Unit 12 Asma Space Physiology

Front 1

Summarize the time course of the body’s major physiologic shifts associated with space/microgravity acclimation and re-adaptation to the earth’s surface.

Back 1

This summary presupposes that all biological systems are in a state of homeostasis at the beginning of the flight. Some susceptible systems exhibit changes almost immediately as the vehicle begins orbiting Earth. For example, neurovestibular adjustments, and their associated symptoms, are likely to place during the first hours or days in orbit; in contrast, decreases in red blood cell mass are detected only after a period of subclinical latency and peak after 60 days in flight. Other physiologic functions do not seem to shift early in flight, but later undergo gradual and progressive changes. In particular, loss of calcium and lean body mass and possible effects from cumulative radiation seems to increase continually, regardless of flight duration or level of acclimatization achieved by other body systems. Most physiologic systems seem to reach a new steady state compatible with “normal” function in the space environment within 4 to 6 weeks. Complete acclimatization may require a very long period of exposure to weightlessness, probably in the absence of countermeasures; complete acclimatization thus has yet to be observed even after one-year missions. The greatest change from baseline seems to occur after 4 to 6 months in space (e.g. bone mass and muscle mass loss). Cardiovascular function and body fluid levels change within hours of exposure to weightlessness. The cardiac index of deconditioning indicates severity of orthostatic intolerance exhibited by crewmembers subjected to gravitational stress. Wide variability probably exists in individual tolerance and ability to acclimate to weightlessness.

Front 2

Distinguish between the 2 phases of human adaptation to microgravity

Back 2

Initial response (weeks) and adaptation response (months). The first phase (initial response) represents gradual adjustments in all body systems that take place over the first 3 to 6 weeks of flights. This phase is characterized by fluid shifts and changes in: neurovestibular receptors, sympathetic and parasympathetic function, fluid volume (losses), metabolism, hemodynamics, endocrine regulation, and morphologics. The second phase begins after several months in space and is characterized by regional losses of bone and muscle mass, changes in neurotransmitter and receptor functions, and perhaps decreased immune responses and compensated metabolic acidosis, mild dehydration, anemia, as well as central nervous system function.

Front 3

Describe the consequences fluid shift in microgravity

Back 3

Many of the cardiovascular changes that occur in response to the relative absence of gravitational force in space can be traced to changes in body fluid volume. When a person first enters weightlessness, fluids shift toward the head and torso because the mechanisms that normally counter the pooling continue to act, unopposed by gravity. This fluid shift distends the central vasculature, which contains the primary sensors for the cardiovascular system, causing the body to sense a fluid-volume overload. This can also lead to nasal congestion and preorbital puffiness, facial edema, thickening of the eyelids, and the jugular veins and veins in the temple, scalp, and forehead seem full and distended. Test results suggest that fluids shift quickly early in flight (within 24 hours) and reach a steady state within 3 to 5 days. The body responds to the need to eliminate the fluid-volume overload by reducing the central volume. Plasma volume declines during missions within hours and stabilizes about 12% below normal. The cephalad shift of fluid probably contributes to decreased thirst and fluid intake, which in turn decrease total body water. Although the body adapts appropriately to the weightless environment, upon return to Earth, the reduced plasma volume may contribute to orthostatic stress. Headward fluid shift is also a theory in the cause of SMS.

Front 4

Describe orthostatic dysfunction countermeasures used in microgravity.

Back 4

The operational countermeasure used by NASA since 1984 calls for crewmembers to ingest 32 ounces of water or juice and 8 salt tablets beginning about 1 hour before leaving orbit, to produce 1L of isotonic saline in the stomach. The efficacy of the fluid-loading protocol seems to vary with flight duration. For the shortest flights, only the CID (cardiovascular index of deconditioning) for subjects who used the fluid-loading countermeasure did not change. After 10 days of flight, however, this index was no different for those who used countermeasures and those who did not. Thus, the fluid loading countermeasure seems to protect orthostatic tolerance only for shorter flights.

