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1,180 records · Page 66Linked to original sources
PubMed1997

Head positioning for high +Gz loads: an analysis of the techniques used by F/A-18 pilots.

A study was undertaken among Royal Australian Air Force fighter pilots to determine whether, as an occupational group, they had developed any particular protective head positioning strategies in order to minimize their risk of sustaining a +Gz-induced neck injury during air combat maneuvering. There were 42 F/A-18 Hornet pilots who responded to an anonymous questionnaire which asked about head positioning strategies. Of these, 29 pilots reported using a protective strategy. Several pilots reported using several different techniques. The most popular strategy reported was positioning the head prior to the application of +Gz (13 respondents). Eleven pilots reported using aircraft structures to wedge or brace their heads against. The results of this study show that fighter pilots who are regularly exposed to high +Gz forces develop an individualized approach to protecting their cervical spines from +Gz-induced injury.

Adult↗
PubMed1998

The effects of linear acceleration on distortion product otoacoustic emissions in human ears.

BACKGROUND: The effect of high levels of linear acceleration (G) on the cochlea has never been studied prospectively. HYPOTHESIS: Linear acceleration at high levels has no effect on the human cochlea as demonstrated by a comparison of pre- and post-exposure measurements. METHODS: There were 22 healthy volunteers who underwent exposure to up to 9 G in a military aviation training centrifuge. Prior to exposure they were screened for cochleovestibular disorders and underwent tympanometry, audiometry and distortion product otoacoustic emissions testing (DPOAE). Immediately after exposure, they underwent serial testing of each of these parameters until they returned to baseline. RESULTS: There was no significant change in tympanometry in any subject. Audiometry revealed a temporary threshold shift of 30 db at 6 kHz in one ear of a single subject. This was accompanied by a complete loss of DPOAE at the same frequency. DPOAE did not return to baseline at 2 weeks even though the audiogram had reverted to baseline by 8 d. Four other ears displayed significant losses of emissions at single frequencies without an accompanying change on the audiogram. CONCLUSIONS: This study demonstrates that accelerative stress may cause transient injury to the cochlea. The mechanism of injury due to acceleration is probably ischemia, although a purely mechanical effect on the outer hair cells cannot be precluded. These data also reinforce a growing body of evidence that demonstrates the greater sensitivity of DPOAE over psychoacoustic testing in detecting early or subclinical cochlear damage.

Acceleration↗
PubMed1998

Female exposure to high G: echocardiographic evaluation for chronic changes in cardiac function.

BACKGROUND: Significant changes in cardiac preload and afterload are generated by a number of factors present during the operation of high performance aircraft. These include high levels of +Gz, positive pressure breathing and anti-G straining maneuvers. Centrifuge subjects are exposed to these same factors in doses that are comparable to their operational counterparts. The question of whether such exposures produce long-term adverse effects on the heart has not been definitively answered. METHODS: In an effort to further address this issue, a longitudinal study was conducted on 18 newly recruited centrifuge panel members (7 males and 11 females) who did not have a previous history of significant high +Gz exposure. In order to document the cumulative long-term effects of high +Gz exposure and G protection measures, baseline echocardiographic studies were conducted prior to any +Gz exposure on the Dynamic Environment Simulator (DES) centrifuge. The echocardiograms were repeated after each panel member completed eight sessions of indoctrination. These follow-up echos were performed after all 18 subjects had been exposed to over 45 min (cumulative) of sustained acceleration > or = 2 G. Each subject served as his/her own control. All studies were evaluated independently by a cardiologist who was blinded to the order in which the studies were performed. Although complete echocardiographic studies were performed, only the parameters identified as significant in prior studies were evaluated. RESULTS: No significant differences were found between the initial and follow-up echo parameters. No significant differences were found between male and female responses. CONCLUSIONS: We found no significant differences in cardiac function after 45 min (cumulative) of exposure to G > or = 2 in men or women. These subjects will be monitored during a longitudinal study throughout their centrifuge subject career.

Aerospace Medicine↗
PubMed1998

Female exposure to high G: performance of simulated flight after 24 hours of sleep deprivation.

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. Active-duty personnel (8 male and 8 female) were trained to fly the F-16 simulation while 30 performance measures were recorded. Performance was re-evaluated after 24 h of sleep deprivation. RESULTS: Neither male nor female overall performance was affected significantly by sleep status, although individual tasks showed sensitivity; call-sign reaction time was longer by 33%, and missile survival was less likely. Also, when sleep deprived, perceived effort and physical demand were higher while perceived performance was lower. No differences in performance were found in either gender due to lay-off, although some physiologic deconditioning was apparent. Women commanded and endured the same amount of G load as men, however, on average they could not perform the tracking task quite as well. CONCLUSIONS: Sleep deprivation (24 h) produced sensations of fatigue and frustration, but overall performance was not reduced. The ability of personnel to complete a complex defensive maneuver was reduced when they were sleep deprived. The women that we tested apparently could not optimize the tracking task as well as their male counterparts when Gz was in the simulation. None of these results were sufficient to suggest that women should not be allowed to compete for flying assignments in high-performance aircraft.

Aerospace Medicine↗
PubMed1998

Female exposure to high G: effects of simulated combat sorties on cerebral and arterial O2 saturation.

