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At least 451 records · Page 25Linked to original sources
PubMed1994

The "push-pull effect".

The purpose of this study was to prove or refute previous authors' suggestions that tolerance to +Gz is reduced when preceded by 0 Gz or -Gz. Six men and six women were subjected to one session of acceleration stresses that varied between -2 and +2.25 Gz on the NAMRL Coriolis Acceleration Platform (CAP). At the beginning and end of each session, we exposed the relaxed subjects to identical control segments that were comprised of +1 Gz for 30 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects were also exposed to three experimental segments that were comprised of 0, -1, or -2 Gz for 10 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects verbally reported any decrements in peripheral vision during exposure to +2.25 Gz. Blood pressure (BP) was reduced during each 15-s period at +2.25 Gz. The minimum BP was progressively lower during the 15-s period as the preexposure experimental conditions became more negative (+1, 0, -1, and -2 Gz). Episodes of peripheral vision loss increased as the preceding -Gz became more negative. BP during exposure to +Gz was significantly affected by the preceding 10-s exposure to -Gz, and is indicative of reduced +Gz tolerance. As this "push-pull effect" may result in unexpected incapacitation, it has important implications for aviation safety.

Acceleration↗
PubMed1994

Factors influencing aeromedical decision-making: operational versus research environments.

The aeromedical research and operational flying communities have at least one common goal; ensuring the optimum combination of mission performance and safety for the aircrew. This is a continual challenge as aerospace technology leaps ahead while the human factor remains relatively constant. However, several issues interfere with the smooth interaction between these communities: 1) perceptions that the research and operational communities have towards human subjects and pilots respectively; 2) the legal and ethical considerations involved in exposing individuals to risk; and 3) the ever-present personality dynamics involved in any decision-making process (e.g., returning individuals to a centrifuge panel or flying duty after a medically disqualifying incident). All of these factors influence decisions made in both communities, and how they interact with each other. It is a dynamic process that varies between countries, individual services (e.g., Navy vs Air Force), and even between different geographical locations within the same service.

Aerospace Medicine↗
PubMedDate not supplied

[Tolerance of chest-to-back [+Gx] and head-to-feet [+Gx] acceleration in drug-induced hypohydration].

The effect of drug-induced hypohydration (furosemide, 40 mg per os) on the tolerance of chest-to-back (+Gx) and head-to-feet (+Gz) acceleration was investigated in 9 healthy male test subjects, aged 25-45 years. The test subjects were rotated in a 7.5 m arm centrifuge. The first exposure during which they were centrifuged at 4 G (+Gx and +Gz) served as a control. The second time they were exposed to centrifugation after diuretic administration. Prior to second exposure, the subjects showed increased diuresis (5.7 +/- 0.7 ml/min) and increased excretion of osmotically active compounds, including electrolytes. This led to a decrease of the circulating blood volume by 7.0 +/- 1.8% on an average. During centrifugation the following parameters were recorded: electrocardiogram, blood pressure in the arm and ear lobe vessels, ear pulsogram, and pneumogram. After diuretic intake +Gx tolerance remained essentially unchanged whereas +Gz tolerance was good but required greater efforts. It is concluded that moderate diuretic-induced hypohydration did not result in a drastic deterioration of acceleration tolerance.

Acceleration↗
PubMed1996

The severity of nauseogenic effect of cross-coupled rotation is proportional to gyroscopic angular acceleration.