Front 5

Describe the significance of muscle atrophy in microgravity

Back 5

Skeletal muscle constitutes nearly 40% of the volume of the human body. Animal studies have shown that 5 days in microgravity leads to slight muscle atrophy, and 12.5 days leads to significant muscle-fiber atrophy. Flights of 18 to 22 days induced more pronounced changes, including reduction in muscle-fiber mass, diameter, elasticity, and muscle strength, accompanied by significant up-regulation of fast myosin heavy chains and an expression of fast myosin light chain. Symptoms of muscle damage (fiber vacuolation, necrosis, centralized nuclei and satellite cell proliferation) also were found, although whether the damage was related only to muscle atrophy, or resulted from injury to blood vessels upon return to 1 g was unclear. The muscle adaptations seen over time in flight seem to reflect the structural changes in the muscle; however, the mechanisms of these adaptations, and their precise relationship to muscle function, still are elusive. In human studies weightlessness seems to induce significant structural changes in the muscle and spindle fibers. These changes are manifested as loss of muscle and strength accompanied by neuromuscular changes including muscle fatigue, abnormal relex behavior, and diminished neuromuscular efficiency. Without countermeasures a 35 day space flight may cause as much as 23-25% muscle atrophy. This decrease in muscle volume indicates a true atrophy of muscle tissue rather than a shift in body fluids. No significant recovery in muscle size was seen seven days after return to Earth. Muscle atrophy negatively affects muscle function (which includes muscle force, muscle fatigue and motor control).

Front 6

Describe the changes in bone and mineral metabolism after long-duration space flight.

Back 6

Space flight invokes continuous, possibly progressive changes in the skeletal and connective tissue systems. These changes are manifested in the way the body conserves calcium and other minerals that normally are stored in the skeleton. Loss of total body calcium and skeletal changes have been observed in animals and in people who have flown from 1 week to more than 365 days in space. These changes in bone and mineral metabolism may be among the most profound biomedical changes associated with long-duration space flight. Whether space flight induces mineral losses only in weight-bearing bones remains unclear. Studies show that calcium is loss through the urine, the rate of loss is slow at first but increases to almost 300mg/day by the 84th day of flight which can calculate into a loss of 300g or 25% of the initial body pool after 1 year in flight. Recovery of calcium lost during flight begins soon after return to 1 g. Calcium balance possibly could return to zero long before losses induces by space flight could be replenished, perhaps resulting in irreversible damage to the skeleton. Urinary output of hydroxyproline gradually increased, indicating deterioration of the collagenous matrix of weight bearing bones. Output of nitrogen also increased, reflecting muscle atrophy. In-flight animal studies showed marked skeletal changes after as few as 7 days in flight, including decreased bone growth, decreased mineralization, decreased bending strength and decreased weight of lumbar spine. Other functional rearrangements such as reduction in bone cell size and number at the bone surface have also been documented. Studies suggest that the loss of bone mineral might be due primarily to inhibited bone formation rather than increased bone reabsorption. In summary, it is clear based on information obtained from space missions, that bone and mineral metabolism is altered substantially during space flight. Calcium balance becomes increasingly negative throughout flight, and the bone-mineral content of weight-bearing bones declines. The major health hazards associated with skeletal changes include signs and symptoms of hypercalcemia with rapid bone turnover, the risk of kidney stones from hypercalciuria, the lengthy recovery of lost bone mass after flight, the possibility of irreversible bone loss (particularly trabecular bone) the possible effects of calcification in the soft tissues, and the possible increase in fracture potential.

