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At least 955 records · Page 53Linked to original sources
PubMed1999

[Two high performance fighter pilots with low +Gz tolerance rectified by centrifuge training].

OBJECTIVE: To demonstrate the effects of training on rectifying two high performance fight aircraft pilots with low +Gz tolerance. METHODS: Anti-G straining maneuver (AGSM) and pressure breathing for +Gz (PBG) maneuver were trained during centrifuge +Gz stress. RESULTS: After training, the +Gz tolerances with AGSM, and with PBG and anti-G suit were enhanced by 3.0 ~ 3.25 G and 2.75 ~ 3.0 G, respectively. The combined +Gz tolerance was higher than the relaxed +Gz tolerance by 4.25 ~ 4.5 G. Both two pilots had passed the 8 G 10 s SACM +Gz profile and reached the standard of training.

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PubMed1999

[Cardiovascular response to high sustained +Gz stress in dogs].

Objective. To investigate features of electrocardiography (ECG) and arterial pressure in dog during and after +Gz stress. Method. Six anesthetized dogs were catheterized for the measurement of ascending aortic pressure (AP) and common iliac arterial pressure (CIAP). A lead of ECG was monitored continuously. Then, dogs were placed supine in rotatable platform on one arm of an 1.7 m radius centrifuge. The animals were exposed serially to acceleration profiles of up to +7 Gz, consisting of a slow onset to peak acceleration, 90 s peak G, and a rapid decline back to control. A recovery time of at least 20 min was allowed after each acceleration profile. Result. (1) The amplitude of P-wave was influenced by the magnitude of the acceleration (2.3 +/- 0.2 mV at rest vs. 4.5 +/- 0.5 mV at +3 Gz, 4.8 +/- 0.3 mV at +5 Gz and 5.3 +/- 0.7 mV at +7 Gz, respectively P<0.05). (2) It appeared that arterial mean pressure increased and pulse pressure decreased in CIAP during high +Gz stress. (3) AP increased greatly after +Gz stress (17.29 +/- 5.59/11.31 +/- 3.86 kPa at rest vs. 27.53 +/- 6.12/20.62 +/- 1.86 kPa 30s after +7 Gz P<0.01). Conclusion. (1) The change of the amplitude of P-wave reflected the atrial displacement which may be the reason of arrhythmia. (2) The perfusion pressure is an important physiological parameter to the cardiovascular dysfunction during high +Gz stress. (3) Greatly higher AP after +Gz stress could be a feature of vascular exhaustion.

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PubMed2000

[Data analysis of 492 times centrifuge examination].

Objective. To sum up the experiences and to find the regularity of centrifuge examinations. Method. The data of nine years of centrifuge examination (from 1988 to 1996) of pilots who suffered from black out or LOC frequently were analyzed. Result. There were totally 492 times centrifuge examinations. First centrifuge examination included 229 pilots, 49 qualified, 180 unqualified. Second centrifuge examination included 263 pilots, 50 qualified, 213 unqualified. The pilots were all male. The average age of first centrifuge examination was 29.27 +/- 4.87 years. Average flying time was 1015.24 +/- 131.89 h. 68.7% of their plane was JJ-6 or above. Conclusion. Most pilots undergoing centrifuge examination these nine years were 26-35 year old, and had flown for 601-1200 h. The planes they flew are mostly high-performance fighter aircraft. Close attention must be paid to pilots under similar condition by the flight surgeon. It is recommended that the special equipment of G-tolerance training should be added to the fighter aircraft units.

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PubMed2001

[Experimental studies of the protective effects of basic fibroblast growth factor and Radix Salviae Miltiorrhizae on brain injury in rats caused by repeated exposures to +Gz].

Objective. To investigate the preventive and theralseutive (therapeutic) effects of basic fibroblast growth factor (bFGF) and Radix Salviae Miltiorrhizae (RSM) on brain injury caused by repeated +Gz exposures. Method. bFGF and RSM were injected intraperitoneally into SD rats before and after repeated +Gz exposures. The contents of excitatory amino acids (EAAs), nitric oxide (NO) and the number of cell apoptosis in the brain were measured, and were compared to those of the control group and normal saline (NS) group. Result. The contents of EAAs, NO and the number of cell apoptosis were significantly higher in repeated +Gz exposures group than those in control group. The values were markedly lower in bFGF and RSM group than those in repeated +Gz exposures group and NS group. Conclusion. bFGF and RSM showed distinct preventive and therapeutic effect on the brain injury induced by repeated +Gz exposures.

