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At least 19 recordsLinked to original sources

PubMed2003

[Weightlessness or weightlessness simulation and vascular remodeling].

Weightlessness is inavoidable during spaceflight. It brings profound physiological effects on human body. Vascular remodeling is one of the important changes of cardiovascular system caused by weightlessness or simulated weightlessness. The paper summarized the studies on the effects of weightlessness or weightlessness simulation on vascular remodeling in recent years. The emergence and development of the concept of vascular remodeling were briefly reviewed. The advances of study on vascular remodeling in recent years was briefly discussed with the points focused on the effects of weightlessness or weightlessness simulation on cardiovascular remodeling and its mechanism. It is proposed that cardiovascular remodeling might be important in studying the causes of orthostatic intolerance after spaceflight.

Adaptation, Physiological↗

PubMed2002

[Changes of leg compliance during weightlessness or simulated weightlessness].

Weightlessness or simulated weightlessness causes increase of leg compliance. It leads to more blood pooling in the legs and less blood returning to the heart during orthostatic test, which may partly explain the occurrence of orthostatic intolerance induced by weightlessness or simulated weightlessness. This article is a review covering published materials about the methods of measurement, mechanisms and countermeasures of the increase of leg compliance during weightlessness or simulated weightlessness.

Compliance↗

PubMed1988

Correlation of macro and micro cardiovascular function during weightlessness and simulated weightlessness.

The investigation of cardiovascular function necessarily involves a consideration of the exchange of substances at the capillary. If cardiovascular function is compromised or in any way altered during exposure to zero gravity in space, then it stands to reason that microvascular function is also modified. We have shown that an increase in cardiac output similar to that reported during simulated weightlessness is associated with a doubling of the number of post-capillary venules and a reduction in the number of arterioles by 35%. If the weightlessness of space travel produces similar changes in cardiopulmonary volume and cardiac output, a reasonable expectation is that astronauts will undergo venous neovascularization. We have developed an animal model in which to correlate microvascular and systemic cardiovascular function. The microcirculatory preparation consists of a lightweight, thermo-neutral chamber implanted around intact skeletal muscle on the back of a rat. Using this technique, the performed microvasculature of the cutaneous maximus muscle may be observed in the conscious, unanesthetized animal. Microcirculatory variables which may be obtained include venular and arteriolar numbers, lengths and diameters, single vessel flow velocities, vasomotion, capillary hematocrit anastomoses and orders of branching. Systemic hemodynamic monitoring of cardiac output by electromagnetic flowmetry, and arterial and venous pressures allows correlation of macro- and microcirculatory changes at the same time, in the same animal. Observed and calculated hemodynamic variables also include pulse pressure, heart rate, stroke volume, total peripheral resistance, aortic compliance, minute work, peak aortic flow velocity and systolic time interval. In this manner, an integrated assessment of total cardiovascular function may be obtained in the same animal without the complicating influence of anesthetics.

Animals↗

PubMed2000

[Changes of learning and memory function under weightlessness or simulated weightlessness].

The work efficiency of astronauts has an intimate connection with the brain function state during space flight. The research results of the learning and memory mechanism of the brain in recent years were introduced. The effects of weightlessness or simulated weightlessness on brain's learning, memory, focused attention and many other higher neural activities and on the relative neural transmitters were summarized. Several research aspects were put forward in the future.

Aerospace Medicine↗

PubMed2000

[Changes of cerebral circulation during weightlessness or simulated weightlessness].

The results about studies on changes of the cerebral circulation during weightlessness/simulated weightlessness were reviewed in this paper. The possible influencing mechanism of weightlessness on cerebral circulation and its physiological significance were summarized. It could be concluded that the changes of cerebral circulation were the results of self-regulation of the brain to maintain its normal function, and it might play an important role in the genesis of postflight orthostatic intolerance.

Aerospace Medicine↗

PubMed1999

[The effect of weightlessness and simulated weightlessness on the expression of genes].

