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At least 685 records · Page 38Linked to original sources
PubMed2004

Reproducibility of the respiratory dead space measurements in mechanically ventilated children using the CO2SMO monitor.

OBJECTIVES: To assess the reproducibility of respiratory dead space measurements in ventilated children. DESIGN: Prospective study. SETTING: University pediatric intensive care unit. PATIENTS: Thirty-two mechanically ventilated children (0.13-15.4 years) who were clinically stable. METHODS: The single-breath CO(2) test (SBT-CO(2)) was recorded using the CO(2)SMO Plus from the mean of 30 ventilatory cycles during 1 h (at T0, T15, T30, T45, and T60). Airway dead space was determined automatically (Novametrix Medical Systems, USA), and manually by Bohr- Enghoff equations using data obtained by SBT-CO(2). At the end of the study period, arterial blood gas was sampled in order to calculate alveolar and physiologic dead space. Intrasubject reproducibility of measurements was evaluated by the intraclass correlation coefficient. Two-way analysis of variance was used to evaluate the relationships between time and measurements. The two methods for calculating airway dead space were compared by using two-tailed Student's t-test and Bland-Altman analysis. RESULTS: Airway dead space measurement had a good reproducibility during the 1-h period, whatever the method used (intraclass correlation coefficient: 0.84 to 0.87). No significant difference was observed with time. Airway dead space values from the SBT-CO(2) method were smaller than those from Bohr-Enghoff equations. Physiologic dead space values from the SBT-CO2 method were similar to those from Bohr-Enghoff equations. CONCLUSION: The measurement of airway dead space by the CO(2)SMO Plus was reproducible over a 1-h period in children requiring mechanical ventilation, provided ventilatory parameters were constant throughout the study. SBT-CO(2) analysis may provide a bedside non-invasive monitoring of volumetric capnography.

Adolescent↗
PubMed2006

Gravitational biology within the German Space Program: goals, achievements, and perspectives.

Gravity plays an important role for the evolution, orientation and development of organisms. Most of us, however, tend to overlook its importance because--due to its constant presence from the beginning of evolution some 4 billion years ago--this environmental parameter is almost hardwired into our interpretation of reality. This negligence of gravity is the more surprising as we all have our strong fights with this factor, especially during the very early and again during the late phases of our lives. On the other hand, scientists have been fascinated to observe the effects of gravity especially on plants and microorganisms for more than a hundred years, since Darwin and Sachs demonstrated the role of the root cap for downward growing plants. Different experimental approaches are nowadays available in order to change the influence of gravity and to study the corresponding influences on the physiology of biological systems. With the advent of spaceflight, a long-term nearly nullification of gravity is possible. Utilisation of this so-called "microgravity" condition for research in life sciences thus became an important asset in the space programs of various space agencies around the world. The German Space Life Sciences Program is managed--like all other space programs and activities in Germany--by the German Aerospace Center (DLR) in its role as space agency for Germany. Within the current space program, approved by the German government in May 2001, the overall goal for its life sciences part was defined as to gain scientific knowledge and to disclose new application potential by research under space conditions, especially by utilising the microgravity environment of the International Space Station. Three main scientific fields have been identified in collaboration with the scientific community: integrative human physiology, biotechnological applications of the microgravity environment, and fundamental biology of gravity and radiation responses (i.e., gravitational and radiation biology). In the present contribution, specific goals as well as achievements and perspectives of research in gravitational biology are given. In addition, some information is provided on spaceflight opportunities available.

Animals↗
PubMed1996

Evidence for rapid fluid flow from the subarachnoid space into the spinal cord central canal in the rat.

Horseradish peroxidase (HRP) was used as a CSF tracer in Sprague-Dawley rats. One group of rats received an injection of HRP in the cisterna magna and a second group was injected in the thoracic spinal subarachnoid space. The animals were sacrificed 0, 10 or 30 min after HRP injection by rapid perfusion with paraformaldehyde and glutaraldehyde. In both groups, there was rapid HRP labeling of brain and spinal cord perivascular spaces. HRP was present in the central canal in a pattern that was not consistent with flow from the fourth ventricle: in both groups there were segments of unlabeled central canal between the fourth ventricle and central canal segments containing HRP. HRP-labeled perivascular spaces were seen in the central gray matter adjacent to the central canal. There was a distinctive pattern of interstitial HRP between perivascular spaces and the central canal. The results suggest that there is a normal flow of fluid from the subarachnoid space, into the perivascular spaces, across the interstitial space and into the central canal. The function of this flow may be to clear metabolites from the interstitial space. The existence of such a flow would add considerable support to the theory that non-communicating syringomyelia develops in segments of central canal isolated by occlusion or stenosis at each end.