Animals↗
PubMed2002

High +Gz induced acute inguinal herniation in an F-16 aircrew member: case report and review.

This paper describes previously unreported, acute inguinal herniation during high +Gz air combat maneuvers. The flight surgeon aircrew member involved incorrectly analyzed the etiology of the abdominal wall discomfort during and immediately after the mission. Several factors contributed to the delayed diagnosis. Surgical exploration and repair revealed larger than expected defects. An open, anterior "tension-free" repair using polypropylene mesh grafts adequately reinforced the muscular and fascial defects. Return to full flight status occurred 4 wk following surgery. Post-operatively, repeat exposures to both a high +Gz flight environment and exertionally induced increased intra-abdominal pressures were well tolerated. Minimal sequelae from the injury and repair resolved within 1 yr of the surgery and did not affect mission capability or lifestyle activities. This article includes a review of hernia repairs and their aeromedical implications, with a discussion of epidemiology, surgical techniques, risk factors, surgical complications and recovery times for return to full activity.

Adult↗
PubMed2001

[The effect of G-loads on gravity tolerance of monkeys Macaca rhesus during antiorthostatic hypokinesia].

Reported are results of 200 centrifuge runs of 24 monkeys Macaca mulatta. Microgravity effects were simulated by 4-wk immobilization with the head tilted down at -6 degrees. The investigation was divided into two series. During series-1, one group of animals was not exposed to centrifugal training, whereas the other group was exposed to +Gz at the magnitudes of 1.2, 1.4 and 1.6 G for 30-40 min 4 to 5 times a week. In series-2, again one group of animals was not trained on the centrifuge but the other was trained at +1.2 Gz for 30 min 2 or 3 times a week. Functional testing by 30-s runs at +3 Gz was performed before and after head-down immobilization. Deterioration of g-load tolerance following simulated microgravity in both groups of untrained macaques was ascribed to the deconditioning effect of simulated microgravity on the body systems. Centrifugal training had, as a rule, positive effect on g-tolerance of the animals though it failed to fully eliminate the negative consequences of simulated microgravity. This means that search after optimal protocols of application of artificial gravity generated by centrifuge needs to be continued. Evaluation of the effectiveness of combining centrifugation with other countermeasures against the adverse effects of microgravity and development of associated protocols can be another area of future research.

Adaptation, Physiological↗
PubMed2001

[Counter-effect of intermittent +Gz exposures on vasoreactivity in decline in hind body arteries of rats under simulated weightlessness].

Objective. To investigate the counter-effect of intermittent artificial gravity, the present study examined vasoreactivity changes of femoral and mesenteric arteries in rats subjected to simulated weightlessness plus standing or centrifugation. Method. Forty male Sprague-Dawley rats were divided into simultaneous control (CON), simulated weightlessness (SUS), simulated weightlessness plus 1 h standing (STD1), simulated weightlessness plus 1.5 G centrifugation (1.5 G), and simulated weightlessness plus 2.6 G centrifugation (2.6 G) groups. Responses of arteries to vasoconstrictor were examined in vitro using isolated femoral and mesenteric arterial rings. Result. The contractile responsiveness to KCl or PE of femoral and mesenteric arterial rings isolated from SUS significantly decreased as compared with CON. And those of STD1 and the two centrifuged groups significantly enhanced as compared with that of SUS. Whereas there was no difference among STD1, 1.5 G, 2.6 G and CON. Conclusion. Simulated weightlessness may result in decreased contractile responses to KCl and PE of rat femoral and mesenteric arteries. Both STD1, 1.5 G, and 2.6 G prevented the decrease of contractile response to KCl and PE of femoral arteries.

Animals↗
PubMed1964

Effects of gravity on the functions of the central nervous system.