The research results of the relationship between gene expression and weightlessness or simulated weightlessness were studied. The influence of weight on the expression of genes in central nervous system were summarized in three aspects. It can be concluded that the expression of genes in central nervous system were precisely regulated by weight. It was important to study the effects of microweight on central nervous system in the molecular level.

Aerospace Medicine↗

PubMed1989

Acute hemodynamic responses to weightlessness in humans.

As NASA designs space flights requiring prolonged periods of weightlessness for a broader segment of the population, it will be important to know the acute and sustained effects of weightlessness on the cardiovascular system since this information will contribute to understanding of the clinical pharmacology of drugs administered in space. Due to operational constraints on space flights, earliest effects of weightlessness have not been documented. We examined hemodynamic responses of humans to transitions from acceleration to weightlessness during parabolic flight on NASA's KC-135 aircraft. Impedance cardiography data were collected over four sets of 8-10 parabolas, with a brief rest period between sets. Each parabola included a period of 1.8 Gz, then approximately 20 seconds of weightlessness, and finally a period of 1.6 Gz; the cycle repeated almost immediately for the remainder of the set. Subjects were semi-supine (Shuttle launch posture) for the first set, then randomly supine, sitting and standing for each subsequent set. Transition to weightlessness while standing produced decreased heart rate, increased thoracic fluid content, and increased stroke index. Surprisingly, the onset of weightlessness in the semi-supine posture produced little evidence of a headward fluid shift. Heart rate, stroke index, and cardiac index are virtually unchanged after 20 seconds of weightlessness, and thoracic fluid content is slightly decreased. Semi-supine responses run counter to Shuttle crewmember reports of noticeable fluid shift after minutes to hours in orbit. Apparently, the headward fluid shift commences in the semi-supine posture before launch. is augmented by launch acceleration, but briefly interrupted immediately in orbit, then resumes and is completed over the next hours.

Adult↗

PubMed1996

An optimized index of human cardiovascular adaptation to simulated weightlessness.

Prolonged exposure to weightlessness is known to produce a variety of cardiovascular changes, some of which may influence the astronaut's performance during a mission. In order to find a reliable indicator of cardiovascular adaptation to weightlessness, we analyzed data from nine male subjects after a 24-hour period of normal activity and after a period of simulated weightlessness produced by two hours in a launch position followed by 20 hours of 6 degrees head-down tilt plus pharmacologically induced diuresis (furosemide). Heart rate, arterial pressure, thoracic fluid index, and radial flow were analyzed. Autoregressive spectral estimation and decomposition were used to obtain the spectral components of each variable from the subjects in the supine position during pre- and post-simulated weightlessness. We found a significant decrease in heart rate power and an increase in thoracic fluid index power in the high frequency region (0.2-0.45 Hz) and significant increases in radial flow and arterial pressure powers in the low frequency region (<0.2 Hz) in response to simulated weightlessness. However, due to the variability among subjects, any single variable appeared limited as a dependable index of cardiovascular adaptation to weightlessness. The backward elimination algorithm was then used to select the best discriminatory features from these spectral components. Fisher's linear discriminant and Bayes' quadratic discriminant were used to combine the selected features to obtain an optimal index of adaptation to simulated weightlessness. Results showed that both techniques provided improved discriminant performance over any single variable and thus have the potential for use as an index to track adaptation and prescribe countermeasures to the effects of weightlessness.

Adaptation, Physiological↗

PubMed1994

Small animal model of weightlessness for pharmacokinetic evaluation.

