Lipid metabolic indices in man during head-down tilt hypokinesia and their correction

Twenty one test subjects exposed to head-down tilt for 120 days were subdivided to four groups: Group 1--nine subjects used as controls, Group 2--three bed rested subjects who performed regular exercises, Group 3--four bed rested subjects who were given selected drugs, including Vitamin F-99 that influenced lipid metabolism, and Group 4--four bed rested subjects who performed regular exercises and received Vitamin F-99. At different stages of bed rest and recovery the content of lipoprotein fractions and lipids of different classes in serum was measured by thin-layer chromatography. The concentration of cholesterol in biliary lipids was determined. In Group 1 and 2 subjects bed rest led to a drastic and significant increase of cholesterol esters in blood, a decrease of phospholipids, variations of triglycerides and non-esterified fatty acids, and a lower percentage content of alpha-lipoproteins. The use of Vitamin F-99 produced positive changes in the above parameters of lipid metabolism (it normalized the level of cholesterol and phospholipids). In Group 4 subjects the effect of exercise combined with drugs was most distinct.     

Metabolic characteristics during 120-day head-down tilt hypokinesia

Nine healthy test subjects, aged 25 to 44 years, were exposed to bed rest (at -5 degrees) for 120 days. Venous blood and 24-hour urine samples were used to measure Na, K, total and ionized Ca, Mg, total protein, protein fractions, creatinine, urea, uric acid, malate, isocitric and lactate dehydrogenases, aspartate and alanine aminotransferases, and creatine phosphokinase and its isoforms, acid and alkaline phosphatase and its isoenzymes. Prolonged exposure to head-down tilting resulted in a negative balance of fluid and electrolytes, lowered concentration of total protein and albumins, and an increased concentration of urea and creatinine, basic products of protein metabolism. In blood, the activity of dehydrogenases of the tricarboxylic acid cycle and creatine kinase decreased at the expense of its muscle isoenzyme and the activity of acid phosphatase, total alkaline phosphatase and bone isoenzyme of alkaline phosphatase increased.     

Central blood circulation in the healthy human being during 7 days' head-down tilt hypokinesia

The effect of 7-day head-down tilt (-15 degrees) and lower body negative pressure on circulation and oxidative metabolism was investigated on 13 healthy male test subjects. For 7-10 days they had Swan-Ganz catheters implanted in the pulmonary artery and a special cannula in the radial artery. The most marked changes were seen in the pulmonary artery pressure (PAP) and central venous pressure (CVP) that varied in a phase-like manner. By the 7th hour of bed rest the PAP increased significantly; this was followed by increases in the total lung resistance and the right ventricle function, as well as by a slight decrease of renin and aldosterone. Beginning with bed rest days 2 or 3 the PAP and CVP declined and remained lowered, as compared to the pretest level, till the end of bed rest. The responses to LBNP tests changed by bed rest day 2. Possible mechanisms of the above changes at rest and during LBNP tests are discussed.     

Clinico-physiological aspects of the tissue oxygen supply of the human body during head-down tilt hypokinesia

In three antiorthostatic hypokinesia studies of varying duration gas exchange, central and regional hemodynamics were investigated. The hypokinetic effect on oxygen changes in the human body was evaluated by comparing the above results with biochemical data. It is concluded that bed rested subjects developed hypoxic changes of mixed circulatory-respiratory type. When oxygen supply changes drastically under the conditions that were simulated in our study, it is recommended to use oxygen therapy.     

Bile acid spectrum during 120 days of head-down tilt hypokinesia in man

The composition of bile acids in the B and C portions of the duodenal juice of six essentially healthy test subjects exposed to 120-day head-down bed rest was investigated. As the exposure continued, the percentage content of bile acids conjugated with taurine increased and that of bile acids conjugated with glycine decreased. The rapid and significant decrease of the ratio of glycine conjugated to taurine conjugated bile acids suggests a specific modification of the synthetic function of hepatocytes under the above conditions.     

