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At least 307 records · Page 17Linked to original sources
PubMed1982

Measurement of cardiopulmonary performance during acute exposure to a 2440-m equivalent atmosphere.

Each of 20 subjects was given two Bruce Protocol symptom-limited maximum treadmill stress tests breathing sea-level compressed air (20.9% 02) for one test and a 2440-m equivalent (15.5% 02) for the other. Subjects ranged from 18-38 years of age; 15 were male and 5 female. Half of the population was tested first on the sea-level air, the other half on the altitude mixture. Real time measurements included heart rate, blood pressure, exercise time, oxygen consumption, carbon dioxide production, respiratory rate and volume, CO2 production, and several other derived parameters. A significant difference existed between measured VO2 max (p less than 0.002) and exercise time (p less than 0.004) for the two conditions. Mean differences were 8.3% and 6.7%, respectively. No significant differences were observed in heart rate or the recovery time to a respiratory quotient of less than 1. Hemoglobin saturation, as measured by an ear oximeter, averaged 95% for sea-level and 91% for the 2440-m equivalent gases. These results support a 2440-m equivalent contingency atmosphere in the NASA Space Shuttle prior to donning a low pressure suit for the purpose of reducing nitrogen washout times.

Adolescent↗
PubMed1985

Stereometry in very close-range stereophotogrammetry with non-metric cameras for human movement analysis.

In this paper a stereophotogrammetric algorithm based on a black-box approach to the modelling of object to image spaces relationship is proposed. The algorithm is well suited for 'very close-range photogrammetry', with respect to experiments in which the measurement field is 0.5 X 0.5 X 0.5 m or smaller, as in the analysis of a few or small body segments movements. The attainable accuracy is high, better than 0.1% of the observation distance. Non-professional and even different cameras can be used. Consequently an inexpensive experimental set-up can be realized. A very simple, cheap and easily usable calibration object is needed. Computation time for the reconstruction of object-space co-ordinates of point body landmarks is one order of magnitude lower than in the case of the Direct Linear Transformation (DLT) (Abdel Aziz and Karara, Proceedings of the ASP/U1 Symposium on Close-Range Photogrammetry, pp. 1-18. American Society of Photogrammetry, 1971; Marzan and Karara, Proceedings of the Symposium on close-range Photogrammetric Systems, pp. 420-467. American Society of Photogrammetry, 1975). Computation time for calibration is two-fold in respect of the DLT. An example of application to the recording of the movements of the index finger with respect to the metacarpophalangeal joint is given.

Biomechanical Phenomena↗
PubMedDate not supplied

Design, operation, and modeling of a membrane photobioreactor to study the growth of the Cyanobacterium Arthrospira platensis in space conditions.

A membrane photobioreactor was designed, implemented and used to grow the cyanobacterium Arthrospira platensis PCC 8005 in batch mode. Growth was followed directly by monitoring optical density and indirectly by measuring pressure increase due to the oxygen produced and separated from the liquid phase by diffusion through a hydrophobic membrane, and pH increase due to carbon consumption. When the pressure attained an upper limit, valves opened automatically, and the oxygen in the gas chamber was flushed out with nitrogen. As expected, two growth phases were observed, a short exponential phase followed by a linear phase, indicating limitation by light transfer. Growth rate during the second phase was measured easily and accurately, and consistency of optical density, pressure and pH data values was checked using a model of the system. Pressure measurement was found best suited to monitoring and measuring growth rate in space in terms of accuracy, precision and reliability.

Bioreactors↗
PubMed1994

Long-duration +Gz acceleration on cardiac volumes determined by two-dimensional echocardiography.

To enhance protection of humans exposed to long-duration low-gravity environments such as the Space Shuttle and National Aerospace Plane during re-entry or in the short-duration high(-)+Gz environment of fighter aircraft, the effects of +Gz acceleration on cardiovascular hemodynamics must be understood. This study reports the use of two-dimensional echocardiography in normal men during +Gz acceleration. The heart's position in relation to the chest did not change during acceleration up to +7 Gz. The success in maintaining high-quality images during exposures to G-forces of this magnitude may be attributed to the relatively low rate of G onset. End-diastolic volumes (EDV) and stroke volumes (SV) decreased during a +Gz acceleration ramp that increased until the subject experienced peripheral light loss (PLL) (P < .05). An inflated G-suit partially counteracted this effect. By 30 seconds of a +3 Gz acceleration plateau, the protective effects of the inflated G-suit to maintain EDV is lost and the EDV of the inflated G-suit was lower than the EDV of the uninflated G-suit (P < .05).