METHOD AND RESULTS: Subjects underwent cross-coupled rotation of the head (i.e., Coriolis stimuli) during which the upper body was tilted from side to side during horizontal rotation of the whole body about the Earth-vertical axis. In Experiment 1, the angle between the two axes of cross-coupled rotation was changed to vary the magnitude of gyroscopic angular acceleration without wide variations in Coriolis linear acceleration. The severity of nausea evoked by cross-coupled rotation stimuli varied relative to the magnitude of gyroscopic angular acceleration. It is noteworthy that nausea was not evoked unless gyroscopic angular acceleration was generated, even though Coriolis linear acceleration was equally induced. In Experiment 2, subjects tilted the upper body with or without restriction of head movement to a vertical plane during Earth-vertical axis rotation of the body at various angular velocities. The severity of evoked nausea was in direct proportion to angular velocity of body rotation irrespective of the restriction. CONCLUSION: These results indicated that the severity of nauseogenic effect of cross-coupled rotation is directly proportional to gyroscopic angular acceleration.

Acceleration↗
PubMedDate not supplied

Modification of vertical OKN and vertical OKAN asymmetry in humans during parabolic flight.

Characteristics of human vertical optokinetic nystagmus (OKN) and afternystagmus (OKAN) were examined by ISCAN imaging system on the ground and on board NASA's KC-135 aircraft in a parabolic flight study. The aircraft produced alternating periods of micro-(ca. 10(-2) G) and hyper-(ca. 1.8 G) gravitoinertial forces. Each phase lasted approximately 20 to 25 s. As compared to the baseline data on the ground, there was a significant increase of downward OKN/OKAN, whereas the upward OKN/OKAN did not change significantly in either micro- or hyper-G. As a consequence, the asymmetry of vertical OKN/OKAN, normally seen on the ground, was lost. It is postulated that the increase of downward OKN/OKAN in non-1-G conditions was governed by two different mechanisms. In micro-G, the normal inhibition effect in 1 G on the downward eye movement mediated by otolith organ activity to vertical velocity storage was removed. In hyper-G, downward OKN/OKAN was facilitated by augmented otolith-ocular reflex because of increased gravitoinertial force, so as to produce enhanced compensatory downward eye movement.

Adult↗
PubMed1997

An engineering approach to miogravity syndrome.

The human species is rapidly expanding. Barring global catastrophe and unnatural constraints, it will, in a brief time on the scale of natural history, fill the uttermost reaches of the solar system. The beachhead established by President Kennedy's lunar program will lead to lunar, Martian and free space settlements in the next century. In a single generation of those who call them home, the constant 9.81 m.s-2 pull of Earth's gravity, which has influenced the evolution and development of terrestrial life forms for billions of years, will fade from common experience. Miogravity syndrome, a prognosticated complex arising in reduced gravity environments such as the surfaces of the Moon and Mars and principally encompassing muscle atrophy, cardiovascular deconditioning and bone demineralization, stands to replace physics and rocketry as the fundamental challenge of interplanetary astronautics. Mirroring our past few million years of changing climate and resources, the mobility of humans between diverse gravitational environments on the high frontier will critically depend on our ability to adapt. Tomorrow, as ever, a mushrooming penchant for toolmaking will spearhead the human career.

Adaptation, Physiological↗
PubMedDate not supplied

Immersed false vertical room. A new motion sickness model.

We evaluated a new model of motion sickness--an enclosure decorated with visual cues to upright which was immersed either inverted or "front"-wall down, in Johnson Space Center's Weightless Environment Training Facility (WETF) pool. This "WETF False Vertical Room" (WFVR) was tested with 19 male and 3 female SCUBA diver subjects, aged 23 to 57, who alternately set clocks mounted near the room's 8 corners and made exaggerated pitch head movements. We found that (1) the WFVR test runs produced motion sickness symptoms in 56% and 36% of subjects in the room-inverted and room-front-down positions, respectively. (2) Pitch head movements were the most provocative acts, followed closely by setting the clocks--particularly when a clock face filled the visual field. (3) When measured with a self-ranking questionnaire, terrestrial motion sickness susceptibility correlated strongly (P < 0.005) with WFVR sickness susceptibility. (4) Standing instability, measured with a modified Fregly-Graybiel floor battery, also correlated strongly (P < 0.005) with WFVR sickness susceptibility. This result may reflect a relationship between visual dominance and WFVR sickness. (5) A control study demonstrated that the inverted and front-down positions produced WFVR sickness, but the upright position did not, and that adaptation may have occurred in some subjects with repeated exposure. The WFVR could become a useful terrestrial model of space motion sickness (SMS) because it duplicates the nature of the gravity-dependent sensory conflicts created by microgravity (visual and otolith inputs conflict while somatosensory gravity cues are minimized), and it also duplicates the nature of the provocative stimulus (sensory environment "rule change" versus application of motion to passive subject) more closely than any other proposed terrestrial SMS model. Also, unlike any other proposed terrestrial SMS model, the WFVR incorporates whole-body movement in all three spatial dimensions. However, the WFVR's sensory environment differs from that created by spaceflight in several respects, including the presence of frictional drag on limb movement, magnification at the face-mask-water interface, greater otolith conflict, exhaled bubbles, and the presence of some gravity-dependent somatosensory inputs.

