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At least 1,171 records · Page 65Linked to original sources
PubMed1996

Spinal shrinkage due to +Gz forces.

BACKGROUND: Fighter pilots frequently complain of inflight pain in the cervical or lumbar spine. As to the cervical spine, there is evidence that repeated exposures to high +Gz forces and inflight neck pain may cause premature cervical disk degeneration. Whether inflight lumbar pain caused by high +Gz forces has a similar effect on the lumbar spine has not been studied. HYPOTHESIS: The aim of the study was to investigate whether high +Gz forces during aerial combat maneuvering reduces the body height. Investigation to determine whether any long-term degenerative changes occur in the lumbar spine was beyond the scope of this study. METHODS: The body height of 20 junior fighter pilots was measured before and after 30 min of recumbent rest and after high-G flights. A special measuring device was used. Measurements were also made with the pilots sitting fully equipped in a fighter aircraft on the ground. RESULTS: Maneuvering under high +Gz forces for 40 min caused a 4.9 mm decrease in body height. Recumbent rest before flights increased body height by 2.5-3.5 mm, and sitting in an aircraft returned body height to the values measured before rest. CONCLUSIONS: The findings indicate that +Gz forces place a high stress on the spinal column. Therefore, the work of a fighter pilot can be considered to be physically demanding with respect to the spinal column.

Adult↗
PubMed1996

Bioenergetic effects of repeated +Gz acceleration on rat heart: a 31P-NMR study on isolated hearts.

This investigation was designed to determine whether repeated exposure to high sustained +Gz acceleration induces persisting changes in the myocardial energetic metabolism. Rats were exposed to three plateaus of 30 s at 10 +Gz, four times a week, for 4 weeks. Myocardial concentrations of high-energy phosphorylated compounds were evaluated by 31P-nuclear magnetic resonance (NMR) spectroscopy on isolated hearts submitted to isovolumic aortic perfusion. Heart performances were recorded using the intraventricular balloon method. Compared to the hearts of control rats (n = 5), the hearts of centrifuged rats (n = 5) had higher concentrations of inorganic phosphate (Pi:1.40 +/- 0.33 nM vs. 0.36 +/- 0.07 mM; p < 0.01), decreased phosphocreatine concentrations (PC:15 +/- 0.39 mM vs. 15.69 +/- 0.19 mM; p < 0.01), and a lower left ventricular developed pressure (LVDP) (21 +/- 1 mmHg vs. 34 +/- 2 mmHg; p < 0.01). The workload was increased by sequential augmentation of calcium in the perfusion medium. The relationship between LVDP and the Pi/PC ratio showed that the cost of the cardiac work was greater for the centrifuged rats.

Animals↗
PubMed1996

Cervical intervertebral disc protrusion in an RAAF F-111C pilot: a case report.

This case report describes a serious cervical spine injury occurring in an F-111 pilot of the RAAF. The pilot developed a significant cervical intervertebral disc protrusion with severe, progressive neurological signs and symptoms in his right arm for a period of 4 mo. Multiple investigations including MRI and myelography established the site of the lesion as C6/7. He eventually responded to bed rest and made a complete recovery. The aeromedical disposition of this aviator and the roles of different treatment modalities in the aviation environment are discussed. The need for more research into +Gz-related neck injuries and the requirement for preventive strategies to protect the cervical spines of high performance pilots are also highlighted.

Adult↗
PubMed1996

Instrument flying performance after G-induced loss of consciousness.