The sensitivity of the mammalian central nervous system to gravitational influences involves both direct and indirect factors. Gradual loss of cerebral circulation with increasing acceleration beyond 5 G has been shown to evoke changes in patterns of brain electrical activity, with epileptiform discharges triggered primarily in the hippocampal system of the temporal lobe, and spreading into other brain systems. The relationship of these structures to judgment and discriminative functions is discussed. Complete loss of cerebral circulation is associated with electrical silence in the brain. The possible effects of weightlessness on intracranial fluid distribution are reviewed. Tests of vibrational stimuli in the monkey have disclosed "driving" of electrical brain rhythms at the shaking frequency, particularly in the range from 11 to 15 cycles per second. These effects are unrelated to photic stimulation, and are abolished by anesthesia or death. Tests of discriminative capability at frequencies producing maximum driving have shown increased response latencies and increased errors. The neurophysiological basis for adaptive phenomena in recurrent vestibular stimulation has been found to reside partly in the vestibular nuclei of the medulla, and not to require integrity of connections with higher vestibular centers. The potentiation of responsiveness to vestibular stimulation in the weightless state has been shown to have a basis in the exaggerated responsiveness of medullary vestibular centers following loss of proprioceptive influxes from the spinal cord. The possible contribution of weightlessness to anomalous psychophysiological functions is reviewed. This area presents a major challenge in experimental design, and may require evaluation of such phenomena as distortion of the body image, modified sleep patterns and changes in optimal sleep-work cycles.

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PubMed2001

[Effects of repeated high +Gz exposure on several enzyme activities in cardiomyocytes in rats and some protective measures].

Objective. To determine the changes of several myocardial enzymes in rats after repeated high +Gz exposure and the protective effects of preconditioning of low-G exposure and tea polyphenols (TP). Method. Thirty-two male Wistar rats were randomly divided into 4 groups (n = 8 each): control group (group A), +10 Gz group (group B), low-G preconditioning group (group C) and TP protection group (group D). Group B, C and D were exposed to repeated +10 Gz stress (each for 30s, 5 times/d with +1 Gz 1 min intervals, 3 d/wk, 3 weeks in total), but group A was only submitted to +1 Gz for 5 min. Group C was exposed to +2 Gz for 5 min about 1 h prior to +10 Gz stress. Additionally, TP (200 mg/kg) was given orally to group D about 1 h prior to the +Gz experiment, while distilled water was given to groups A, B and C instead. On the next day after the last centrifuge run, the hearts were taken out immediately for making frozen tissue sections. Enzyme histochemical staining and image analysis were carried out for acid phosphatase (ACP), succinate dehydrogenase (SDH), cytochromeoxidase (Cyt aa3) and adenosine triphosphatase (ATPase). Result. As compared with the control, the activities of ACP and SDH in +10 Gz stressed rats decreased significantly (P<0.05), and there was a declining trend for Cyt aa3. But, low-G preconditioning and TP had protective effects on +10 Gz stress-induced reduction of these enzymatic activities (P<0.05). Conclusion. The results showed that repeated high +Gz exposure could bring about decreases of activities in ACP (the marker enzyme of lysosome) and SDH (the marker enzyme of mitochondrial endomembrane), which indicated a reduction of oxidative metabolism in myocardial tissue; but preconditioning with low-G and natural antioxidant TP had protective effects.

Acceleration↗
PubMed2001

[Analysis of the changes of temporomandibular joint under repeated +Gz stress].

Changes of temporomandibular joint (TMJ) under repeated +Gz stress were discussed. From the etiological point of view in TMJ, many papers in the fields of aviation medicine, microcirculation, maxillofacial surgery and bone surgery were reviewed. +Gz forces can cause inadequacy of blood of oxygen supply to TMJ area. This situation can be worsened by release of free radical agent and cellular factors, ischemia/reperfusion injury, and/or hemorrheologic changes. Furthermore, G-induced injury of cervical muscles and spine may break the maxillofacial muscle chain balance. In addition to the above factors, mental stress may do harm to TMJ. This paper introduced the researches on this area in an attempt to enlighten the concern about TMJ responses to increased +Gz acceleration forces.

Aerospace Medicine↗
PubMed2001

[Heat shock protein 70 and stimulation induced by +Gz].

High sustained +Gz acceleration produced by modern high performance aircrafts can induce brain damage because of ischemia and hypoxia. Heat shock protein 70 (HSP70) is one of the proteins broadly exist in organisms. The expression of HSP70 is an important reaction in the brain, and it has close relationship with brain ischemic injury. Now, the common view thinks that the expression of HSP70 during stimulation can protect nerve cells. This paper reviewed the biologic characteristics of HSP70 and the protective effect of HSP70 on nerve cells after brain ischemia. Also, the relationship of HSP70 expression and exposure value of +Gz were discussed.

