A model illustrating possible instability of cellular structure under conditions of weightlessness.
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Cell Biology↗
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Testes size and testosterone levels in a model for weightlessness.
The purpose of this study was to test whether the lack of testicular growth found in suspended rats would affect testosterone production in a way that might have consequences on muscle atrophy and function studies. Body and testes weight, food consumption, and testosterone levels in testes and plasma were measured at the beginning of the experiment and after 1, 3 or 8 weeks of suspension. Suspended animals ate more but gained less weight than their pair-fed controls. Testes testosterone concentration (microgram/g tissue) was increased at 3 and 8 weeks, but total tissue testosterone (microgram/testes) was not. Up to 3 weeks of suspension, tissue concentration was dependent on testes size and independent of treatment. Plasma testosterone was increased only after 8 weeks of suspension. At 8 weeks, plasma levels correlated with total testes testosterone. Our results show that use of the Morey-Holton rat tail-suspension model up to 3 weeks did not induce testosterone changes of consequence to a skeletal muscle study. For long term studies consideration should be given to possible hormonal effects as tissue and plasma testosterone levels increase after 8 weeks of suspension.
Animals↗
Weightlessness: a case history.
The facts presented represent, for convenience, a composite clinical picture of the three crewmen aboard Skylab II as observed by me.
Adaptation, Physiological↗
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.
Adult↗
Amino aciduria in weightlessness.
Urinary excretion of amino acids by the 9 Skylab crewmen was studied as an indicator of the metabolic effects caused by exposure to the space flight environment. Intake was consistent in quality and quantity throughout the 28, 59 and 84-day flights for each of the crewmen and complete collections were accomplished. The results indicated an increased excretion in most amino acids during the first month of flight which remained elevated in the second and third months but to a lesser extent. Additional indications of change in muscle and skeletal metabolism were observed. These results point to the desirability of obtaining additional indices of alterations in protein synthetic processes in conjunction with future space flights.
Adaptation, Physiological↗
Equipment for surgical interventions and childbirth in weightlessness.
A transparent plastic sack has been devised for surgical interventions in space. Fixed airtight on the patient, containing sterilized medical equipment and comprising long sleeves for the operations, it retains all its contents for the rest of the flight.
Aerospace Medicine↗
Simple technique to evaluate on the ground the energetic expenditure of physical exercise carried out in weightlessness.
A simple method is described to evaluate the energetic expenditure of graded muscular exercises carried out on the ground in such a way as to approximate the state of space microgravity. Consumption of O2 measured at different rates of execution is shown as well as a tentative computation of the mechanical work on the basis of the accelerations impressed alternately on the mass of the trunk and upper limbs. The practicability of the method proposed under space conditions is pointed out; it does not require any ergometer, in fact, but only the fixing of the subject's feet to the floor of the vehicle.
Adult↗
Orthostatic hypotension of prolonged weightlessness: clinical models.
Orthostatic intolerance on return from space is a widely known consequence of space travel. Development of countermeasures against this problem is a major priority of the field of space physiology and medicine. The bedrest model is widely used in the investigation of this phenomenon, and has provided important data, but questions remain. In this article, we suggest that the disorders that produce chronic orthostatic hypotension have significant potential as models of microgravity-induced orthostatic intolerance. Understanding the pathophysiology of these syndromes may be useful to those involved in improving the operational aspects of manned space flight; four such syndromes and their possible relevance to space flight are described.
Autonomic Nervous System Diseases↗
Voluntary head stabilization in space during trunk movements in weightlessness.
The ability to voluntarily stabilize the head in space during lateral rhythmic oscillations of the trunk has been investigated during parabolic flights. Five healthy young subjects, who gave informed consent, were examined. The movements were performed with eyes open or eyes closed, either during phases of microgravity or phases of normal gravity. The main result to emerge from this study is that the head may be stabilized in space about the roll axis under microgravity conditions with, as well as without vision, despite the reduction of the vestibular afferent and the muscle proprioceptive inputs. Moreover, the absence of head stabilization about the yaw axis confirms that the degrees of freedom of the neck can be independently controlled, as it was previously shown. These results seem to indicate that voluntary head stabilization does not depend crucially upon static vestibular afferents. Head stabilization in space may be in fact organized on the basis of either dynamic vestibular afferents or a postural body scheme.
Head Movements↗
Effect of weightlessness on posture and movement control during a whole body reaching task.
Here are reported preliminary results of the "Synergy" experiment performed aboard the Russian orbital station "MIR" in July 1993 (Altair Mission). The experiment was carried out before, during, and after the space flight of two astronauts (S1 and S2). The duration of the flight was 21 days for S1 and 6 month for S2. The subjects were tested during preflight, inflight and postflight. The astronaut subjects were fixed on the ground by the feet. They were asked to pick up a box in front of them on the ground. Two velocities of movement and two distances of the target to be reached were tested. The movement of several small markers placed on the body was recorded on video tape. Results show that the shape of head and hand trajectories in the sagittal plane remains roughly the same during the flight in spite of the modification of mechanical constraints. Trajectory invariance does not result in joint angular displacement invariance. These data indicate that the planning of the movement takes place in terms of head and hand trajectories rather than joint rotations as it was previously suggested for simple arm reaching movement.
Adaptation, Physiological↗
Postural control in weightlessness: a dual process underlying adaptation to an unusual environment.