INTRODUCTION: While both the USAF and the USN have characterized the immediate sequelae of G-induced loss of consciousness (G-LOC) as resulting in approximately 24 s of incapacitation, very little is known about the effect of a G-LOC immediately after this incapacitation period. This study is an attempt to determine the effect of G-LOC on instrument flying performance immediately after G-LOC. METHOD: In order to establish their flying performance baselines, 29 Canadian Forces (CF) pilots attending the high sustained G (HSG) course flew 3 iterations of a 15-min instrument flying task on the day prior to their HSG course. All 29 pilots performed this same task the next day within 5 min of completing the centrifuge training. In addition, the pilots who experienced G-LOC flew the task again 45 min after G-LOC. Flying performance was assessed by calculating Root Mean Square (RMS) error on 11 flight parameters. These RMS values were submitted to a multivariate analysis of variance. RESULTS: Of the 29 pilots, 12 experienced G-LOC during the centrifuge training. The flying performance of the 17 non-G-LOC pilots was not affected by their exposure to HSG. Of the 12 G-LOC pilots, 11 had no measurable performance decrement while 1 pilot, after a severe G-LOC, stalled and "spun-in" on take-off and then (after being re-established on the outbound radial) could not complete the task. This same pilot flew the task very well 45 min later. This study did not identify a degradation in flying performance after HSG nor after G-LOC except in the 1 pilot. CONCLUSIONS: Whether or not a pilot's flying performance is affected after G-LOC may be related to the severity of the G-LOC. Some pilots may experience seizure activity relating to the G-LOC with a resulting sustained performance decrement that appears to resolve by 45 min. It is possible that some of the other G-LOC pilots in the study might have had measurable performance decrements if we had been able to have them fly the task while they were still in the gondola (i.e., immediately after the G-LOC).

Adult↗
PubMed1996

Cerebral artery blood flow velocity changes following rapid release of lower body negative pressure.

BACKGROUND: Circulatory changes occur during exposure to Lower Body Negative Pressure (LBNP). These changes may have some similarities to exposure to moderately and slowly increased G-loads in a relaxed subject without anti-G suit. HYPOTHESIS: Changes will also occur in cerebral blood circulation during a rapid release of LBNP. METHODS: Transcranial Doppler ultrasound (TCD) was used to measure middle cerebral artery blood flow velocity (CBFV) in 14 human subjects following rapid release of a ramped lower body negative pressure (LBNP) (0.33 mm Hg.s) to presyncope (mean peak negative pressure of -124 mm Hg). RESULTS: The mean CBFV decreased to an average of 60% (p < 0.05) of the baseline value at peak LBNP. Mean CBFV was still decreased to 65% and 84% of the baseline value (p < 0.05) at the third heart beat and 30 s, respectively, after pressure release. The systolic CBFV decreased similarly to 57% (p < 0.05) of baseline during peak LBNP, and was still 63% (p < 0.05) at the third heart beat after pressure release. Heart rate increased by a mean of 51% (p < 0.001) and systolic heart level blood pressure decreased by 28% (p < 0.001) during peak negative pressure. Both heart rate and blood pressure returned to baseline levels within 30 s after pressure release. CONCLUSIONS: Following a presyncopal LBNP, the CBFV is not fully restored up to 30 s after the release of the negative pressure. This delayed returning of cerebral circulation following orthostatic stress may have some similarities to what occurs after the release of a gradual onset G-load in a relaxed subject without anti-G suit.

Adult↗
PubMed1996

[Study of human orientation with respect to vertical under effect of lateral and combined longitudinal-lateral accelerations].

Six test subjects were subjected to NZ and Ny/Nz accelerations in centrifuge cabin having rotation radius of 6.55 m. During rotation, test subjects have determined the position of the subjective visual vertical. The performed studies have demonstrated that during exposure to NZ and Ny/NZ accelerations the image of subjective vertical the direction of which with rise of lateral component approaches the direction of the vector of resultant acceleration. The expressivity of this effect decreases with an increase of the longitudinal component of acceleration. It was suggested that pulling of high lateral accelerations (up to 2-3 units of g) in the flight of advanced highly manoeuvrable aircrafts can hinder in-flight spatial orientation of a pilot due to appearing of the stable illusions of spatial position.

Acceleration↗
PubMed1996

Prevalence and significance of spinal disc abnormalities in an asymptomatic acceleration subject panel.

