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PubMedDate not supplied

[Sensitivity of the respiratory regulatory apparatus to CO2 under simulated space flight conditions].

Using the rebreathing method, CO2 sensitivity of the respiration regulation system was investigated during a year-long enclosure study and head-down tilt tests of varying duration (up to 120 days). During the exposures CO2 and H+ were built up in the body. In the course of the enclosure study CO2 sensitivity was reduced. During bed rest experiments this parameter changed differently: it increased on day 7 and significantly decreased on days 55 to 100. These findings show that respiration regulation may vary markedly and indicate that it is worthwhile to carry out similar investigations in an actual space flight.

Adult↗
PubMedDate not supplied

[Dehydration therapy in human exposure to simulated space flight factors].

The effect of intravenous injections of 20% mannitol in a dose of 1 g per kg of body weight at a rate of 5 ml/min on the central circulation and cardiac contractile function was investigated. The infusions were performed to 18 healthy male volunteers, who participated in a head-down tilt test at -8 degrees, during the control period, on days 3, 7 and 14 of bed rest, and during the recovery. It was found that the prolonged osmo-therapy produced a clinically distinct dehydration effect without influencing central circulation. The therapy also led to positive cardiodynamics which was indicative of a decrease of the heart unproductive work and an improvement of left ventricle contractile function.

Adult↗
PubMed1993

Epidemiology of decompression sickness under simulated space extravehicular activities.

Several ground-based trials were conducted by NASA at the Lyndon B. Johnson Space Center, Houston, TX, during 1982-90 to examine the risk of altitude decompression sickness (DCS) during space extravehicular activities. There were 22 different pressure profiles involving single and staged decompression procedures, each lasting from 180 to 360 min at the final altitude. A total of 164 healthy subjects participated in 426 exposures to altitude. Symptoms of DCS occurred in 17% (74/426) and circulating microbubbles by precordial Doppler ultrasound were detected in 42% (179/426) of all exposures. About 27% (20/74) of exposures with symptoms resulted in test abort, and one-third of all test aborts required treatment in the hyperbaric chamber. There was about 3.20 times (95% Confidence Interval [95% CI] = 1.56-6.66) higher risk of symptoms in the presence of Doppler-detectable microbubbles. Examination of individual risk factors showed that there was about 4.3 times (95% CI = 1.62-11.50) higher risk of symptoms with increasing number of exposures. These findings emphasize the importance of evaluating risk factors from ground-based trials for application in operational decision-making and treatment strategies.

Adult↗
PubMed1989

Space vehicle approach velocity judgments under simulated visual space conditions.

There were 35 volunteers who responded when they first perceived an increase in apparent size of a collimated, two-dimensional perspective image of an Orbiter vehicle. The variables of interest included the presence (or absence) of a fixed reticle within the field of view (FOV), background starfield velocity, initial range to the vehicle and vehicle closure velocity. It was found that: 1) increasing vehicle approach velocity yielded a very small (but significant) effect of faster detection of vehicle movement, nevertheless, response variability was relatively large; 2) including the fixed reticle in the FOV produced significantly slower detection of vehicle radial movement, however this occurred only at the largest range and the magnitude of the effect was only about 15% of the one sigma value; and 3) increasing background star velocity during this judgment led to slower detection of vehicle movement. While statistically significant, this effect was small and occurred primarily at the largest range. A possible explanation for the last two findings is that other static and dynamic objects within the visual field may compete for available attention which otherwise would be available for judging image expansion; thus, the target's retinal image has to expand more than otherwise for its movement to be detected. This study also showed that the Proximity Operations Research Mockup at NASA/Ames can be used effectively to investigate a variety of visual judgment questions related to future space operations. These findings are discussed in relation to previous research and possible underlying mechanisms.

Adult↗
PubMed1996

Crewmember interactions during a Mir space station simulation.