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Adaptation, Physiological↗
Changes of contractile responses due to simulated weightlessness in rat soleus muscle.
Some contractile and electrophysiological properties of muscle fibers isolated from the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles of rats were compared with those measured in SOL muscles from suspended rats. In suspended SOL (21 days of tail-suspension) membrane potential (Em), intracellular sodium activity (aiNa) and the slope of the relationship between Em and log [K]o were typical of fast-twitch muscles. The relation between the maximal amplitude of K-contractures vs Em was steeper for control SOL than for EDL and suspended SOL muscles. After suspension, in SOL muscles the contractile threshold and the inactivation curves for K-contractures were shifted to more positive Em. Repriming of K-contractures was unaffected by suspension. The exposure of isolated fibers to perchlorate (ClO4-)-containing (6-40 mM) solutions resulted in a similar concentration-dependent shift to more negative Em of activation curves for EDL and suspended SOL muscles. On exposure to a Na-free TEA solution, SOL from control and suspended rats, in contrast to EDL muscles, generated slow contractile responses. Suspended SOL showed a reduced sensitivity to the contracture-producing effect of caffeine compared to control muscles. These results suggested that the modifications observed due to suspension could be encounted by changes in the characteristics of muscle fibers from slow to fast-twitch type.
Animals↗
The mechanical control system of bone in weightless spaceflight and in aging.
Bone loss is notable in elderly persons and in astronauts returning from spaceflight, however, the bone changes in these radically different patient populations appear morphologically similar. Bone structure depends upon several independent basic processes: growth, modeling, and remodeling. Each process follows a stereotyped sequence of steps. Alteration of any step may yield a similar bone loss, although from an entirely different mechanism. Mechanical forces appear to coordinate the fundamental bone shaping processes by a negative feedback control system. Determining how mechanical signals control the mass, architecture, and strength of bone may establish the limits by which exercise can prevent osteoporosis in the elderly and in astronauts despite obvious differences in etiology.
Adult↗
A monkey metabolism pod for space flight weightlessness studies.
An experiment system is described which will permit quantitative physiological studies in 8-14 kg adult monkeys during future space flight opportunities such as the NASA Shuttle. The system comprises a fiberglass pod containing a comfortable restraint couch for the animal. The pod is divided into upper and lower halves. When the monkey occupies the couch, a rubber belly-band forms a gas seal between the upper and lower portions of the animal. The upper-pod ventilating air stream monitored for PO2, PCO2, PN2 and PH2O to permit continuous metabolic gas-exchange measurements for computation of metabolic energy expenditure. The lower pod is lined with ashless filter paper for excreta collection and entrapment of liquid urine, and is ventilated separately. At the end of experimental periods of 1 to 7 days, all excreta plus the filter paper are removed for chemical analysis. The lower-pod ventilating gas ports also allow application of lower-body negative pressure to test cardiovascular competency when desired. The upper pod is provided with automatic food pellet and drinking water dispensers for quantitative measurement of nutrient intake. Balance assessment of the following elements can be made: N, Ca, P, Mg, K, Na, Cl, S and Fe. Animals have been kept in continuous restraint in the system for as long as 30 days without apparent ill effects.
Animals↗
Histological studies on the vestibular organ of frog embryos and larvae after simulated weightlessness.
The ontology of gravity receptors is discussed. As well as phylogenetic aspects of the question, we may ask whether the different gravity receptors in plants and animals derive from the same source; did they evolve from a general sensitivity of the living cell or do they represent parallel inventions. One may also ask whether during ontogeny of the receptor it receives information from gravity or whether the development of function of the organ is an autonomous process. In many cases ontogeny shows traces of phylogeny. Statoliths, e.g. the differentiating statolith membranes of the frog embryo, look somewhat like sedimentational structures. Furthermore the amphibian embryo in its relatively early stages takes up a special position in relation to the direction of gravity. Which mechanism is involved here? The materials studied were frog embryos and larvae which developed within a fast rotating clinostat. The results may help to answer the question as to whether the differentiation of the frog statolith membrane is an autonomous process.
Animals↗
Physiological aspects of automatic physical training control by biofeedback in weightlessness.
An automatically regulated biofeedback apparatus "UN-1" is described for enabling astronauts to maintain specified levels of exercise or lower body negative pressure within acceptable limits of cardiac function. The apparatus was also used to assess the workload tolerance of cosmonauts during space flight. Under these conditions the cosmonaut was unable to exercise on the cycloergometer when his heart rate reached 140 beats/minute steady state.
Adaptation, Physiological↗
Growth and cell structure of Proteus vulgaris when cultivated in weightlessness in the Cytos apparatus.
Growth data and electron-microscopic analyses are presented for Proteus vulgaris cultures which were grown during space flight in polyethylene packets in a semisolid medium with Tryptose for 96 h. In the suboptimal culture conditions the growth and morphological characteristics of the flight and ground control variants were nearly identical, but we were able to detect a number of differences between the cellular ultrastructure of these variants. These differences testify to changes in the bacterial cell metabolism during space flight.
Colony Count, Microbial↗
Positive pressure breathing by total body negative pressure: a new simulation model for fluid balance in weightlessness?
A systems study is proposed to explore correctly the effects of the combination of HDT (Head Down Tilt) and TBNP (Total Body Negative Pressure).
Bed Rest↗