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At least 685 records · Page 38Linked to original sources
PubMed1984

Static spatial effects in motor cortex and area 5: quantitative relations in a two-dimensional space.

We describe the relations between active maintenance of the hand at various positions in a two-dimensional space and the frequency of single cell discharge in motor cortex (n = 185) and area 5 (n = 128) of the rhesus monkey. The steady-state discharge rate of 124/185 (67%) motor cortical and 105/128 (82%) area 5 cells varied with the position in which the hand was held in space ("static spatial effect"). The higher prevalence of this effect in area 5 was statistically significant. In both structures, static effects were observed at similar frequencies for cells that possessed as well as for those that lacked passive driving from the limb. The results obtained by a quantitative analysis were similar for neurons of the two cortical areas studied. It was found that of the neurons with a static effect, the steady-state discharge rate of 78/124 (63%) motor cortical and 63/105 (60%) area 5 cells was a linear function of the position of the hand across the two-dimensional space, so that the neuronal "response surface" was adequately described by a plane (R2 greater than or equal to 0.7, p less than 0.05, F-test in analysis of variance). The preferred orientations of these response planes differed for different cells. These results indicate that individual cells in these areas do not relate uniquely a particular position of the hand in space. Instead, they seem to encode spatial gradients at certain orientations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Smooth pursuit deficits in space flights of variable length.

The maintenance of stable vision is a primary function of the neurovestibular and sensory-motor systems. There is, however, strong evidence suggesting that space flight results in a modification of the central nervous system and subsequent control of ocular-motor responses. These changes effect those neural mechanisms which are responsible for holding images steady on the retina during brief, self-initiated, head rotations or during the voluntary pursuit of moving targets. Recent studies have shown significant saccadic intrusions in both of these experimental paradigms, including an inability to null the vestibulo-ocular reflex (VOR) during the head/eye pursuit task. The maintenance of vision, while not entirely stable, both inflight and immediately postflight is now believed to be due to neural strategies that evolve for the purpose of assisting in directing the moving target onto the retina.

NASA Center JSC↗
PubMed1987

Air space: the embryonic medium.

Normalization of gas exchange and growth of chicken embryos incubated under abnormal conditions with regard to eggshell conductance and barometric pressure is directed to restoring the normal water loss from the eggs and the normal pattern of air space gas tensions during development. The latter is achieved by maintaining an O2 tension of 149 torr in the gas mixture supplied to the incubator and by reducing the incubator ventilation rate to compensate for increased, standard or effective, eggshell conductances. Thus, for maintenance of normal air space gas tensions, a decrease of the diffusive resistance of an egg requires a similar increase of the convective resistance so that the total resistance against gas transport remains normal. The latter must be set at a value given by (149-PA)/M, where PA is the normal air space O2 tension, torr, and M is the normal O2 uptake, ml(STPD)/day. This value is independent of embryonic age, because PA is directly proportional to M during development. Thus the convective resistance required for maintenance of normal PA and M values is given by the difference between (149-PA)/M and the diffusive resistance. Such PA and M values can be maintained in eggs with the minimum diffusive conductance, M/(149-PA), thus requiring an infinite convective conductance, to infinite diffusive conductance, which requires a minimum convective conductance, M/(149-PA). This minimum is predicted for all shell-less eggs, viz., for the continuous replacement of diffusive by convective gas transport.

Altitude↗
PubMed1996

Skill maintenance in extended spaceflight: a human factors analysis of space and analogue work environments.

This paper discusses the implications of increasing mission lengths of manned spaceflight for the design of future space systems from a human factors point of view. It is argued that the increase in mission duration has brought about a number of new problems, which have not been sufficiently addressed in space research. Therefore, a review of analogue work environments is carried out to make up for the paucity of space research found in the area of human performance in long-duration spaceflight. This resulted in an evaluation of seven analogue environments concerning their similarity to space with industrial process control and nuclear submarines coming out as the closest match on the technical dimension. Finally, some recommendations are given from the lessons learned in spaceflight, simulation studies and appropriate analogue environments.