BACKGROUND: Interpersonal problems may negatively affect crews on long-duration space missions. These problems stem from crewmember tension and its displacement to the outside monitoring personnel and from disruptions in crew cohesion and unclear leadership roles. HYPOTHESES: We hypothesized that crew tension and dysphoria would transiently increase following stressful events and be greater in the second half of a mission; that cohesion would be less during the second half of a mission; that tension and dysphoria would be displaced to the outside monitoring personnel; and that high levels of leader support and control would produce high levels of cohesion. METHODS: We tested these hypotheses during a 135-d Mir space station simulation study in Moscow. At weekly intervals, the three crewmembers completed items from two group climate questionnaires, a mood questionnaire, and a log of stressful events. RESULTS: Contrary to expectations, there was significantly (p < 0.05) more total mood disturbance and tension during the first 9 wks than during the subsequent 10 wks of the simulation. Although levels of cohesion remained the same over time, cohesion scores dropped at a significantly greater rate during the last third of the seclusion. There was evidence for the displacement of tension and dysphoria to the outside monitoring personnel. There were significant correlations in the predicted direction between leader support and control and crew cohesion, as well as evidence of status leveling in the mission commander. CONCLUSIONS: Crewmember tension, cohesion, and leadership are important issues affecting people working in secluded environments, and they need to be studied further in space.

Adult↗
PubMed1986

Orientation of gingival fibroblasts in simulated periodontal spaces in vitro. SEM observations.

The present study examined the orientation of gingival fibroblasts in simulated periodontal spaces in vitro. Extracted human teeth were root planed followed by root resection and root canal instrumentation. The middle and cervical thirds of each root were cut transversely to create 600-micron thick sections. Cortical bovine bone was cut, sectioned and contoured to create bone rings 600 micron thick with an internal diameter large enough to accommodate a root slice leaving a circumferential space varying from approximately 0.1 to 1.0 mm. Root slices and bone rings were incubated in a solution of collagenase and hyaluronidase to remove all remaining soft tissue and partially demineralized in EDTA (18%) for 30 minutes. Human gingival fibroblasts (HGF) were plated to confluency in tissue culture dishes. The dentin slices were then gently placed over the HGF monolayer along with bone rings around them to create simulated periodontal spaces. Control root slices were placed without bone rings around them. Cultures were maintained under standard tissue culture conditions. Representative specimens were obtained after 2, 3 and 4 weeks of culture and processed for scanning electron microscopy (SEM). At 2 weeks, the HGF had formed sheets of cells attached to the periphery of the root slices at one end and to the inner surface of bone rings at the other end. The orientation of cell sheets varied from being perpendicular to the periphery of the slice to oblique. At 3 and 4 weeks, the density and size of cell sheets increased and the orientation was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Process↗
PubMed1987

Orientation of gingival fibroblasts in simulated periodontal spaces in vitro containing collagen gels.

The present study examined the orientation of cultured human gingival fibroblasts in simulated periodontal spaces in vitro containing three dimensional hydrated collagen gels. Extracted human teeth were root planed followed by root resection and root canal instrumentation. The middle and cervical thirds of each root were cut transversely to create 600-micron thick sections. Cortical bovine bone was cut, sectioned, and contoured to create bone rings 600 micron thick with an internal diameter large enough to accommodate a root slice leaving a circumferential space varying from approximately 0.1 to 1.0 mm. Root slices and bone rings were incubated in an enzyme solution to remove all remaining soft tissues and then completely demineralized in EDTA (18%) for 72 hours. Human gingival fibroblasts (HGF) were plated to confluency in tissue culture dishes. The dentin slices were then gently placed over the HGF monolayer along with bone rings around them to create simulated periodontal spaces. Five days later, when initial cell attachment to the dentin and root slices had occurred, a collagen gel was poured in the space. The cultures were maintained for six weeks and were then processed for transmission electron microscopy. The HGF appeared to have formed multilayered cell sheets extending from the periphery of the root slices to the inner surface of bone rings. The HGF had apparently attached to both the bone and root surfaces. There was a close interaction of cells with the matrix fibrils of the gel. The cells and matrix fibrils were oriented parallel to each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Adhesion↗