with a change-over pressure valve in the peak mode using muscle straining and breathing maneuvers. To counteract the negative effects of extended flight, various seat configurations: with a back inclination at 30 degrees to the +Gz vector and changeable geometry with a back inclination at 55 degrees to the vector. The other counter-measures applied were cool air shower, suit ventilation, physical exercises, lower body massage with AGS, electrostimulation of the back and lumber region, profiling of the supporting and soft parts of the seat, and 30-s exposure to +5 Gz. Hemodynamic and respiration parameters as well as body temperature were measured in the course of 8 hrs of flight and during and shortly after centrifugation. According to the results of the investigation, seat inclination at 55 degrees to the +Gz vector and tested system of countermeasures prevent degradation of tolerance of large (9 u.) loads following 8-hr flight simulation with the use of the modern anti-g gear,

Acceleration↗
PubMedDate not supplied

[+Gx-tolerance by the Cosmonauts of ISS crews 1, 6-9 and visiting crews 1-7 aboard Soyuz vehicles].

Analysis of +Gx tolerance of 15 members of short-term ISS missions and 9 members of long-term ISS missions aboard the Soyuz vehicles showed good tolerance during insertion and satisfactory during descent provided the use of in-flight countermeasures and anti-g suit Kentaur inside the vehicle. Objective data about the tolerance of off-nominal +Gx (6.26 and 8.1 G) pointed to a more pronounced sinus tachycardia and tachypnea in a ballistic descent following long-duration weightlessness as compared with nominal. Physiological deviations were transient, functional by character. Cardiac arrhythmia was largely observed during return to Earth. Two cosmonauts were found to develop prognostically unfavorable ECG indications during off-nominal descent. Main factors in these deviations could be age (above 45) and existence of some individual specifics of cardiac rhythm regulation. These results emphasize the necessity of more careful screening of candidates older than 45 years, as weightlessness may impact their general condition and tolerance of g-loads during return to Earth.

Adult↗
PubMedDate not supplied

[Comparative characteristics of the gas-exchange parameters during exposure to lateral (Gy), longitudinal (Gz) and latero-longitudinal (Gz/Gy) G-loads].

Subject of the investigation was dynamics of gas-exchange parameters during exposure to lateral and laterolongitudinal g-loads (Gy, Gz, Gz/Gy) in a coach inclined at 300 from the horizontal with a rigid restraint system. Gy values varied between 0.5 and 5.0 units, Gz - between 3.0 and 9.9 units and Gz/Gy - between 2.6/1.8 and 5.0/3.0 units. In all instances, growth gradient of the radial loads was 1.0 u/s, and a period of exposure was up to 30 s. Comparison of the Gz vs. Gy tolerance revealed as a substantial increase of the physiological "cost", so a more visible disbalance of the diffusion/perfusion ratio of the lung. This is consistent with the gas-exchange data according to which lateral g-loads are a stronger stress-factor and more challenging for pilots than the longitudinal g-loads.

Aerospace Medicine↗
PubMed2006

Practice ameliorates deficits of isometric force production in +3 Gz.

BACKGROUND: In our earlier work, we have shown that human subjects produce exaggerated isometric forces when exposed to three times terrestrial gravity (+3 Gz). In the present work, we investigated whether prolonged practice under +3 Gz reduces this deficit, and whether it affects the cognitive costs of force production. METHODS: There were 24 young male student volunteers who produced forces without visual feedback of prescribed directions and magnitudes with their dominant hand, and used their other hand for a four-choice reaction-time task. Both tasks were performed separately and concurrently, in normal terrestrial gravity (normal G), 30 s after the beginning of +3 Gz, and after practice in +3 Gz. RESULTS: During early +3 Gz responses, initial force (100 ms into the response) increased abruptly by about 140%, and peak-produced force by 30%. Both values decreased again after prolonged practice; this recovery was complete for peak force, but only partial for initial force. Dual-task interference was observed, which did not vary with G level or practice. DISCUSSION: The detrimental effects of +3 Gz on force production are compensated for by adaptive reprogramming (see initial force) and by additional feedback-based corrections (see difference between peak and initial force). Force production is cognitively demanding, but cognitive costs do not seem to vary with G level or practice.

Adult↗
PubMed2006

G-induced loss of consciousness: retrospective survey results from 2259 military aircrew.