Animals↗
PubMed1979

Characteristics of the washout dead space.

The dead space volume was reproducibly measured in normal and diseased lungs by analysis of an inert gas washout. This washout dead space was appreciably larger than that measured by the Fowler technique. In the patients, the washout dead space (VD(0)) formed 72% of the physiological dead space volume, while the Fowler (VD(F)) method accounted for only 50%. The VD(O) increased significantly with age in males, but not in females. VD(F) was not well related to age in this population. VD(O) and VD(F) did not relate to lung volume in these subjects. Although that portion of the dead space delivered in Phase I was significantly greater in males than in females, it was not responsible for the difference in dead space measured by the two techniques. This volume difference was found in that portion delivered late in the breath (Phase III). The nature of this volume is speculative, but may involve a parallel dead space that is measured in addition to the series dead space.

Adult↗
PubMed1995

The impact of culture on human and space development--new millennial challenge.

The Space Age is causing new applications to the concept of culture, a human coping tool. The exploration and exploitation of outer space resources are altering human culture both on Earth and in orbit. For the first time in history, our species need not merely react and adapt to environment, but plan for a space culture appropriate for extraterrestrial migration. The impact of culture can be analyzed in terms of how space developments alter human perceptions and behavior on this planet; the emergence of a new culture to suit the orbital environment; the organizations that build spacecraft and deploy people aloft; and the technological systems created for spacefaring. This article presents a paradigm for analyzing some of the non-technical human factors involved in space undertakings. It also offers a method for classifying a culture according to ten categories which may be applied both to a macroculture, such as a lunar base; or a microculture, such as a space agency or crew. Human enterprise in space is viewed as both altering the species, and providing a challenge for expanded behavioral and biological scientific research on living and working in space.

Adaptation, Psychological↗
PubMedDate not supplied

Canada's role on space station.

The paper addresses the evolution of the Canadian Space Station Program between 1981 and 2003. Discussions with potential international partners, aimed at jointly developing the current International Space Station program, were initiated by NASA in 1982. Canada chose, through the further development of the technologies of Canadarm on the space shuttle, to provide and operate an advanced and comprehensive external robotics system for space station, and to use the space station for scientific and commercial purposes. The program was to become a corner-stone of the new Canadian Space Agency. The development phase of the Canadian Space Station Program has been completed and two of the three major elements are currently operational in space.

Canada↗
PubMed2006

Space motion sickness: incidence, etiology, and countermeasures.

Space motion sickness is experienced by 60% to 80% of space travelers during their first 2 to 3 days in microgravity and by a similar proportion during their first few days after return to Earth. Space motion sickness symptoms are similar to those in other forms of motion sickness; they include: pallor, increased body warmth, cold sweating, malaise, loss of appetite, nausea, fatigue, vomiting, and anorexia. These are important because they may affect the operational performance of astronauts. Two hypotheses have been proposed to explain space motion sickness: the fluid shift hypothesis and the sensory conflict hypothesis. The fluid shift hypothesis suggests that space motion sickness results from the cranial shifting of body fluids resulting from the loss of hydrostatic pressure gradients in the lower body when entering microgravity. The cranial fluid shifts lead to visible puffiness in the face, and are thought to increase the intracranial pressure, the cerebrospinal-fluid pressure or the inner ear fluid pressures, altering the response properties of the vestibular receptors and inducing space motion sickness. The sensory conflict hypothesis suggests that loss of tilt-related otolith signals upon entry into microgravity causes a conflict between actual and anticipated signals from sense organs subserving spatial orientation. Such sensory conflicts are thought to induce motion sickness in other environments. Space motion sickness is usually treated using pharmaceuticals, most of which have undesirable side effects. Further studies elucidating the underlying mechanism for space motion sickness may be required for developing new treatments.

