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PubMed1997

Visual localization within single geometric planes of a space habitat.

BACKGROUND: The present study investigated how human subjects capture and restore visual information within a line representation drawing the three-dimensional configuration of a space module. METHODS: Nine subjects were asked to perform a visual localization task within this geometric model. The task consisted of localizing a light point appearing during 3 s in 40 different spatial positions and for 8 tilt angles of the model in the following random order: 0 degree, 45 degrees, 180 degrees, 225 degrees, 90 degrees, 315 degrees, 135 degrees, and 270 degrees. RESULTS: Results showed symmetric variations of the point-localizing errors about 180 degrees of tilt angle (vertical orientation) and a decrease of the errors when the points occurred in the distal, then in the median and in the proximal planes (virtual depth). The performance also varied according to the virtual ceiling, floor, right, left and back planes. The results have been discussed using a three-dimensional space representation based on a conservative mode of spatial information up to 90 degrees of tilt (horizontal orientation), and on a transformation mode beyond 90 degrees of tilt. CONCLUSION: We conclude that the visual localization in single geometric planes is orientation-dependent.

Computer Graphics↗
PubMed1997

Effects of exercise during head-down bed rest on postural control.

BACKGROUND: The effects of exercise on postural control during walking were evaluated following exposure to head-down bed rest (BR). METHODS: Two groups of male subjects (N = 18, mean age = 21.4 yr +/- SE 1.0) were exposed to 5 d of 6 degrees head-down bed rest. The experimental group (E) exercised 90 min.d-1 (n = 12 subjects) during the BR while the control group received no intervention (n = 6). The exercise treatment consisted of a combination of isotonic and isokinetic lower extremity exercise training. Electromyographic (EMG) activity in the tibialis anterior, gastrocnemius, vastus lateralis, and biceps femoris was measured during walking before and after BR. RESULTS: Following BR, EMG activity increased in both test subject groups for all muscles (p < 0.05). However, there were no significant differences in EMG activity between the C and E groups either before or after BR. CONCLUSIONS: These data suggest that the ability of the postural control system to adjust to the gravitational environment was compromised as a result of BR. In addition, we conclude that the exercise protocol used was not an effective countermeasure to the alterations in the postural control system.

Adult↗
PubMed1997

[Work capacity evaluation and orthostatic tolerance in experiments with long-term isolation].

Orthostatic tolerance (OT) and physical performance were tested against the ground simulation of several spaceflight factors. Before and after prolonged isolation and confinement three human subjects were tested by tilting, LBNP, and graded incremental aerobic exercise in the sitting position. Results suggested good OT in all the subjects. However, the pattern of orthostatic reaction was modified depending on the initial functional state of each subject. This was especially distinct in subjects 002 and 003 whose OT was slightly reduced by the experimental conditions. Orthostatic reactions in subject 004 showed greater stability in the baseline data collection period and was not much affected by isolation and confinement. HR variations at rest carried an individual character. On the whole, HR tended downward, particularly in 002. Indices of AP and, to a higher degree, its systolic constituent wandered outside the region of baseline values and even the norm limits in 002 and 004. Maximum variations were documented at the end of the second (003 and 004) and the third (002) months in experiment. ECG parameters in all the operators displayed different patterns of the norm. Diffusive repolarization, especially in the left chest leads, was noted to decline in the experiment. Tolerance of LBNP was qualified as good. Meanwhile, subject 003 developed symptoms of strained functioning of compensatory/adaptive mechanisms responsible for the OT maintenance. Repeated testing by LBNP was found to raise HR. Hence, prolonged simulation of space flight causes some reduction of orthostatic and LBNP tolerance, and degradation of physical performance.

Adult↗
PubMed1997

Interproximal access efficacy of Sonicare Plus and Braun Oral-B Ultra compared to a manual toothbrush.

A laboratory testing method, which has previously been shown to correlate with in vivo plaque removal results, was used to test the interproximal access efficacy (IAE) of two powered toothbrushes (Sonicare Plus and Braun Oral-B Ultra), and a manual toothbrush. This method tests IAE by means of simulated interdental spaces covered with pressure-sensitive paper tightly apposed to the surface. Testing was performed under wet conditions using 70, 100 and 140 grams of brushing force. Brushing was done for 15 seconds. The pressure-sensitive papers were removed, dried, and the IAE was quantified by a blinded investigator who measured the markings on the papers with calipers. The Sonicare Plus interproximal access scores were significantly greater than both the Braun Oral-B Ultra and the manual toothbrush at all three brushing forces tested (p < 0.001). These findings demonstrate that in vitro methodology previously used for testing manual toothbrushes is also adaptable for testing powered brushes. While additional studies are needed to confirm the clinical relevance of the present study, these results demonstrate the superiority of interproximal access of the Sonicare Plus sonic toothbrush over the Braun Oral-B Ultra powered brush and a manual toothbrush using this method.

