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At least 73 records · Page 4Linked to original sources
PubMed2006

Positive visual phenomena in space: A scientific case and a safety issue in space travel.

Most astronauts on Apollo, Skylab, and MIR reported 'flashes of light' occurring in different shapes and apparently moving across the visual field, in the absence of auditory, somatosensory, or olfactory abnormal percepts. A temporal correlation with heavy nuclei or protons has been documented in space and comparable phosphenes were observed by volunteers whose eyes were exposed to accelerated heavy ions at intensities below the threshold for Cerenkov visible radiation. An interaction between heavy ions and the retina was suggested. However, the biophysics of heavy ions or protons action remains undefined, the effects on photoreceptors and neuroretina have not been differentiated, and some direct action on the visual cortex never ruled out. Phosphenes are common in migraine and are known to occur also in response to the electrical stimulation of ganglion cells (in retinas without photoreceptors), optic pathways or visual cortex, with mechanisms that bypass the chemically gated channels. Intrinsic photosensitive ganglion cells exist in the retina of teleost fish and mammals. In the hypothesis of a peculiar sensitivity to subatomic particles of the visual system, phosphenes due to the activation of processes by-passing the photoreceptors would raise questions about human safety in space. The issue is particularly relevant with experiments of increasing duration being now operative in the International Space Station (ISS) and with plans of space travel outside the geomagnetic shield. Research is in progress both in the ISS and on animal models, in the framework of the NASA/ESA actions to improve the astronauts' health in space.

Cosmic Radiation↗
PubMed1997

[Tolerance of +Gz loads by space physician Poliakov VV during the active phases of his 438-days space mission].

Tolerance of +Gz loads was assessed in space physician V.V. Polyakov during the active phases of his record, 438-day space mission. On the phases of insertion into orbit the +Gz-tolerance of the space physician was good; a fairly satisfactory g-tolerance during departure of orbit was extenuated by wearing of two anti-g suits (KARKAS-3 and CENTAUR) and administration of countermeasures against the unfavorable effects of space microgravity. His general health state and self-rating were not noticeably altered. +Gz loads in the course of descent from orbit instigated a syndrome characteristic of return to Earth from prolonged microgravity, i.e. a sensation of fierce pressure on the body, difficult breathing and speech, sine tachycardia, tachypnea, singular arrhythmias, petechial hemorrhage in the back integument, and vestibular/autonomous reactions. However, no evidence of any unusual physiological reactions that had never been seen in the other cosmonauts donned in the anti-g suits on earlier and less extended (from 65- to 366-day) missions were found. Extra systoles were registered on the phase of return to Earth after the 438-day but not previous 241-day mission of the space physician; they were probably associated with aging as he made his maiden flight at 47, and the second, at 53. The results speak in favor of the countermeasures against the adverse effects of microgravity applied during the mission, and the anti-g suits worn on the stage of return to Earth.

Adaptation, Physiological↗
PubMed2004

Contribution of dead-space microdomains to tortuosity of brain extracellular space.

The extracellular space (ECS) of the brain is a major channel for intercellular communication, nutrient and metabolite trafficking, and drug delivery. The dominant transport mechanism is diffusion, which is governed by two structural parameters, tortuosity and volume fraction. Tortuosity (lambda) represents the hindrance imposed on the diffusing molecules by the tissue in comparison with an obstacle-free medium, while volume fraction (alpha) is the proportion of tissue volume occupied by the ECS. Diffusion of small ECS markers can be exploited to measure lambda and alpha. In healthy brain tissue, lambda is about 1.6 but increases to 1.9-2.0 in pathologies that involve cellular swelling. Previously it was thought that lambda could be explained by the circumnavigation of diffusing molecules around cells. Numerical models of assemblies of convex cells, however, give an upper limit of about 1.23 for lambda. Therefore, additional factors must be responsible for lambda in brain. In principle, two mechanisms could account for the measured value: a more complex ECS geometry or an extracellular macromolecular matrix. Here we review recent work in ischemic tissue suggesting concave geometrical formations, dead-space microdomains, as a major determinant of extracellular tortuosity. A theoretical model of lambda based on diffusion dwell times supports this hypothesis and predicts that, in ischemia, dead spaces occupy approximately 60% of ECS volume fraction leaving only approximately 40% for well-connected channels. It is further proposed that dead spaces are present in healthy brain tissue where they constitute about 40% of alpha. The presence of dead-space microdomains in the ECS implies microscopic heterogeneity of extracellular channels with fundamental implications for molecular transport in brain.

