Erratum to: New approaches to countermeasures of the negative effects of micro-gravity in long-term space flights: [Acta Astronautica 59 (2006) 13–19]

The results of studies of influence of mechanostimulation of the soles’ support zones on the effects of micro-gravity in the motor system are presented. It was shown that mechanostimulation of the soles’ support zones in the regimen of slow and fast walking, every day during 7 days of dry immersion (DI), eliminates fully or suppresses considerably the effects of micro-gravity. Decrease of the force–velocity properties or atrophic changes in the leg extensors were not developed after exposure to simulated micro-gravity in the subjects who “walked” 20 min of each hour six times a day; the transverse stiffness was only slightly lowered and the amplitude of electromyographic activity at rest stayed unchanged. The level of orthostatic deficiency in this group was also lower than in the group without stimulation. These experimental results being in full agreement with previous studies point out to the leading role of the support deafferentation in gravitational deprivation of the tonic muscle system's activity and thus that adequate mechanostimulation of the soles’ support zones can be proposed as a countermeasure against the negative effects of weightlessness.     

Force and power characteristics of a resistive exercise device for use in space

We have developed a non-gravity dependent mechanical device, which provides resistance during coupled concentric and eccentric muscle actions, through the inertia of a spinning fly-wheel (Fly-Wheel Ergometry; FWE). Our research shows that lower-limb FWE exercise can produce forces and thus muscular stress comparable to what is typical of advanced resistance training using free weights. FWE also offers greater training stimuli during eccentric relative to concentric muscle actions, as evidenced by force and electromyographic (EMG) measurements. Muscle use of specific muscle groups, as assessed by the exercise-induced contrast shift of magnetic resonance images, is similar during lower-limb FWE and the barbell squat. Unlike free-weight exercise, FWE allows for maximal voluntary effort in each repetition of an exercise bout. Likewise, FWE exercise, not unassisted free-weight exercise, produces eccentric "overload". Collectively, the inherent features of this resistive exercise device and the results of the physiological evaluations we have performed, suggest that resistance exercise using FWE could be used as an effective exercise counter-measure in space. The flywheel principle can be employed to any exercise configuration and designed into a compact device allowing for exercises stressing those muscles and bone structures, which are thought to be most affected by long-duration spaceflight.     

Nemaline rod and degeneration of Z band of muscle cell in weightlessness at spaceflight

There are some studies demonstrating the skeletal muscle degeneration associated with the degeneration of Z band and appearance of nemaline rods in experimental animals of the simulation model for spaceflight but not in human heart tissues. In the present study, therefore, we investigated the pathological changes or degeneration in left auricular heart muscles obtained during operations of mitral valves replacement using both electron and light microscopies. The degeneration of Z band even in the myofibrils of comparatively little damaged cell was found. Furthermore, nemaline rods were detected in most of the heart muscle cells. These results suggest that the existence of nemaline rods is involved in the cell injury in the heart muscle of patients with heart disease without nemaline myopathy. Further study is necessary to know whether the similar pathological findings are observed not only in the skeletal muscle but also in the cardiac muscle in experimental animals of the simulation model for spaceflight or in a prolonged spaceflight.     

The ankle ergometer: a new tool for quantifying changes in mechanical properties of human muscle as a result of spaceflight

A mechanical device for studying changes in mechanical properties of human muscle as a result of spaceflight is presented. Its main capacities are to allow during a given experiment investigation of both contractile and visco-elastic properties of a musculo-articular complex using respectively isometric contractions, isokinetic movements, quick-release tests and sinusoidal perturbations. This device is a motor driven ergometer associated to an experimental protocol designed for pre- and post-flight experiments. As microgravity preferentially affects postural muscles, the apparatus was designed to test muscle groups crossing the ankle joint. Three subjects were tested during the Euromir '94 mission. Preliminary results obtained on the european astronaut are briefly reported. During the next two years the experiments will be performed during six missions.     

The natural cytotoxicity in cosmonauts on board space stations

The nature of the changes of resistance to infection seems to be very important. Our studies indicate that different functions of natural killers could be depressed after the spaceflight. The decrease of the percentage of the lymphocytes that can bind target cells lead to the lowering of the “active” NK level and this can be resulted in the depression of total NK activity and lowering of resistance to viral and tumor antigens. The investigation of natural killer cells in cosmonauts before and after short and long-term spaceflights also revealed the important role of spaceflight duration, stress and individual immune reactivity.     