Front 7

Describe the countermeasures used to reduce the skeletal effects in long-duration space flight

Back 7

The major countermeasures being explored to reduce the skeletal effects of space flight include the use of various weight-loading exercises or artificial gravity regimens that counteract the loss of gravitational and muscular stress, and nutritional and pharmacological manipulations. The crews of Skylab-3 and -4 exercised heavily during flight. Three of these six men showed substantial mineral losses, which casts doubt on the effectiveness of the particular exercises used as countermeasures. Soviet findings regarding the effect of in-flight exercise during long space flights have been inconsistent. Nutritional supplements of calcium and phosphorus for brief periods, and drugs such as fluoride or clodronate have shown promise in bedrest studies, and may prove effective during space flight. Because of technical and hardware constraints, artificial gravity thus far has been used only in animal studies. Centrifugation has been shown to prevent changes in the calcium and phosphorus content of rat long bones and to prevent osteoporosis.

Front 8

Describe the in-flight and post flight changes in hormones involved in fluid and electrolyte regulation

Back 8

With respect to fluid and electrolytes, the most significant changes accompanying space flight are reduction of total body fluid volumes and altered regulation of electrolytes. Many of the endocrine and biochemical changes observed in conjunction with space missions fit a consistent picture of homeostatic adjustments of circulatory dynamics, renal function, and endocrine response, probably initiated by fluid shifts and associated environmental stresses. The cephalad shift of fluids is thought to produce a transient increase in central blood volume that is detected by stretch receptors in the heart and interpreted as an increased in total blood volume. A compensatory loss of water and sodium from the renal tubules is thought to be effected through a series of neural, humoral, and directed hydraulic mechanisms. Fluid loss, particularly plasma volume occurs within in the first few days of space flight. The large change in plasma volume relative to the change in extracellular fluid volume suggests that interstitial fluid volume is conserved proportionately more than plasma volume in microgravity. Usually water intake is markedly reduced during the first few days of weightlessness, partly because of motion sickness symptoms and pharmacologic agents taken to prevent or ameliorate them. A decrease in body fluid must be accompanied by losses of electrolytes from the affected fluid compartment(s). Such losses often have reached the point at which blood concentrations of electrolytes have been diminished during flight. Electrolytes are lost mainly through renal excretion. Increases in urinary output of sodium, potassium, and chloride were observed in the Skylab flights and increased rates of potassium and calcium excretion occurred early in the Shuttle mission on which urine was collected during the flight. Studies have led to the conclusion that fluid and electrolyte retention begins very soon after entry into gravity. Because plasma volume almost always has been reduced after space flights of up to 84 days durations, elevated circulating concentrations of ADH apparently do not produce their usual (1-g) effect of increasing plasma volume to its normal value; although if diuresis does not occur, this hormone may effectively contribute to fluid retention. Plasma aldosterone was reduced 20% or more in Spacelab and SLS-1 astronauts at most sampling times during flight. During the first month of flight aldosterone usually was elevated, but from 30 to 48 days it was reduced, and after that seemed to stabilize around its preflight level. This data seem to reflect dynamic changes that are initiated within hours of the onset of weightlessness and continue for 30 days. The changes in aldosterone probably represent the response the response of the body to sodium loss. Plasma rennin activity (PRA) decreased during the first 48 hours of Spacelab flight and then increased. Plasma atrial natriuretic peptide (ANP) was reduced at most sampling times in the first 190 hours of two Spacelab flights, but mean values were above preflight levels between 30-40 hours. The PRA decrease followed by an increase and the decreased ANP during later stages of flight are consistent with an increased fluid load induced by microgravity followed by a relative dehydration and hyponatremia. An early (5 hours) decrease in ANP may be associated with the decrease in ANP may be associated with the decrease in central venous pressure observed on Spacelab missions. Plasma cortisol levels usually increased over preflight levels, but it was reduced at 80 and 130 hours during Spacelab missions. Elevated plasma and urinary cortisol during space flight have been considered an indication of stress, but cortisol, like aldosterone, promotes sodium retention and potassium excretion. Some of the endocrine changes observed to occur during and after space flight are not the responses that might be expected. For example, concentrations of aldosterone and angiotensin I often did not change in the same direction during flight. Anitidiuretic hormone was elevated greatly in plasma during short duration flights. The tendency of blood sodium and osmolality to be reduced plasma volume rather than elevated blood osmotic concentration is the effective stimulus for ADH secretion. The immediate elevation of plasma ADH at landing along with a sometimes delayed rise in blood aldosterone has been considered to indicate that the replenishment of body fluid occurs more rapidly than that of blood sodium. Aldosterone’s function as a sodium-retaining hormone may have been subordinated to its function as a regulator of serum potassium. The apparent loss of potassium from tissue on long-term flights probably would tend to increase blood potassium. In general, the body fluid and endocrine alterations during space flight are thought to represent adaptive responses to weightlessness. Adaptation may require different amounts of time for different systems; the first 4 to 6 weeks seems to be a time of particularly dynamic change. Because space flight also is associated with events such as emotional stress, space motion sickness, variable drug usage, gravity loads (launch and landing), and altered work/rest cycles, the simultaneous adjustment of many physiological variables may mask or negate certain predicted homeostatic responses to fluid shifts and electrolyte loss.