Disruption of the circadian rhythm of the body temperature in monkeys during head-down tilt hypokinesia

A rhesus monkey was restrained in the prone position with the head kept at -6 degrees. The day: night cycle was 16:8 and ambient temperature 20-22 degrees C. Skin temperature (ST) in the ankle area and body temperature (BT) in the armpit were measured by thermistors every 16 min during 14 days. Mean daily values of both temperatures decreased continuously beginning with day 5 and reached a minimum on day 11. Between days 5 and 11 the BT rhythm was split into two components, i. e. morning and evening (with the 12-hour periodicity being predominant in the spectrum). The amplitude of the ST rhythm declined and reached a minimum on day 4. On that day the rhythm phase was sharply shifted (6-7 hour delay) and thereafter the amplitude and phase of the ST rhythm gradually restored. The above effects (dissociation of the BT rhythm, drop of the amplitude and delay of the phase of the BT rhythm) can be explained by a transient attenuation of the relationship (release) of circadian oscillators due to a greater load on the mechanisms of adaptation to simulated microgravity.     

Structural characteristics of the thyroid and parathyroid C cells of monkeys during head-down tilt hypokinesia

Eight monkeys Macaca rhesus were exposed to head-down tilt for 7 days and to clinostatic hypokinesia for 7 days with subsequent 12-day head-down tilt. C cells of the thyroid gland and the parathyroid glands of 5 control and 8 experimental monkeys were investigated histologically, morphometrically and electron-microscopically. On the 7th tilt day the C cell population increased, their nuclei grew significantly, synthesis activated, and secretory granules accumulated. By day 19 most C cells were in the secretion stage. Morphological signs of an increased functional activity of the thyroid gland were seen on experimental day 7 and those of the parathyroid gland on day 19, both in light and electron microscopies. Taking into account the antagonism of C cells and parathyroid glands, it can be assumed that the hypocalcemic effect of calcitonin plays a part in the stimulation of parathyroid glands during head-down tilt.     

Effect of coamide and folicobalamin on erythropoiesis during ordinary vital activities and in head-down tilt hypokinesia

The study was performed on 41 healthy men, aged 19 to 40, who led a normal life or were exposed to short-term or long-term head-down tilts. The effectiveness of hemostimulants was determined with respect to hemoglobin, red blood cells or reticulocyte counts. Folicobalamine and coamide administration in therapeutic doses increased hemoglobin and reticulocyte blood levels in the ambulant subjects or those exposed to a 7-day head-down tilt. The effect was stable and persisted for 2-3 weeks after which the blood parameters returned to the pretest level. Folicobalamine administered at the final stage of 50-day head-down tilt facilitated partial recovery of hemoglobin during the study (which is very important) and rapid recovery after it. The objective and subjective tolerance of the drugs was good. It is therefore concluded that folicobalamine should be taken at the final stage of head-down tilt or space flight to alleviate readaptation to the normal environment.     

Human amino acid metabolism during combined short-term exposure to head-down tilt hypokinesia and ultraviolet irradiation

Changes in the amino acid pool in the plasma of test subjects exposed to short-term head-down tilt combined with ultraviolet irradiation were investigated. Exposure to head-down tilt alone (Group 1 of 3 test subjects) and combined with ultraviolet irradiation (10 sessions) (Groups 2 and 3 of 3 test subjects each) acted as a stress-agent that diminished the amino acid pool. Exposure to 2-hour head-down tilt in combination with 20 UV-irradiations (Groups 2 and 3) increased the amino acid pool as a result of inhibition of anabolic and stimulation of catabolic processes. The amino acid pool did not return to normal within the recovery period allowed.     

Individual characteristics of water-mineral metabolism during 120-day head-down tilt hypokinesia and the effectiveness of prophylactic measures

Sodium balance and circulating plasma, intracellular, extracellular and interstitial fluid volumes were measured in the test subjects exposed for 120 days to head-down tilt at -5 degrees. The large scatter of the above parameters was associated with individual variations and with the use of different countermeasures against demineralization (exercise and drugs-xydiphone and glucamak). The effect of the countermeasures was different both in qualitative and quantitative terms. It appears that the target of their action was different. The best prophylactic effect was seen when exercise and drugs were used in combination. These findings suggest that individual variations of fluid-electrolyte metabolism during prolonged hypokinesia are related to the different capacity of tissues for water and electrolytes.     