Analysis of Variance↗
PubMed1998

Effects of elevated carbon dioxide environment on calcium metabolism in humans.

BACKGROUND: Chronic respiratory acidosis induced by an elevated carbon dioxide (CO2) environment should provoke hypercalciuria with related total body and subsequent bone calcium losses. We examined this hypothesis in four healthy male volunteers, who were exposed during a 25-d period to an 0.7% CO2 environment within a deep diving isolation chamber. Three months later the same subjects were reexamined during a second campaign being exposed to a 1.2% CO2 atmosphere. METHODS: The subjects received a constant calcium intake (1.4 g.d-1) and vitamin D supplement (1000 IU.d-1) during both campaigns. Calcium balance (oral calcium intake minus urinary and fecal calcium output) was evaluated. Serum calcium concentrations and biomarkers of bone metabolism were measured, in order to evaluate bone turnover. Additionally, the response to an acute oral calcium load was examined as a sensitive measure of changes in calcium metabolism. RESULTS: Both, urinary calcium excretion (from 245 +/- 38 to 199 +/- 31 mg.d-1; mean +/- SE, 0.7% and 1.2%, respectively) and fecal calcium losses (from 1229 +/- 128 to 996 +/- 62 mg.d-1) were significantly reduced in the higher (1.2%) CO2 atmosphere. Although more calcium was retained in the body during the 1.2% than during the 0.7% CO2 campaign, serum calcium concentrations and biomarkers of bone formation were significantly lower in the higher CO2 campaign. Furthermore, bone resorption was slightly increased in the 1.2% experiment. CONCLUSION: Elevated CO2 atmosphere may dose-dependently preserve body calcium without a parallel improvement of bone substance.

Acidosis, Respiratory↗
PubMed1998

Effects of sustained low-level elevations of carbon dioxide on cerebral blood flow and autoregulation of the intracerebral arteries in humans.

Cerebral blood flow velocity (CBFv) was measured by insonating the middle cerebral arteries of four subjects using a 2 Mhz transcranial Doppler. Ambient CO2 was elevated to 0.7% for 23 d in the first study and to 1.2% for 23 d in the same subjects in the second study. By non-parametric testing CBFv was elevated significantly by +35% above pre-exposure levels during the first 1-3 d at both exposure levels, after which CBFv progressively readjusted to pre-exposure levels. Despite similar CBFv responses, headache was only reported during the initial phase of exposure to 1.2% CO2. Vascular reactivity to CO2 assessed by rebreathing showed a similar pattern with the CBFv increases early in the exposures being greater than those elicited later. An increase in metabolic rate of the visual cortex was evoked by having the subjects open and close their eyes during a visual stimulus. Evoked CBFv responses measured in the posterior cerebral artery were also elevated in the first 1-3 d of both studies returning to pre-exposure levels as hypercapnia continued. Cerebral vascular autoregulation assessed by raising head pressure during 10 degrees head-down tilt both during the low-level exposures and during rebreathing was unaltered. There were no changes in the retinal microcirculation during serial fundoscopy studies. The time-dependent changes in CO2 vascular reactivity might be due either to retention of bicarbonate in brain extracellular fluid or to progressive increases in ventilation, or both. Cerebral vascular autoregulation appears preserved during chronic exposure to these low levels of ambient CO2.

Adult↗
PubMed1998

[Evaluation of super dwarf wheat growth and development in greenhouse "Svet" during cultivation in inhabited pressurized chamber].

Goals of the 3-month experiment GREENHOUSE using the equipment of greenhouse SVET (ECO-PSY-95) were to feature growth and development of wheat through the entire cycle of ontogeny under the maximally mimicked MIR environment, and to try out the procedures and timeline of space experiment GREENHOUSE-2 as a part of the fundamental biology investigations within the MIR/NASA space science program. Irradiation intensity (PAR) was 65 W/m2 and 38 W/m2 in the experiment and laboratory control, respectively. Values of other environmental parameters were MIR average (18-25 degrees C, relative air humidity in the interval between 40% and 75%, total gas pressure of about 660 to 860 mm Hg, partial oxygen pressure within the range from 140 to 200 mm Hg, partial carbon dioxide pressure up to 7 mm Hg). Experimental results showed that wheat cultivation in inhabited chamber under a modified lighting unit providing greater irradiation of the crop area produced more plant mass although seed production dropped. Low grain content in ears could be the aftermath of the gaseous trace contaminants in the chamber atmosphere.