BACKGROUND: A protocol to allow for human centrifuge exposures up to +12 Gz (12 times gravity) required a screening spinal MRI. MRI-derived spinal disc abnormalities were observed in three of the first four asymptomatic volunteer subjects. The protocol was interrupted and a second study was initiated to determine the possible cause and effect relationship between the disc findings and previous +Gz exposure. METHODS: A T1 or T2 weighted sagittal MRI of the entire spine was accomplished on each of 22 asymptomatic male acceleration panel members, and a similar, age-matched control panel of 19 asymptomatic male subjects with no history of previous acceleration exposure. The MRIs from all 41 subjects were read at 2 diagnostic facilities by 9 radiologists. The evaluating radiologists were aware asymptomatic centrifuge subjects were being evaluated but were unaware a control group was included. RESULTS: Initial results from any one reader revealed spinal disc abnormalities (bulging, degeneration or herniated nucleus pulposus-HNP) in 91% of the centrifuge panel and 79% of the control group, a non-significant difference. Within-reader and between-reader variability was very high. Comparison of 1st vs. 2nd reading of the same data by one radiologist demonstrated a 28% agreement and a 72% disagreement on observed abnormalities. Comparison of the same MRIs read by two different radiologists revealed a 23% agreement and a 77% disagreement, pointing out the ambiguity of the data and subjectiveness of the interpretation. Two additional neuroradiologists agreed to independently read all 41 MRIs after establishing unique reading criteria. There remained a non-significant difference between the two subject groups, whereas reader disagreement was still high (56%). CONCLUSIONS: No significant difference was found between the two subject groups. The power of the test was low because of the small sample size. Our confidence in the interpretation is low because of the high degree of between-reader and within-reader variability.

Adult↗
PubMed1996

Size and myosin heavy chain profiles of rat hindlimb extensor muscle fibers after 2 weeks at 2G.

METHOD: The effects of 14 d of continuous centrifugation at approximately 2G on the hindlimb extensor musculature of male rats were studied. RESULTS: The mean body mass of centrifuged rats was 17% smaller than age-matched controls. In centrifuged rats, the mean absolute masses of the soleus and medial gastrocnemius (MG) were similar to control, while the mean relative masses (expressed as milligram muscle mass/gram of body mass) were larger than control. Based on a battery of monoclonal antibodies for specific myosin heavy chains (MHC), the soleus of centrifuged rats had a lower percentage (68 vs. 74%) of fibers expressing type I MHC only and a higher percentage (15 vs. 10%) that co-expressed type I and IIa MHC's. The MHC composition of fibers from the deep portion of the MG was unaffected by centrifugation. The MHC compositions based on SDS-PAGE gel electrophoresis for each muscle were similar in the two groups. Mean fiber size of each fiber type in the soleus was unaffected by centrifugation. In the MG, the fibers, expressing only type IIb MHC were smaller in the centrifuge compared to control rats. CONCLUSION: Although 2 weeks of chronic centrifugation at 2G resulted in a cessation of body growth, there was essentially no effect on the muscle masses or fiber size in either a slow or fast extensor muscle. These data suggest that periods of centrifugation may be beneficial in maintaining extensor muscle mass in an animal that is not growing at a normal rate e.g., during chronic unloading.

Adaptation, Physiological↗
PubMed1997

Respiratory muscle fatigue during simulated air combat maneuvering (SACM).

HYPOTHESIS: This study tested the hypothesis that respiratory muscle fatigue occurs during a simulated air combat maneuver (SACM) centrifuge profile. METHODS: Six subjects (four males, two females) were exposed to a SACM consisting of alternating +4 Gz to +7 Gz plateaus until volitional fatigue. Electrical activities of the diaphragm, scalene, intercostal and external oblique muscles were monitored along with esophageal pressure and ventilation. RESULTS: SACM times averaged 358 +/- 115 s. The mean frequency of the electromyographic signal of the diaphragm and scalenes during inspiration, and the intercostals during the static expiratory portion of the anti-G straining maneuver (AGSM), decreased significantly (p < 0.05) over the course of the SACM by about 9%, 10% and 4%, respectively, indicating muscle fatigue. Esophageal pressure (PES) during the straining portion of the AGSM decreased significantly from 72 +/- 20 to 66 +/- 21 mmHg (mean +/- SD). Ventilation increased significantly both at +4 Gz and +7 Gz (32 +/- 16 L.min-1 to 56 +/- 19 L.min-1 at +4 Gz and 27 +/- 5 to 35 +/- 9 L.min-1 at +7 Gz) over time. PES during a maximal AGSM at +1.4 Gz (baseline) was decreased post- vs. pre-SACM (p = 0.0575). PES exerted during a maximal static inspiratory maneuver at residual lung volume was not changed after the SACM. Inspiratory work increased significantly during the SACM. The elastance of the respiratory system did not change during the SACM, but it was significantly increased when tested after the SACM. CONCLUSION: Increased inspiratory work, decreased pressure generation during a maximal AGSM and EMG frequency shifts suggest respiratory muscle fatigue coincides with the termination of SACM.