BACKGROUND: One of the key factors in maintaining optimal cognitive performance in the high-G environment is the adequate delivery of oxygen to the cerebral tissue. As eye-level blood pressure is compromised at 22 mmHg x G(-1), perfusion to the peripheral cerebral tissues (cerebral cortex) may not be adequate to support the mental demands of flight. This study measured the effect of closed-loop flight simulations (3 min) on cerebral oxygen saturation changes (rSO2), arterial oxygen saturation (SAO2), and heart rate (HR), in both rested (8 h of rest) and sleepless (24 h without sleep) conditions. METHODS: Subjects (16; 8 males and 8 females) were subjected to G-exposures via closed-loop flight simulations in a series of four 3-min sorties flown by subjects on the Dynamic Environment Simulator (centrifuge) in either a rested or a sleepless state. Prior to the centrifuge flight, subjects were instrumented with sensors for measurement of arterial oxygen saturation (SAO2) and regional cerebral tissue oxygenation (rSO2). Subjects wore the standard flight suit, boots, CSU-13B/P anti-G suit, and the COMBAT EDGE positive-pressure breathing for G-protection system. RESULTS: Significant changes in cerebral and arterial oxygen saturation were observed within groups when comparing pretest baselines and minimum values during the test and pre- and post-G rSO2, SAO2, and HR in both the rested and sleepless state, (p # 0.01), respectively, for each group. Comparisons between groups showed women to have significantly smaller regional cerebral cortex oxygen decreases than men (p # 0.01). No significant changes in SAO2, however, were observed between groups. Both men and women showed a slow recovery of rSO2 values to the prebaseline levels. CONCLUSIONS: Sleeplessness had no effect on the rSO2, SAO2, and HR compared with the rested condition. During acceleration, regional cerebral tissue oxygen decreased 13% in men compared with 9% in women. The recovery of cerebral tissue oxygen levels to prebaseline values was retarded somewhat when compared with the recovery response of arterial oxygen saturation.

Adult↗
PubMed1998

Female exposure to high G: chronic adaptations of cardiovascular functions.

INTRODUCTION: Exposure to microgravity is associated with increased leg venous compliance and reductions in cardiac output, baroreflex functions, and tolerance to orthostatism. However, the effects of chronic exposure to high-G environments are unknown. In addition, there is evidence that females have lower orthostatic tolerance than males, although the underlying mechanisms are unclear. Therefore, we tested the hypotheses that high-G training will enhance baroreflex and orthostatic functions and that females will demonstrate similar adaptations compared with males. METHODS: Calf venous compliance, baroreflex function, and orthostatic performance were measured in six men and seven women before and after repeated exposures on the centrifuge (G-training) for 4 wk, 3 times/wk, with gradual levels of G starting with +3 Gz without G-suit protection during week 1 and advancing to +9 Gz with G-suit protection by the end of week 4. Calf venous compliance was measured by occlusion plethysmography using impedance rheographic recordings of volume change. Baroreflex function was assessed from beat-by-beat changes in heart rate (HR) and mean arterial pressure (MAP) that were measured before, during, and after a Valsalva maneuver strain at 30 mmHg expiratory pressure. The orthostatic performance of reflex responses was assessed from beat-by-beat changes in HR, MAP, stroke volume (SV), cardiac output (Q; by impedance plethysmography), and systemic peripheral resistance during the last 10 cardiac beats of a 4-min squat position and during the initial 10 cardiac beats in a standing position. RESULTS: G-training increased calf compliance in both men and women. SV and Q were increased during the squat-to-stand test in the males, but not in the females, following G-training and provided protection against the development of acute hypotension in the men. CONCLUSIONS: G-training caused adaptations in orthostatic functions opposite to those observed following exposure to microgravity environments. However, adaptations to G-training were limited in females, a finding that may provide a physiological basis for their lower simulated combat tracking performance during simulated aerial combat maneuvers compared with males.

Adaptation, Physiological↗
PubMed1998

Neck training and +Gz-related neck pain: a preliminary study.

This study compared the effects of two neck training methods on workdays lost or flying under +Gz restrictions because of +Gz-related neck pain, and on neck muscle strength and the passive cervical range of motion among fighter pilots. One group (n = 10) participated in dynamic neck and shoulder muscle training, and another (n = 10) participated in helmet training with additional weights. The measurements were done at 0, 3, 6, and 12 months. The loss of workdays or restrictions in +Gz flights were recorded during the 1-year training period and the year preceding it. Neck muscle strength increased similarly in both groups. Nevertheless, during the training year, the pilots doing dynamic exercises had fewer sick leaves and +Gz restrictions than the pilots doing helmet exercises. Because the number of subjects was small and the study included no control group, firm conclusions on the effects of the training methods cannot be drawn.

Absenteeism↗
PubMed1998

[Human tolerance of +Gx loads in anti-G suits during deorbiting of the "Soiuz" space vehicles].

Reported are results of the study of tolerance of the "thorax-back" g-loads (+Gx) during deorbiting of 83 total suited and unsuited cosmonauts in the period of 1997-1997. G-loads averaged 3.7 +/- 0.058 units (from 3.1 up to 5.1 units). Pneumatic gradient G-suits (PGS) Karkas and Centaur had a positive effect on the +Gx tolerance of humans following microgravity. As compared with unsuited crews returning from missions of similar duration, wearing PGS has proven to improve the general health of cosmonauts and to reduce the strain of the leg and abdominal muscles. Tight fitting of PGS abolished visual disorders due to the longitudinal component of G-loads that were registered in 6.6% of observations of unsuited cosmonauts. Sinus tachycardia was significantly weaker (P < 0.05). The authors recommend the use of the standard antiblackout Centaur suit as the efficacy of this PGS was equal to that of Karkas while its ergonomic characteristics were superior.

Astronauts↗