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At least 991 records · Page 55Linked to original sources
PubMed2001

Effect of gravity change on the production of thrombopoietic growth factors.

It is reported that the stay in the space develops anemia, thrombocytopenia, and altered function and structure of red blood cell. The mechanism of these abnormalities was not clarified yet. The cloning of the thrombopoietin (TPO), followed by the analysis of TPO and c-mpl (its cellular receptor) knockout mice confirmed its role as the primary regulator of thrombopoiesis. TPO has been shown to stimulate both megakaryocyte colony growth from marrow progenitor cells and the maturation of immature megakaryocyte to form functional platelet. This process includes the massive cytoskeletal rearrangement, such as proplatelet formation and fragmentation of proplatelet. In this study we have focused on the production of thrombopoietic growth factors in mice those were exposed to gravity change by parabolic flight (PF).

Animals↗
PubMed1973

Effects of chronic acceleration in animals.

Chronic acceleration describes the exposure of animals to increased acceleration fields of sufficient intensity and duration to induce physiological adaptation. By comparing the degree of changes observed in several fields with the acceleration intensity, it is possible to derive an estimate of the biological effect of gravity. For technical reasons, such studies are limited to artificial fields produced by protracted centrifugation. Observations by various investigators indicate a fairly general response to chronic acceleration. Over the size range presented by these species (0.04-5 kg), there appears to be a direct relationship between body mass and the degree of the acceleration-induced effect (tolerable field intensity, growth repression, inhibition of fat (correction of far) deposition, etc.). However, different response patterns may obtain in homeotherms that differ significantly from this body size range.

Acceleration↗
PubMed2002

Heat stress effects for USAF anti-G suits with and without a counter-pressure vest.

BACKGROUND: Aircrew have reported increased heat stress when wearing the USAF Combined Advanced Technology Enhanced Design G-Ensemble or COMBAT EDGE (CE). The perceived thermal burden has been attributed to the fact that CE includes an inflatable counter-pressure vest to ease the work of positive pressure breathing during G (PBG). This study compared the heat load of CE with that of the standard USAF anti-G system (STD) without the vest, and measured heat stress effects on G-tolerance in both suits. METHODS: This study had 12 subjects (6 of them aircrew) who participated. Simulated preflight thermal stress (20 min walking at 35 degrees C with 85% relative humidity and radiant heat) was followed by return to a cooler environment (21 degrees C). G-tolerance and subjective stress levels were determined on the human centrifuge before and after the heat stress. Body weight, rectal and skin temperatures, and blood parameters were also assessed. RESULTS: Baseline relaxed tolerance for +Gz gradual onset runs (GORs) were (mean +/- SD) 7.6 +/- 1.3 G for CE and 7.1 +/- 0.8 G for STD (p < 0.05). Maximal rectal temperature following heat stress peaked at 38.1 +/- 0.4 degrees C for both CE and STD, and mean nude weight loss was 1.10 +/- 0.24 kg for both. Relaxed GOR tolerances after heat stress were 7.1 +/- 1.3 for CE and 6.3 +/- 0.9 for STD (p < 0.01). The heat stress significantly reduced G tolerance for both CE and STD (p < 0.01). CONCLUSIONS: Simulated preflight activity in hot conditions revealed no significant difference between CE and STD with regard to maximal core and skin temperature elevations or dehydration levels. CE supported a significantly higher baseline relaxed G-tolerance than STD, an advantage that persisted after heat stress and dehydration.

Adult↗
PubMed1999

Expression of HSP70 gene in rat brain after exposures to repeated +Gz.

OBJECTIVE: To study the changes of mRNA expression of heat shock protein 70 (HSP70) in the rat brain exposed to repeated +Gz. METHOD: The mRNA expression levels of HSP70 in rat brain were measured by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). RESULT: The HSP70 mRNA expression levels in rat brains taken 30 min and 6 h after repeated +Gz exposures were significantly higher than those in control group, while the difference between the levels of control group and those of experimental rat brains taken 24 h after +Gz exposure was not significant. CONCLUSION: It is suggested that HSP70 mRNA expression in rat brain can be induced by repeated +Gz exposures and the increased HSP70 mRNA expression may play an important role in self-protection against brain damage induced by +Gz exposures.

Animals↗
PubMed1999

[Changes in QT interval of electrocardiogram under +Gz acceleration and its significance].