As the United States seeks a greater presence in space, physiologic changes associated with space flight become of greater concern. Exposure to a weightless environment has been shown to have numerous effects on body composition and organ function. Alterations include decreases in muscle and liver mass, changes in bone structure and integrity, and fluid shifts markedly affecting cardiovascular functioning. Furthermore, metabolic activity of the liver has been found to be altered in rats after extended periods of weightlessness. As the length of space travel increases, the probability for the need to administer pharmacologic agents to crew members during space flight for prophylaxis or treatment becomes greater. Thus, because of the observed physiologic and metabolic changes associated with weightlessness, it is reasonable to assume that the pharmacokinetics and pharmacodynamics of xenobiotics administered during space flight may be different that those found in 1g environment. To address these possible changes, the development of a model of weightlessness to investigate possible alterations in drug pharmacokinetics and pharmacodynamics before space flight is of importance. The tail-suspended rat is a well-described model of weightlessness. During the time of the suspension, the pharmacokinetics of marker compounds can be used to evaluate changes in hepatic and renal physiology. Rats suspended for different periods allow for the investigation of the length of weightlessness exposure and drug pharmacology. Results from the use of the suspended rat model provide valuable information regarding possible pharmacokinetic and pharmacodynamic changes associated with weightlessness, and therefore, provide space biomedical researchers with a method of investigating drug administration during space flight missions.

Animals↗

PubMedDate not supplied

Caloric vestibular test in the weightless phase of parabolic flight.

Twenty-four caloric vestibular tests were conducted in 20 test subjects during parabolic flight, in which weightless periods of about 10 seconds were elicited. The caloric nystagmus disappeared completely in all experiments in weightlessness, whereas in the higher G-periods the speed of the nystagmus increased. With regard to the modes of response during the periods with increased G-values prior to and following the weightlessness, four different types could be distinguished. In mode I the speed of the slow nystagmus phase increased in the higher G-periods, the nystagmus showed a prolonged duration, while in weightlessness it faded out completely. A reversed nystagmus appeared when the primary caloric nystagmus had disappeared. In modes II, III and IV the direction of the nystagmus reversed during weightlessness. In modes II and III this reversed nystagmus appeared even when the primary caloric nystagmus had disappeared. In mode III the nystagmus resembled the type of mode II, with the difference that it faded away much earlier than could be expected. In mode IV the primary nystagmus lasted rather briefly, while the reversed nystagmus during weightlessness was also much shorter. The experiments produced two remarkable facts: the appearance of a nystagmus reversal, a 'secondary nystagmus', in all experiments in weightlessness, and furthermore great differences in findings between the individuals as well as between experiments in the same person. The only explanation for the inconsistency in the findings is the assumption that effects on other canals, otoliths and vestibular nuclei are continuously changing and therefore interfere with the only endproduct measured, the horizontal nystagmus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2000

Effect of simulated weightlessness on phase II drug metabolism in the rat.

BACKGROUND: Exposure to weightlessness is known to alter physiological processes in humans and animals. As a result of these changes, hepatic drug metabolism may be altered as well. Indeed, short term simulated weightlessness in the rat has been shown to increase oxidative metabolism. HYPOTHESIS: Simulated weightlessness will increase Phase II drug metabolism in the rat during short-term tail suspension. METHODS: The tail-suspended rat model was used to simulate weightlessness. Rats were subjected to 1, 3, 7, or 10 d of tail-suspension in order to mimic the effect of exposure to a microgravity environment. One additional rat group was not suspended and served as a control. On the final day of the study, rats we administered a single intravenous bolus dose of acetaminophen 25 mg x kg(-1) through an implanted jugular catheter and serial blood samples were taken for 90 min. Serum acetaminophen concentrations were measured by high-performance liquid chromatography. Pharmacokinetic parameters were determined by using standard model independent methods. RESULTS: The results show that simulated weightlessness in the rat has no effect on Phase II drug metabolism, using acetaminophen as a marker compound. CONCLUSIONS: These data support the hypothesis that simulated weightlessness in the rat modulates oxidative metabolism, but not drug conjugation to glucuronide or sulfate metabolites. These data offer insight into the physiological changes and variability seen in hepatic metabolic profiles in humans and animals following actual spaceflight.

Acetaminophen↗

PubMed2001

[Counter-effect of intermittent +Gz exposures on vasoreactivity in decline in hind body arteries of rats under simulated weightlessness].