Acceleration↗
PubMed1997

Influence of a reduced G-suit pressure schedule on G-duration tolerance using enhanced G-protection ensembles.

BACKGROUND: Reducing pressure to enhanced G-protection ensembles may diminish potential undesirable physiologic effects, as well as improve wear comfort and garment durability. HYPOTHESIS: G-duration tolerance will not be affected by reducing pressure to the Swedish tactical flight combat suit (TFCS). A second objective tested the similarity in G-duration tolerance between the TFCS and Combined Advanced Technology Enhanced Design G-Ensemble (COMBAT EDGE) combined with a prototype enhanced coverage G-suit. METHODS: There were 12 Swedish pilots (mean = 30 yr) who experienced gradual onset (+0.1 G.s-1) runs (GOR) to +9 Gz, rapid (+6 G.s-1) onset runs (ROR) and simulated aerial combat maneuvers (SACM) with +5 to +9 Gz cycles. The GOR and ROR profiles had a sustained times of 60 s after reaching +9 Gz. RESULTS: GOR duration tolerance was statistically decreased (p < 0.01) by the lower pressure (1.1 psig.G-1) when compared to standard pressure (1.5 psig.G-1). No statistical difference between TFCS and COMBAT EDGE was observed during the GOR trials. For all conditions, during the RORs, 90% of the subjects completed at least 30 s at +9 Gz. Many technical or medical difficulties during SACM trials limited statistical treatment of these data. However, no obvious among-condition differences were observed. Noteworthy among SACM trials were those of 3 subjects enduring more than 9 min before stopping; one completing 12.5 min (35 cycles). Neither heart rate, blood pressure, nor perceived exertion data revealed a condition-effect difference. CONCLUSION: Moderately reduced pressure to the extended coverage anti-G suit, combined with positive pressure breathing, may yield decreased G-tolerance results during laboratory evaluation; however, observed differences are sufficiently small they are likely operationally insignificant.

Adult↗
PubMed1997

[Tolerance of +Gz loads by space physician Poliakov VV during the active phases of his 438-days space mission].

Tolerance of +Gz loads was assessed in space physician V.V. Polyakov during the active phases of his record, 438-day space mission. On the phases of insertion into orbit the +Gz-tolerance of the space physician was good; a fairly satisfactory g-tolerance during departure of orbit was extenuated by wearing of two anti-g suits (KARKAS-3 and CENTAUR) and administration of countermeasures against the unfavorable effects of space microgravity. His general health state and self-rating were not noticeably altered. +Gz loads in the course of descent from orbit instigated a syndrome characteristic of return to Earth from prolonged microgravity, i.e. a sensation of fierce pressure on the body, difficult breathing and speech, sine tachycardia, tachypnea, singular arrhythmias, petechial hemorrhage in the back integument, and vestibular/autonomous reactions. However, no evidence of any unusual physiological reactions that had never been seen in the other cosmonauts donned in the anti-g suits on earlier and less extended (from 65- to 366-day) missions were found. Extra systoles were registered on the phase of return to Earth after the 438-day but not previous 241-day mission of the space physician; they were probably associated with aging as he made his maiden flight at 47, and the second, at 53. The results speak in favor of the countermeasures against the adverse effects of microgravity applied during the mission, and the anti-g suits worn on the stage of return to Earth.

Adaptation, Physiological↗
PubMed1997

[The informative value of temporal artery sphygmogram for diagnosis visual disorders during +Gz-loads].

In investigation with centrifuge runs at 5 +Gz for 30 s visual disorders of the grey sheet type were provoked in three test-subjects by short-time relaxation of the leg and abdominal muscles. Alterations in amplitude parameters of the temporal artery sphygmogram elicited in 59 centrifuge runs were of the kind characterizing the well-marked visual disorders. Application of the linear discriminant function including three parameters of sphygmogram allowed to identify the visual disorders with a 10.2% error and a confidential probability of more than 0.999. Validity of the procedure of identification of dangerous states of pilot was attested in real flights with the maneuvering loads up to 5.8 g. Data of the investigation give the authors the right to recommend the method of indirect diagnosis of visual disorders as a tool to tackle the applied problems of aviation and space medicine.