Aerospace Medicine↗
PubMed1995

Light treatment for NASA shiftworkers.

Intense artificial light can phase-shift circadian rhythms and improve performance, sleep, and well-being during shiftwork simulations. In real shiftworkers, however, exposure to sunlight and other time cues may decrease the efficacy of light treatment, and occupational and family responsibilities may make it impractical. With these considerations in mind, we designed and tested light-treatment protocols for NASA personnel who worked on shifted schedules during two Space Shuttle missions. During the prelaunch week, treatment subjects self-administered light of approximately 10,000 lux at times of day that phase-delay circadian rhythms. Treatment continued during the missions and for several days afterward. No treatment was administered to subjects in the control group. Treatment subjects reported better sleep, performance, and physical and emotional well-being than control subjects and rated the treatment as highly effective for promoting adjustment to their work schedules. Light treatment is both feasible and beneficial for NASA personnel who must work on shifted schedules during Space Shuttle missions.

Adult↗
PubMed1996

Working aboard the Mir space station.

For more than ten years, the Mir station has been the World's only permanently manned laboratory in low earth orbit. With an orbital inclination of 51.6 degrees, its ground track covers more than 85% of the Earth's surface, where approximately 95% of the population lives. For the transfer of up to three crew members per trip to and from Mir, the 6.9 t Soyuz spacecraft is used. In general, the station's crew is changed every six months, with an overlap during the exchange of between one and two weeks. A Progress spacecraft (an unmanned derivative of the Soyuz vehicle) visits the station every three months to resupply it, with up to 2.1 t of payload, and to reboost it to maintain its nominal orbital altitude. The station's core module, injected into orbit in February 1986, contains the central control post for most onboard systems, the computer for attitude control, and the telemetry and communications system. It also contains the station's largest work space, which is 7.0 m long and varies in width between 1.5 and 2.5 m.

Air Conditioning↗
PubMed1995

Extravehicular activity training and hardware design consideration.

Preparing astronauts to perform the many complex extravehicular activity (EVA) tasks required to assemble and maintain Space Station will be accomplished through training simulations in a variety of facilities. The adequacy of this training is dependent on a thorough understanding of the task to be performed, the environment in which the task will be performed, high-fidelity training hardware and an awareness of the limitations of each particular training facility. Designing hardware that can be successfully operated, or assembled, by EVA astronauts in an efficient manner, requires an acute understanding of human factors and the capabilities and limitations of the space-suited astronaut. Additionally, the significant effect the microgravity environment has on the crew members' capabilities has to be carefully considered not only for each particular task, but also for all the overhead related to the task and the general overhead associated with EVA. This paper will describe various training methods and facilities that will be used to train EVA astronauts for Space Station assembly and maintenance. User-friendly EVA hardware design considerations and recent EVA flight experience will also be presented.

Astronauts↗
PubMed1984

Biochemical and ultrastructural studies of human eccrine sweat glands isolated by shearing and maintained for seven days.

A new method of isolating human eccrine sweat glands by the repeated dissection of skin biopsies with scissors is described. The success of the technique is attributed to a potential line of weakness between the investing capsule and the surrounding connective tissue, which parts under shear forces. The yield is 20-50 glands per biopsy (5 cm X 0.5 cm). The glands are judged to be viable by: (i) light and electron microscopy; (ii) ATP, ADP and AMP contents of 81.0 +/- 12.7, 13.8 +/- 3.3 and 3.8 +/- 1.0 pmol/gland, respectively (mean +/- S.E.M.), which gave an energy charge of 0.90; (iii) the 28-fold rise in cyclic GMP content and the sevenfold rise in cyclic AMP content effected by treatment for 2 min with 10(-5) M-acetylcholine and for 10 min with 10(-5) M-isoprenaline, respectively; (iv) the rate of [3H]leucine uptake into protein; and (v) the concentration of Neutral Red by the collecting duct. Glands were maintained for 7 days on polycarbonate filters floating on RPMI 1640 tissue-culture medium. After this time the ATP, ADP and AMP contents were 63.2 +/- 7.3, 8.5 +/- 2.2 and 3.5 +/- 0.8 pmol/gland, respectively (mean +/- S.E.M.), which gave an energy charge of 0.90. During maintenance a dilatation of the intercellular spaces developed in both secretory coil and collecting duct. Following maintenance there was a significant rise in the rate of [3H]leucine uptake into protein. Maintained glands demonstrated a fivefold greater accumulation of cyclic AMP in response to isoprenaline than did freshly isolated glands, but there was no comparable maintenance hypersensitivity of cyclic GMP to acetylcholine. This pattern of adrenergic, but not cholinergic, maintenance hypersensitivity matches the known lack of denervation hypersensitivity of human eccrine sweat glands to acetylcholine in vivo.