Front 9

Describe the in-flight and post flight hematologic changes in humans after long duration space flight.

Back 9

The most significant hematologic changes resulting from space flight are reductions in plasma volume and red blood cell mass. Decreases in plasma volume have been observed almost every time plasma volume was measured after U.S. space missions. Plasma volume decreases soon after onset of microgravity and recovers to preflight levels within 2 weeks after return to Earth.Decrease in red cell mass seems to begin within 4 days of launch and reaches a maximum after about 40 to 60 days of exposure to weightlessness, recovery is attained within 45 days of return to 1 g. Recovery of red cell mass seems to begin between 40 and 60 days after launch, whether landing had occurred or not. Observed changes in red blood cell count have been even more variable than those noted in red cell mass and hemoglobin mass. Hematocrit, hemoglobin, and erythrocyte count vary considerable. There is a consistent decrease after 20 days of flight. Original theories for red cell mass loss included oxygen toxicity, frequent phlebotomy, and changes in mean red cell volume however studies have discounted these theories. Loss of red blood cell mass now is thought to occur as the result of regulatory mechanisms that accompany the decrease in plasma volume. Some evidence exists that the rate of destruction of red blood cells by the reticulo-endothelial system increases during space flight. Studies have shown a change in red blood cell shape, however this readily reversed after even the longest space flights suggesting that no permanent alteration of bone marrow function occurs. The slow recovery of red blood cell mass after landing suggests that significant numbers of mature red blood cells are not returned to the circulation soon after landing. The mechanism that now is considered most likely to account for the majority of the red blood cell mass deficit is suppression of red blood cell production. Reticulocyte count, as a percentage of erythrocyte count, usually has been reduced during and immediately after space flight, but has recovered at rates that seem to depend on flight duration. In summary, exposure to microgravity and the associated cephalad shift of fluids result in a series of compensatory mechanisms. A rapid, significant reduction in plasma volume is followed by a decrease in erythropoietin levels and a subsequent reduction in red blood cell mass. The decrease in RBD mass results from a depression of erythropoiesis, which is caused primarily by low erythropoiesis or intramedullary destruction of red blood cell precursors. During long space flight, red blood cell mass apparently reaches an equilibrium that is optimal for the microgravity environment. The immune system also seems to be affected by space flight or its associated stresses. A blunted response in delayed-type hypersensitivity suggests that the cell-mediated portion of the immune system may be impaired by space flight. Analysis of the white blood cell populations has revealed consistent neutrophilia and lymphocytopenia, with a more recent observation of the existence of a unique monocyte population, on landing day. Depressed in vitro mitogen activation and production of cytokines in lymphocytes from crewmembers also has been a frequent observation. Changes in serum proteins and immunoglobulins also have been observed. These data suggest that immune responsiveness, both cell-mediated and humoral, may be altered by space flight.