Aerospace Medicine↗
PubMed1997

[Tolerance of +Gx-loads by females before and after a 120-day hypokinesia].

The goal of the work was to study female tolerance of g-loads before and after simulated weightlessness, and evaluate the effectiveness of countermeasures and anti-g means proposed for space flight. Centrifuge with a 7.25 m arm was used for 29 runs of 8 female subjects. The subjects were exposed to the transverse loads (+GX) at 8.2 g on a special regimen with the total run time of 9 min to simulate the ballistic descent from orbit in a SOYUZ-TM vehicle. Baseline tolerance of the females to transverse loads up to +8GX was good and satisfactory. Following 120 days of bed rest without the countermeasures or the anti-g suit g-tolerance was significantly lowered as evidenced by visual disorders in 67% of cases and exaggerated, if compared with the pre-hypokinesia levels, heart and respiration rates, i.e. 20% and 23.5%, respectively. The countermeasures and anti-g suit Centaur maintained g-tolerance at essentially the baseline level and precluded visual disorders. Results of the study speak in favor of the countermeasures and anti-g means used by the females in simulated long-duration weightlessness which can be recommended for the final phase of extended space mission.

Adaptation, Physiological↗
PubMed1996

[Multinuclear neurons in the ganglia of the gastrointestinal tract].

Findings of light optical and electron microscopy studies on formation of multinuclear neurons in gastrointestinal tract myenteric plexus in mammals affected by extreme factors (vagotomy, modelling of portal hypertension. Hyperbaric oxygenation and hypergravitation) were presented. A model for original transformation of multinuclear neuron as a mechanism of new nerve cells formation in the course of the organism compensatory-adaptive reaction to extreme action was obtained.

Animals↗
PubMed1997

Female acceleration tolerance: effects of menstrual state and physical condition.

INTRODUCTION: The literature contains a paucity of information on female tolerance to high sustained acceleration. With women now flying high-performance aircraft, gender-specific factors that may affect female acceleration tolerance have become increasingly important. The purpose of this investigation was to determine how menstrual state and physical condition affect acceleration tolerance. We hypothesized the menstrual cycle would have no effect on acceleration tolerance and that a positive correlation would exist between physical fitness level and tolerance to high sustained acceleration. METHODS: Centrifuge exposures on 8 female subjects consisted of a relaxed gradual-onset run (0.1 G.s-1) to the visual endpoint, a rapid-onset run (6 G.s-1) to +5 GZ for 15 s, and a +4.5 to +7 GZ simulated aerial combat maneuver (SACM) to physical exhaustion. Acceleration tolerance data were collected at onset of menstruation and 1, 2 and 3 weeks following the onset for two complete menstrual cycles. On separate days, body composition, anaerobic power output and peak oxygen uptake were determined. Retrospective data from 10 male subjects who had performed the +4.5 to +7 GZ SACM were analyzed and compared to these data. RESULTS: Analysis of variance revealed no significant difference in relaxed tolerance or SACM duration between the four selected menstrual cycle time points. Time-to-fatigue on the +4.5 to +7 GZ SACM was positively (p < or = 0.05) correlated with absolute fat-free mass (r = 0.87) and anaerobic power production (r = 0.76) in female subjects. However, when these variables were adjusted for total body mass, the significant correlations no longer existed. No correlation was found between SACM duration and absolute (L min-1) nor relative (ml.kg-1.min-1) aerobic fitness. Time-to-fatigue during the SACM was not significantly different between male and female subjects (250 +/- 97 and 246 +/- 149 s, respectively).

Acceleration↗
PubMed1996

[The general and specific mechanisms of adaptation of the body to extreme exposures].