Antiemetics↗
PubMedDate not supplied

Hydrodynamics of the spinal epidural space in pigs determined by constant-flow methods.

BACKGROUND AND OBJECTIVES: Impressive quantities of fluid can be infused into the epidural space of the spine without causing dramatic or sustained increases in pressure. The epidural space is considered "leaky," but questions remain about how fluid leaves the epidural space. We used constant-flow infusions of saline to gain insight into the hydrodynamics involved. METHODS: We infused saline at a constant rate into the lumbar epidural space of 6 anesthetized pigs while measuring pressure at the adjacent interspace. Three or 4 infusions were performed at different flow rates in each animal. RESULTS: Epidural space pressure in the absence of flow was consistently 2 to 3 mm Hg above right atrial pressure. During each infusion, pressure increased slowly to a steady plateau value between 15 and 70 mm Hg. When flow was stopped, pressure declined exponentially to the starting pressure. The presence of a plateau indicates that fluid leaving the epidural space ends up in a structure with high capacitance. Plateau pressures were linearly related to flow rate in each animal, indicating constant resistance to outflow. The flow-pressure relation showed neither a critical opening pressure nor moderating pressures with increased flow. CONCLUSIONS: Fluid leaves the porcine spinal epidural space through channels that are open at baseline rather than being recruited as epidural pressure increases. This behavior is inconsistent with the view that the epidural space behaves like a Starling resistor.

Animals↗
PubMed2003

Split-brain patients neglect left personal space during right-handed gestures.

Since some patients with right hemisphere damage or with spontaneous callosal disconnection neglect the left half of space, it has been suggested that the left cerebral hemisphere predominantly attends to the right half of space. However, clinical investigations of patients having undergone surgical callosal section have not shown neglect when the hemispheres are tested separately. These observations question the validity of theoretical models that propose a left hemispheric specialisation for attending to the right half of space. The present study aims to investigate neglect and the use of space by either hand in gestural demonstrations in three split-brain patients as compared to five patients with partial callosotomy and 11 healthy subjects. Subjects were asked to demonstrate with precise gestures and without speaking the content of animated scenes with two moving objects. The results show that in the absence of primary perceptual or representational neglect, split-brain patients neglect left personal space in right-handed gestural demonstrations. Since this neglect of left personal space cannot be explained by directional or spatial akinesia, it is suggested that it originates at the conceptual level, where the spatial coordinates for right-hand gestures are planned. The present findings are at odds with the position that the separate left hemisphere possesses adequate mechanisms for acting in both halves of space and neglect results from right hemisphere suppression of this potential. Rather, the results provide support for theoretical models that consider the left hemisphere as specialised for processing the right half of space during the execution of descriptive gestures.

Adult↗
PubMed2000

Attentional grasp in far extrapersonal space after thalamic infarction.

Studies of animals and humans with focal brain damage suggest that attention in near and far extrapersonal space may be mediated by anatomically separate systems. Thalamic lesions have been associated with spatial neglect, but whether asymmetric attention specific to near or far space occur after thalamic damage has not been explored. It is also unclear if thalamic injury can induce contralesional defective response inhibition. We tested a woman with a left thalamic infarction who reported that, when driving, she had a tendency to veer towards people or objects on the right side of the road. Our patient and four controls performed a line bisection task with a laser pointer in near and far extrapersonal space. The experimenter marked each bisection either from the right of the presented line (right-distractor, RD) or the left (left-distractor, LD). RD and LD trials were pseudo-randomized. Our patient performed similarly to controls (mean -0.7 mm, controls -0.6 mm) on the line bisection task in near space. In far space she erred significantly rightward compared to her performance in near space (p<0.001). Controls performed similarly in near and far space. The experimenter position did not affect our patient's performance on near line bisections, nor did controls demonstrate a distractor effect for the near condition. In the far condition, however, our patient showed a significant distractor effect (LD -3.3 mm, RD 35.3 mm, p<0.001). Controls also demonstrated a distractor effect in the far condition (LD -6.4 mm, RD 0.7 mm, p<0.01), though of much smaller magnitude. Our results suggest that frontal-thalamic systems regulating visual attention may be disrupted by thalamic infarction. Such damage may produce an attentional grasp specific to far extrapersonal space.