Effect of short-term head-down tilt hypokinesia on the dynamics of the cardiorespiratory indices during graduated physical loading

Seven healthy volunteers were exposed to head-down tilt at -15 degrees for 5 h. Before and after exposure they exercised on a bicycle ergometer in the supine and seated positions. During the study their respiration function, gas exchange, and arterialized blood parameters were measured. It was found that after exposure the physical aerobic performance diminished. The changes detected suggest that a lower exercise tolerance can be caused not only by a decreased circulating blood volume but also by increased energy expenditures of the cardiorespiratory system itself.     

Morphological study of the muscle fibers and the microcirculatory bed of the muscles in monkeys during head-down tilt hypokinesia

Primates were exposed to head-down tilt for 7 and 12 days. As the study continued, the body mass and muscle mass decreased, muscles became atrophic, and the number of functioning capillaries lessened. Out of the three muscles examined (gastrocnemius, soleus, and biceps brachii), the soleus muscle showed the greatest changes. It can be concluded that, in spite of blood redistribution and blood pooling in the upper body (seen during autopsy), no blood displacement occurs in the microcirculatory bed. The decrease in the number of functioning capillaries is normally regarded as a change that is concomitant with muscle atrophy.     

Bioelectrical activity of the heart and blood electrolytes in virtually healthy subjects during 120-day head-down tilt hypokinesia

Electrocardiographic parameters and serum concentrations of potassium, sodium, calcium (total and ionized) and magnesium in 6 essentially healthy men, aged 30-45 years, were measured before, during and after 120-day head-down tilt at -4.5 degrees. A close correlation was demonstrated between T-wave depression and serum concentrations of potassium (direct correlation) and calcium and magnesium (inverse correlation). No consistent changes in the sodium content during the 120-day test were seen. In spite of electrolyte changes in blood induced by head-down tilt, ECG variations showed minor hypokalemia that was not followed by any clinical symptoms. These data can be used to evaluate the status of healthy people exposed to prolonged hypokinesia and to develop adequate prophylactic measures.     

Comparison of the bone tissue reaction of rats to clinostatic and head-down tilt hypokinesia

Examination of spongy bones of rats exposed to clino- and antiorthostatic hypokinesia showed that changes in bone mass, bone cells and their precursors were similar in both cases. The bone resorption-bone formation process remained balanced. However, bone responses clino- and antiorthostatic hypokinesia exhibited certain differences. Clinostatic hypokinesia produced greater osteoporosis in the femoral bone, whereas bone losses in the humerus, sternum and pelvis were identical. Antiorthostatic hypokinesia led to osteoporosis that was identical in every bone examined. In addition, clino- and antiorthostatic hypokinesia caused different reactions of stromal precursor cells, the latter model producing a greater effect on them. It is concluded that immobilization-induced skeletal disorders are associated with a decreased rate of bone histogenesis which proceeds at a lower level rather than with the stress-reaction.     

Vestibular function of middle-aged persons exposed to 30-day head-down tilt hypokinesia

Vestibular responses of 15 men (aged 42-50) to 30-day head-down tilt (-8 degrees) were investigated. The test subjects showed atherosclerotic symptoms and neuro-circulatory dystonia of the hypertensive type. They were exposed to the Fitzgerald-Hallpike caloric test, indirect otolithometry (eye counter-rolling reflex according to the method of successively presented images), and motion sickness according to Bryanov. In the pretest period vestibular changes were seen at the level of labyrinths and central formations (change in the nystagmic pattern, dissociation of the components of the caloric reaction, vestibular asymmetry, negative counter-rolling). During head-down tilt cupular reflexes remained essentially unaltered, except for the asymmetry and enhancement of the sensory and autonomic components of the caloric reaction. The otolith function was modified in all the test subjects. After exposure tolerance to motion sickness was not deteriorated. The time-course variations of the vestibular reactions of the tilted subjects were similar to those seen in young and healthy test subjects. The results of this simulated study suggest that vestibular reactions of crewmembers of the above age group in real space flight should be close to those of the young and healthy crewmembers.     

头低位—15°倾斜期间鼻粘膜微循环的变化

采用激光多普勒血流计，观察到１９名青年被试者在２．５ｈ头低位－１５°倾斜期间鼻粘膜微循环发生了明显改变。头低位后，微血管血流量、浓度和流速明显高于实验前，并出现明显的微血管规律性波动。结果提示：体液头向分布所引起的鼻粘膜微循环变化是造成航天中航天员鼻塞和呼吸不畅的重要起因之一。