Acceleration↗
PubMed2004

Effects of 2 G hypergravity exposure on Bobwhite (Colinus virginianus) and Japanese quail (Coturnix coturnix japonica).

We compared reproductive fitness and early postnatal growth of Bobwhite (Colinus virginianus) and Japanese (Coturnix coturnix japonica) quail incubated and hatched during 2 G centrifugation. Fertilized Bobwhite and Japanese quail eggs were placed in portable incubators on the 8-ft International Space Station Test Bed (ISSTB) Centrifuge at NASA Ames Research Center. The quail eggs were incubated throughout hatching and reared until Postnatal day (P)4 at either 1.0, 1.2 or 2.0 G. Two days before hatching, candling revealed significantly greater numbers of viable Bobwhite than Japanese quail eggs at all g-loads. Bobwhite quail exhibited significantly better hatching success at all g-loads than did Japanese quail. Bobwhite hatchlings were sensitive to gravitational loading as evidenced by reduced postnatal body mass and length of 2 G hatchlings relative to 1 G control hatchlings. In contrast, mass and length of Japanese quail hatchlings were unaffected by 1.2 or 2 G exposure. Together, our findings provide evidence for superior viability and hatching success in Bobwhite quail relative to Japanese quail, coupled with greater sensitivity of postnatal body growth and development to 2 G loading. Bobwhite quail may be better suited than Japanese quail for scientific studies on space biology platforms.

Animals↗
PubMed1992

Comparison of current Shuttle and pre-Challenger flight suit reach capability during launch accelerations.

The Challenger accident prompted the creation of a crew escape system which replaced the former Launch Entry Helmet (LEH) ensemble with the current Launch Entry Suit (LES). However, questions were raised regarding the impact of this change on crew reach capability. Our study addressed the question of reach capability and its effect on realistic ground-based training for Space Shuttle missions. Eleven subjects performed reach sweeps in both the LEH and LES suits during 1 and 3 Gx acceleration trials in the Brooks AFB, TX, centrifuge. These reach sweeps were recorded on videotape and subsequently analyzed using a three-dimensional motion analysis system. The ANOVA procedure of the Statistical Analysis System (SAS) program was used to evaluate differences in forward and overhead reach. The results showed that the LES provided less reach capability than its predecessor, the LEH. This study also demonstrated that, since there was no substantial difference between 1 and 3 Gx reach sweeps in the LES, realistic Shuttle launch training may be accomplished in ground-based simulators.

Acceleration↗
PubMedDate not supplied

A 6 D.O.F. opto-inertial tracker for virtual reality experiments in microgravity.

Gravity plays a role in many different levels of human motor behavior. It dictates the laws of motion of our body and limbs, as well as of the objects in the external world with which we wish to interact. The dynamic interaction of our body with the world is molded within gravity's constraints. The role played by gravity in the perception of visual stimuli and the elaboration of human movement is an active research theme in the field of Neurophysiology. Conditions of microgravity, coupled with techniques from the world of virtual reality, provide a unique opportunity to address these questions concerning the function of the human sensorimotor system. The ability to measure movements of the head and to update in real time the visual scene presented to the subject based on these measurements is a key element in producing a realistic virtual environment. A variety of head-tracking hardware exists on the market today, but none seem particularly well suited to the constraints of working with a space station environment. Nor can any of the existing commercial systems meet the more stringent requirements for physiological experimentation (high accuracy, high resolution, low jitter, low lag) in a wireless configuration. To this end, we have developed and tested a hybrid opto-inertial 6 degree-of-freedom tracker based on existing inertial technology. To confirm that the inertial components and algorithms will function properly, this system was tested in the microgravity conditions of parabolic flight. Here we present the design goals of this tracker, the system configuration and the results of 0g and 1g testing.

Acceleration↗
PubMed2006

Molecular simulations of the pressure, temperature, and chemical potential dependencies of clay swelling.

A new method for the determination of clay swelling thermodynamics from computer simulation is discussed and evaluated. This method allows for the determination of temperature, pressure, and water chemical potential dependence of clay swelling from simulations at a single thermodynamic state point. The temperature dependence and pressure dependence of clay swelling are shown to be directly related to the composite system entropy and volume change, respectively, that accompany swelling. Expressions for the chemical potential dependence of clay swelling are used to determine constant pressure layer spacing and adsorption isotherms, quantities that are well suited for comparison with experimental measurements. This method is evaluated through grand isoshear ensemble simulations of Na-montmorillonite, a prototypical swelling clay. Approximations associated with all expressions are discussed with explicit calculations used to demonstrate their regimes of validity.

