Short-arm Centrifuge Research Articles

Space physiology VI: exercise, artificial gravity, and countermeasure development for prolonged space flight

When applied individually, exercise countermeasures employed to date do not fully protect the cardiovascular and musculoskeletal systems during prolonged spaceflight. Recent ground-based research suggests that it is necessary to perform exercise countermeasures within some form of artificial gravity to prevent microgravity deconditioning. In this regard, it is important to provide normal foot-ward loading and intravascular hydrostatic-pressure gradients to maintain musculoskeletal and cardiovascular function. Aerobic exercise within a centrifuge restores cardiovascular function, while aerobic exercise within lower body negative pressure restores cardiovascular function and helps protect the musculoskeletal system. Resistive exercise with vibration stimulation may increase the effectiveness of resistive exercise by preserving muscle function, allowing lower intensity exercises, and possibly reducing risk of loss of vision during prolonged spaceflight. Inexpensive methods to induce artificial gravity alone (to counteract head-ward fluid shifts) and exercise during artificial gravity (for example, by short-arm centrifuge or exercise within lower body negative pressure) should be developed further and evaluated as multi-system countermeasures.

Cerebral circulation during mild +Gz hypergravity by short-arm human centrifuge

We examined changes in cerebral circulation in 15 healthy men during exposure to mild +Gz hypergravity (1.5 Gz, head-to-foot) using a short-arm centrifuge. Continuous arterial pressure waveform (tonometry), cerebral blood flow (CBF) velocity in the middle cerebral artery (transcranial Doppler ultrasonography), and partial pressure of end-tidal carbon dioxide (ETco(2)) were measured in the sitting position (1 Gz) and during 21 min of exposure to mild hypergravity (1.5 Gz). Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis between beat-to-beat mean arterial pressure (MAP) and mean CBF velocity (MCBFV). Steady-state MAP did not change, but MCBFV was significantly reduced with 1.5 Gz (-7%). ETco(2) was also reduced (-12%). Variability of MAP increased significantly with 1.5 Gz in low (53%)- and high-frequency ranges (88%), but variability of MCBFV did not change in these frequency ranges, resulting in significant decreases in transfer function gain between MAP and MCBFV (gain in low-frequency range, -17%; gain in high-frequency range, -13%). In contrast, all of these indexes in the very low-frequency range were unchanged. Transfer from arterial pressure oscillations to CBF fluctuations was thus suppressed in low- and high-frequency ranges. These results suggest that steady-state global CBF was reduced, but dynamic cerebral autoregulation in low- and high-frequency ranges was improved with stabilization of CBF fluctuations despite increases in arterial pressure oscillations during mild +Gz hypergravity. We speculate that this improvement in dynamic cerebral autoregulation within these frequency ranges may have been due to compensatory effects against the reduction in steady-state global CBF.

Artificial gravity with ergometric exercise preserves the cardiac, but not cerebrovascular, functions during 4 days of head-down bed rest

Cardiovascular and musculoskeletal deconditioning occurring in long-term spaceflight requires new strategies to counteract these adverse effects. We previously reported that a short-arm centrifuge produced artificial gravity (AG), together with ergometer, has an approving effect on promoting cardiovascular function. The current study sought to investigate whether the cardiac and cerebrovascular functions were maintained and improved using a strategy of AG combined with exercise training on cardiovascular function during 4-day head-down bed rest (HDBR). Twelve healthy male subjects were assigned to a control group (CONT, n=6) and an AG combined with ergometric exercise training group (CM, n=6). Simultaneously, cardiac pumping and systolic functions, cerebral blood flow were measured before, during, and after HDBR. The results showed that AG combined with ergometric exercise caused an increase trend of number of tolerance, however, there was no significant difference between the two groups. After 4-day HDBR in the CONT group, heart rate increased significantly (59±6 vs 66±7beats/min), while stroke volume (98±12 vs 68±13mL) and cardiac output (6±1 vs 4±1L/min) decreased significantly (p<0.05). All subjects had similar drops on cerebral vascular function. Volume regulating hormone aldosterone increased in both groups (by 119.9% in CONT group and 112.8% in the CM group), but only in the CONT group there were a significant changes (p<0.05). Angiotensin II was significantly increased by 140.5% after 4-day HDBR in the CONT group (p<0.05), while no significant changes were observed in the CM group. These results indicated that artificial gravity with ergometric exercise successfully eliminated changes induced by simulated weightlessness in heart rate, volume regulating hormones, and cardiac pumping function and partially maintained cardiac systolic function. Hence, a daily 1h alternating +1.0 and +2.0Gz with 40W exercise training appear to be an effective countermeasure against cardiac deconditioning.