Attention↗
PubMed2003

Farming in space: environmental and biophysical concerns.

The colonization of space will depend on our ability to routinely provide for the metabolic needs (oxygen, water, and food) of a crew with minimal re-supply from Earth. On Earth, these functions are facilitated by the cultivation of plant crops, thus it is important to develop plant-based food production systems to sustain the presence of mankind in space. Farming practices on earth have evolved for thousands of years to meet both the demands of an ever-increasing population and the availability of scarce resources, and now these practices must adapt to accommodate the effects of global warming. Similar challenges are expected when earth-based agricultural practices are adapted for space-based agriculture. A key variable in space is gravity; planets (e.g. Mars, 1/3 g) and moons (e.g. Earth's moon, 1/6 g) differ from spacecraft orbiting the Earth (e.g. Space stations) or orbital transfer vehicles that are subject to microgravity. The movement of heat, water vapor, CO2 and O2 between plant surfaces and their environment is also affected by gravity. In microgravity, these processes may also be affected by reduced mass transport and thicker boundary layers around plant organs caused by the absence of buoyancy dependent convective transport. Future space farmers will have to adapt their practices to accommodate microgravity, high and low extremes in ambient temperatures, reduced atmospheric pressures, atmospheres containing high volatile organic carbon contents, and elevated to super-elevated CO2 concentrations. Farming in space must also be carried out within power-, volume-, and mass-limited life support systems and must share resources with manned crews. Improved lighting and sensor technologies will have to be developed and tested for use in space. These developments should also help make crop production in terrestrial controlled environments (plant growth chambers and greenhouses) more efficient and, therefore, make these alternative agricultural systems more economically feasible food production systems.

Agriculture↗
PubMed2003

The response of endocrine system to stress loads during space flight in human subject.

The responses of endocrine system to the exposure to stress-work load and hormonal changes during oral glucose tolerance tests were studied in the Slovak astronaut before (three weeks before flight), during (on the 4th and the 6th days of space flight), and after space flight (1-3 days and 15-17 days after space flight) on board of space station MIR. Blood samples during the tests were collected via cannula inserted into cubital vein, centrifuged in the special appliance Plasma-03, frozen in Kryogem-03, and at the end of the 8-day space flight transferred to Earth in special container for hormonal analysis. Preflight workload produced an increase of plasma norepinephrine and a moderate elevation of epinephrine levels. Plasma levels of insulin, growth hormone, prolactin and cortisol were not markedly changed immediately or 10 min after the end of work load. The higher increases of plasma growth hormone, prolactin and catecholamine levels were noted after workload during space flight as compared to preflight response. The higher plasma glucose and insulin levels were noted during the oral glucose tolerance test in space flight and also in the post flight period. Plasma epinephrine levels were slightly decreasing during glucose tolerance test; however, plasma norepinephrine levels were not changed. The similar patterns of catecholamine levels during glucose tolerance test were found when compared the preflight, in-flight and post flight values. These data demonstrate the changes of the dynamic responses of endocrine system to stress-work and metabolic loads during space flight in human subject.

Adaptation, Physiological↗
PubMed2003

Aquatic modules for bioregenerative life support systems: developmental aspects based on the space flight results of the C.E.B.A.S. MIN-MODULE.