Animals↗
PubMed2003

How human sleep in space--investigations during space flights.

Sleep problems have been observed during many of the space flights. The existence of poor quality of sleep, fatigue, insomnia or different alterations in sleep structure, organization and sleep cyclicity have been established. Nevertheless results obtained from investigations of human sleep on board manned space vehicles show that it is possible to keep sleep patterns related to the restorative and adaptive processes. For the first time in the frame of the "Intercosmos" program a multi-channel system for recording and analysis of sleep in space was constructed by scientists of the Bulgarian Academy of Sciences and was installed on board the manned Mir orbiting station. In 1988 during the joint Bulgarian-Russian space flight continues recording of electro-physiological parameters necessary to estimate the sleep stages and sleep organization was made. These investigations were continued in next space flights of different prolongation. The results were compared with the findings obtained under the conditions during the pre- and post-flight periods.

Aerospace Medicine↗
PubMedDate not supplied

Epidural space as a Starling resistor and elevation of inflow resistance in a diseased epidural space.

BACKGROUND AND OBJECTIVES: The origin and the presence of negative pressure in the epidural space as well as the relationship of the extent of epidural anesthesia to epidural pressure has long been a subject of controversy. To further elucidate epidural pressure and its time course, the pressure at the needle tip was continuously measured as it traversed the interspinous ligament and the ligamentum flavum. METHODS: In a group of 22 patients, fluid was infused under gravity, and in a second group of 25 patients, boluses of fluid were administered at controlled infusion rates and under gravity. The volume-pressure-flow relationship was thus measured in one of two ways, either with a manual syringe and pressure transducer or with a pressure-monitoring-computer-controlled volumetric infusion pump. RESULTS: Natural pressure, (i.e., pressure in the epidural space before instrumentation is applied) could be approached when the space was first entered before fluid was infused (initial pressure); or after fluid had been infused (residual pressure). Epidural pressure could be extrapolated from the upsweep of the volume-pressure-flow relationship by projecting it back to just before the first injection. The extrapolated pressure lay between the initial and residual pressures. Medicinal solution placed in the barrel of the syringe did not infuse under gravity until the syringe barrel was lifted to a certain height, at which flow began and continued at a perceptible rate, with very little or no further increase in height required to maintain flow. The pressure at which flow began was the critical opening pressure, a characteristic of a Starling resistor. Furthermore, resistance to inflow of fluid was related to the presence or absence of natural or surgical disease in the epidural space. Resistance was significantly higher in the diseased than in the surgical group, at 114 (range, 22-226) mm Hg/L/h versus 46 (range, 8-86) mm Hg/L/h. Three phases were seen in the pressure-time recordings. CONCLUSIONS: Volume-pressure-flow relationships in the epidural space can be explained by a model in which epidural and subarachnoid pressures are inextricably related with the Starling pressure, dependent on the subarachnoid pressure. This model suggests reasons why spread of anesthetics might be difficult to predict.

Adult↗
PubMed2005

Limitations to the spacing effect: demonstration of an inverted u-shaped relationship between interrepetition spacing and free recall.

The spacing effect refers to the finding that memory for repeated items improves when the interrepetition interval increases. To explain the spacing effect in free-recall tasks, a two-factor model has been put forward that combines mechanisms of contextual variability and study-phase retrieval (e.g., Raaijmakers, 2003; Verkoeijen, Rikers, & Schmidt, 2004). An important, yet untested, implication of this model is that free recall of repetitions should follow an inverted u-shaped relationship with interrepetition spacing. To demonstrate the suggested relationship an experiment was conducted. Participants studied a word list, consisting of items repeated at different interrepetition intervals, either under incidental or under intentional learn instructions. Subsequently, participants received a free-recall test. The results revealed an inverted u-shaped relationship between free recall and interrepetition spacing in both the incidental-learning condition and the intentional-learning condition. Moreover, for intentionally learned repetitions, the maximum free-recall performance was located at a longer interrepetition interval than for incidentally learned repetitions. These findings are interpreted in terms of the two-factor model of spacing effects in free-recall tasks.