Artificial gravity with ergometric exercise as a countermeasure against cardiovascular deconditioning during 4 days of head-down bed rest in humans

We have shown previously that combined short-arm centrifuge and aerobic exercise training preserved several physiologically important cardiovascular functions in humans. We hypothesized that artificial gravity (AG) and exercise is effective to prevent changes of physical problems during head-down bed rest (HDBR). To test this hypothesis, 12 healthy male subjects had undergone 4 days of 6° HDBR. Six of them were exposed to AG of an alternating 2-min intervals of +1.0 and +2.0 Gz at foot level for 30 min twice per day with ergometric exercise of 40 W as a countermeasure during bed rest (CM group), while the remaining six served as untreated controls (no-CM group). Before and after 4 days of bed rest, leg venous hemodynamics was assessed by venous occlusion plethysmography and autonomic cardiovascular control estimated by power spectral analysis of blood pressure and heart rate. Further, orthostatic tolerance was evaluated by a 75° head-up tilt test and physical working capacity was surveyed by near maximal physical working capacity test before and after bed rest. The data showed that combined centrifuge and exercise applied twice daily for a total of 60 min during 4 days of HDBR prevented (a) a decrease in working capacity, (b) autonomic dysfunction (a decrease in the activity of parasympathetic cardiac innervation) and (c) an increase in leg venous flow resistance. The combination of a 30 min alternating of +1.0 and +2.0 Gz for twice per day of AG with 40 W ergometric exercise may offer a promising countermeasure to short duration simulated microgravity.

The problem of artificial gravity: The current state and prospects

The review deals with the use of artificial gravity in manned space flights. The need for studying this problem is substantiated, with special emphasis on its implications for future interplanetary flights. The deconditioning of astronauts and a loss of their tolerance to gravitational loads despite the use of various preventive procedures are briefly discussed. The efficiency of artificial gravity generated by a short-arm centrifuge (SAC) is evaluated; the possibility of the use of an SAC in space flights (the effect of the main parameters of G-load on humans, and its tolerability, efficiency, etc.) is considered. Both Russian and foreign data are presented on the use of SAC for simulating microgravity effects under ground-based conditions (immersion and ANOH) and in experiments on board biosatellites. It is emphasized that all the data (both original and the data in the literature) testify to the efficiency of SAC as a preventive and therapeutic facility alleviating the negative effects of simulated microgravity. The problems that have not been resolved to date are also presented.

The problem of artificial gravity in piloted space exploration missions

The review deals with the problem of using artificial gravity in piloted space missions, its history and relevance to the proclaimed goals of remote space exploration. It contains a brief discussion of deconditioning and loss of acceleration tolerance developing in cosmonauts despite a variety of preventive procedures. Key issues pertaining short-arm centrifuge (SAC) design and in-flight utilization are acceleration tolerance, effectiveness and g-prescriptions. The Russian and international literature on SAC experience in ground-based investigations with simulated microgravity effects (immersion, HDT) gives credence to this approach to counteracting the negative physiological effects of microgravity. Open issues and goals to be gained are described.

Respiratory sinus arrhythmia on the ESA-short-arm human centrifuge

In this article, we investigated the hypothesis that the effects of hypergravity on respiratory sinus arrhythmia (RSA) can mimic the effects observed after spaceflight cardiovascular deconditioning. Artificial gravity along the head-to-feet axis on a short-arm centrifuge induces gravity gradients. This physiological condition of significantly higher g at the feet than at the heart level is specific and likely induces blood sequestration in the lower limbs. After spaceflight, astronauts are in a condition of cardiovascular deconditioning, where blood pooling in the lower part of the body and autonomic adaptation are factors contributing to orthostatic intolerance and changes in heart-rate variability (HRV). ECG and respiration were recorded during imposed and controlled breathing (ICB) protocols, which were repeated at different levels of artificial gravity as well as during supine and standing control conditions, and the changes were analyzed.