The Closed Equilibrated Biological Aquatic System (C.E.B.A.S.) is an artificial aquatic ecosystem which contains teleost fishes, water snails, ammonia oxidizing bacteria and edible non-gravitropic water plants. It serves as a model for aquatic food production modules which are not seriously affected by microgravity and other space conditions. Its space flight version, the so-called C.E.B.A.S. MINI-MODULE was already successfully tested in the STS-89 and STS-90 (NEUROLAB) missions. It will be flown a third time in space with the STS-107 mission in January 2003. All results obtained so far in space indicate that the basic concept of the system is more than suitable to drive forward its development. The C.E.B.A.S. MINI-MODULE is located within a middeck locker with limited space for additional components. These technical limitations allow only some modifications which lead to a maximum experiment time span of 120 days which is not long enough for scientifically essential multi-generation-experiments. The first necessary step is the development of "harvesting devices" for the different organisms. In the limited space of the plant bioreactor a high biomass production leads to self-shadowing effects which results in an uncontrolled degradation and increased oxygen consumption by microorganisms which will endanger the fishes and snails. It was shown already that the latter reproduce excellently in space and that the reproductive functions of the fish species are not affected. Although the parent-offspring-cannibalism of the ovoviviparous fish species (Xiphophorus helleri) serves as a regulating factor in population dynamics an uncontrolled snail reproduction will also induce an increased oxygen consumption per se and a high ammonia concentration in the water. If harvesting locks can be handled by astronauts in, e. g., 4-week intervals their construction is not very difficult and basic technical solutions are already developed. The second problem is the feeding of the animals. Although C.E.B.A.S.-based aquaculture modules are designed to be closed food loop systems (edible herbivorous fish species and edible water plants) which are already verified on Earth this will not be possible in space without devices in which the animals are fed from a food storage. This has to be done at least once daily which would waste too much crew time when done by astronauts. So, the development of a reliable automated food dispenser has highest priority. Also in this case basic technical solutions are already elaborated. The paper gives a comprehensive overview of the proposed further C.E.B.A.S.-based development of longer-term duration aquatic food production modules.

Animals↗
PubMed2001

Space environment, electromagnetic fields, and circadian rhythm.

Human space activity began in 1961. About 400 persons have gone to space since then, and about 70 of them have stayed more than 1 month. Circadian rhythm and sleep in space have been investigated several times, though the effect of longer stays in space has not been adequately clarified. Electromagnetic fields are different in the space environment, especially in deeper space missions, such as the Moon or Mars, but their effects on human health have rarely been studied. In this article, we summarize the current status of the International Space Station project, study circadian rhythm and sleep in space, investigate electromagnetic fields, and state the necessity for investigating this research field.

Circadian Rhythm↗
PubMed1997

Respiratory oxygen cost for dead space challenge is characteristically increased during exercise in patients with chronic heart failure: does it further decrease exercise capacity?

BACKGROUND: Although the work of the respiratory muscles is markedly increased during exercise in patients with chronic heart failure, the role of this abnormality in exercise intolerance is still controversial. This issue may be clarified directly by dead space challenge, as this technique increases minute ventilation. Therefore, in this study, the effects of an external dead space on exercise ventilation, gas exchange data, and exercise capacity in patients with chronic heart failure were examined. METHODS AND RESULTS: Dead space challenge was performed by adding an external dead space to the airway in 20 patients with chronic heart failure and 10 normal subjects. Two hours after completion of the control maximal bicycle exercise, the second exercise was performed under application of an external dead space equivalent to 10% of peak tidal volume. Respiratory gas exchange data were collected during exercise. Aerobic exercise capacity was assessed from the exercise time and the time to anaerobic threshold. The sensation of exertional dyspnea was assessed using Borg's rating scale. As compared with data during the control exercise, minute ventilation was increased by approximately 25% with the external dead space throughout exercise in both groups. A parallel 20% increase in systemic oxygen uptake was observed in the heart failure group, likely reflecting an increase in respiratory muscle work. This response was not observed in the normal group. Despite an additional increase in respiratory muscle work, neither aerobic exercise capacity nor exertional dyspnea was exacerbated in the heart failure group by the external dead space. CONCLUSIONS: Dead space challenge appears to be a unique technique that characteristically increases the work of respiratory muscles during exercise in patients with chronic heart failure. By use of this technique, it was demonstrated that an increase in respiratory muscle work is not important in reducing exercise capacity of patients with chronic heart failure.

Adult↗
PubMed1998

Medical baseline data collection on bone and muscle change with space flight.