Adult↗
PubMed1998

[Role of age in +Gz and +Gx tolerance by female candidates to astronauts].

Analyzed was the role of age in the tolerance of +Gz (up to 5 units) and +Gx (up to 8 units) by female candidates to cosmonauts on the stage of initial centrifuge selection in the years of 1979 through to 1993. Selection was made of 26 healthy non-flying women aged 23 to 39 who were divided into 4 groups with 5-year intervals. Female tolerance of g-loads and shifts in a number of physiological parameters during centrifugation were discovered to be age-dependent. The poorest tolerance of +Gz and +Gx loads was typical of women below 25 years, the best, at the age of 31 to 40 years. It was stated that tolerance of these demanding g-loads by women, especially below 30, was generally worse compared with men. There were also some distinctions in the cardiovascular response in women and men. These results point to the significance of centrifugation in selection female candidates to cosmonauts irrespective of their age.

Adult↗
PubMed1998

[The effect of a two-week anti-orthostatic hypokinesia on the cardiac function and on the latter's regulation in monkeys].

Investigated were the effects of 2-week exposure of four Macaca mulattas to the head-end tilted downward at 10 degrees on contractility of the left myocardium and its controls basing on the data of functional loading tests on the tilting table and at two regimes of centrifugation. The experiment included registration of the left heart pressure, volumetric blood flow in the aorta, and EKG in order to determine stroke volume, maximal isovolumetric pressure, end-systolic and end-diastolic pressures, maximal contraction and relaxation velocities, end-systolic myocardial elasticity, and a constant of the isovolumetric relaxation. As was stated, HDT does not impair contractility of the left myocardium; however, sensitivity of the HR baroreflex control wakens.

Animals↗
PubMed1989

Insects as test systems for assessing the potential role of microgravity in biological development and evolution.

Gravity and radiation are undoubtedly the two major environmental factors altered in space. Gravity is a weak force, which creates a permanent potential field acting on the mass of biological systems and their cellular components, strongly reduced in space flights. Developmental systems, particularly at very early stages, provide the larger cellular compartments known, where the effects of alterations in the size of the gravity vector on living organisms can be more effectively tested. The insects, one of the more highly evolved classes of animals in which early development occurs in a syncytial embryo, are systems particularly well suited to test these effects and the specific developmental mechanisms affected. Furthermore, they share some basic features such as small size, short life cycles, relatively high radio-resistance, etc. and show a diversity of developmental strategies and tempos advantageous in experiments of this type in space. Drosophila melanogaster, the current biological paradigm to study development, with so much genetic and evolutionary background available, is clearly the reference organism for these studies. The current evidence on the effects of the physical parameters altered in space flights on insect development indicate a surprising correlation between effects seen on the fast developing and relatively small Drosophila embryo and the more slowly developing and large Carausius morosus system. In relation to the issue of the importance of developmental and environmental constraints in biological evolution, still the missing link in current evolutionary thinking, insects and space facilities for long-term experiments could provide useful experimental settings where to critically assess how development and evolution may be interconnected. Finally, it has to be pointed out that since there are experimental data indicating a possible synergism between microgravity and space radiation, possible effects of space radiation should be taken into account in the planning and evaluation of experiments designed to test the potential role of microgravity on biological developmental and evolution.

