Exercise response to simulated weightlessness

Two bed rest analog studies of space flight were performed; one 14 d and the other 28 d in duration. Exercise response was studied in detail during the 28 d study and following both the 14 d and 28 d studies. This paper relates the results of these studies to physiologic changes noted during and following space flight. The most consistent change noted after both bed rest and space flight is an elevated heart rate during exercise. A second consistent finding is a postflight or postbed rest reduction in cardiac stroke volume. Cardiac output changes were variable. The inability to simulate inflight activity levels and personal exercise makes a direct comparison between bed rest and the results from specific space flights difficult.     

Structural and functional changes in man accompanying the weightlessness in "Skylab" flights: a mathematical approach

The present paper reports a kinetic analysis of changes of some physiological parameters, obtained from international literature, after changes in gravitational environment. The overall phenomenology of the adaptation to weightlessness is characterized by a rapid process followed by a slow one. The two processes show half time values differing by about five times. Also in the case of readaptation to gravity, after recovery on the Earth, two well resolved processes, showing different half time values, are observed. It is of interest to notice that the rate of response to weightlessness is lower than that to gravity. Of course, the half time values observed depend on the different physiological parameters considered. In any case, the experimental data suggest a general trend of many adaptive changes, that may all be described by a simple mathematical model.     

Skylab experiment M-092: results of the first manned mission

Blood pressure at 30-sec intervals, heart rate, and percentage increase in leg volume continuously were recorded during a 25-min protocol in the M092 Inflight Lower Body Negative Pressure (LBNP) experiment carried out in the first manned Skylab mission. These data were collected during six tests on each crewman over a 5-month preflight period. The protocol consisted of a 5-min resting control period, 1 min at -8, 1 min at -16, 3 min at -30, 5 min at -40, and 5 min at -50 mm Hg LBNP. A 5-min recovery period followed. Inflight tests were performed at approximately 3-day intervals through the 28-day mission. Individual variations in cardiovascular responses to LBNP during the preflight period continued to be demonstrated in the inflight tests. Measurements of the calf indicated that a large volume of fluid was shifted out of the legs early in the flight and that a slower decrease in leg volume, presumably due to loss of muscle tissue, continued throughout the flight. Resting heart rates tended to be low early in the flight and to increase slightly as the flight progressed. Resting blood pressure varied but usually was characterized by slightly elevated systolic blood pressure, lower diastolic pressure, and higher pulse pressures than during preflight examinations. During LBNP inflight a much greater increase in leg volume occurred than in preflight tests. Large increases occurred even at the smallest levels of negative pressure, suggesting that the veins of the legs were relatively empty at the beginning of the LBNP. The greater volume of blood pooled in the legs was associated with greater increases of heart rate and diastolic pressure and larger falls of systolic and pulse pressure than seen in preflight tests. The LBNP protocol represented a greater stress inflight, and on three occasions it was necessary to stop the test early because of impending syncopal reactions. LBNP responses inflight appeared to predict the degree of postflight orthostatic intolerance. Postflight responses to LBNP during the first 48 hours were characterized by marked elevations of heart rate and instability of blood pressure. In addition, systolic and diastolic pressures were typically elevated considerably both at rest and also during stress. The time required for cardiovascular responses to return to preflight levels was much slower than in the case of Apollo crewmen.     

Mineral and nitrogen balance study: results of metabolic observations on Skylab II 28-day orbital mission

Prediction that the various stresses of flight, particularly weightlessness, would bring about significant derangements in the metabolism of the musculoskeletal system has been based on various observations of long-term immobilized or inactive bed rest. The only attempt at controlled measurement of metabolic changes in space prior to Skylab, a study during the 14-day Gemini VII flight, revealed rather modest losses of important elements. The three astronauts of Skylab II consumed a planned day-by-day, quite constant, dietary intake of major metabolic elements in mixed foods and beverages and provided virtually complete collections of excreta for 31 days preflight, during the 28 days inflight, and for 17 days postflight. Analyses showed that, in varying degree among the crewmen, urinary calcium increased gradually during flight in a pattern similar to that observed in bed-rest studies: the mean plateau peak of urinary calcium excretion in the latter part of flight was double preflight levels. Fecal calcium excretion did not change significantly, but calcium balance, owing to the urinary calcium rise, became either negative or less positive than in preflight measurement. Increased excretion and negative balance of nitrogen and phosphorus indicated appreciable loss of muscle tissue in all three crewmen. Significant losses also occurred inflight in potassium, sodium, and magnesium. Based on the similarity in pattern and degree between these observations and those in bed rest of the losses in calcium, phosphorus, and nitrogen, musculoskeletal integrity would not be threatened in space flights of up to at least 3 months. However, if similar changes occur, indicative of continuing losses of these elements, in the planned Skylab flights for considerably more than 28 days, concern for capable musculoskeletal function should be serious for flights of very many months' duration, and greater research attention will need to be given to development of protective counter-measures.     

Vibration and pulsation processes in feed systems of liquid rocket engines

Pulsation and vibration process in high speed centrifugal pumps and feed lines were investigated. Linear and quadratic relations between pulsation parameters and main factors were obtained. The investigation of turbopump low frequency oscillations showed that the intensity of pulsations is proportional to the pump specific linear size. Linear mathematic models with lumped parameters fairly well demonstrate the vibration influence on low frequency flow pressure vibrations in pumps and feed lines. It is shown that, in some conditions, the pressure oscillation amplitude distribution by the vibrating feed lines length may be characterized by the presence of a node in an intermediate section. A one-dimensional mathematic model based on wave equations proved to be suitable for calculations of vibration and pulsation parameters within a wide frequency range.     