Humans↗
PubMed2005

The nutritional status of astronauts is altered after long-term space flight aboard the International Space Station.

Defining optimal nutrient requirements is critical for ensuring crew health during long-duration space exploration missions. Data pertaining to such nutrient requirements are extremely limited. The primary goal of this study was to better understand nutritional changes that occur during long-duration space flight. We examined body composition, bone metabolism, hematology, general blood chemistry, and blood levels of selected vitamins and minerals in 11 astronauts before and after long-duration (128-195 d) space flight aboard the International Space Station. Dietary intake and limited biochemical measures were assessed during flight. Crew members consumed a mean of 80% of their recommended energy intake, and on landing day their body weight was less (P = 0.051) than before flight. Hematocrit, serum iron, ferritin saturation, and transferrin were decreased and serum ferritin was increased after flight (P < 0.05). The finding that other acute-phase proteins were unchanged after flight suggests that the changes in iron metabolism are not likely to be solely a result of an inflammatory response. Urinary 8-hydroxy-2'-deoxyguanosine concentration was greater and RBC superoxide dismutase was less after flight (P < 0.05), indicating increased oxidative damage. Despite vitamin D supplement use during flight, serum 25-hydroxycholecalciferol was decreased after flight (P < 0.01). Bone resorption was increased after flight, as indicated by several markers. Bone formation, assessed by several markers, did not consistently rise 1 d after landing. These data provide evidence that bone loss, compromised vitamin D status, and oxidative damage are among critical nutritional concerns for long-duration space travelers.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2004

Evaluation of shoulder integrity in space: first report of musculoskeletal US on the International Space Station.

Investigative procedures were approved by Henry Ford Human Investigation Committee and NASA Johnson Space Center Committee for Protection of Human Subjects. Informed consent was obtained. Authors evaluated ability of nonphysician crewmember to obtain diagnostic-quality musculoskeletal ultrasonographic (US) data of the shoulder by following a just-in-time training algorithm and using real-time remote guidance aboard the International Space Station (ISS). ISS Expedition-9 crewmembers attended a 2.5-hour didactic and hands-on US training session 4 months before launch. Aboard the ISS, they completed a 1-hour computer-based Onboard Proficiency Enhancement program 7 days before examination. Crewmembers did not receive specific training in shoulder anatomy or shoulder US techniques. Evaluation of astronaut shoulder integrity was done by using a Human Research Facility US system. Crew used special positioning techniques for subject and operator to facilitate US in microgravity environment. Common anatomic reference points aided initial probe placement. Real-time US video of shoulder was transmitted to remote experienced sonologists in Telescience Center at Johnson Space Center. Probe manipulation and equipment adjustments were guided with verbal commands from remote sonologists to astronaut operators to complete rotator cuff evaluation. Comprehensive US of crewmember's shoulder included transverse and longitudinal images of biceps and supraspinatus tendons and articular cartilage surface. Total examination time required to guide astronaut operator to acquire necessary images was approximately 15 minutes. Multiple arm and probe positions were used to acquire dynamic video images that were of excellent quality to allow evaluation of shoulder integrity. Postsession download and analysis of high-fidelity US images collected onboard demonstrated additional anatomic detail that could be used to exclude subtle injury. Musculoskeletal US can be performed in space by minimally trained operators by using remote guidance. This technique can be used to evaluate shoulder integrity in symptomatic crewmembers after strenuous extravehicular activities or to monitor microgravity-associated changes in musculoskeletal anatomy. Just-in-time training, combined with remote experienced physician guidance, may provide a useful approach to complex medical tasks performed by nonexperienced personnel in a variety of remote settings, including current and future space programs.

Humans↗
PubMed1972

Correction for mechanical dead space in the calculation of physiological dead space.