Decrease of contractile properties and transversal stiffness of single fibers in human soleus after 7-day “dry” immersion

The simulation model of “dry” immersion was used to evaluate the effects of plantar mechanical stimulation (PMS) and high frequency electromyostimulation (EMS) on the mechanical properties of human soleus fibers under the conditions of gravitational unloading. We examined contractile properties of single fibers by means of tensometry, transversal stiffness of sarcolemma and different areas of the contractile apparatus by means of atomic force microscopy. It was shown that there is a reduction of transversal stiffness in single muscle fibers under hypogravitational conditions. Application of different countermeasures could compensate this effect. Meanwhile pneumostimulation and electro stimulation act in quite different way. Therefore, pneumostimulation seems to be more effective. The data obtained can be considered as the evidence of the fact that such countermeasures as PMS and electromyostimulation influence on muscle fibers in quite different ways and PMS efficiency is likely to be higher. On the basis of our experimental data on transverse stiffness of mechanotransductional nodes and the contractile apparatus, we can assume that support stimulation allows prevention of destructive processes in muscle fibers. Electrostimulation seems to stimulate contractile activity only without suppression of impairment of the fiber mechanical properties.     

A mathematical and experimental simulation of the hematological response to weightlessness

Two ground-based methods of weightlessness simulation--a computer model of erythropoiesis feedback regulation and bedrest--were used to investigate the mechanisms which lead to loss of red cell mass during spaceflight. Both methods were used to simulate the first Skylab mission of 28 days. Human bedrest subjects lose red cell mass linearly with time and in this study the loss was 6.7% at the end of four weeks (compared to 14% in Skylab). Postbedrest recovery of red cell mass was delayed for two weeks during which time a further decline in this quantity was noted. This is consistent with the first Skylab mission but not with the two longer flights of two and three months. Hemoconcentration, observed early in the study, was essentially maintained despite red cell loss because of continued loss of plasma volume. The computer model, using the time-varying hematocrit data to estimate red cell production rates, predicted dynamic behavior of plasma volume and red cell mass that was in close agreement with the measured values. The results support the hypothesis that red cell loss during supine bedrest is a normal physiological feedback process in response to hemoconcentration enhanced tissue oxygenation and suppression of red cell production. In contrast, the delayed postbedrest recovery of red cell mass was more difficult to explain, especially in the light of enhanced reticulocyte indices observed at the onset on ambulation. Model simulation suggested the possibilities, still to be experimentally demonstrated, that this period was marked by some combination of increased oxygen-hemoglobin affinity, small reductions in mean red cell life span, ineffective erythropoiesis, or abnormal reticulocytosis. The question of whether hemoconcentration is the sole contributor to spaceflight red cell losses also remains to be resolved.     

Autonomic function testing aboard the ISS using “PNEUMOCARD”

Investigations of blood pressure, heart rate (HR), and heart rate variability (HRV) during long term space flights on board the “ISS” have shown characteristic changes of autonomic cardiovascular control. Therefore, alterations of the autonomic nervous system occurring during spaceflight may be responsible for in- and post-flight disturbances. The device “Pneumocard” was developed to further investigate autonomic cardiovascular and respiratory function aboard the ISS. The hard-software diagnostic complex “Pneumocard” was used during in-flight experiment aboard ISS for autonomic function testing. ECG, photoplethysmography, respiration, transthoracic bioimpedance and seismocardiography were assessed in one male cosmonaut (flight lengths six month). Recordings were made prior to the flight, late during flight, and post-flight during spontaneous respiration and controlled respiration at different rates.HR remained stable during flight. The values were comparable to supine measurements on earth. Respiratory frequency and blood pressure decreased during flight. Post flight HR and BP values increased compared to in-flight data exceeding pre-flight values. Cardiac time intervals did not change dramatically during flight. Pulse wave transit time decreased during flight. The maximum of the first time derivative of the impedance cardiogram, which is highly correlated with stroke volume was not reduced in-flight.Our results demonstrate that autonomic function testing aboard the ISS using “Pneumocard” is feasible and generates data of good quality. Despite the decrease in BP, pulse wave transit time was found reduced in space as shown earlier. However, cardiac output did not decrease profoundly in the investigated cosmonaut.Autonomic testing during space flight detects individual changes in cardiovascular control and may add important information to standard medical control. The recent plans to support a flight to Mars, makes these kinds of observations all the more relevant and compelling.     