It has been documented that astronauts suffer from a progressive and continuous negative calcium balance in space flight. The National Space Development Agency of Japan (NASDA) discussed the experimental protocols with the National Aeronautics and Space Agency's (NASA's) Johnson Space Center (JSC) and has started a medical baseline collection on bone and calcium metabolism, and muscle changes with space flight. The subjects were two astronauts, a 42-year-old female and a 32-year-old male, who experienced real space flights. Fractional excretion of calcium (FECa) increased in both subjects just after the space flight. There was a negative calcium balance with urinary calcium leak even after a short flight. We also noticed a decrease (-3.0%) of bone mineral density (BMD) of the lumbar spine (L2-4), a weight bearing bone. These bone changes may be due to a negative calcium balance. However, the BMD of the skull, a nonweight bearing bone, increased after the flight. This indicates that the effect of weightlessness on bone is different in respective bones, depending on the weight loading. Our data of the bone metabolic marker clearly indicate that bone resorption is stimulated, shown by an elevation of urinary pyridinolinks and plasma tartrate-resistant acid phosphate (TRACP) activity. Bone specific alkaline phosphatase, a bone formation marker, was elevated in both subjects, but not intact osteocalcin. Whether this pathophysiological phenomenon is due to an accelerated bone resorption or suppressed bone formation is still obscure. In addition, the physiological cross-sectional area (PCSA) of muscle in the legs greatly decreased (from - 10% to -15%) after the flight, and it took over a month to be recovered in both subjects. However, the muscle volume loss in the legs seemed to be reversible. To examine bone and muscle metabolism with space flight, further investigations and international standardization of experimental protocols are necessary.

Adult↗
PubMedDate not supplied

Light-dependent hydration of the space surrounding photoreceptors in the cat retina.

We have studied the effect of retinal illumination on the concentration of the extracellular space marker tetramethylammonium (TMA+) in the dark-adapted cat retina using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Retinal illumination produced a slow decrease in [TMA+]o, which was maximal in amplitude in the most distal portion of the space surrounding photoreceptors, the subretinal space. The light-evoked decrease in [TMA+]o was considerably slower and of a different overall time course than the light-evoked decrease in [K+]o, also recorded in the subretinal space. [TMA+]o decreased to a peak at 38 s after the onset of illumination, then slowly recovered towards the baseline, and transiently increased following the offset of illumination. It resembled the light-evoked [TMA+]o decreases previously recorded in the in vitro preparations of frog (Huang & Karwoski, 1990, 1992) and chick (Li et al., 1992, 1994) but was considerably larger in amplitude, 22% compared with 7%. As in frog, where it was first recorded, the light-evoked [TMA+]o decrease is considered to originate from a light-evoked increase in the volume of the subretinal space (or subretinal hydration). A mathematical model accounting for [TMA+]o diffusion predicted that the volume increase underlying the response was 63% on average and could be as large as 95% and last for minutes. The estimated volume increase was then used to examine its effect on K+ concentration in the subretinal space. We conclude that a light-dependent hydration of the subretinal space represents a significant physiological event in the intact cat eye, which should affect the organization of the interphotoreceptor matrix, and the concentrations of all ions and metabolites located in the subretinal space.

Animals↗
PubMed2004

Length perception and production of normal subjects in proximal versus distal peripersonal space.

We investigated whether the perception or production of a given line length in normal subjects varies according to where in peripersonal space the line is perceived or produced. We also investigated the influence of the direction of movement used to make the line. In Experiment 1, blindfolded normal subjects were asked to estimate distances while the examiner moved the subject's hand in proximal (medial) or distal (lateral) space, moving centripetally or centrifugally. The subjects showed a spatial effect, perceiving the same length as shorter in proximal space than distal space. This result could be related to either a proximal spatial attentional bias or an anisometric representation of spatial distances. In Experiment 2, we attempted to dissociate these hypotheses by studying blindfolded normal subjects, who were requested to produce horizontal lines of a given length (100 or 200 mm) in proximal versus distal peripersonal space using centripetal or centrifugal movements. Centrifugal movements in proximal space were the longest; centrifugal movements in distal space were the shortest: in between were the proximal centripetal and distal centripetal movements which did not differ from each other. These results suggest that in peripersonal space the perception of length in normal subjects is most consistent with anisometric mental representation where the size of mental representations of length units decreases as a function of the distance from the subject's midsagittal plane. Length production, however, may depend on an interaction of the anisometric mental representation and the premotor/intentional factors.

Adult↗