One of the most important and urgent issues in the field of space medicine is to reveal the potential mechanism underlying the disused muscle atrophy during the weightlessness or microgravity environment. It will conduce to find out effective methods for the prevention and treatment of muscle atrophy during a long-term space flight. Increasing data show that muscle spindle discharges are significantly altered following the hindlimb unloading, suggesting a vital role in the progress of muscle atrophy. In the last decades, we have made a series of studies on changes in the morphological structure and function of muscle spindle following simulated weightlessness. This review will discuss our main results and related researches for understanding of muscle spindle activities during microgravity environment, which may provide a theoretic basis for effective prevention and treatment of muscle atrophy induced by weightlessness.
Animals ; Hindlimb Suspension ; Muscle Spindles ; physiopathology ; Muscle, Skeletal ; physiopathology ; Muscular Atrophy ; physiopathology ; Space Flight ; Weightlessness Simulation

The Chinese space station will be built around 2020. As a national space laboratory, it will offer unique opportunities for studying the physiological effects of weightlessness and the efficacy of the countermeasures against such effects. In this paper, we described the development of countermeasure systems in the Chinese space program. To emphasize the need of the Chinese space program to implement its own program for developing countermeasures, we reviewed the literature on the negative physiological effects of weightlessness, the challenges of completing missions, the development of countermeasure devices, the establishment of countermeasure programs, and the efficacy of the countermeasure techniques in American and Russian manned spaceflights. In addition, a brief overview was provided on the Chinese research and development on countermeasures to discuss the current status and goals of the development of countermeasures against physiological problems associated with weightlessness.
China ; Humans ; Program Evaluation ; Space Flight ; Weightlessness ; Weightlessness Simulation

Space flight experiments have suggested that microgravity can affect cellular processes in microorganisms. To simulate the microgravity environment on earth, several models have been developed and applied to examine the effect of microgravity on secondary metabolism. In this paper, studies of effects of space flight on secondary metabolism are exemplified and reviewed along with the advantages and disadvantages of the current models used for simulating microgravity. This discussion is both significant and timely to researchers considering the use of simulated microgravity or space flight to explore effects of weightlessness on secondary metabolism.
Humans ; Metabolism ; physiology ; Models, Theoretical ; Space Flight ; Weightlessness Simulation

Cardiac remodeling is the heart's response to external or internal stimuli. Weightlessness/simulated weightlessness leads to cardiac atrophy and heart function declining. Understanding the mechanism of cardiac atrophy under weightlessness is important to help astronaut recover from unloading-induced cardiovascular changes after spaceflight. Unloading-induced changes of hemodynamics, metabolic demands and neurohumoral regulation contribute to cardiac atrophy and function declining. During this process, Ca(2+)-related signaling, NF-κB signaling, ERK signaling, ubiquitin-proteasome pathway and autophagy are involved in weightlessness-induced cardiac atrophy. This article reviews the underlying mechanism of cardiac atrophy under weightlessness/simulated weightlessness.
Atrophy ; Heart ; Heart Diseases ; Hemodynamics ; Humans ; NF-kappa B ; Space Flight ; Weightlessness ; Weightlessness Simulation

Exposure to thermal environment is one of the main concerns for manned space exploration. By focusing on the works performed on thermoregulation at microgravity or simulated microgravity, we endeavored to review the investigation on space thermal environmental physiology. First of all, the application of medical requirements for the crew module design from normal thermal comfort to accidental thermal emergencies in a space craft will be addressed. Then, alterations in the autonomic and behavioral temperature regulation caused by the effect of weightlessness both in space flight and its simulation on the ground are also discussed. Furthermore, countermeasures like exercise training, simulated natural ventilation, encouraged drink, etc., in the protection of thermoregulation during space flight is presented. Finally, the challenge of space thermal environment physiology faced in the future is figured out.
Aerospace Medicine ; Body Temperature Regulation ; Environment ; Exercise ; Humans ; Space Flight ; Weightlessness ; Weightlessness Simulation

BACKGROUND: Changes in the volume of the fluid space expanded by i.v. infusion of crystalloid solution have been analysed recently using mathematical models. The models are based on the assumption that the body strives to maintain volume homeostasis of fluid spaces and that the rate of restoration is a function of deviation from resting volume. METHODS: In this work mathematical models were developed to represent the kinetics of volume changes of fluid spaces associated with infusion of Ringer's solution. Based on the characteristics of fluid transportation, two expansion models were tested. The single-fluid space model has a single volume into which fluid is fed and from which fluid is left, and the two-fluid space model has another space in addition to the first volume so that fluid exchanges between these two spaces are possible. Volunteers (six men) were given Hartman's solution for 30 min and the changes in blood hemoglobin were detected. RESULTS: From the comparison with experimental data, the single-fluid space model was found to represent adequately in all volunteers, however, two-fluid space model was found to represent 75% of volunteers. CONCLUSIONS: These models may be useful in the description and analysis of the effects of i.v. fluid therapy.
Blood Volume ; Body Fluids* ; Fluid Therapy ; Homeostasis ; Kinetics ; Models, Theoretical ; Space Simulation ; Transportation ; Volunteers