Front 10

Describe microgravity-induced visual and orientation illusions how it effects crewmembers in space

Back 10

During reentry and immediately after landing, crewmembers frequently report that voluntary head motions produce illusions that the visual surrounding are moving. These illusions probably are related to disturbances of the gaze control system. The term oscillopsia refers to an apparent displacement of visual targets during passive or voluntary head movement. Hypothesis that signals from receptors that respond to linear acceleration are reinterpreted during adaptation to weightlessness. Almost all crewmembers perceive themselves or their surroundings to move when they move their heads during flight, during re-entry and after landing. The intensity of the on-orbit disturbances seems to increase with length of time in flight: the longer the flight, the more illusory phenomena reported. Even though individual experiences with self- and surround-motion vary, 3 categories of disturbances are commonly reported: (1) “input-output” gain disturbances, in which the perceived self/surround-motion seems exaggerated in rate, amplitude, or position after the head or body movement; (2) temporal disturbances, in which the perception of self- and surround-motion lags behind the head-body movement, persists after the real physical motion has stopped, or both: and (3) path disturbances, in which angular head and body movements elicit perceptions of linear or combined linear and angular self- or surround-motion. In general, these perceptual disturbances seem to be most intense or compelling during re-entry, less so immediately after wheel-stop, lesser still late in flight, and weakest shortly after achieving weightlessness. Also, a given head or body movement usually induces perceptual disturbances in more than one category. Cosmonauts often describe illusion of inversion that occur immediately after the onset of weightlessness and persist for minutes to hours. US astronauts seldom report illusions of inversion, but frequently report what they call “the downs’, referring to a very strong sensation that the floor is wherever their feet are. Some astronauts report this sensation almost immediately; others indicate that it takes 2 or 3 days to occur, and still others only experience it intermittently. Mittelstaedt (1986) proposed that the inversion illusion can be understood using a model that includes an internal (“ideotropic”) orientation vector. This vector may also explain “the downs”.

Front 11

Distinguish between the symptoms and incidences of Space Motion Sickness (SMS) and terrestrial motion sickness.

Back 11

Exposure to provocative real or apparent motion leads to the progressive cardinal symptoms of terrestrial motion sickness, which typically include pallor, increased body warmth, cold sweating, dizziness, drowsiness, nausea, and vomiting. The signs and symptoms of space motion sickness, when considered together with the time course of symptoms development and movements encountered upon exposure to microgravity, suggest that sickness experienced during space flight is similar to terrestrial motion sickness. However, the symptoms experienced as part of SMS may differ slightly from those exhibited during acute provocation on the ground. In particular, sweating has been the least frequently reported in-flight symptom and flushing is more common than pallor. Nearly universal are malaise, anorexia or loss of appetite, lack of initiative and irritability. Stomach awareness, vomiting, headache (perhaps due to headward fluid shifts), impaired concentration, lack of motivation, and drowsiness are reported more frequently in microgravity than during acute motion sickness on Earth. In SMS vomiting is usually sudden, infrequent (bouts are separated by 1 to 3 hours with no dry heaves), and often without prodromal nausea. Bowel sounds are decreased or absent. Gastrointestinal symptoms appear minutes to hours after orbital insertion. Symptoms usually resolve after 30 to 48 hours, with a reported range of 12 to 72 hours and recovery is rapid. Unless all movement is inhibited, most susceptible astronauts begin to experience space sickness within the first hour of orbital flight. Although symptoms generally resolve between 30 and 48 hours into the flight, the rate of recovery, degree of adaptation, and specific symptoms vary widely between individual astronauts. Antimotion sickness drugs offer some protection against SMS; however, some (e.g. scopolamine) may interfere with the adaptation process, and symptoms controlled by these drugs are experienced when treatment ceases. Adaptation to provocative motion during flight does not convey immunity to motion sickness immediately afterward. Approximately 10% of the Shuttle astronauts experience motion sickness during entry from orbit or immediately upon landing. Recovery from “return from orbit” motion sickness is variable, and has the same characteristics as in-flight space sickness. Microgravity by itself does not induce space sickness. As the volume of spacecraft and the mobility of their inhabitants have increased, the incidence of SMS has increased as well. In particular, movements that produce changes in orientation, particularly whole-body or head movements, are necessary to induce SMS symptoms.