Air Pressure↗
PubMed1998

[Cytoembryologic studies of super dwarf wheat grown in "Svet" greenhouse in the ground-based experiments].

The Project of scientific programs MIR/SHUTTLE and MIR/NASA was allowed for studying the productional, cytoembryological, morphological, biomechanical and other characteristics of superclub wheat on cultivation in the Svet greenhouse on-board orbital complex. This work was aimed at studying the duration of the complete cycle of ontogenesis of wheat and its individual stages, the peculiarities of forming the reproductive organs, processes, fertilization and formation of the seed production while cultivating in the Svet greenhouse under terrestrial conditions. Superclub wheat has been the object of experimentation. On cultivation of superclub wheat in the Svet greenhouse at designated conditions it was found that the cycle duration "from seed to seed" was 90-97 days. The number of granules in the wheat-ears studied was quite low and ranged from 15 to 30%. Performed studies with applying the light microscopy have indicated that in superclub wheat the embryological processes occur in compliance with those regularities which are described for the other forms of soft wheat.

Biomechanical Phenomena↗
PubMed1996

Simulations of circadian system and vigilance during space missions.

The effects of various space scenarios on the circadian system and alertness were investigated. The study of the circadian system under various conditions is important because core body temperature and many other physiological parameters (e.g., hormone levels) exhibit prominent circadian variation. The circadian system has a direct influence on the sleep-wake behavior and thus on performance. Alertness is an easily accessible subjective parameter which is strongly linked to cognitive performance. Simulation of alertness for different sleep-wake schedules may help to delineate crucial phases during missions and to plan counteractions. Although the level of alertness can be accounted for by the combination of circadian and homeostatic processes, additional factors such as motivation or excitement play a role.

Arousal↗
PubMedDate not supplied

Stress under normal conditions, hypokinesia simulating weightlessness, and during flights in space.

Stress due to intensive mental work under normal conditions was compared to stress under a sharp limitation of motor activity (hypokinesia), simulating weightlessness on the human body. Mental stress causes typical alterations of cerebral circulation under normal conditions: increase of blood flow in the supramarginal and angular gyri of the parietal lobe, in the frontal lobe, and in the superior temporal gyrus of the left hemisphere, and changes in cardiac activity and in the tonus of vessels. Dynamics of human stress reactions, among other features of this process, is best reflected in the parameters of a electrocardiogram, a rheoencephalogram, and total peripheric vascular resistance. An increase in the latter is an informative index of stress development. Human reaction to stress under hypokinesia and during flights in space have specific features. Prolonged hypokinesia causes an imbalance in an organism's control systems, specifically depressor reactions are distorted. In the context of hypokinesia, anxiety and mental stress lose their adaptive nature to a large extent. They provoke disturbances of the heartbeat and hypertensive reactions. A whole complex of factors affects the living organism during space flights. An imbalance of the body's control systems, emotional and physical overloads, which arise episodically, changes in electrolyte and energetic metabolism, and alterations in the head vessels increase the probability of reactions to stress and reinforce their effect. Stress can be retarded by using on elaborated system of preventive measures which includes physical training, psychological support of astronauts and, to some degree, reduction of the hypothalamus adrenergic centers' tonus through muscle relaxation. Astronauts' reactions to being in space occur during flights under heavy loading tests and in emergency situations. Weightlessness does not generate stress when one has adapted to it. Returning from weightlessness to the Earth's gravitation causes stress. After prolonged flights, stress associated with readaptation to the Earth's gravitation is atypical in character (increase of sympatoadrenalic system activity against the background of a reduction in hypothalamo-hypophysial system activity). We explain the voltage decrease of the T-wave of the electrocardiogram, the phenomenon repeatedly occurring both during prolonged space flights and under hypokinesia, by a lowering of cardiomyocytes, energetic potential due to hypokalemia, insufficient glucose usage, and a decrease in the coupling of oxidative phosphorylation processes. [Translated from Fiziologiya Cheloveka, vol. 22, no. 2, 1996, p. 10-19]

Adaptation, Physiological↗
PubMed2003

[Comparative evaluation of several methods preventing orthostatic disorders during simulation of the end-of-space-mission factors].