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. RESULTS: Responses were received from 2259 (56.2%) individuals, 882 (39%) of whom were current fast jet aircrew. At least one episode of G-LOC was reported by 20.1% of all respondents. In front line aircraft, prevalence of G-LOC among the 882 fast jet aircrew who responded was 6%. In the whole group, G-LOC was reported most commonly in aircrew under training (70.9%), and was most prevalent in training aircraft (77.4% of G-LOC events). At the time of the G-LOC, 64% of aircrew had less than 100 h total flying time. G-LOC was reported most frequently between +5 to +5.9 Gz, and "push-pull" maneuvers were associated with 31.3% of G-LOC events. Pulling G was not considered a problem by 50.6% of respondents, although over 80% recognized the value of flying currency, use of an anti-G suit, and physical fitness, and 55.6% felt that centrifuge training would be valuable. DISCUSSION: The prevalence of G-LOC in the RAF has changed little since 1987, and there remains considerable scope for aircrew education, particularly with the introduction of the Typhoon.

Adult↗
PubMedDate not supplied

[Inertial forces during muscle contractions as a factor compensating for the insufficiency of gravitation influence].

An idea has been advanced that inertial forces emerging during active movements are able to compensate for the deficiency of weight. The idea is based on the conception that these forces are by their effect on biological objects analogous to gravity forces. Training facilities have been developed, and tentative estimations have been made. The definition of "inertial massage" is introduced.

Humans↗
PubMed2006

Carotid sinus pressure changes during push-pull maneuvers.

INTRODUCTION: The push-pull maneuver (PPM) is defined as a reduction in G-tolerance when positive acceleration (+Gz) immediately follows negative acceleration (-Gz) exposure, with the carotid baroreceptors presumably playing a dominant role in the ensuing BP (SBP) responses. The objective of this study was to determine whether application of neck pressure (NP) during the preceding -Gz phase maintains +Gz tolerance during subsequent +Gz. METHODS: There were 10 experienced men who were exposed to 3 centrifuge run types using a multi-axis centrifuge: a relaxed control run from +1.4 baseline to visual tolerance; a relaxed control PPM run (PPM-C) consisting of 5 s of -1 Gz followed by 15 s of +Gz to visual tolerance; and an experimental PPM run performed with pressurized neck (PPM-NP) consisting of -1 Gz for 5 s followed by 15 s of +Gz at the previous PPM-C G-tolerance level. RESULTS: Relaxed control G tolerance (3.6 _ 0.26 Gz) was greater vs. the PPM-C (3.0 +/- 0.21 Gz) and PPM-NP (3.1 +/- 0.20 Gz) conditions, but the two PPM conditions did not differ significantly. During -Gz, mean R-R interval for PPM-NP was significantly shorter than in the PPM-C from second 1 to second 3. During the +Gz phase, however, R-R interval responses between PPM-C and PPM-NP differed only at seconds 8 and 9. There were no differences in carotid sinus SBP between PPM-C and PPM-NP during -Gr. During +Gz, carotid sinus SBP was significantly depressed in PPM-NP and PPM-C conditions vs. Control. DISCUSSION: Application of NP during the -Gz phase, despite altering R-R interval, did not ameliorate SBP responses or reductions in G tolerance during subsequent +Gz exposure. Despite neck compression counteracting increased carotid hydrostatic pressure during -Gz, the carotid baroreceptor response is likely opposed by the aortic or other baroreceptors.

Adolescent↗
PubMed2006

[Changes in the pancreas structure after exposure of the body to gravitational overloads].

The aim of this study was to determine the changes in the pancreas structure after acute and chronic exposure of organism to gravitational overloads (GO). The experiments were conducted in 36 outbred albino male rats, 12 rats formed the control group. GO effect was modeled using the centrifuge; the value of the overload thus created amounted to 4,0-6,0 gravitational units. Pancreas structure was studied using histological, electron microscopic and morphometric methods. It was found that after acute exposure to GO, mainly the reactive changes were demonstrated all the pancreatic structures studied: acinocytes, endocrinocytes, blood vessels and nervous apparatus. Chronic exposure to GO resulted in both reactive modifications, similar to those described after an acute exposure, and various compensatory-adaptive and destructive changes.

Animals↗
PubMed1995

The effect of varying time at -Gz on subsequent +Gz physiological tolerance (push-pull effect).