Front 12

List the different theories and hypotheses of SMS

Back 12

Fluid shifts and sensory conflict (aka neural mismatch, sensory mismatch, or sensory rearrangement) are two major theories advanced to account for SMS. Although the fluid-shift theory could be associated with sensory conflict, mechanisms exist whereby the cephalad fluid shift accompanying microgravity could bypass the classic vestibular inputs to induce vomiting. Fluid shift, sensory-conflict, Treisman's theories, otolith-asymmetry, otolith-compensation, otolith tilt-translation reinterpretation hypotheses

Front 13

Discuss the fluid shift theory

Back 13

Fluid shift theory: Several mechanisms proposed to explain how the headward fluid shift associated with microgravity may produce SMS. One suggestion is that headward fluid shifts may change angiotensin activity and produce SMS by altering hormonal or neurotransmitter balance in the chemoreceptor trigger zone. Alternately, the fluid shift may alter biomechanical properties of the vestibular system. According to this hypothesis, the cephalad fluid shifts accompanying weightlessness would produce concomitant changes in intracranial pressure, the cerebrospinal fluid column, or the inner ear, thereby altering the response properties of vestibular receptors. Most evidence favors neither a nonspecific nor a sensory-conflict mechanism associated with fluid shifts. Anecdotal reports from Space Shuttle crewmembers and limited in0flight measurements of responses presumably sensitive to increased intracranial fluid pressure do not favor the fluid shift hypothesis. Data that would allow interpretation of individual differences are not available and therefore a fluid-shift theory should not be ruled out.

Front 14

Discuss the sensory-conflict theory

Back 14

Sensory-conflict theory: Advanced by Reason and Brand (1975). It assumes that human orientation in three-dimensional space, under normal gravitational conditions, is based on at least four sensory inputs to the central nervous system. The otolith organs provide information about linear accelerations and tilt relative to the gravity vector; information on angular acceleration is furnished by the semicircular canals; the visual system provides information concerning body orientation with respect to the visual scene; and touch, pressure and kinesthetic systems supply information about limb and body position. When the environment is altered in such a way that information from the sensory systems is not compatible and does not match previously stored neural patterns, motion sickness may result. Shortcomings of the sensory-conflict theory include its lack of predictive power, inability to explain those situation in which conflict exists without sickness, failure to include sensory-motor conflict, inability to explain specific mechanisms by which conflict actually gives rise to vomiting, and failure to address the observation that adaptation is not possible without conflict. Treisman’s Theory, Otolith-Asymmetry Hypotheis, Sensory –Compensation hypothesis, and Otolith Tilt-Translation Reinterpretation Hypothesis may be helpful in overcoming some of the weaknesses associated with the sensory-conflict theory.

Front 15

Describe Treisman's Theory

Back 15

Treisman’s Theory: Treisman suggested that the purpose of mechanisms underlying motion sickness, from an evolutionary perspective, was not to produce vomiting in response to motion, but rather to remove poisons from the stomach. He believed that motion was simply an artificial stimulus that activated these mechanisms or that provocative motions act on mechanisms developed to respond to minimal physiological disturbances produced by absorbed toxins. The neural activity that coordinates sensory inputs in order to control limb and eye movements would be disrupted by the central effects of neurotoxins. Disruption of this activity by unnatural motions thus would be interpreted as an early indication of the absorption of toxins, which then activates a mechanism to produce vomiting. It was hypothesized that if a vestibular mechanism exists to facilitate vomiting in response to poisons, then surgical removal of the vestibular apparatus in animals should result in a defective vomiting response to poisons. Tests of this revealed that the vomiting response was not influenced by removal of the vestibular apparatus and concluded that the mechanism to facilitate vomiting in response to toxins is partly vestibular.