Adenosine Diphosphate↗
PubMed1998

Inhibition of salivary fluid secretion by occlusion of the intercellular space.

The effects of HCO3- on fluid secretory rate, cell volume and tissue structure were studied in perfused submandibular salivary glands under hyposmotic conditions (240 mosM). Fluid secretion was elicited by acetylcholine (ACh) in a hyposmotic HCO3(-)-free solution. Upon switching the perfusate from the HCO3(-)-free to the HCO3(-)-containing solution during ACh stimulation, the fluid secretory rate exhibited a small transient increase followed by a sharp decrease. ACh stimulation evoked rapid cell shrinkage in the absence of HCO3-, but upon switching from the HCO3(-)-free to the HCO3(-)-containing solution during ACh stimulation, the acinar cells exhibited increases in volume. In laser confocal microscopic examination of isolated acini, fluorescence of lucifer yellow was detected in the lateral intercellular spaces during ACh stimulation in the absence of HCO3-, but not in the presence of HCO3-. Electron microscopic examination revealed similar findings. We propose that the occlusion of the lateral intercellular space induced by cell swelling may result in an increase in the resistance to fluid flow in the space and consequently a decrease in the fluid secretion rate. Maintenance of an open lateral intercellular space may be an important requirement for fluid secretion. These observations suggest that a paracellular pathway may play a significant role in salivary fluid secretion.

Acetylcholine↗
PubMed1998

A strategy for nonextraction Class II treatment.

Class II nonextraction treatment, which commonly includes distal movement of the maxillary molars to correct the molar relationship, most often can be successful when treatment is started in the late-mixed dentition stage of development. At least two factors contribute to this success. One is that the molars can be distalized routinely at this age. The second is that the "E" space is available and can be used either to help correct the molar relationship or to resolve any crowding that may exist. This article describes and illustrates the treatment of a late mixed-dentition patient with this type of Class II nonextraction treatment that includes distal movement of the maxillary molars with a 100 g NiTi coil system and the maintenance of the "E" space with a lip bumper.

Dental Alloys↗
PubMed2003

Purchasing, installing and operating dental amalgam separators: practical issues.

BACKGROUND: Growing environmental concern over the accumulation of mercury in some fish has led some state and local environmental agencies to pursue stricter regulation of mercury in wastewater. Dental offices are an identifiable source of mercury in the form of dental amalgam. Although mercury in dental amalgam is not immediately bioavailable (that is, it has not been shown to contribute significantly to the problem of mercury in fish tissue), environmental agencies in some locales are asking dental offices to install amalgam separators in an effort to reduce amalgam discharges beyond those already achieved through chairside traps and vacuum filters. Field experience indicates that the configuration and operation of the dental office infrastructure can significantly affect the choice of separator, as well as the operation and maintenance of the installed equipment. OVERVIEW: The authors review factors related to office infrastructure and operation that dentists should consider when investing in an amalgam separator. They also provide a cost-analysis worksheet and checklist that may be useful to dentists who are considering purchasing a separator. CONCLUSIONS AND CLINICAL IMPLICATIONS: Before purchasing or installing an amalgam separator, dentists should consider factors specific to the available models, including size and maintenance requirements. In addition, office-specific actors should be considered (such as the plumbing configuration, available space for installation and subsequent access to that space for equipment replacement and maintenance). Dentists also should research whether any local or state regulations exist that might influence product selection or installation. Dentists should consider the effect an amalgam separator could have on existing suction equipment. Finally, dentists will want to consider the short- and long-term costs (including maintenance and parts replacement) of the available options.