Objective. To investigate the counter-effect of intermittent artificial gravity, the present study examined vasoreactivity changes of femoral and mesenteric arteries in rats subjected to simulated weightlessness plus standing or centrifugation. Method. Forty male Sprague-Dawley rats were divided into simultaneous control (CON), simulated weightlessness (SUS), simulated weightlessness plus 1 h standing (STD1), simulated weightlessness plus 1.5 G centrifugation (1.5 G), and simulated weightlessness plus 2.6 G centrifugation (2.6 G) groups. Responses of arteries to vasoconstrictor were examined in vitro using isolated femoral and mesenteric arterial rings. Result. The contractile responsiveness to KCl or PE of femoral and mesenteric arterial rings isolated from SUS significantly decreased as compared with CON. And those of STD1 and the two centrifuged groups significantly enhanced as compared with that of SUS. Whereas there was no difference among STD1, 1.5 G, 2.6 G and CON. Conclusion. Simulated weightlessness may result in decreased contractile responses to KCl and PE of rat femoral and mesenteric arteries. Both STD1, 1.5 G, and 2.6 G prevented the decrease of contractile response to KCl and PE of femoral arteries.

Animals↗

PubMed2000

Changes in myocardial contractility and contractile proteins after four weeks of simulated [correction of simulate] weightlessness in rats.

The interaction between the gravitational field, the position of the body, and the functional characteristics of the blood vessels determines the distribution of intravascular volume. In turn, this distribution determines cardiac pump function. One of the most profound circulatory changes that occurs in man during exposure to weightlessness is a cephalad redistribution of fluid caused by the lack of hydrostatic pressure in this microgravitative environment. The cephalad redistribution of fluid results in a loss of blood volume and then induces a decrease in preload. Recently, a decrease in sensitivity of arteriole to catecholamine has reported in rats of simulated weightlessness. This change in arteriole may reduce afterload. As a result, cardiovascular system may be shifted to a hypokinetic state during weightlessness condition for long-term. Echocardiographic data from astronauts during space flight showed an increase in heart rate, a 12 % decrease in stroke volume, and a 16 % decrease in left end diastolic volume. Electron-microscopic studies have shown changes in cardiac morphology in rats after exposure to microgravity for 7-12.5 days. After the COSMOS 2044 flight for 14 days, the light-microscopic studies have shown an atrophy of papillary muscles in rats left cardiac ventricle. It is not clear whether the function of atrophic myocardium is impaired. The data in three aspects as mentioned above suggest that weightlessness or simulated weightlessness may decrease the myocardial function. However, definite changes in cardiac performance have been hard to prove due to many limits. This studies were to answer two questions: Is the myocardial contractility depressed in rats subjected to simulated weightlessness for four weeks? What are the underlying mechanisms of the changing contractility?

Animals↗

PubMed2001

Endoscopic surgery in weightlessness: the investigation of basic principles for surgery in space.

BACKGROUND: Performing a surgical procedure in weightlessness, also called 0-gravity (0-g), has been shown to be no more difficult than in a 1-g environment if the requirements for the restraint of the patient, operator, surgical hardware, are observed. The performance of laparoscopic and thorascopic procedures in weightlessness, if feasible, would offer several advantages over the performance of an open operation. Concerns about the feasibility of performing minimally invasive procedures in weightlessness have included impaired visualization from the absence of gravitational retraction of the bowel (laparoscopy) or thoracic organs (thoracoscopy) as well as obstruction and interference from floating debris such as blood, pus, and irrigation fluid. The purpose of this study was to determine the feasibility of performing laparoscopic and thorascopic procedures and the degree of impaired surgical endoscopic visualization in weightlessness. METHODS: From 1993 to 2000, laparoscopic and thorascopic procedures were performed on 10 anesthetized adult pigs weighing approximately 50 kg in the National Aeronautics and Space Administration (NASA) Microgravity Program using a modified KC-135 airplane. The parabolic simulation system for advanced life support was used in this project, and 20 to 40 parabolas were used for laparoscopic or thorascopic investigation, each containing approximately 30 s of 0-g alternating with 2-g pullouts. The animal model was restrained in the supine position on a floor-level Crew Medical Restraint System, and the abdominal cavity was insufflated with carbon dioxide. The intraabdominal and intrathoracic anatomy was visualized in the 1-g, 0-g, and 2-g periods of parabolic flight. Bleeding was created in the animals, and the behavior of the blood in the abdominal and thoracic cavities was observed. In the thoracic cavity, gas insufflation and mechanical retraction was used at times unilaterally to decrease pulmonary ventilation enough to increase the thoracic domain. RESULTS: Visualization was improved in laparoscopy, from tethering of the bowel by the elastic mesentery, and from the strong tendency for debris and blood to adhere to the abdominal wall because of surface tension forces. The lack of adequate thoracic domain made thorascopy more difficult. Fluid in the thoracic cavity did not impair visualization because the fluid at 0-g does not loculate posteriorly, but disperses along the thoracic wall and mediastinal reflections. CONCLUSIONS: Performing minimally invasive procedures instead of open surgical procedures in a weightless environment has theoretical advantages, especially in the ability to prevent cabin atmosphere contamination from surgical fluids (blood, pus, irrigation). Visualization will become more important and practical as the endoscopic hardware is miniaturized from its current form, as endoscopic technology becomes more advanced, and as more surgically capable medical crew officers are present in future long-duration space exploration missions.