Journal Article↗
PubMed1994

Raster3D Version 2.0. A program for photorealistic molecular graphics.

Raster3D Version 2.0 is a program suite for the production of photorealistic molecular graphics images. The code is hardware independent, and is particularly suited for use in producing large raster images of macromolecules for output to a film recorder or high-quality color printer. The Raster3D suite contains programs for composing illustrations of space-filling models, ball-and-stick models and ribbon-and-cylinder representations. It may also be used to render figures composed using other graphics tools, notably the widely used program Molscript [Kraulis (1991). J. Appl. Cryst. 24, 946-950].

Journal Article↗
PubMed1992

[Comparison of CT and MRI in diagnosis of parapharyngeal tumors].

Recently, the usefulness of CT and MRI in diagnosing parapharyngeal tumors has been established. At the same time, several modalities for these imagings, i.e. plane and enhanced CT, T1, 2 weighted MRI and Gadolinium enhanced MRI, have been developed. We compared the image findings of 12 tumors involving the parapharyngeal space with their operative records. T1 was most suited to diagnosing the sites of origins of tumors because of its superior depiction of the internal carotid artery and parapharyngeal fat. Enhanced CT was also superior in depicting these structures, but in cases where the parapharyngeal fat was diminished, or the parapharyngeal fat had been invaded by malignant tumor, enhanced CT was inferior to T1. The spatial resolution of T2 was poor, T2 was thus not useful in diagnosing the sites of origins of tumors. Because tumor intensity tended to be similar to that of fat in Gadolinium enhanced MRI imaging, Gadolinium was not as useful as T1. In diagnosing the extents of tumors, we examined the depiction of both tumor-fat and tumor-muscle interfaces. With regard to the depiction of the tumor-fat interface, enhanced CT and T1 were most useful. In diagnosing the tumor-muscle interface, Gadolinium enhanced MRI was most suitable. The net result is that MRI is superior to CT.

Adipose Tissue↗
PubMedDate not supplied

Criteria for implant selection: surgical and prosthetic considerations.

With the availability of osseointegrated implants in an assortment of diameters as well as lengths, the implant selection process has become more complex. To expand treatment options and optimize outcome, implant selection should be guided by a number of surgical considerations and prosthetic requirements specific to each implant site. Small diameter implants are appropriate in areas of narrow ridge dimension or where prosthetic space is limited. Wide diameter implants are well suited to posterior regions with poorer bone quality and restricted vertical height. They provide a higher degree of implant-to-bone contact, increased stability, reduced screw stress, and an improved emergence profile. The learning objective of this article is to discuss these considerations and to outline the implant selection criteria.

Alveolar Bone Loss↗
PubMed1999

A thermal physiological comparison of two HAZMAT protective ensembles with and without active convective cooling.

Wearing impermeable garments for hazardous materials (HAZMAT) cleanup can often present a health and safety problem for the wearer. Even short duration cleanup activities can produce heat-stress injuries in HAZMAT workers. It was hypothesized that an internal cooling system might increase worker productivity and decrease the likelihood of heat-stress injuries in typical HAZMAT operations. Two HAZMAT protective ensembles were compared during subjects' treadmill exercise. The different ensembles were created using two different suits: a Trelleborg vapor protective suit representative of current HAZMAT suits and a prototype suit developed by engineers at the National Aeronautics and Space Administration (NASA). The two life-support systems used were a current-technology Interspiro Spirolite breathing apparatus and a liquid air breathing system that also provided convective cooling. Twelve local members of a HAZMAT team served as test subjects. They were fully instrumented to allow a complete physiological comparison of their theramal responses to the different ensembles. Results showed that cooling from the liquid air system significantly decreased thermal stress. The results of the subjective evaluations of new design features in the prototype suit were also highly favorable. Incorporation of these new design features could lead to significant operational advantages in the future.

Adult↗
PubMed1997

Recovery of protein structure from contact maps.