Costs and Cost Analysis↗
PubMed1999

Pharmaceutical use by U.S. astronauts on space shuttle missions.

We evaluated in-flight use of medications from astronaut debriefings after 79 U.S. Space Shuttle missions. From the 219 records obtained (each representing one person-flight), 94% included some medication being taken during flight; of that number, 47% were for space motion sickness, 45% for sleep disturbances, and smaller percentages for headache, backache, and sinus congestion. Drugs were taken most often orally, followed in decreasing order of frequency by intranasal, intramuscular, and rectal routes. Drugs for space motion sickness were taken mostly during the first 2 d of flight, drugs for pain during the first 4 d, and drugs for sleeplessness and sinus congestion were taken consistently for 9 flight days. About 85% of all doses had no reported side effects, and most of the side effects that were reported happened during the first mission day. About 80% of the drug-dose events were perceived effective by the recipients; most of the reports of ineffectiveness occurred during the first mission day. Promethazine, the only drug given by three different routes (orally, intramuscularly, and rectally), was most effective and had minimal side effects when taken intramuscularly. This information, although useful, should be expanded to include objective measures of effectiveness so that therapeutic efficacy can be assessed during flight.

Astronauts↗
PubMed2006

Evolution and development of Hertwig's epithelial root sheath.

Periodontal regeneration and tissue engineering has re-awakened interest in the role of Hertwig's Epithelial Root Sheath (HERS), an epithelial tissue layer first discovered in amphibians more than a century ago. Using developmental, evolutionary, and cell biological approaches, we have, therefore, performed a careful analysis of the role of HERS in root formation and compared our data with clinical findings. Our developmental studies revealed HERS as a transient structure assembled in the early period of root formation and elongation and, subsequently, fenestrated and reduced to epithelial rests of Malassez (ERM). Our comparative evolutionary studies indicated that HERS fenestration was closely associated with the presence of a periodontal ligament and a gomphosis-type attachment apparatus in crocodilians and mammals. Based on these studies, we are proposing that HERS plays an important role in the regulation and maintenance of periodontal ligament space and function. Additional support for this hypothesis was rendered by our meta-analysis of recent clinical reports related to HERS function.

Animals↗
PubMed1993

Utilization of microgravity bioreactors for differentiation of mammalian skeletal tissue.

Bioreactor cell and tissue culture vessels can be used to study bone development in a simulated microgravity environment. These vessels will also provide an advantageous, low maintenance culture system on space station Freedom. Although many types of cells and tissues can potentially utilize this system, our particular interest is in developing bone tissue. We have characterized an organ culture system utilizing embryonic mouse pre-metatarsal mesenchyme, documenting morphogenesis and differentiation as cartilage rods are formed, with subsequent terminal chondrocyte differentiation to hypertrophied cells. Further development to form bone tissue is achieved by supplementation of the culture medium. Research using pre-metatarsal tissue, combined with the bioreactor culture hardware, could give insight into the advantages and/or disadvantages of conditions experienced in microgravity. Studies such as these have the potential to enhance understanding of bone development and adult bone physiology, and may help define the processes of bone demineralization experienced in space and in pathological conditions here on earth.

Animals↗
PubMed1991

Correlations between hyaluronan and epidermal proliferation as studied by [3H]glucosamine and [3H]thymidine incorporations and staining of hyaluronan on mitotic keratinocytes.

The rates of keratinocyte proliferation and synthesis of Hyaluronan (HA) were studied in human whole-skin organ culture by labeling with [6-3H]glucosamine and [3H]thymidine, respectively, to reveal possible correlations between the two functions of the cell. HA distribution in epidermis was examined by staining with a specific probe prepared from cartilage proteoglycan. The keratinocyte proliferation rate was low on the first 2 culture days, but showed a tenfold increase on the third and fourth days while the synthesis of HA proceeded at a relatively stable level throughout the same period. The most intensive staining of HA occurred in the uppermost spinous cell layer, whereas mitotic cells resided in the basal and suprabasal layers. The keratinocytes under various stages of mitosis were surrounded by a HA staining not more intense than that around nondividing basal cells, but a thick pad of HA appeared rapidly between the daughter cells. These findings suggest that newly synthesized HA is associated with the separation of keratinocytes following mitosis but the majority of the synthesis and content of HA in epidermis is involved in other keratinocyte activities such as maintenance of the extracellular space and cell--cell interactions during migration and differentiation.