A new method for mitigation of the negative consequences of blood shift toward the cranial end as a result of simulation of the hemodynamic effects of microgravity (head-down tilt at -6 degrees) combines the lower body negative pressure (LBNP) and negative pressure respiration (NPR) to accelerate blood outflow from cerebral vessels and, additively, to restrain blood inflow from the lower body. The longitudinal hydrostatic pressure gradient is thus reproduced but main hemodynamic parameters assume values characteristic of the vertical posture. The objective was to compare the strength of LBNP and LBNP + NRP training in preventing orthostatic disorders following 7-d HDT. Subjects were 6 male volunteers aged 24 to 40 yrs. In the control experiment, every subject experienced episodes of orthostatic disorders. In the second experiment (LBNP), 4 subjects were afflicted; in the third experiment (LBNP + NPR), orthostatic disorders were minor, if at all. Absence of profound hemodynamic, autonomic or pre-syncope symptoms leads to the conclusion that combination LBNP + NPR is a more favorable preventive method than discrete LBNP.

Adult↗
PubMed1967

Cardiovascular studies during and following simulation and weightlessness.

Two major characteristics of space flight may be simulated to some degree by bed rest and by water immersion. These are inactivity and the lack of the hydrostatic stress on the systematic circulation. Studies prior to the advent of space flight led to the prediction of orthostatic intolerance, muscular weakness, and calcium loss. Prolonged space flight has heightened the interest in these simulations to provide information concerning the temporal cause of the "deconditioning" or disuse syndrome and the value of simulation for testing the effectiveness of remedial measures. This report will evaluate the extent to which the simulation appears valid. In its gross effects, orthostatic intolerance can be studied with respect to its temporal course, etiology and effectiveness of remedial measures. The intolerance develops more rapidly during water immersion with respect to cause as well as effect. The short term of immersion studies does not allow study of the secondary change in blood volume due to red cell mass changes, Remedial measures seem clearly defined in water immersion simulation and less clear in bed rest. Measures of venous pooling following water immersion appear different than those obtained following weightlessness. There also appear to be differences in the results of evaluation of protective devices and measures and in the time course of development and recovery of orthostatic intolerance. Correlates of the cardiovascular responses such as muscle tone, skeletal strength, and endocrine change (catecholamines, vasopressin and aldosterone) suggest a marked alteration in physiology during hypodynamic status. To date, work on exposure to increased G force has provided only extrapolated data concerning metabolic requirements.

Bed Rest↗
PubMed2006

Chaotic properties of planar elongational flow and planar shear flow: Lyapunov exponents, conjugate-pairing rule, and phase space contraction.

The simulation of planar elongational flow in a nonequilibrium steady state for arbitrarily long times has recently been made possible, combining the SLLOD algorithm with periodic boundary conditions for the simulation box. We address the fundamental questions regarding the chaotic behavior of this type of flow, comparing its chaotic properties with those of the well-established SLLOD algorithm for planar shear flow. The spectra of Lyapunov exponents are analyzed for a number of state points where the energy dissipation is the same for both flows, simulating a nonequilibrium steady state for isoenergetic and isokinetic constrained dynamics. We test the conjugate-pairing rule and confirm its validity for planar elongation flow, as is expected from the Hamiltonian nature of the adiabatic equations of motion. Remarks about the chaoticity of the convective part of the flows, the link between Lyapunov exponents and viscosity, and phase space contraction for both flows complete the study.

Journal Article↗
PubMed2006

Generalization of the Gaussian electrostatic model: extension to arbitrary angular momentum, distributed multipoles, and speedup with reciprocal space methods.

The simulation of biological systems by means of current empirical force fields presents shortcomings due to their lack of accuracy, especially in the description of the nonbonded terms. We have previously introduced a force field based on density fitting termed the Gaussian electrostatic model-0 (GEM-0) J.-P. Piquemal et al. [J. Chem. Phys. 124, 104101 (2006)] that improves the description of the nonbonded interactions. GEM-0 relies on density fitting methodology to reproduce each contribution of the constrained space orbital variation (CSOV) energy decomposition scheme, by expanding the electronic density of the molecule in s-type Gaussian functions centered at specific sites. In the present contribution we extend the Coulomb and exchange components of the force field to auxiliary basis sets of arbitrary angular momentum. Since the basis functions with higher angular momentum have directionality, a reference molecular frame (local frame) formalism is employed for the rotation of the fitted expansion coefficients. In all cases the intermolecular interaction energies are calculated by means of Hermite Gaussian functions using the McMurchie-Davidson [J. Comput. Phys. 26, 218 (1978)] recursion to calculate all the required integrals. Furthermore, the use of Hermite Gaussian functions allows a point multipole decomposition determination at each expansion site. Additionally, the issue of computational speed is investigated by reciprocal space based formalisms which include the particle mesh Ewald (PME) and fast Fourier-Poisson (FFP) methods. Frozen-core (Coulomb and exchange-repulsion) intermolecular interaction results for ten stationary points on the water dimer potential-energy surface, as well as a one-dimensional surface scan for the canonical water dimer, formamide, stacked benzene, and benzene water dimers, are presented. All results show reasonable agreement with the corresponding CSOV calculated reference contributions, around 0.1 and 0.15 kcal/mol error for Coulomb and exchange, respectively. Timing results for single Coulomb energy-force calculations for (H(2)O)(n), n=64, 128, 256, 512, and 1024, in periodic boundary conditions with PME and FFP at two different rms force tolerances are also presented. For the small and intermediate auxiliaries, PME shows faster times than FFP at both accuracies and the advantage of PME widens at higher accuracy, while for the largest auxiliary, the opposite occurs.