BACKGROUND: Prediction of a protein's structure from its amino acid sequence is a key issue in molecular biology. While dynamics, performed in the space of two-dimensional contact maps, eases the necessary conformational search, it may also lead to maps that do not correspond to any real three-dimensional structure. To remedy this, an efficient procedure is needed to reconstruct three-dimensional conformations from their contact maps. RESULTS: We present an efficient algorithm to recover the three-dimensional structure of a protein from its contact map representation. We show that when a physically realizable map is used as target, our method generates a structure whose contact map is essentially similar to the target. furthermore, the reconstructed and original structures are similar up to the resolution of the contact map representation. Next, we use nonphysical target maps, obtained by corrupting a physical one; in this case, our method essentially recovers the underlying physical map and structure. Hence, our algorithm will help to fold proteins, using dynamics in the space of contact maps. Finally, we investigate the manner in which the quality of the recovered structure degrades when the number of contacts is reduced. CONCLUSIONS: The procedure is capable of assigning quickly and reliably a three-dimensional structure to a given contact map. It is well suited for use in parallel with dynamics in contact map space to project a contact map onto its closest physically allowed structural counterpart.

Algorithms↗
PubMed1998

Plants and somatic embryos in space: what have we learned?

Space provides a unique environment that can affect the interplay between cell cycle controls and environment and can thus modify the processes of cell division, development and growth. It is proposed that the chromosomal and nuclear abnormalities frequently encountered in cells of various plants exposed to space are due to a combination of factors including the biological status of the systems and the way in which they are grown, exposed to, and ultimately, the way in which they experience multiple stresses. The extent to which space-specific changes become manifest is dependent on the extent of pre-existing stresses in the system. This has become evident in a variety of plant species grown in space but has been particularly amenable to study using in vitro systems, especially in developing embryoids. The following observations allow us to harmonize disparate results from a variety of space experiments:- (a) the more completely developed a system, the less likely it is to show cell stress during growth; the less morphologically complex, the greater the vulnerability; (b) the size/"packaging" of the genome (karyotype) are significant experimental variables; plants with larger genomes (e.g. polyploids) seem to be more space-stress tolerant; (c) a single space-associated stress is inadequate to produce a significant adverse response unless the stress is severe, or a biological parameter necessary to 'amplify' it exists. On this view, an appropriate "stress match" with other non-equilibrium determinants, much like a 'tug of war', can result in genomic variations in space. All this emphasizes that fastidiously-controlled growing environments must be devised if one is to resolve the matter of direct versus indirect effects of space. Better understanding of the novel physico-chemical equilibrium phenomena associated with space will allow those interested in space cell and developmental biology to pick and choose procedures best suited to their exploitation for specific objectives.

Cell Physiological Phenomena↗
PubMed2005

The management of web space contractures.

Multiple reconstructive options exist for the web space contracture: skin grafts, local flaps, and distant flaps have all been used to release the contracture and resurface the resultant defect. Local flaps are frequently more suited to web contractures between the fingers, whereas the thumb-index web space is amenable to a broader range of surgical techniques. The authors present a review of the anatomy of the web and options for reconstruction of web space contractures.

Amputation, Surgical↗
PubMedDate not supplied

[Effect of exogenous cardiosynchronized contrapulsation on human regional and central hemodynamics].

Variations in regional and central hemodynamics of man under the influence of exogenous contrapulsation (ECP) were examined rheographically. In recumbent subjects, ECP increased cerebral pulse blood filling, particularly of the vertebrobasilar system. It appears that the significant increase of the tone of arterioles and veins may be important when it becomes necessary to correct cerebral circulation in the situations that may lead to brain ischemia. It has been found that in the orthostatic tilt test ECP can be an effective tool for enhancing brain and lung blood supply and increasing stroke volume, cardiac output and blood pressure. This may help maintain homeostasis and improve orthostatic tolerance. The observation that ECP may facilitate blood supply of the vitally important organs, specifically brain, enables us to recommend this procedure to be used at an early stage of readaptation after simulation or real space flights.

Adaptation, Physiological↗
PubMed1993

Overhead and forward reach capability during exposure to +1 to +6 Gx loads.

The lack of reach performance data obtained under space-flight conditions has led to questions regarding the operational impact of higher G loads on crew performance. This investigation studied the effect of increasing G loads on reach capability. Ten subjects were exposed in a stepwise fashion to increasing accelerations resulting in G loads of from +1 to +6 Gx in the Brooks AFB centrifuge. Four subjects wore the pre-Challenger Launch Entry Helmet (LEH) ensemble and six the current Launch Entry Suit (LES). The subjects performed standardized reach sweeps at each G level. These sweeps were recorded on videotape and subsequently analyzed using a 3-dimensional motion analysis system. Significant differences in forward and overhead reach were determined using the General Linear Models (GLM) procedure of the Statistical Analysis System (SAS) program. The results from this study suggest that purposeful movement can be realistically performed in the LEH at the 5 G level and in the LES up to the 4 G level.

Gravitation↗