Animals↗
PubMed2004

The transparent testa4 mutation prevents flavonoid synthesis and alters auxin transport and the response of Arabidopsis roots to gravity and light.

We examined whether flavonoids act as endogenous auxin transport regulators during gravity vector and light intensity changes in Arabidopsis thaliana roots. Flavonoid deficient transparent testa4 [tt4(2YY6)] seedlings had elevated root basipetal auxin transport compared with the wild type, consistent with the absence of a negative auxin transport regulator. The tt4(2YY6) roots had delayed gravitropism that was chemically complemented with a flavonoid intermediate. Flavonoid accumulation was found in wild-type columella cells, the site of gravity perception, and in epidermal and cortical cells, the site of differential growth, but flavonoid accumulation was absent in tt4(2YY6) roots. Flavonoid accumulation was higher in gravity-stimulated root tips as compared with vertical controls, with maximum differences coinciding with the timing of gravitropic bending, and was located in epidermal cells. Exogenous indole-3-acetic acid (IAA) also elevated flavonoid accumulation, suggesting that flavonoid changes in response to gravity might be partly as a result of changing IAA distribution. Acropetal IAA transport was also elevated in roots of tt4(2YY6). Flavonoid synthesis was repressed in the dark, as were differences in root acropetal transport in tt4(2YY6). These results are consistent with light- and gravity-induced flavonoid stimulation that alters auxin transport in roots and dependent physiological processes, including gravitropic bending and root development.

Arabidopsis↗
PubMed2004

Adaptation of plants to altered shoot orientation relative to the gravity vector.

Wheat Triticum aestivum L., carrots Daucus carota L., Chinese cabbage Brassica pekinensis Rupr., and African marigold Tagetes patula L. were grown at natural and inverted orientation in the Earth gravitational field. Light vector was set unidirectional or opposite directional relative to the gravity vector. Shoot orientation relative to the gravity vector was set natural or invert. Plants grew in the special pots furnished with plane or cylindrical hydrophilic porous membranes. The membrane allowed to stabilize a water potential in the root zone at the fixed level. Seeds were put into a fiber ion-exchange artificial soil overlaying horizontal hydrophilic plates of porous titanium or anchored to porous metal-ceramic tubes. Plants grew at the PPF level 550 +/- 20 micromoles/(m2 s) during 24-hr lighting and at the water potential level at the membrane surface (-1.00) +/- 0.08 kPa. Normal plants were obtained both at the natural and at the inverse shoot orientation in the all experiments. The wheat plants were yielded healthy germinating seeds no matter plant orientation. In the inverse orientation, no negative influence for plant biomass accruing was marked, but the increasing of shoot to root mass ratio was considerable. However carrot root crop mass decreasing was not revealed in the inverse orientation. The results demonstrated substantial dependence of morphological and physiological characteristics of higher plants on the gravity factor.

Biomass↗
PubMed2002

Evidence of short-term adaptation to microgravity of neuromuscular synergy during a whole body movement.

Human, like any other animal systems, moves in the terrestrial gravity field and must learn gravity-related motor strategies during his ontogenetic development. Considering continuous gravity action upon body segments, movement involves particular muscle activation patterns depending on body orientation to gravity. Gravitational-altered environments provided by parabolic flight or orbital space mission offer a great opportunity to investigate how gravity is taken into account in posture and movement planning. Indeed, in a context where the mechanical constraints are modified, movement execution involves that new muscular activity have to be produced. Almost, only few studies in microgravity environment are included electromyographic analysis and this parameter is generally used only to confirm modification of the muscular activation patterns. This study is focused to analyse the adaptation capacity of the brain to a modified gravitational environment. In this aim, EMG activity have been recorded during a whole body movement execution in both normo- and microgravity environment during parabolic flight. This procedure allowed us to analyse the EMG patterns recorded during the very first moments of weightlessness. In this study are reported the results of this analyse.

