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At least 847 records · Page 47Linked to original sources
PubMed1995

Characteristics of the venous hemodynamics of the leg under simulated weightlessness: effects of physical exercise as countermeasure.

In order to test the hypothesis that increases in calf venous distensibility in microgravity are partly due to the changes affecting the surrounding skeletal muscles (muscular atrophy), 12 healthy volunteers were exposed for 28 d to microgravity simulated by -6 degrees head-down bed rest. Half these subjects were exposed to countermeasures during bed rest: a) repeated LBNP (Lower Body Negative Pressure) sequences starting on the 15th d with one 15 min sequence at -35 mb, every other day from the 15th until the 21st d, and then every day until the end of bed rest; b) physical training including isotonic type exercise and isometric or isokinetic work by all muscle mass of upper and lower limbs (from the 8th until the 28th d). The other six subjects forming the control group were not subjected to any countermeasure. Calf venous hemodynamics were determined by mercury strain gauge plethysmography with venous occlusion. Distensibility (delta Vmax) and venous emptying (venous outflow at the 6th s of emptying: VO6, half-emptying time: T1/2, maximum venous outflow (MVO) could also be measured. Nuclear magnetic resonance (NMR) was used to study changes in volume of calf muscles. Plethysmographic measurements made for each subject prior to, during (once a week), and after bed rest show a parallel increase in calf venous distensibility in both groups of subjects until the 20th d of bed rest. Filling and emptying times then tended to stabilize in the group treated with countermeasures (group CM) whereas high venous distensibility was observed until the end of bed rest and 5 d thereafter in the control group (group C).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

[Biogenic amines in the small intestines in guinea pigs in simulated weightlessness and vibration].

The dynamics of changes in epinephrine (E), norepinephrine (NE), dopamine (DA), serotonin (5-HT) and its metabolite 5-HIAA in the duodenal and iliac wall was studied in the initial period of support unloading (the "dry" immersion method) and general low frequency vibration (LFV). It was found that 15-min unloading led to a sharp increase in 5-HT and DA in the duodenum, accompanied by an elevation in total electrical activity of smooth muscles, to a decrease in E, NE, and DA and, in contrast, to an increase in 5-HT and 5-HIAA in the ileum. Normalization of monoamine metabolism observed 2 h after the beginning of the unload 4 hour later was followed by inactivation of duodenal serotoninergic structures and iliac adrenergic structures. The LFV induced mostly the opposite response, decreasing 5-HT in the duodenum with accumulation of E and NE in it, and a more marked activation of inhibitory adrenergic innervation of the ileum.

Animals↗
PubMed1993

Morphological changes in rat vestibular system following weightlessness.

Mammalian gravity receptors (maculas) are morphologically organized for weighted, parallel distributed processing of information. There are two basic circuits: 1) highly channeled, type I cell to calyx; and 2) distributed modifying, type II cells to calyces and processes. The latter circuit should be the more adaptable since it modifies final output. To test this hypothesis, rats were flown in microgravity for 9 days aboard a space shuttle and euthanized shortly after landing. Hair cells and ribbon synapses from maculas of 3 flight and 3 ground control rats were studied ultrastructurally in blocks of 50 serial sections. Synapses increased by approximately 41% in type I cells and by approximately 55% in type II cells in flight animals. There was a shift toward the spherular form of ribbon synapse in both types of hair cells in flight animals (P < or = 0.0001), a near doubling of pairs in the flight rats (P < or = 0.0001), and an increase, by a factor of 12, in groups of synapses in type II cells (P < or = 0.0001). Current findings tend to support the stated hypothesis and indicate that mature utricular hair cells retain synaptic plasticity, permitting adaptation to an altered gravitational environment.

Acoustic Maculae↗
PubMedDate not supplied

[The effect of weightlessness on sensorimotor interaction during operator activity: visual feedback. Motor response latency time].

During the second joint French-Soviet space mission efficiency of compensating tracking was investigated in operator by velocity. It was shown that in spite of considerable changes in proprioceptive feedbacks, performance quality remained essentially as preflight. This evidences that visual feedback during operational activity is apt to offset losses in proprioceptive feedbacks.

Feedback↗
PubMedDate not supplied

[The effect of weightlessness on erythrocyte resistance in vivo and in vitro].

One of the significant changes developing in animals and humans in the space mission environments is a decreased volume of red blood mass. For the analysis of causes of this phenomenon it is reasonable to compare the data on erythrocyte resistance to hemolysis in vivo and in vitro obtained in the rat experiments on Cosmos biosatellites. After 18 to 22-day space missions, the osmotic resistance of erythrocytes in vitro in animal blood samples and the level of spontaneous hemolysis in vivo directly in the vascular bed of rat have been determined. To this end, an original method based on a quantitative determination of 14Co in the expired air following previous (prior to space mission) 2(14)C glycine labeling in vivo of erythrocyte 2 group has been utilized. In both cases there were a decreased erythrocyte resistance and an increased hemolysis level. During the studies in vivo these changes were significantly great. Inflight application of artificial gravity of 1 G prevented microgravity-induced changes in the characteristics of the erythrocyte life cycle. The changes in erythrocyte shape and membrane properties as well as the factors affecting the cells in vascular bed (altered concentration of fatty acids in blood plasma and others) are discussed as possible causes of the above alterations.

Animals↗
PubMed1994

Issues of health care under weightlessness.

This review will address issues of effects of space flights on the body. Cardiovascular deconditioning often induce symptoms like orthostatic intolerance after flight, and during flight there will be space motion sickness during the first few days with headache, malaise, nausea and eventually vomiting. These symptoms disappear and do not interfere with the performance of the astronauts after several days. During long-term flights, effects will be muscle atrophy and calcium loss from the skeleton. Radiation effects will be a significant issue, increasing with the length of the space flight. Also during long-term flights, psychological problems will become of increasing importance. Astronaut health care will be discussed related to Space Shuttle missions and Space Station missions. Furthermore, countermeasures for long-term space flights (up to 6 months) will be outlined. The NASA health care programme is reviewed, and the frequency of illnesses and injuries encountered in the NASA programme is discussed. There will be a need for setting up an international health care programme in view of the upcoming international cooperation in the Space Station era. It is emphasized that the Space Station is an international platform. Therefore, the health care team will be composed of international personnel, mainly from NASA with participation of Europe, Canada, Russia, and Japan. Specialized medical doctors will form the team and support the crew members from the ground. Some issues, such as medical licensing and responsibility, remain to be solved.

Aerospace Medicine↗
PubMed1993

Review of the biological effects of weightlessness on the human endocrine system.

Studies from space flights over the past two decades have demonstrated that there are basic physiological changes in humans during space flight. These changes include cephalad fluid shifts, loss of fluid and electrolytes, loss of muscle mass, space motion sickness, anemia, reduced immune response, and loss of calcium and mineralized bone. The cause of most of these manifestations is not known but the general approach has been to investigate systemic and hormonal changes. However, data from the 1973-1974 Skylabs, Spacelab 3 (SL-3), Spacelab D-I (SL-DI), and now the new SLS-1 missions support a more basic biological response to microgravity that may occur at the tissue, cellular, and molecular level. This report summarizes ground-based and SLS-1 experiments that examined the mechanism of loss of red blood cell mass in humans, the loss of bone mass and lowered osteoblast growth under space flight conditions, and loss of immune function in microgravity.

Anemia↗