Models, Chemical↗
PubMed1997

Conformational analysis of methyl 6-O-[(R)- and (S)-1-carboxyethyl]-alpha-D-galactopyranoside by MM and Langevin dynamics simulations.

The conformational space of methyl 6-O-[(R)- and (S)-1-carboxyethyl]-alpha-D-galactopyranoside has been investigated. A grid search employing energy minimization at each grid point over the three major degrees of freedom, namely phi, psi and omega, identified low energy regions. The R-isomer shows five low energy conformers within ca. 1 kcal mol(-1) of the global energy minimum. The S-isomer has two conformers within a few tenths of a kcal mol(-1) of the global energy minimum. Langevin dynamics simulations have been have been performed at 300 K for 30 ns of each isomer. The phi dihedral angle has as its major conformer (g-) for the R-isomer whereas it is the (g+) conformer for the S-isomer. For the psi dihedral angle the (t) conformer has the highest population for both isomers. The dihedral angle omega has the (g+) conformer most highly populated, both for the R- and S-isomer. The above five and two conformational states for the R- and S-isomers, respectively, make up 90% in each case of the populated states during the Langevin dynamics (LD) simulations. Rate constants for the omega dihedral angle have been calculated based on a number correlation function. Three bond homo- and heteronuclear, i.e. proton and carbon-13, coupling constants have been calculated from the dynamics trajectories for comparison to experimental values. The heteronuclear coupling constant H2',C6 has been measured for the S-isomer and found to be 3.3 Hz. The J value calculated from the LD simulations, namely 2.6 Hz, is in fair agreement with experiment. A comparison to the X-ray structure of the R-isomer shows that the conformation of the crystalline compound occupies the low energy region most highly populated as a single R-conformer (30%) during the LD simulations.

Carbohydrate Conformation↗
PubMed2006

Proteomic analysis of mice hippocampus in simulated microgravity environment.

Space travel induces many deleterious effects on the flight crew due to the '0' g environment. The brain experiences a tremendous fluid shift, which is responsible for many of the detrimental changes in physical behavior seen in astronauts. It therefore indicates that the brain may undergo major changes in its protein levels in a '0' g environment to counteract the stress. Analysis of these global changes in proteins may explain to better understand the functioning of brain in a '0' g condition. Toward such an effort, we have screened proteins in the hippocampus of mice kept in simulated microgravity environment for 7 days and have observed a few changes in major proteins as compared to control mice. Essentially, the results show a major loss of proteins in the hippocampus of mice subjected to simulated microgravity. These changes occur in structural proteins such as tubulin, coupled with the loss of proteins involved in metabolism. This preliminary investigation leads to an understanding of the alteration of proteins in the hippocampus in response to the microgravity environment.

Animals↗
PubMed2004

First step toward a benchtop model of the Laser Interferometer Space Antenna.

A technique for simulating large optical path lengths by use of digital delay buffers is presented. This technique is used to generate a synthetic interferometer with one arm having an arbitrary length. The response of the interferometer to phase and frequency modulation is measured and found to be in agreement with predictions. This technique could be used to simulate long-baseline interferometric space missions such as the Laser Interferometer Space Antenna.

Journal Article↗
PubMed2003

Higher-order spatial discretisations in electrochemical digital simulations. Part 4. Discretisation on an arbitrarily spaced grid.

A systematic approach to the construction of finite difference formulae for the approximation to first and second derivatives with respect to space on an arbitrarily spaced grid is presented. The finite difference formulae, combined with backward implicit (BI) and extrapolation methods, are used for electrochemical simulations and tested for efficiency. Excellent results are obtained with second and third order discretisations even for very small space intervals in the vicinity of the electrode and strongly expanding grid spacings. This ensures efficient simulation of kinetic-diffusion systems where, due to a fast homogeneous reaction, a thin reaction layer is formed adjacent to the electrode.

Journal Article↗