Adult↗
PubMed2005

Rheological characterisation of primary and binary interactive bioadhesive gels composed of cellulose derivatives designed as ophthalmic viscosurgical devices.

In this study the formulation and rheological characterisation of novel candidate ophthalmic viscosurgical devices (OVD) based on binary interactive polymer gels is described. Primary systems containing either hydroxyethylcellulose (HEC) or sodium carboxymethylcellulose (NaCMC) or binary interactive gels composed of HEC and NaCMC were manufactured. Rheological characterisation was performed using texture profile analysis and oscillatory rheometry. All formulations exhibited pseudoplastic flow. Systems composed of HEC or HEC and NaCMC behaved as gels (G' > G") over the range of oscillatory frequencies whereas systems composed of NaCMC were primarily elastoviscous. Increasing the polymer concentration in all systems increased the compressional rheological properties (hardness, compressibility), zero frequency viscosity (derived from the Cross model) and the viscoelastic properties (G', G" and eta'). Rheological synergy was observed in the binary gels and was indicative of interaction between the parent polymers. Importantly, the range of rheological properties offered by the binary mixtures was greater than those exhibited by the primary systems. The binary systems described in this study possessed viscoelastic properties and steady-state viscosities that were similar to commercially available systems and would therefore be appropriate for the maintenance of the ocular space. The acceptable compressional rheological and pseudoplastic properties of these systems would facilitate administration into the eye using a syringe. Additionally and uniquely, the excellent adhesive properties of the binary interactive gels would suggest an ability to interact with the corneal endothelium that would offer protection during phacoemulsification. Based on the described rheological properties it is suggested that binary gels composed of mass ratios of HEC to NaCMC of either 3.6: 2.4 or 2.4: 3.6 would be acceptable as OVD and would uniquely offer duality of function.

Adhesiveness↗
PubMed2005

Enhanced osteoinduction by controlled release of bone morphogenetic protein-2 from biodegradable sponge composed of gelatin and beta-tricalcium phosphate.

Biodegradable gelatin sponges at different contents of beta-tricalcium phosphate (beta-TCP) were fabricated to allow bone morphogenetic protein (BMP)-2 to incorporate into them. The in vivo osteoinduction activity of the sponges incorporating BMP-2 was investigated, while their in vivo profile of BMP-2 release was evaluated. The sponges prepared had an interconnected pore structure with an average pore size of 200 microm, irrespective of the beta-TCP content. The in vivo release test revealed that BMP-2 was released in vivo at a similar time profile, irrespective of the beta-TCP content. The in vivo time period of BMP-2 retention was longer than 28 days. When the osteoinduction activity of gelatin or gelatin-beta-TCP sponges incorporating BMP-2 was studied following the implantation into the back subcutis of rats in terms of histological and biochemical examinations, homogeneous bone formation was histologically observed throughout the sponges, although the extent of bone formation was higher in the sponges with the lower contents of beta-TCP. On the other hand, the level of alkaline phosphatase activity and osteocalcin content at the implanted sites of sponges decreased with an increase in the content of beta-TCP. The gelatin sponge exhibited significantly higher osteoinduction activity than that of any gelatin-beta-TCP sponge, although every sponge with or without beta-TCP showed a similar in vivo profile of BMP-2 release. In addition, the in vitro collagenase digestion experiments revealed that the gelatin-beta-TCP sponge collapsed easier than the gelatin sponge without beta-TCP incorporation. These results suggest that the maintenance of the intrasponge space necessary for the osteoinduction is one factor contributing to the osteoinduction extent of BMP-2-incorporating sponges.

Absorbable Implants↗