When physiological dead space (Vd(p)) is calculated for a patient who has alveolar dead space, e.g., after pulmonary vascular occlusion, less than the full volume of attached mechanical dead space (Vd(m)) appears in the measured dead space (Vd(n)). Under these conditions the traditional subtraction of Vd(m) from Vd(n) leads to underestimation of Vd(p) and can give a falsely small ratio of Vd(p) to tidal volume (Vt) when, in fact, an abnormally large Vd(p)/Vt exists. To make the proper correction for Vd(m), two equations have been derived and validated with seven subjects having Vd(p)/Vt from 0.29 to 0.87, using Vd(m)'s from 120 to 322 ml. With only a small modification, these equations are suitable for routine clinical use and give Vd(p)/Vt within 0.02 of that by the validated equations (32 of 33 comparisons). The fraction of Vd(m) subtracted from Vd(n) is the square of the ratio of effective alveolar to total alveolar ventilation and is never > 1. This fraction is (Pa(CO2)/Pa(CO2))(2), where Pa(CO2) and Pa(CO2) are the mean partial pressures of expired alveolar and of arterial CO(2); in the other equation this fraction is [Pe(CO2)/Pa(CO2) (Vt - Vd(an) - Vd(m))](2) where Pe(CO2) is mixed expired Pco(2) and Vd(an) is anatomical dead space. The second equation requires an estimated Vd(an) and is applicable when Pa(CO2) is not measured or does not plateau (as in exercise).

Adult↗
PubMed2004

Bone markers, calcium metabolism, and calcium kinetics during extended-duration space flight on the mir space station.

UNLABELLED: Bone loss is a current limitation for long-term space exploration. Bone markers, calcitropic hormones, and calcium kinetics of crew members on space missions of 4-6 months were evaluated. Spaceflight-induced bone loss was associated with increased bone resorption and decreased calcium absorption. INTRODUCTION: Bone loss is a significant concern for the health of astronauts on long-duration missions. Defining the time course and mechanism of these changes will aid in developing means to counteract these losses during space flight and will have relevance for other clinical situations that impair weight-bearing activity. MATERIALS AND METHODS: We report here results from two studies conducted during the Shuttle-Mir Science Program. Study 1 was an evaluation of bone and calcium biochemical markers of 13 subjects before and after long-duration (4-6 months) space missions. In study 2, stable calcium isotopes were used to evaluate calcium metabolism in six subjects before, during, and after flight. Relationships between measures of bone turnover, biochemical markers, and calcium kinetics were examined. RESULTS: Pre- and postflight study results confirmed that, after landing, bone resorption was increased, as indicated by increases in urinary calcium (p < 0.05) and collagen cross-links (N-telopeptide, pyridinoline, and deoxypyridinoline were all increased >55% above preflight levels, p < 0.001). Parathyroid hormone and vitamin D metabolites were unchanged at landing. Biochemical markers of bone formation were unchanged at landing, but 2-3 weeks later, both bone-specific alkaline phosphatase and osteocalcin were significantly (p < 0.01) increased above preflight levels. In studies conducted during flight, bone resorption markers were also significantly higher than before flight. The calcium kinetic data also validated that bone resorption was increased during flight compared with preflight values (668 +/- 130 versus 427 +/- 153 mg/day; p < 0.001) and clearly documented that true intestinal calcium absorption was significantly lower during flight compared with preflight values (233 +/- 87 versus 460 +/- 47 mg/day; p < 0.01). Weightlessness had a detrimental effect on the balance in bone turnover such that the daily difference in calcium retention during flight compared with preflight values approached 300 mg/day (-234 +/- 102 versus 63 +/- 75 mg/day; p < 0.01). CONCLUSIONS: These bone marker and calcium kinetic studies indicated that the bone loss that occurs during space flight is a consequence of increased bone resorption and decreased intestinal calcium absorption.

Alkaline Phosphatase↗
PubMed2002

A 'membrane in syringe' technique that allows identification of the epidural space with saline while avoids injection of air into the epidural space.