Bone loss during long term space flight is prevented by the application of a short term impulsive mechanical stimulus

In long term space flight, the mechanical forces applied to the skeleton are substantially reduced and are altered in character. This reduced skeletal loading results in a reduction in bone mass. Exercise techniques currently used in space can maintain muscle mass but the mechanical stimulus provided by this exercise does not prevent bone loss. By applying an external impulsive load for a short period each day, which is intended to mimic the heel strike transient, to the lower limb of an astronaut during a long term space flight (5 months), this study tests the hypothesis that the bone cells can be activated by an appropriate external mechanical stimulus to maintain bone mass throughout prolonged periods of weightlessness. A mechanical loading device was developed to produce a loading of the os-calcis similar to that observed during the heel strike transient. The device is activated by the astronaut to provide a transient load to the heel of one leg whilst providing an equivalent exercising load to the other leg. During the EUROMIR95 mission on the MIR space station, an astronaut used this device for a short period daily throughout the duration of the mission. Pre- and post-flight measurements of bone mineral density (BMD) of the os-calcis and femoral neck of the astronaut were made to determine the efficacy of the device in preventing loss of bone mineral during the mission. On the os-calcis which received the mechanical stimulus, BMD was maintained throughout the period of the flight, while it was reduced by up to 7% on the os-calcis which received no stimulus. Post-flight, BMD in both the stimulated and non-stimulated os-calcis reduces, the extent of this reduction however is less in the stimulated os-calcis. For the femoral neck, the mechanical stimulation does not produce a positive effect.     

Caenorhabditis elegans survives atmospheric breakup of STS-107, space shuttle Columbia

The nematode Caenorhabditis elegans, a popular organism for biological studies, is being developed as a model system for space biology. The chemically defined liquid medium, C. elegans Maintenance Medium (CeMM), allows axenic cultivation and automation of experiments that are critical for spaceflight research. To validate CeMM for use during spaceflight, we grew animals using CeMM and standard laboratory conditions onboard STS-107, space shuttle Columbia. Tragically, the Columbia was destroyed while reentering the Earth's atmosphere. During the massive recovery effort, hardware that contained our experiment was found. Live animals were observed in four of the five recovered canisters, which had survived on both types of media. These data demonstrate that CeMM is capable of supporting C. elegans during spaceflight. They also demonstrate that animals can survive a relatively unprotected reentry into the Earth's atmosphere, which has implications with regard to the packaging of living material during space flight, planetary protection, and the interplanetary transfer of life.     

Using radiation risk for assessment of space radiation hazard

Radiation hazard caused by exposure during a spaceflight is characterized by radiobiological consequences at all levels of organism. These consequences have a stochastic nature. Even deterministic effects are basically random quantity having all attributes of such mathematical values. The radiation risk is defined in this case as an additional probability of health damage or as a death probability in extreme case. For the manned spaceflight additional peculiarity of a human’s exposure is added. A natural space radiation environment has a stochastic character because solar particle events and crew of a spacecraft can be exposed to dose from background level up to lethal one.The report presents a procedure of radiation risk assessment for quantitative expression of radiation hazard level during a flight and using this value for developing protection recommendations. It is emphasized that the risk value is connected specifically with the time interval of possible hazard’s existent. The form of risk representation must be chosen depending on a time scale of radiobiological processes induced by the exposure (expressing in fact the radiation hazard model). Surviving function specified for the crewmember mortality rate changed by the professional exposure must be used for risk calculation. Solar particle events determine a stochastic character of radiation environment in space that must be taken into account for a risk assessment. The reliability of radiation risk assessment can be used for this goal.     

Role of support afferentation in control of the tonic muscle activity

The paper summarizes the results of experimental studies advocating for the leading role of support afferentation in control of the functional organization of the tonic muscle system. It is shown that transition to supportless conditions is followed by a significant decline of transverse stiffness and maximal voluntary force of postural (extensor) muscles limiting their participation in locomotion and increasing involvement of phasic muscles. Mechanical stimulation of the support zones of the soles under the supportless conditions eliminates all the above-mentioned effects, including changes in transverse stiffness and maximal voluntary forces of postural muscles, and consequent loss of influence of postural muscles in the locomotor activity. It is suggested that support afferentation, facilitating (support is present) or suppressing (support is absent) the tonic motor units (MUs) activities, defines the coordination patterns of postural synergies, and ensures the optimal strategy of corrective postural responses.     