OBJECTIVE: To define whether QT interval could be used to predict the response of pilots to +Gz stress. METHOD: 37 pilots underwent +4 Gz acceleration on a human centrifuge. According to their responses to +Gz stress, subjects were divided into group A (good reaction group, n=18), group B (hyperfunction reaction group, n=14) and group C (inhibition reaction group, n=1). QT and RR interval were measured pre-, during and post-G. The data of 33 subjects (89.2%) whose QT interval could be measured were analyzed statistically. RESULT: During +Gz, QT and RR interval were shortened and sensitivity of QT interval to RR interval was augmented significantly (vs. pre-G, P<0.001); group B had higher sensitivity of QT interval to RR interval during +Gz (P<0.001, as compared with group A); discrimination functions established by QT and RR interval during +Gz were efficient and their accurate judgement rate was 81.8%. CONCLUSION: The changes in QT interval of ECG were related to autonomic nervous imbalance under +Gz; QT interval and RR interval could be used to predict the response of pilots to +Gz stress. These suggested that the parameters and method in this study might be used in G-LOC warning system.

Acceleration↗
PubMed1999

[Mechanisms and detection of G-induced loss of consciousness].

High sustained +Gz acceleration induced loss of consciousness (G-LOC) is the main factor that causes flying accident. This paper reviewed the mechanisms and its physiological detection. During slow onset rate (SOR) acceleration, cerebral ischemia/hypoxia are the mechanisms of G-LOC, during rapid onset rate (ROR) acceleration, G-LOC might be related to mechanical intracranial hypertension, but the direct experimental data were lacking. Arterial blood pressure of eye level and cerebral oxygen saturation are important among the physiological indices of G-LOC detection.

Acceleration↗
PubMed1963

United States experience on the utilization of man's capabilities in a space environment.

This paper concerns the stresses on the flight crew in various phases of space flight missions and the ability of the crew to perform piloting-type tasks as well as other specific operations in the presence of these stresses. The mission phases include powered flight, free flight, space maneuvers, atmospheric entry, terminal phase, and surface operation. The stresses of the space environment are caused by forces and or motions or lack thereof, the space environment itself, the nature of the environment within the spacecraft, and the mental and physical demands on the flight crew. Among crew functions are control of the onboard systems, navigation and guidance of the spacecraft, maintenance and emergency operation, communications, and the conduct of scientific experiments. The paper draws on information obtained from the flight research to date as well as from ground tests and analyses. From the results one can conclude that man can very ably withstand the stresses of short duration missions into near space and has demonstrated ability to perform the type of tasks associated with flight crew operation. The chief unknown factors of future flight operations are the stresses produced by longer duration missions. Consideration of the problems involved leads to the conclusion that they are amenable to engineering solution at some expense to spacecraft weight and performance. It appears desirable therefore to utilize the flight crew to a high degree in future missions in the type of tasks where human judgment is needed or where significant simplification of on-board equipment may result.

Acceleration↗
PubMed1963

[Contribution to the study of the effects of weightlessness on the central nervous system of the rat].

We have studied the effects of various states of acceleration on the physiological activity of white rats. Initial experimental trials were carried out in the course of a flight of the Veronique missile. In another series of experiments the trials took place in an airplane in the course of successive parabolic flights at several minutes intervals producing periods of weightlessness of 33 to 44 seconds. We recorded the electrical activity of a large area lying between one electrode located in the somesthesic area and another electrode located in the homolateral visual area. In addition, cardiac and respiratory rate and electrical activity of the mesencephalic reticular formation and of the muscles of the neck were recorded. We found an intense cortical activation during the entire duration of the missile flight. In the airplane during the periods of weightlessness basic electrical activity has not been modified. Recordings of electrical activity in the mesencephalic reticular formation do not show any modification during missile flight. Afterwards appeared a flattening with the reduction of frequency. In the course of periods of weightlessness in airplane flight we have observed no modification of background electrical activity. Recording of neck muscle potentials shows, during weightlessness in airplane flight, a distinct augmentation of background tone. These findings seem in favor of a facilitation of reticular origin as a result of the abrupt diminution of volume of sensory information following the disappearance of the stimulus of gravity.

Acceleration↗
PubMed2002

Effect of muscle tensing on cerebral oxygen status during sustained high +Gz.