BACKGROUND: The 'MEMBRANE IN SYRINGE' technique is, in principle, a modification of the loss of resistance technique for identifying the epidural space in epidural anaesthesia. A plastic membrane is placed halfway inside a syringe dividing the syringe into two compartments. The saline compartment encompasses the nozzle of the syringe (the distal compartment). The plunger is installed in the opposite half of the hallow cylinder. Air is trapped in the space between the membrane and the rubber plunger (air compartment). METHODS: There were altogether 20 epidural procedures to put to the test for this technique. The time spent in the undertaking of the procedure, the amount of normal saline injected, whether there was a feel of loss of resistance with wrinkling of the membrane in the syringe, inadvertent puncture of the dura, the level of epidural block and the insertion depth of epidural needle were recorded. RESULTS: The procedure took less than 4 minutes to complete in most of the cases. There was no inadvertent dural puncture. The average amount of normal saline injected was less than 1 ml. In 3 cases, despite the absence of the feel of loss of resistance the epidural space was still successfully identified by visible wrinkling of the membrane in the syringe. All catheters were inserted smoothly through the epidural needle and appropriate level of anesthesia was achieved in all the cases. CONCLUSIONS: The advantage of this technique is twofold. Firstly when the syringe is filled with both normal saline and air, it can prevent injection of the air into the epidural space during identification while at the same time it does not molest the feel of compressibility. Secondly, with the membrane separating the normal saline and air, correct placement of the needle tip can also be ascertained with loss of resistance while, as will be seen, the plastic membrane will wrinkle when saline is released into the epidural space.

Adolescent↗
PubMed2002

Space life sciences: biological research and space radiation. Proceedings of the F1.2, F1.3, F2.2 and F2.6 Symposia of COSPAR Scientific Commission F which were held during the Thirty-third COSPAR Scientific Assembly, Warsaw, Poland, July, 2000.

This issue of Advances in Space Research contains a large number of manuscripts in the discipline of Space Life Sciences including papers from the following sessions of the Warsaw COSPAR Assembly: Gravity-related research with animals--past, present, future; The nervous system: space flight environmental factors effects--present results and new perspectives; Investigating space radiation effects at particle accelerators--biology and physics experiments; Perspectives on radiation risks on long space missions: deterministic and stochastic effects.

Adaptation, Physiological↗
PubMed2003

The space elevator: a new tool for space studies.

The objective has been to develop a viable scenario for the construction, deployment and operation of a space elevator using current or near future technology. This effort has been primarily a paper study with several experimental tests of specific systems. Computer simulations, engineering designs, literature studies and inclusion of existing programs have been utilized to produce a design for the first space elevator. The results from this effort illustrate a viable design using current and near-term technology for the construction of the first space elevator. The timeline for possible construction is within the coming decades and estimated costs are less than $10 B. The initial elevator would have a 5 ton/day capacity and operating costs near $100/lb for payloads going to any Earth orbit or traveling to the Moon, Mars, Venus or the asteroids. An operational space elevator would allow for larger and much longer-term biological space studies at selectable gravity levels. The high-capacity and low operational cost of this system would also allow for inexpensive searches for life throughout our solar system and the first tests of environmental engineering. This work is supported by a grant from the NASA Institute for Advanced Concepts (NIAC).

Acceleration↗
PubMed1985

Compatible atmospheres for a space suit, space station, and shuttle based on physiological principles.

Fundamental physiological principles have been invoked to design compatible environments for a space suit, space station, and the space craft used to transport the astronauts from Earth. These principles include the long-term memory of tissues for a bubble-provoking decompression, the intermittent nature of blood flow in the tight connective tissues(s) responsible for the bends whose incidence in aviators has been shown to be related to bubble volume by the Weibull distribution. In the overall design an astronaut breathing a mixture of 30% O2 in N2 for 4-5 h in a space craft at 11.9 psia can transfer to a space station filled with the same mix at 8.7 psia and, after a further 4-5 h, go EVA at any time without any oxygen prebreathing at any stage. The probable incidence of decompression sickness has been estimated as less than 0.5% using the present suit operating at 4.3 psia but the risk could be reduced to zero if the suit pressure were increased to 6.5 psia.

Aerospace Medicine↗
PubMed1984

1984 Bauer lecture. The space station--mankind's permanent presence in space.

The Space Station is a means of furthering mankind's investigation of space and studying his responses to long-duration residency in the environs of space and weightlessness. The historical development of the NASA Space Station is reviewed from President Reagan's announcement of this as a new national commitment. The very tenuous history of the Space Station and it's course through technical/political reviews is the text of this Lecture.