INTRODUCTION: Previous studies have demonstrated decreased +Gz tolerance when preceded by 0 Gz or -Gz, referred to as the "push-pull effect." The purpose of this experiment was to observe the effect of varying time duration at -Gz on the push-pull effect. METHODS: During single sessions, six subjects (three men, three women) were subjected to five relaxed exposures to +2.25 Gz on the NAMRL Coriolis Acceleration Platform (CAP). The first and last exposures were control runs that were preceded by +1 Gz. Each experimental run was preceded by -2 Gz for 2, 5, or 15 s. Blood pressure (BP) was monitored using the Finapres at the level of the clavicle. Visual light loss was assessed at +2.25 Gz using a light bar. RESULTS: Mean BP was significantly reduced when the +2.25 Gz exposures were preceded by -2 Gz. Following 15 s of -2 Gz, mean BP decreased more and was slower to recover than for 2 and 5 s of -2 Gz. Reported incidents of visual light loss were: 1 following 2 s, 2 following 5 s, and 4 following 15 s at -2 Gz. There were no reports of visual light loss during control runs. CONCLUSION: During relaxed conditions, the push-pull effect is augmented by increasing duration of the preceding -Gz.

Adult↗
PubMed1995

Evaluation of integrated night vision goggle (NVG) helmets under sustained +Gz.

Three integrated night vision goggle (NVG) helmets from different manufacturers were evaluated under high-G conditions. Structural and operational integrity, as well as neck forces in pounds, were determined via instrumented manikin testing before human exposure with the helmets during sustained +Gz. Results of the manikin testing showed that the helmets could withstand the rigors of high-G, and that predicted forces (using helmet weights and centers-of-gravity) matched those obtained experimentally from load cells in the x-axis of the manikin's neck. After manikin testing, 10 subjects were randomly exposed to four different high-G profiles on the Dynamic Environmental Simulator (DES) man-rated centrifuge located at Wright-Patterson AFB, OH: gradual onset to +8 Gz, a simulated aerial combat maneuver (SACM) profile, and two +4 Gz profiles, one with the mask dangling from the helmet and the other with the mask removed. Fit assessments were conducted before high-G exposure, and one helmet was affected significantly by failure of fit. The degree of migration of the NVG intensified image away from the eyes was affected most by the following helmet characteristics: design of the nape strap, size of the NVG image provided by each helmet system, goodness of helmet fit, and the use of the mask as a stabilizer. Although neck strength of each subject was measured and compared to the degree of head stability while wearing each helmet, no effects were found. However, subjects were not allowed to perform fast, high-amplitude head movements in the centrifuge for safety reasons.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Findings of a working group on chronic health effects of sustained high-G exposure.

A Working Group of scientists from the Armstrong Laboratory, Brooks Air Force Base, met to determine the physiologic effects of repetitive high sustained G exposures over the lifetime of an exposed individual. The literature is mute on this issue. The Working Group concluded that such operational exposures have been present only since the onset of high-G aircraft (F-15/F-16); human centrifuge experience indicates no pathology, although long-term follow-up has not been accomplished; and the index of suspicion of significant clinical pathology is low, based on historical considerations. Considerations for future studies of lifetime G effects include: a determination of what organs to study; the realization that animal studies are probably not valuable; the determination that prospective longitudinal studies are optimal but costly in time and funds; and the opinion that a properly conducted cross-sectional study based on past exposure may be feasible, acceptable, and less costly.

Aerospace Medicine↗
PubMed1995

[The effect of high gravity on embryonic development in birds].

An experiment was conducted on Japanese quail and hen hatching eggs that had been incubated, and the embryos were subjected to hypergravitation of 10 G for 10 min on days 1 to 9 of embryonic development. Both the experimental group and the control contained each 20 hatching eggs every day of the experiment (360 eggs in total). A centrifuge of the diameter 1,300 mm was used to create overload (hypergravitation) at the speed of 118 rotations per min. Tab. I shows the layout of the experiment. Embryonic mortality in Japanese quail was investigated during incubation by egg candling on days 1 to 8 and 9 to 14 while suffocated embryos were investigated on days 15 to 17. As for chicks, embryonic mortality was determined by egg candling on days 1 to 8 and 9 to 18, suffocated embryos were determined on days 19 to 21. After incubation was terminated, hatchability in per cent of the fertilized eggs was determined. The results were processed in two stages of development: the first stage days 1 to 5, the second stage days 6 to 9. As can be seen in Fig. 1, hypergravitation did not influence the hatchability of quail eggs in the first stage. But this experimental treatment resulted in a steep fall of hatchability in the second stage of observation in comparison with the control group (the difference is significant P < 0.01). Fig. 2 shows hatchability.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Mammalian cardiovascular morphology and the maintenance of cerebral function at high Gz.