BACKGROUND: Successful monitoring of oxyhemoglobin during +Gz exposure was recently achieved using near-infrared spectroscopy (NIRS). To assess the effects of muscle tensing on sustained +Gz tolerance, we measured muscle activity and cerebral oxygen status (COS) during anti-G straining maneuvers at sustained high +Gz. METHOD: We exposed 21 male pilots wearing CSU-13/P anti-G suit to two different centrifuge profiles: 1) short-term repeated exposure (5 to 20 s) at 4, 5, 6, 5.5, or 7 Gz; 2) sustained exposure to a + 7Gz plateau for 30 s. During the Gz exposures, surface electromyographic (EMG) measurements were taken from the vastus medialis (VM) and rectus abdominis (RA) muscles. At the same time, the COS was recorded from the left forehead area using a commercial NIRS system. Mean muscular tensing for each muscle was calculated as a percentage of maximal voluntary contraction (% MVC). RESULTS: Oxyhemoglobin (O2Hb) and total hemoglobin (sum of O2Hb and deoxyhemoglobin) were decreased during both short-term and sustained +Gz exposure. RA muscle tensing was positively correlated with changes in the concentration of O2Hb during sustained + 7Gz exposure (r = 0.540, p < 0.05). RA tensing ranged from 6.2 to 36.8%MVC, and O2Hb ranged from -41.3 to -7.28 micromol x L(-1) during the exposures. No significant correlation was observed between VM tensing and O2Hb. CONCLUSION: NIRS measurements confirmed that a muscle straining maneuver increases G tolerance. Higher RA muscle tensing helps preserve brain blood volume during sustained high +Gz.

Adult↗
PubMed2002

Noninvasive monitoring of human consciousness by near-infrared spectroscopy (NIRS) during high +Gz stress.

Noninvasive monitoring of the relative change in oxygen saturation (rSO2) in cerebral tissue by near-infrared multi-wavelength spectroscopy (NIRS) was investigated in humans under high acceleration (+Gz) stress. These profiles included sustained 15-second +Gz plateaus and repeated short duration +Gz pulses of varying duration. The end points in this study were loss of consciousness due to high +Gz exposure (GLOC). In many cases subjects demonstrated cognitive and physical symptoms related to reduced cerebral blood flow without frank unconscious, which has been called Almost Loss of Consciousness (ALOC). Both the rSO2 levels during and after the +Gz exposures and the total time subjects were incapacitated after GLOC were recorded. It was found that while the drop in rSO2 at the onset of GLOC was lower during pulse exposures as compared to sustained exposures, the total time to recovery from GLOC was longer during the sustained runs. By applying a better understanding of the nature and timing of +Gz-induced changes in cerebral tissue oxygenation, more efficient control systems for personal protective gear for pilots of high performance aircraft can be implemented.

Acceleration↗
PubMed2002

[Structural changes in spinal cord gray matter induced by gravitational overloads].

After acute exposure of rats to gravitational overloads (GO) the reactive changes in neurons and interneuronal synapses of spinal cord were found. These are interpreted as morphologic signs of increased functional activity of neurons and activation of interneuronal impulse transmission. Chronic application of GO results in both reactive changes and damage of spinal cord structures. These changes were not seen after an acute exposure to GO, and thus they are associated with the repeated GO, indicating GO cumulative effect. Administration of "Vitavis" provides a membrane-protective effect, especially in respect to mitochondria of neurons and perineuronal glial cells in cervical and thoracic segments of spinal cord. The effect was less pronounced in spinal cord lumbar segments as a result of pericapillary edema, preventing the transport or drug from capillary bed to the neural structures.

Animals↗
PubMed2000

Effects of 2G exposure on lean and genetically obese Zucker rats.

Changes in the ambient force environment alter the regulation of adiposity, food intake and energy expenditure (i.e., energy balance). Lean (Fa/Fa) and obese (fa/fa) male Zucker rats were exposed to 2G (twice Earth's normal gravity) for eight weeks via centrifugation to test the hypothesis that the Fa/Fa rats recover to a greater degree from the effects of an increased ambient force environment on body mass and food intake, than do the fa/fa rats which have a dysfunctional leptin regulatory system. The rats (lean and obese exposed to either 1G or 2G) were individually housed in standard vivarium cages with food and water provided ad libitum. The acute response to 2G included a transient hypophagia accompanied by decreased body mass, followed by recovery of feeding to new steady-states. In the lean rats, body mass-independent food intake had returned to 1G control levels six weeks after the onset of centrifugation, and body mass increased towards that of the 1G rats. In contrast, food intake and body mass of the 2G obese rats plateaued at a level lower than that of the 1G controls. Although percent carcass fat was reduced more in the 2G leans vs. 2G obese rats, the latter lost significantly more grams of fat than did the leans. Our data suggest that with respect to food intake and body mass, the lean rats recover from the initial effects of 2G exposure to a greater degree than do the fatty rats, a difference that likely reflects the functionality of the leptin regulatory system in the leans.

Adaptation, Physiological↗