Animals↗

PubMedDate not supplied

Effect of simulated and real weightlessness on early regeneration stages of Brassica napus protoplasts.

Results from experiments using protoplasts in space, performed on the Biokosmos 9 satellite in 1989 and on the Space Shuttle on the IML-1-mission in 1992 and S/MM-03 in 1996, are presented. This paper focuses on the observation that the regeneration capacity of protoplasts is lower under micro-g conditions than under 1 g conditions. These aspects have been difficult to interpret and raise new questions about the mechanisms behind the observed effects. In an effort to try to find a key element to the poor regeneration capacity, ground-based studies were initiated focusing on the effect of the variable organization and quantity of corticular microtubules (CMTs) as a consequence of short periods of real and simulated weightlessness. The new results demonstrated the capacity of protoplasts to enter division, confirming the findings in space that this was affected by gravity. The percentage of dividing cells significantly decreased as a result of exposure to simulated weightlessness on a 2-D clinostat. Similar observations were made when comparing the wall components, which confirmed that the reconstitution of the cell wall was retarded under both space conditions and simulated weightlessness. The peroxidase activity in protoplasts exposed to microgravity was slightly decreased in both 0 g and 1 g flight samples compared with the ground controls, whereas activity in the protoplasts exposed to simulated weightlessness was similar to activity in the 1 g control. The observation that protoplasts had randomized and more sparse corticular microtubules when exposed to various forms of simulated and real weightlessness on a free-fall machine on the ground could indicate that the low division capacity in 0 g protoplasts was correlated with an abnormal CMT array in these protoplasts. This study has increased our knowledge of the more basic biochemical and cell biological aspects of g effects. This is an important link in preparation for the new space era, when it will be possible to follow the growth of single cells and tissue cultures for generations under microgravity conditions on the new International Space Station, which will be functional on a permanent basis from the year 2003.

Brassica napus↗

PubMed1976

Human tolerance to acceleration after exposure to weightlessness.

The major role in the genesis of varying human tolerance to decelerations that follow weightlessness is evidently played by hypodynamic and hydrostatic factors. Long disuse of compensatory antigravity mechanisms in weightlessness may bring about their deconditioning and reduction of their functional capabilities, and may finally affect general tolerance of crewmembers to decelerations. Laboratory experiments demonstrated changes in the human tolerance to Gx accelerations of varying duration (from 3 to 100 days) and tested the efficacy of different countermeasures. A decrease in the human tolerance to +Gx is on the average -2.0g. It should be noted that an elongation of simulated weightlessness (from 7 to 100 days) caused no further decrease in the +Gx tolerance. Our investigations helped to assess the threshold of human tolerance to accelerations after an exposure to simulated weightlessness and to delineate the value of real risk. The tolerance limit to +Gx accelerations which followed simulated weightlessness of the above duration ranged from 9.5 to 13.0g, averaging 11.6 +/- 1.6g. The information on the tolerance of Soviet and American astronauts to decelerations shown during re-entry in real space flights give support to the laboratory results and predictions.