Journal Article↗
PubMed1986

Recirculation after cerebral ischemia. Simultaneous measurement of cerebral bloodflow, brain edema, cerebrovascular permeability and cortical EEG in the rat.

The 4-vessel occlusion rat model of cerebral ischemia was modified to permit the simultaneous measurement of cerebral blood flow (hydrogen clearance), brain edema (specific gravity), cerebrovascular permeability (14C-AIB) and electrocardiogram. Surgery was performed in one stage in the anesthetised, paralysed and ventilated rat and severe hemispheric ischemia was produced in all animals. Electrode implantation did not alter cortical specific gravity or Ki for 14C-AIB. During 4-vessel occlusion mean cortical CBF was 5.8 +/- 1.4 ml-1 100 g-1 min. and this was associated with an isoelectric ECoG; 15 min of ischemia produced a significant reduction in mean cortical specific gravity (increase in brain edema). Following 15 min ischemia, 180 min of recirculation were permitted. Post-ischemic blood flow showed an immediate hyperemia (CBF = 202 +/- 12 ml-1 100 g-1 min.) followed by hypoperfusion (CBF = 58 +/- 8 ml-1 100 g-1 min). There was an early further decrease in cortical specific gravity. Further recirculation led to a significant increase in cortical specific gravity (resolution of brain edema). The transfer constant (Ki) for 14C-AIB was not altered at any stage in recirculation. This appears to be a model of pure cytotoxic edema until 180 min recirculation after 15 min cerebral ischemia. Recirculation permitted return of cortical electrical activity.

Animals↗
PubMed1983

[Effect of ischemia and postischemic circulatory recovery on the ultrastructure of neurons].

In the investigation performed, a comparative analysis on the effect of ischemia and postischemic recirculation upon the neuron in the rat cerebral cortex and the dog spinal ganglia, common regularities and differences in appearance of pathological ultrastructural alterations were revealed. A general tendency towards increasing gravity of the pathological alterations was noted, as the period of ischemia and recirculation grew large. A leading type of the changes in the group of the injured neurons both in the spinal ganglia and in the cerebral cortex were changes of a chromatolitic type and they made one more general regularity. Hyperchromatosis was presented by an essentially less number of cases. The differences observed were presented as a rather greater polymorphism in the cortical neurons alterations comparing to the spinal ganglia cells at ischemia and postischemic recirculation. Besides, in the cortical neurons, more sensitive to the ischemic factor, diverced forms of the compensatory-adaptive reactions were revealed, that demonstrated plastic potentials of the cortical neurons.

Animals↗
PubMed1992

[Brain stem auditory evoked potentials in spinocerebellar degeneration].

A study was made of brainstem auditory evoked potentials (BAEP) in 66 patients from 56 families with different forms of spinocerebellar degenerations (SCD). 27 patients with olivopontocerebellar degeneration (OPCD), 13 patients suffering from Friedreich's disease (FD), 10 patients with Pierre Marie's familial ataxia (PMFA), 6 patients with late onset cerebellar atrophy (LOCA), and 10 patients with other forms of SCD were examined. The changes in BAEP turned out extremely diverse which can be regarded as a manifestation of marked phenotypic pleomorphism common to SCD. The most considerable changes in BAEP were discovered in FD and OPCD, whereas the least marked ones in PMFA and LOCA. The character and degree of BAEP disorders reflect the spreading and gravity of degenerative alterations in the brain stem in different forms of SCD. The authors discuss the possibility of the use of BAEP for objective estimation of the gravity and spreading of the pathological process as well as of the electrophysiological control over its course in SCD patients.

Adult↗