The persistence of consciousness at low cerebral perfusion pressures during exposure to high sustained G force in a head-to-foot direction (+Gz), is the rule. Concomitant changes in cerebrospinal fluid and cerebral venous dynamics together with cerebral autoregulation have been proposed to explain this preservation of cerebral function at high Gz. The non-uniform distensibility of the mammalian aortic distributing system plays a fundamental role in maintaining optimal cardiac energy exchange. Morphological evidence is presented suggesting that such a non-uniformity probably extends cranially as well as caudally in man. One consequence of such a cranial extension would be the amplification of the arterial pressure waves to the brain, with the potential for significant pulsatile flow at relatively low mean arterial blood pressures. Such phenomena would result from fundamental design properties of the mammalian cardiovascular system, would not be detected by conventional invasive pressure monitoring, and would serve as a mechanism to maintain optimal cerebral perfusion under condition of increasing +Gz.

Animals↗
PubMed1994

Unexplained unilateral vision loss during centrifugation.

Vision loss during a centrifuge run is an expected occurrence given the G-profile, physical fitness of the subject, expected visual endpoint [central light loss (CLL) or peripheral light loss (PLL)] of the experimental protocol, and the cyclic nature of the anti-G straining maneuver (AGSM). During a relatively low level G exposure, a subject experienced a unilateral loss of vision that did not resolve spontaneously upon removal of the G load. An extensive medical workup did not reveal any medical explanation for the vision loss.

Adult↗
PubMed1995

The role of anaerobic power in human tolerance to simulated aerial combat maneuvers.

The relationships of anaerobic power, blood lactate levels, and selected anthropometric measurements to +Gz tolerance were examined in 10 adult males. Upper and lower body anaerobic indices were determined by Wingate anaerobic tests (WT). Acceleration tolerance was measured as duration time for a simulated aerial combat maneuver (SACM) centrifuge profile with alternating 4.5 and 7 +Gz 15-s plateaus until exhaustion. Group mean (+/- SD) for SACM duration was 250 +/- 97 s. Peak blood lactate concentration was 4.9 +/- 1.5 mmol/L and overall rating of perceived exertion was 7.4 +/- 2.1 using the Borg Category-Ratio Scale. Group mean for WT lower body 30-s mean power (MP, index of anaerobic performance) was 620 +/- 128 W; peak power (PP, highest 5-s power output) was 851 +/- 169 W. Upper body MP and PP were 380 +/- 68 W and 497 +/- 81 W, respectively. SACM duration time was positively correlated (p < 0.05) with lower body MP and PP, upper body PP, various body circumferences, weight, fat-free body weight, and height; but did not correlate with WT power outputs relative to body weight, or with other SACM variables. Results suggest that anaerobic power is an important physiologic component in SACM tolerance.

Acceleration↗
PubMedDate not supplied

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.

Adult↗
PubMedDate not supplied

Effects of long duration centrifugation on head movements and a psychomotor task.

Previous investigations suggest strong similarities between aftereffects of an 1.5-hour 3 gx centrifuge run (Sickness Induced by Centrifugation; SIC) and the Space Adaptation Syndrome (SAS). Head movements proved to be especially nauseogenic in both cases. Until recently, during SIC experimentation, the performance of head movements was not adequately operationalized, which hampered a statistical evaluation. For this purpose, a test was designed by which head movements in four directions (left, right, up, and down) were provoked and registered, once before and once after a 1-h 3 g centrifuge run. Subjects had to execute these head movements in order to perform well on a psychomotor task. The results indicate that the test described is sensitive in discriminating between subjects who are seriously affected after a long duration centrifugation and those who are not. Because differences in performance were found only on those parts of the task in which head movements were involved, objective evidence is obtained in favour of a vestibular cause in the etiology of SIC.

Centrifugation↗