Acceleration↗

PubMed1984

Adaptation of postural control to weightlessness.

Adaptation of motor control to weightlessness was studied during a 7-day spaceflight. The maintenance of control of upright posture was examined during a voluntary raising movement of the arm and during the voluntary raising on tiptoe. In order to evaluate the contribution of visual cues, three types of visual situations were examined: normal vision, central vision, and without vision. On the basis of cinematographic and mechanographic data, the postural perturbations consecutive to the movement of a body part in conditions of weightlessness were found to be similar to those observed on earth. However, in weightlessness, in contrast to the ground-based situation, erectness of posture was maintained primarily due to the predominant contraction of the ankle flexor muscles. The sequences of postural leg muscle activity associated with the arm or foot movement were well structured and varied slightly in the course of the flight. In addition, the initial posture, that is the erect posture before the movement was executed, changed throughout the flight from an exaggerated oblique position to a terrestrial standing position. Visual information was preponderant at the beginning of the space mission for the recalibration of other sensory cues affected by weightlessness. The findings are indicative of two types of adaptation of the central program of posture regulation to weightlessness: fast, short-term adaptation, characterized by a quasi-instantaneous redistribution of motor commands between ankle flexors and extensors (an "operative process") and slow, long-term adaptation, exemplified by the loss of anticipatory activation of certain muscles by the end of the flight (a "conservative process").

Adaptation, Physiological↗

PubMed1974

The role of gravity in the phylogeny of structure and function in animal sensors of spatial orientation, and their predicted action in weightlessness.

The evolution of the structural, functional and cytochemical organization of the gravity receptor which determines a body position in the gravitational field of the earth by means of muscular regulation was traced both invertebrates and vertebrates, using electron microscopic and histochemical methods. In the course of evolution of vertebrates, the specialized gravity receptor-statocyst which, as a rule, consists of primary sensory cells and supplies otoliths, is formed. In vertebrates, there exists a vestibular apparatus made up of secondary sensory cells and also having otoliths. The receptor cells, both of statocysts and the vestibular apparatus, are supplied with special antennas (kinocilia and stereocilia). Deviation of the antennas stimulated by displacement of the otoliths resulting from locomotor activity of animals leads to excitation of the receptor cells. When exposed to a modified gravitational field (linear accelerations of 10 g, for 3 min), the receptor cells of the vestibular apparatus, in all classes of vertebrates, show progressive changes in RNA content and protein synthesis (increase followed by decrease) which return to normal only after 12 days. Thus, immediate transfer of animals and man from acceleration to weightlessness appears to be a reason for movement disease. The above consideration showed the need for an experiment in which an animal (with its vestibular apparatus) which had not undergone previous accelerations, would be exposed to weightlessness. Frog embryos, Rana temporaria, at the stage preceding the organogenesis, when the vestibular apparatus and other organs were lacking, were chosen as a suitable subject. Frog embryos at the stage of an early gastrula were placed in a special container Emkon aboard the Soyuz 10 spacecraft. After short accelerations, they were exposed to weightlessness for 44 hours. The embryos were allowed to continue to develop to the stage of early tail bud. The experimental embryos showed normally developed acoustic vesicles and vestibular ganglia. Clear differentiation of the receptor cells with antennas (kinocilia and stereocilia) was found in the acoustic vesicles. Thus, in weightlessness, vestibular apparatus develops just as well as in the gravitational field of the earth. However, only a much longer stay in weightlessness conditions will indicate whether there are any changes in the structural, cytochemical and functional organization of vestibular apparatus. The similarity in the structural, functional and cytochemical organization of the gravity receptor in vertebrates and invertebrates appears to allow the prediction of the behaviour of the gravity receptor as a whole, and of its receptor elements, both in normal and changed gravitational fields. The first attempts were carried out only on the vestibular apparatus of vertebrates.

Acetylcholinesterase↗