Front 16

Describe the Otolith-Asymmetry Hypothesis

Back 16

Otolith-Asymmetry Hypothesis: Some individuals possess slight functional imbalances (e.g. weight differences) between the right and left otolith receptors, which are compensated for in 1 g by the central nervous system. This compensation is inappropriate in 0 g sine the weight differential is nullified and the compensatory response (either central or peripheral) is no longer correct for the new inertial environment. The result would be a temporary asymmetry that produces rotary vertigo, inappropriate eye movements, and posture changes until the imbalance is compensated or adjusted to the new situation. A similar imbalance would be produced upon return to 1 g, resulting in postflight vestibular disturbances. Individuals with a greater degree of asymmetry in otolith morphology thus would be more susceptible to SMS. Until recently, no tests were available to evaluate this hypothesis adequately. There are at least 2 problems with this hypothesis. First, if release from Earth-based compensation for otolith asymmetry were enough to produce motion sickness, then crewmembers should develop symptoms without head and body movements. However, movement is required to develop systems. Secondly, this hypothesis suggests that orientational illusions could be perceived without head or body movements. No such illusions have been reported.

Front 17

Describe the sensory-compensation hypothesis

Back 17

Senesory-Compensation Hypothesis: In the absence of an appropriate graviceptor signal in microgravity, information from the other spatial-orientation receptors can be used to maintain spatial orientation and movement control. Astronauts frequently report increased reliance on visual cues for spatial orientation and motion control.

Front 18

Describe otolith tilt-translation reinterpretation (OTTR) hypothesis

Back 18

Otolith Tilt-Translation Reinterpretation (OTTR) Hypothesis: Assumptions are: first, weightlessness is a form of sensory rearrangement to which people adapt. Secondly, graviceptors signal both orientation with respect to gravity (tilt) and linear acceleration, which is perceived as translation. Thirdly, in weightlessness, graviceptors do no respond to static pitch or roll, but do respond to linear acceleration. Because stimulation from gravity is absent during space flight, interpretation of the graviceptor signals as tilt is meaningless. Therefore, during adaptation to weightlessness, the brain reinterprets all graviceptor output to indicate translation. According to this hypothesis, at landing, a forward pitch head movement would be perceived as a rearward translation, and a clockwise roll head movement would be perceived as linear translation to the right. Several reports from crewmembers suggest that this is not the case, that the direction of self-motion associated with roll or pitch head movement during entry and immediately after landing may be opposite to that predicted by OTTR. There are several possibilities that may account for this difference: graviceptor ambiguity, motion attribution ambiguity, resolution of graviceptor ambiguity – signal temporal dynamics, resolution of graviceptor ambiguity – semicircular canal contributions, resolution of graviceptor ambiguity – “top-down” processes. These considerations may help to account for the discrepancy between crewmember reports of self- or surround-motion during head tilts and predictions from the OTTR hypothesis. A graviceptor signal change may result in perceived translation, and the direction of this perceived translation may be determined by concurrent semicircular canal signals, signals associated with top-down processes, or both. Most of the findings concerning locomotion, postural control, and sensory reports associated with space flight reported can be explained by the OTTR hypothesis, sensory compensation, or a combination of the two.

Front 19

Describe the various mechanical and electrical devices that have been explored to alleviate the symptoms of SMS.