Influence of the gravitational vertical on geometric visual illusions

The occurrence of geometric orientation illusions and the perception of ambiguous figures were analyzed in 24 subjects during static body tilt relative to gravity on Earth. Results showed that illusions such as the Rock's diamond/square, the Ponzo illusion, and orientation contrast illusions occurred less frequently, and that depth reversal of ambiguous figures took more time when subjects were lying on their side or supine compared to upright, thus suggesting that the gravitational reference plays a significant role in these “visual” illusions. The structure of images, our representation of the environment, and orientation relative to gravity are all integral parts in interpreting visual images. In a weightless environment where no gravitational reference can be used, it is expected that similar alterations in visual perception will occur.     

Fluid volumes changes induced by spaceflight

The blood volume (BV), plasma volume (PV), and extracellular fluid volume changes produced in crewmembers during spaceflights of 11-84 days were compared to changes after 14 or 28 days of bedrest. Spaceflight and bedrest produce approximately equal BV changes but the recorded PV change after spaceflight was less. However, the diurnal change in PV may explain the smaller decreases recorded after spaceflight. The cardiovascular deconditioning caused by spaceflight and bedrest was compared using the mean heart rate response to lower body negative pressure (LBNP) testing at -50 mmHg pressure. These tests show approximately equal LBNP produced heart rate changes after bedrest and spaceflight. A countermeasure which includes 4 hr of LBNP treatment at -30 mmHg and the ingestion of one l. of saline was studied and found capable of returning the heart rate response and the PV of bedrested subjects to control (prebedrest) levels suggesting that it would be useful to the crewmembers after a spaceflight.     

Gender specific changes in cortical activation patterns during exposure to artificial gravity

Keeping astronauts healthy during long duration spaceflight remains a challenge. Artificial gravity (AG) generated by a short arm human centrifuges (SAHC) is proposed as the next generation of integrated countermeasure devices that will allow human beings to safely spend extended durations in space, although comparatively little is known about any psychological side effects of AG on brain function.     

Sympathetic nervous system and spaceflight

Purpose: Orthostatic stability on Earth is maintained through sympathetic nerve activation sufficient to increase peripheral vascular resistance and defend against reductions of blood pressure. Orthostatic instability in astronauts upon return from space missions has been linked to blunted vascular resistance responses to standing, introducing the possibility that spaceflight alters normal function between sympathetic efferent traffic and vascular reactivity.Methods: We evaluated published results of spaceflight and relevant ground-based microgravity simulations in an effort to determine responses of the sympathetic nervous system and consequences for orthostatic stability.Results: Direct microneurographic recordings from humans in space revealed that sympathetic nerve activity is increased and preserved in the upright posture after return to Earth (STS-90). However, none of the astronauts studied during STS-90 presented with presyncope postflight, leaving unanswered the question of whether postflight orthostatic intolerance is associated with blunted sympathetic nerve responses or inadequate translation into vascular resistance.Conclusions: There is little evidence to support the concept that spaceflight induces fundamental sympathetic neuroplasticity. The available data seem to support the hypothesis that regardless of whether or not sympathetic traffic is altered during flight, astronauts return with reduced blood volumes and consequent heightened baseline sympathetic activity. Because of this, the ability to withstand an orthostatic challenge postflight is directly proportional to an astronaut's maximal sympathetic activation capacity and remaining sympathetic reserve.     

Spaceflight and clinorotation cause cytoskeleton and mitochondria changes and increases in apoptosis in cultured cells.