In order to explore the reason why hypokalemia could increase the vulnerable window (VW) for unidirectional conduction block in Long QT Syndromes (LQTS), we observed the effect of hypokalemia on the spatial gradients of Na channel conductance (G(Na)) and gating factors by using the LR91 1-dimensional heterogeneous virtual cardiac ventricular tissue model quatitively. The computer simulation experiments were divided into two groups, namely control and LQTS groups. The action potential was elicited after the basic stimulus S1 (-70 microA/microF, 1.5 ms) was given 10 times with basic cycle length (BCL) 500, 1000 and 2000 ms. To test the VW in unit of time (VWtime), the S1-S2 programmed stimuli were used with shortening S1S2 interval at the decrement of 1 ms. At the same time, the spatial gradients of Na channel conductance (G(Na)) and gating factors, m, h, j, were investigated. The APD and ionic channel currents were also detected under the conditions of normal and lower concentration of K+ outside of cell. We found that hypokalemia, LQTS and slow pacing rate enhanced the spatial gradient of G(Na) by increasing the spatial gradient of inactive gating factors h x j. The results also showed that hypokalemia deduced the peak values of I(K) and I(K1), which prolonged the action potential duration and enlarged the repolarization dispersion in this 1-D tissue cable model. Possibly these are the important factors to cause the spatial gradient of h x j and G(Na). enlargement. These changes increase the incidence of unidirectional conduction block of VW, and are vital reasons to increase the possibility of ventricular arrhythmia generation.
Computer Simulation ; Extracellular Space ; metabolism ; Humans ; Hypokalemia ; metabolism ; Long QT Syndrome ; etiology ; metabolism ; physiopathology ; Models, Biological ; Myocardium ; metabolism ; Sodium Channels ; metabolism

We studied the effects of simulated microgravity on mouse oocytes maturation, and analyzed whether the tail-suspended model can be applied to investigate simulated microgravity effects on reproductive processes in female mice. Mouse oocytes were cultured in vitro with microgravity simulated by a rotating wall vessel bioreactor and by tail-suspended model, and the maturation rate of the mouse oocytes in the two models were examined in vivo. The maturation rate of mouse oocytes cultured in simulated microgravity was 8.93%, and that was 72.33% in 1g gravity. In ratio, oocyte maturation rate had no significant difference between the rotational group and control group. Microgravity simulated by the tail-suspended model inhibited mouse oocytes maturation and increased the rate of oocytes abnormity. The maturation rate of tail-suspended mouse oocytes was 14.54%, which was significantly lower than that of control group. Tail-suspended model should be an ideal model to investigate simulated microgravity effects on reproductive processes of female mice.
Animals ; Cells, Cultured ; Female ; Hindlimb Suspension ; Mice ; Oocytes ; cytology ; physiology ; Oogenesis ; physiology ; Weightlessness Simulation

The aim of the present study was to examine whether there are changes in systolic and diastolic blood pressure (SBP and DBP) and heart rate (HR) and their spectral indices in conscious free-moving rats after tail-suspension for 28 d. The tail-suspended hindlimb-unloaded (HU) rat model was used to simulate the cardiovascular effect of microgravity and the post-spaceflight cardiovascular dysfunction. The auto- and cross-spectral analysis of SBP variability (SBPV) and HR variability (HRV) were performed by the method based on the autoregressive model (AR), and the auto-spectral results was compared with the results from the classical periodogram method. The baroreceptor-heart rate reflex sensitivity (BRS) was estimated using transfer function analysis from SBP to HR. The results indicated that auto-spectral results based on the two methods were comparable, while smoother power spectral curves with distinguished peaks were trained by the AR method. The means of SBP, DBP, and HR, the main spectral indices of SBPV and HRV, and the mean average gain of transfer functions computed at low- and high-frequency ranges (0.25-0.8 Hz and 0.8-2.4 Hz) did not show significant changes before and after release from suspension. Furthermore, the main spectral indices of SBPV and HRV at different time points did not show significant differences between the control and suspension groups. However, the means of SBP, DBP, and HR at different time points were significantly higher in simulated weightless rats than those in the control rats. The findings of the present study suggest that a mid-term simulated microgravity might induce hypertension and tachycardia upon removal from the suspension which reflects a general sympathetic hyperactivity. We speculated that the sympathetic hyperactivity might be a compensatory mechanism activated in the intact animal to counteract HU-induced hypo-responsiveness of resistance vessels. In addition, lack of clear and distinct changes in HRV and BRS have also been reported in some recent space and ground-based human studies.
Animals ; Baroreflex ; Blood Pressure ; Heart Rate ; Hindlimb Suspension ; Hypertension ; Rats ; Weightlessness Simulation

OBJECTIVETo study the effects on rats' bone mineral density and bone biomechanics by suspensory simulated weightlessness and removing suspension.

METHODSTwenty Wistar rats were divided into two groups randomly as control group and model group. Suspend the model group rats for 14 days, then remove suspension and continue to feed for another 14 days. Feed control group rats for 28 days. Detect the bone mineral density (BMD) in vivo of cranial bone, second thoracic vertebra, fourth lumbar vertebra, pelvis, right radioulna and right femoral bone of each group at the 14th day. At the 28th day,execute all the rats and take out of right femoral bone and fourth lumbar vertebra for detecting BMD and the intensity of biomechanics.

RESULTSAt the 14th day in experiment, being compared with control group,the BMD of femoral bone, pelvis and lumbar vertebra in model group decreased significantly (P < 0.001, P < 0.001, P < 0.01) and the change of BMD of cranial bone, thoracic vertebra and radioulna in model group was not remarkable (P > 0.05). At the 28th day in experiment, the BMD of femoral bone and lumbar vertebra, the maximal load of femoral bone decreased significantly in model group as compared with control group (P < 0.01, P < 0.001, P < 0.01).

CONCLUSIONBMD in vive body showed that suspensory simulated weightlessness for 14 days could cause disorder of bone metabolism and remarkable mineral loss of weight bearing bone, even BMD and biomechanical intensity of weight bearing bone decrease obviously when removing suspension for 14 days. The results suggest that the disorder of bone metabolism could not be recovered in short time.

Animals ; Biomechanical Phenomena ; Bone Density ; Bone and Bones ; physiology ; Hindlimb Suspension ; Male ; Rats ; Rats, Wistar ; Weightlessness Simulation