Back 19

The mechanical devices, designed to prevent the complete adaptation of the body to weightlessness, are intended to counteract deconditioning during long missions as well as relieve motion-sickness symptoms during the first days of flight. The electrical devices, which pass an electrical current through the body, operate via mechanisms that as yet are unclear. Explored in the former Soviet Union. Pressurized insoles, load suit, pneumatic occlusion cuff, neck pneumatic shock absorber, electronic devices

Front 20

Describe pressurized insoles

Back 20

Pressurized insoles: the Cupola SAND-501 device is a pair of sandals with spring-loaded insoles containing a cuff that can be inflated to 20 to 60 mmHg with an attached bulb and manometer. The claim is that the pressure on the soles of the feet created a sensation of heaviness in the lower limbs which help overcome the illusion of turning upside down.

Front 21

Describe load suits

Back 21

Load suits: include adjustable bands that produce tension over the chest, back abdomen, side and leg seams. First worn by the crew of Soyuz-13. Although wearing the load suits was considered ‘pleasant’ by the cosmonauts, they still experienced illusions, headward fluid shifts and symptoms of SMS.

Front 22

Describe neck pneumatic shock absorber (NPSA)

Back 22

Neck Pneumatic Shock Absorber (NPSA): is a cap with rubber cords that provide a load to the cervical vertebrae and neck muscles. Wearing this device requires stretching the neck muscles to maintain an erect head position and restrains the wearer from turning or tilting the head. Cord tension can be adjusted to the wearer. Designed to be worn during working hours for the first 3 or 4 days of a mission. Cosmonauts reported the NPSA to be effective in alleviating dizziness, illusions, discomfort, and nausea with no adverse effect on performance. The effectiveness of this device was attributed to ‘normalization of the vestibulocervical reflex system’; however, head movements, which provoke space motion sickness symptoms, were limited by this device.

Front 23

Describe pneumatic occlusion cuff

Back 23

Pneumatic Occlusion Cuff: To reduce or prevent the cephalad shift of body fluids that occurs in microgravity, the Soyuz-38 crew wore a pneumatic occlusion cuff on the hips. Reportedly it decreased or eliminated dizziness, illusions, nausea, and the sensation of head pulsation.

Front 24

Describe electrical devises used to alleviate symptoms of SMS.

Back 24

Electrical devices: The use of weak electrical currents also has been explored to prevent or treat motion sickness. Electroanalgesia or electrotranquilization used two electrodes, one placed on the forehead and one on the mastoid process. Electroanalgesia did not increase resistance to experimentally induced motion sickness when sessions were performed before stressful motion; however, sessions conducted between two motion-stressor tests reduced or eliminated the residual symptoms from the first test and increased tolerance to the test performed after the electroanalgesia session. A second electroanalgesia session after the second motion-stressor test also improved recovery from symptoms induced by that test. No undesirable side effects were reported. Some researchers have suggested that passing a weak current through the frontal lobes of the brain corrects autonomic disorders through a beneficial effect on the limbic-hypothalamic-reticular system. It is hypothesized that electroanalgesia helps the central nervous system adapt to stress by generating an area of ‘cathodic depression’ in the frontal lobes, thereby reducing peripheral perception and changing the functional associations of the frontal cortex with the hypothalamus. There is also one suggestion that learning is facilitated by alternating periods of environmental interaction with periods of sleep because sleep plays an important role in the processing and assimilation of new information. Termed ‘fractional adaptation’, Polyakov reported that ‘electrosleep’ has been used effectively to hasten adaptation aboard ships.

Front 25

Describe electroacupuncture

Back 25

It was observed that motion sickness affected conductivity along standard acupuncture pathways regardless of symptom severity. Electoacupuncture wa used successfully by a group to treat seasickness. Subthreshold multichannel electrical stimulation of the antigravity cervical muscles also was reported to be promising as a countermeasure against motion sickness. Although electrical devices reportedly are effective in counteracting terrestrial motion sickness, they have not been tested in the space environment. The mechanical devices have been tested under weightless conditions; however, the small number of individuals tested and the lack of control subjects makes it difficult to determine their efficacy.