Changes in organ perfusion and weight ratios in post-simulated microgravity recovery

Head-down tilt models have been used as ground-based simulations of microgravity. Our previous animal research has demonstrated that there are significant changes in fluid distribution within 2 h after placement in a 45 degrees head-down tilt (45HDT) position and these changes in fluid distribution were still present after 14 days of 45HDT. Consequently, we investigated changes in fluid distribution during recovery from 16 days of 45HDT. Changes in radioactive tracer distribution and organ/body weight ratio were examined in rats randomly assigned to a 45HDT or prone control group. The 45HDT rats were suspended for 16 days and then allowed to recover at the prone position 0, 77, 101, or 125 h post-suspension. Animals were injected with technetium-labeled diethylenetriamine pentaacetate (99mTcDTPA, MW=492 amu, physical half-life of 6.02 h) and then killed 30 min post-injection. Lungs, heart, liver, spleen, kidneys, and brain were harvested, weighed, and measured for radioactive counts. Statistical analyses included two-way analysis of variance (ANOVA) that compared 45HDT versus controls at the four experimental time points. The organ weight divided by the body weight ratio for the brain, heart, kidneys and liver in the 45HDT rats was significantly different than the control rats, regardless of time (treatment). There was no difference between the different time points (time). The average 99mTcDTPA count divided by the organ weight ratio values for the heart, liver, and spleen were significantly higher in the 45HDT group than the control group. The average counts for the heart and spleen were significantly higher at 77, 101, and 125 h than at time zero. We conclude that the major organs have different recovery patterns after 45HDT for 16 days in the rat.     

Future investigations onboard Soviet biosatellites of the Cosmos series.

Many rat experiments onboard Cosmos biosatellites have furnished information concerning the effects of weightlessness, artificial gravity, and ionizing radiation combined with weightlessness on structural and biochemical parameters of the animal body. The necessity to expand the scope of physiological investigations has led to the project of flight primate studies. It is planned to carry out the first primate experiments onboard the Cosmos biosatellite in 1982. At present investigations of weightlessness effects on the cardiovascular and vestibular systems, higher nervous activity, skeletal muscles and biorhythms of two rhesus monkeys are being developed and tested. It is also planned to conduct a study of weightlessness effects on embryogenesis of rats and bioenergetics of living systems onboard the same biosatellite. Further experiments onboard Cosmos biosatellites are planned.     

Diuretic as a means for rapid adaptation to weightlessness

In a number of flights, cosmonauts and astronauts have experienced aggravation of their health status and general condition in the initial hours and days in a weightless environment. One of the trigger mechanisms for the onset of these unfavourable conditions at the start of space flight is a redistribution of body fluids and a blood shift towards the head. To ensure controlled hypohydration as a countermeasure to the deleterious effects of 0-g and to investigate the feasibility to control adaptation, six cosmonauts were administered lasix once a day during the first 3 days of a mission. All data of the experiment (correction test, questionnaire, hematocrit) were recorded on a special form in the logbook and transmitted to the control centre for processing. Results showed that the diuretic weakened the sensation of discomfort and improved the cosmonauts' general condition. Objective indices of the correction test indicate an increased work ability of cosmonauts. After hypohydration, circulating plasma volumes in the group were reduced by 6.8 + 1.0% on average.     

Muscle atrophy associated with microgravity in rat: basic data for countermeasures

Morphological, contractile properties and myosin heavy chain (MHC) composition of rat soleus muscles were studied after 2 weeks of unloading (HS) and after 2 weeks of HS associated with selective deafferentation (HS + DEAF) at the level L4 and L5. The same significant reductions in muscle mass and tetanic tension were found after HS and HS + DEAF. However, the transformation of the slow-twitch soleus muscle towards a faster type characterized by a decrease in twitch time parameters and an increase in fast-twitch type MHC isoforms in HS did not appear in HS + DEAF conditions. Our results also showed that a pattern similar to firing rate of motoneurones innervating slow-twitch muscles inhibited the slow to fast fiber changes observed during HS. Nevertheless, neither the loss of mass or force output in the HS muscles were prevented by electrostimulation. Immobilization in a stretched position during HS maintained the muscle wet weight, mechanical and electrophoretical characteristics close to control values. We concluded that the decrease in mechanical strains imposed on the muscle during unloading was the main factor for the development of atrophy, while the kinetic changes might be predominantly modulated by the nervous command. These basic data suggested that some experimental conditions such as electrostimulation or stretching, could participate in countermeasure programmes.     

Effect of fluid and salt supplements in preventing the development of "osteopenia" in hypokinetic rats

It has been suggested that a daily intake of fluid and salt supplements may be used to prevent bone demineralization in human subjects after prolonged exposure to hypokinesia (diminished muscular activity). Thus, the objective of this investigation was to evaluate the effect of fluid and salt supplementation in the prevention of development of osteoporosis in 64 Wistar rats with an initial body weight of 339-345 g, after exposure to 90 days of hypokinesia. They divided into 4 equal groups: the first group of rats placed under ordinary vivarium conditions and served as vivarium control; the second group were also placed under ordinary vivarium conditions but received daily fluid and salt supplements; the third group were subjected to pure hypokinesia, i.e. without the use of any preventive measures; and the fourth group were submitted to hypokinesia and received daily fluid and salt supplements. For the simulation of the hypokinetic effect the experimental group of rats were kept in small, individual, wooden cages. Through the experimental period the second and fourth group of rats received 8 ml/100 g body wt water and 5 ml 100 g body wt NaCl daily. By the end of the experimental period the animals were decapitated and the spongy matter of tibia and vertebrae of the rats were examined for changes referable to osteoporosis. It was found that the daily intake of fluid and salt supplements caused an increase in the volume density of primary spongiosa of bones. It was concluded that a daily intake of fluid and salt supplements may be used to prevent the development of osteoporosis in rats subjected to prolonged motor activity restriction.