Aerospace Medicine↗
PubMed2000

[A study of apoptosis and related gene bcl-2 and p53 expression in hippocampus of rats exposed to repeated +Gz].

Objective. To investigate the role of apoptosis in mechanisms of brain damage induced by +Gz exposures. Method. Twenty conscious SD rats were randomly divided into 5 groups. Rats in the control group (n=4) were exposed to +1 Gz and rats in the 4 experimental groups (n=16) were exposed to +14 Gz for three times, each for 45 seconds with 30 min interval in between. All the +Gz exposured were on an animal centrifuge. The rat brains were taken 30 min, 6 h, 24 h and 48 h after the last centrifuge run and fixed and embedded. The apoptosis and expression changes of related gene bcl-2 and p53 were detected by terminal deoxynucleotide (correction of deoxynuleotide) transferase-mediated dUTP nick end labeling (TUNEL) technique and immunohistochemical method, respectively. Result. Apoptotic cells and expression changes of bcl-2 and p53 were observed in CA1 subregion of rat hippocampus taken 6 h after repeated +Gz exposures, but returned to normal after 24-48 h. Conclusion. It suggests that apoptosis and expression changes of bcl-2 and p53 in rats hippocampus can be induced by repeated +Gz exposures and the apoptosis is one of the molecular mechanisms of brain damage induced by repeated +Gz exposures.

Animals↗
PubMed2000

[Changes of mRNA expression of IL-1beta and TNF-alpha in rat brains after repeated exposures to +Gz].

Objective. To study changes of mRNA expression of IL-1beta and TNF-alpha in rat brains after repeated exposures to +Gz. Method. Twenty conscious SD rats served as the subjects. They were randomly divided into 5 groups. Using an animal centrifuge, control rats (n = 4) were exposed to +1 Gz and experimental rats (n = 16) were exposed to +14 Gz three times, each for 45 s with 30 min interval in between. The rat brains were taken 30 min, 6 h, 24 h and 48 h after the last centrifuge run and total RNA was isolated. mRNA expression levels of IL-1beta and TNF-alpha in rat brain were measured by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Result. mRNA expression levels of IL-1beta and TNF-alpha in rat brains taken 30 min, 6 h and 24 h after repeated +Gz exposures were significantly higher than those in control rats, but returned to normal after 48 h. Conclusion. It suggested that mRNA expressions of IL-1beta and TNF-alpha in rat brains can be stimulated by repeated +Gz exposures and the increased expression of IL-1beta and TNF-alpha may play a role in the pathologic course of brain damage induced by +Gz exposures, but the damage is reversible.

Acceleration↗
PubMed2002

Physiological implications of mechanical effects of +Gz accelerations on brain structures.

BACKGROUND: In certain flight configurations, fighter pilots are exposed to high Gz acceleration (G) which may induce inflight loss of consciousness (G-LOC). When acceleration is of high amplitude, and the onset rate very rapid, G-LOC can occur extremely suddenly. HYPOTHESIS: Mechanisms other than brain hypoxia could be involved, enhancing its effects. In order to study the mechanical effects induced by such accelerations on cerebral structures, we estimated the stresses imposed on cerebral tissue when the brain is exposed to +Gz acceleration forces. METHODS: An "in vitro" experiment was performed to measure brain deformations during centrifugation. A finite element model of the brain was formulated. RESULTS: Computations indicate that traction and shear stresses are enhanced around the tentorial notch, and that compression stresses increase at the base of the cerebral hemispheres. CONCLUSION: The amplitude of these stresses is not sufficient to directly disturb proper nerve cell functioning. However, they could interfere with brain vessels as external surface forces, thus enhancing vessel collapse and brain ischemia.

Aerospace Medicine↗
PubMed1975

Gravitational effects on body composition in birds.

Gallinaceous birds, presenting a wide range of body size, were adapted physiologically to hyperdynamic environments, provided by chronic centrifugation. Chemical composition was measured directly on prepared carcasses, which were anatomically comparable, and more amenable to analysis than the intact body. Body mass and body fat decreased arithmetically with increasing field strength and also with increasing body mass. Water content of lean tissue increased in hyperdynamic environments, but irrespectively of body size.

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