The cytoskeleton is a complex network of fibers that is sensitive to environmental factors including microgravity and altered gravitational forces. Cellular functions such as transport of cell organelles depend on cytoskeletal integrity; regulation of cytoskeletal activity plays a role in cell maintenance, cell division, and apoptosis. Here we report cytoskeletal and mitochondria alterations in cultured human lymphocyte (Jurkat) cells after exposure to spaceflight and in insect cells of Drosophila melanogaster (Schneider S-1) after exposure to conditions created by clinostat rotation. Jurkat cells were flown on the space shuttle in Biorack cassettes while Schneider S-1 cells were exposed to altered gravity forces as produced by clinostat rotation. The effects of both treatments were similar in the different cell types. Fifty percent of cells displayed effects on the microtubule network in both cell lines. Under these experimental conditions mitochondria clustering and morphological alterations of mitochondrial cristae was observed to various degrees after 4 and 48 hours of culture. Jurkat cells underwent cell divisions during exposure to spaceflight but a large number of apoptotic cells was also observed. Similar results were obtained in Schneider S-1 cells cultured under clinostat rotation. Both cell lines displayed mitochondria abnormalities and mitochondria clustering toward one side of the cells which is interpreted to be the result of microtubule disruption and failure of mitochondria transport along microtubules. The number of mitochondria was increased in cells exposed to altered gravity while cristae morphology was severely affected indicating altered mitochondria function. These results show that spaceflight as well as altered gravity produced by clinostat rotation affects microtubule and mitochondria organization and results in increases in apoptosis. Grant numbers: NAG 10-0224, NAG2-985.     

Respective effects of hindlimb suspension, confinement and spaceflight on myotendinous junction ultrastructure

This study compares the effects of 14-day confinement and spaceflight with the respective effects of 8, 18 and 29-day hindlimb suspension on rat soleus and plantaris MTJ ultrastructure. Independently of the experimental situation, greater morphological changes were observed in the soleus as compared to the plantaris MTJ. 18 days of suspension and 14 days of confinement resulted in ultrastructural modifications of the digit-like processes in the soleus MTJ. Additional changes were observed in the myofibrils, microtendon and tendon after 29 days of suspension and 4 days of spaceflight. These results emphasize the influence of the intensity and duration of the muscle loading on the MTJ ultrastructure.     

Plant molecular biology in the space station era: utilization of KSC fixation tubes with RNAlater

Spaceflight experiments involving biological specimens face unique challenges with regard to the on orbit harvest and preservation of material for later ground-based analyses. Preserving plant material for gene expression analyses requires that the tissue be prepared and stored in a manner that maintains the integrity of RNA. The liquid preservative RNAlater (Ambion) provides an effective alternative to conventional freezing strategies, which are limited or unavailable in current spaceflight experiment scenarios. The spaceflight use of RNAlater is enabled by the Kennedy space center fixation tube (KFT), hardware designed to provide the necessary containment of fixatives during the harvest and stowage of biological samples in space. Pairing RNAlater with the KFT system provides a safe and effective strategy for preserving plant material for subsequent molecular analyses, a strategy that has proven effective in several spaceflight experiments. Possible spaceflight scenarios for the use of RNAlater and KFTs are explored and discussed.     

Choroidal responses in microgravity. (SLS-1, SLS-2 and hindlimb-suspension experiments)

Fluid and electrolyte shifts occuring during human spaceflight have been reported and investigated at the level of blood, cardio-vascular and renal responses. Very few data were available concerning the cerebral fluid and electrolyte adaptation to microgravity, even in animal models. It is the reason why we developed several studies focused on the effects of spaceflight (SLS-1 and SLS-2 programs, carried on NASA STS 40 and 56 missions, which were 9- and 14-day flights, respectively), on structural and functional features of choroid plexuses, organs which secrete 70–90 % of cerebrospinal fluid (CSF) and which are involved in brain homeostasis. Rats flown aboard space shuttles were sacrificed either in space (SLS-2 experiment, on flight day 13) or 4–8 hours after landing (SLS-1 and SLS-2 experiments). Quantitative autoradiography performed by microdensitometry and image analysis, showed that lateral and third ventricle choroid plexuses from rats flown for SLS-1 experiment demonstrated an increased number (about x 2) of binding sites to natriuretic peptides (which are known to be involved in mechanisms regulating CSF production). Using electron microscopy and immunocytochemistry, we studied the cellular response of choroid plexuses, which produce cerebrospinal fluid (CSF) in brain lateral, third and fourth ventricles. We demonstrated that spaceflight (SLS-2 experiment, inflight samples) induces changes in the choroidal cell structure (apical microvilli, kinocilia organization, vesicle accumulation) and protein distribution or expression (carbonic anhydrase II, water channels,…). These observations suggested a loss of choroidal cell polarity and a decrease in CSF secretion. Hindlimb-suspended rats displayed similar choroidal changes. All together, these results support the hypothesis of a modified CSF production in rats during long-term (9, 13 or 14 days) adaptations to microgravity.