History, 20th Century↗
PubMed1993

[Space medicine and life sciences in space].

The examination of pathophysiological disturbances and the process of adaptation in man during space flight is not for optimizing of the biological systems during the training of cosmonauts and astronauts for their stay in space only. These results are also important for medical application on patients. In real microgravity disturbances of motor performances, coordination of movements, accuracy of movements, muscle function as well as structural changes in muscles is found in real microgravity. Spinal reflexes and the control of vestibular system on eye movements are also afflicted. Higher brain functions, especially associative reactions, critical abilities, memory, as well as high brain function like space orientation, body scheme control, geometric and arithmetic analysis and its reproduction, at last speech production, writing and reading are decreased. Vegetative disorders, bone decalcification, primary muscular atrophy occur as well as changes in sleep--wake regulation and diminishing of vigility. Disturbances of blood and body fluid circulation and biologic radiation damage are further effects of man space flight. Several problems of space adaptation can be studied with the methods of the simulated microgravity using the dry water immersion, examination and the bed rest model in special laboratories. The routine medicine is learning from the scientific results of the research in real and simulated microgravity.

Adaptation, Physiological↗
PubMedDate not supplied

[Perception in space. Visual aspects of space perception].

The ability to apprehend and appropriate space is based on a series of perceptive and cognitive processes, in which vision plays a leading part. Preliminary, elementary operations first allow a subject to achieve the elaboration of a visually structured percept. Both experiences on healthy subjects, and pathological data have provided evidence for a right hemisphere superiority in tasks such as localization of stimuli and discrimination of line orientation. Depth perception rests both on indirect cues (e.g. relative size of objects, perspective and movement parallax) and on two types of specific stereoscopic processes: the so-called local and global stereoscopies, which depend respectively on the integrity of visual cortices and of inferior occipito-temporal areas (with a right-hemisphere dominance). Movement perception is integrated at the level of area V5, at the lateral occipito-temporal junction on both sides. The accuracy of reaching movements and displacements within space require the elaboration of a system of coordinates in which the position of the egocentric reference will then be taken into account. This is achieved by successive coding of eye and head position relative to the body axis, and by building the body reference from proprioceptive and vestibular afferences to the parietal cortex. Finally, attention must be both diffusely scattered throughout the whole space and voluntarily allocated as needed on a given object. Simultanagnosia and unilateral spatial neglect (USN) are examples of disruption of these attentional processes. Simultanagnosia illustrates the loss of the ability to shift attention from one point to another, but both shrinking of the attentional field and poorly sustained fixation are also possible mechanisms of this syndrome. USN probably has several components. Unilateral brain damage causes interhemispheric attentional imbalance that explains the attentional preference for the ipsilesional side of space. The predominance of neglect following right-sided lesions might be the consequence of hemispheric specialization regarding directed attention, with the left hemisphere preferentially allocating attention to objects and the right one being able to attend to the whole space. The anatomical basis of such a functional differentiation is still unclear.

Animals↗
PubMed2002

Reducing CAS-SDCI space. Using selected spaces in configuration interaction calculations in an efficient way.

A new method is presented, which allows an important reduction of the size of some Configuration Interaction (CI) matrices. Starting from a Complete Active Space (CAS), the numerous configurations that have a small weight in the CAS wave function are eliminated. When excited configurations (e.g., singly and doubly excited) are added to the reference space, the resulting MR-SDCI space is reduced in the same proportion as compared with the full CAS-SDCI. A set of active orbitals is chosen, but some selection of the most relevant excitations is performed because not all the possible excitations act as SDCI generators. Thanks to a new addressing technique, the computational time is drastically reduced, because the new addressing of the selected active space is as efficient as the addressing of the CAS. The presentation of the method is followed by two test calculations on the N(2) and HCCH molecules. For the N(2) the FCI results are taken as a benchmark reference. The outer valence ionization potentials of HCCH are compared to the experimental values. Both examples allow to test the accuracy of the MR-SDCI compared to that of the corresponding CAS-SDCI, despite the noticeable reduction of the CI space. The algorithm is suitable for the dressing techniques that allow for the correction of the size-extensivity error. The corrected results are also shown and discussed.

Journal Article↗