The authors studied the dynamic of changes in auditory-vestibular system as well as the mechanisms of general and specific adaptation of organism to different extreme effects. 94 volunteers were examined in conditions of hyperbarism, hypobarism, hypergravitation and sea extreme factors. For registration of morphological changes and their correlation with biochemical and electrophysiological changes, experiments were performed on 272 animals using the same extreme factors. Complex clinical, biochemical, electrophysiological psychophysiological, and in the animals-morphological studies were performed. The state of the auditory-vestibular, cardiovascular, nerve, respiratory systems as well as the metabolism of carbohydrates, proteins, lipids, mineral-electrolytes and biogenic amines are followed up. It is well known that the immediate adaptation to extreme effects occurs on three levels-biochemical, anatomo-physiological and nerve-psychic. These levels are comparatively independent but also mutually related and determining each other. It was found out that in the different types of extreme effects the leading role is played by a different level. For example in sea extreme effects the nerve psychic adaptation level is dominating while in hyperbaric overstrain the anatomo-physiologic level plays the leading role. It is found out that 70% of the incidents during divers' experience is due to changes mainly in the middle year and in the labyrinth. Attention is paid on the role of genotype characteristics of adaptation as well as on the organism's tolerance towards the nitrous narcosis and oxidative intoxication. An interesting finding is that the animals and volunteers who decrease the blood serotonin values following the extreme effect are with higher stability and the immediate adaptation occurs quicker and is more effective. There is no data in the literature on this topic. These results could be used for prognosing the stability of the organism and for decreasing the health risk for the working under extreme effects, for their prevention and treatment as well as in the professional selection.

Adaptation, Physiological↗
PubMed1997

Echocardiographic findings in NATO pilots: do acceleration (+Gz) stresses damage the heart? AGARD, Neuilly-sur-Seine, France.

BACKGROUND: Based on physiologic considerations, observations in animal experiments and the results of a preliminary French study, there has been an aeromedical concern that repeated exposure to high sustained G-forces might have a deleterious effect on the heart. The AGARD Aerospace Medical Panel initiated a multi-national study to address the question. HYPOTHESIS: The study addressed the null hypothesis that "there is no difference in cardiac chamber dimensions, wall thickness or echocardiographic functional parameters between pilots who fly high sustained G (HSG) aircraft and pilots who fly primarily rotary wing or transport aircraft." METHODS: The study was a cross-sectional design comparing echocardiographic parameters in NATO active duty male pilots of HSG aircraft with a control group of transport and rotary wing pilots (CNTL). Some 13 NATO nations participated using a detailed protocol which included specific echocardiographic technical instructions, and procedures for collecting quantitative data on demographic variables including exercise, smoking and flying hours. Data was forwarded on a specially-designed software program to a central data registry. Careful quality control was carried out. RESULTS: Comparing data from 289 HSG pilots with 254 CNTL pilots, when corrected for the covariates, there were no differences for any of 16 echocardiographic parameters including right and left ventricular dimensions and wall thickness, aortic and left atrial dimensions, and tricuspid and mitral inflow velocities. CONCLUSIONS: The results support the null hypothesis. The conclusions are limited to the resolution of the technology employed and to the flight envelopes and +Gz exposure in the current generation of fighter aircraft.

Adult↗
PubMed1997

Arm arterial occlusion cuffs as a means of alleviating high +Gz-associated arm pain.

In an aircraft used under sustained high +Gz conditions, if the stick and throttle are positioned such that the pilot's hands are 20 cm or more below heart level, the consequent rise in forearm venous pressure (FVP) may give rise to arm pain, which is exacerbated by positive pressure breathing for G protection (PBG). This study examined the use of arm arterial occlusion cuffs (AAOC) as a means of pain alleviation. Six subjects were exposed on a human centrifuge to a simple acceleration profile of +7 Gz for 15 s, (onset rate 1 G.s-1), and to a complex profile of +4.8 Gz for 10 s followed by +7 Gz for 10 s, repeated 3 times. Subjects wore full coverage anti-G trousers, used PBG (+2 Gz out-in and 10 mm Hg/G), and performed runs with and without inflation of AAOC, during which invasive measurement of FVP was made. During the simple acceleration profile without AAOC, FVP rose to a mean peak of 209 mm Hg and arm pain was severe. With inflation of the AAOC, FVP rise was curtailed at a mean peak of 158 mm Hg and pain was absent. However, during sequential +7 Gz plateaus of the complex profile, AAOC inflation was associated with serially increasing FVP, which was significantly higher than that without AAOC inflation (p < 0.05 and p < 0.001 for second and third plateaus, respectively), giving rise to immediate and severe arm pain. Therefore, the use of arm arterial occlusion as a means of alleviating arm pain is unsuccessful.

Acceleration↗