Artificial gravity as a countermeasure to microgravity: a pilot study examining the effects on knee extensor and plantar flexor muscle groups

The goal of this project was to examine the effects of artificial gravity (AG) on skeletal muscle strength and key anabolic/catabolic markers known to regulate muscle mass. Two groups of subjects were selected for study: 1) a 21 day-bed rest (BR) group (n = 7) and 2) an AG group (n = 8), which was subjected to 21 days of 6 degrees head-down tilt bed rest plus daily 1-h exposures to AG (2.5 G at the feet). Centrifugation was produced using a short-arm centrifuge with the foot plate approximately 220 cm from the center of rotation. The torque-velocity relationships of the knee extensors and plantar flexors of the ankle were determined pre- and posttreatment. Muscle biopsy samples obtained from the vastus lateralis and soleus muscles were used for a series of gene expression analyses (mRNA abundance) of key factors implicated in the anabolic vs. catabolic state of the muscle. Post/pre torque-velocity determinations revealed greater decrements in knee extensor performance in the BR vs. AG group (P < 0.04). The plantar flexors of the AG subjects actually demonstrated a net gain in the torque-velocity relationship, whereas in the BR group, the responses declined (AG vs. BR, P < 0.001). Muscle fiber cross-sectional area decreased by approximately 20% in the BR group, whereas no losses were evident in the AG group. RT-PCR analyses of muscle biopsy specimens demonstrated that markers of growth and cytoskeletal integrity were higher in the AG group, whereas catabolic markers were elevated in the BR group. Importantly, these patterns were seen in both muscles. We conclude that paradigms of AG have the potential to maintain the functional, biochemical, and structural homeostasis of skeletal muscle in the face of chronic unloading.

Immune and Neuroendocrine Responses to Head-Down Rest and Countermeasures

Head-down bed rest (HDBR) at -6 degrees is used as a model for studying physiological changes during microgravity in spaceflight. The aim of the present study was to investigate whether exposure to such an environment is associated with alterations in the synthesis of some acute-phase proteins and cytokines, and whether countermeasures would prevent these changes. There were 12 male volunteers who were subjected to HDBR for 20 d; 6 formed the countermeasure (CMS) group and exercised on a short-arm centrifuge for 30 min/d, while the other 6 served as controls (CTL). Variables measured before and after HDBR included plasma noradrenaline, adrenaline, dopamine, leukocyte count, interleukin 6, total serum protein, C-reactive protein, and alpha-1 antichimotrypsin. Adrenaline and noradrenaline concentrations increased significantly in both groups, while the concentration of C-reactive protein decreased. The concentration of C-reactive protein was significantly higher (CTL: 0.028 +/- 0.005 mg x dl(-1); CMS: 0.025 +/-0.003 mg x dl(-1)), and that of adrenaline was significantly lower in CTL compared to CMS (CTL: 46.8 +/- 7.5 pg x ml(-1); CMS: 71 +/- 22.5 pg x ml(-1)). The results indicate that several neuroendocrine and immunological parameters are modulated by prolonged HDBR and these changes may be counteracted at least in part by artificial gravity with exercise.

Respiratory Muscle Training and the Performance of a Simulated Anti-G Straining Maneuver

This study represents the first step toward testing the hypothesis that hypergravity can be used as a unique resistance training modality for maintaining the health and function of skeletal muscle in microgravity. The primary objectives of this study were to use a human-powered short-arm centrifuge for the following: 1) to determine whether subjects could perform squats under hypergravity conditions without developing motion sickness or illusory motion; 2) to measure foot forces while performing squats under hypergravity conditions; and 3) to determine the mechanical power required to produce 1.5, 2.0, 2.5, and 3.0 Gz (head to foot) at the feet. Subjects (22 males and 19 females) performed 10 squats each at 1.5, 2.0, 2.5, and 3.0 Gz on a human-powered short-arm centrifuge, the space cycle. Foot forces during each squat were monitored using insole force sensors, and normalized to foot forces measured at 1 Gz (relative foot forces). Illusory motion was minimized using a visual focal point, and did not affect the ability of subjects to perform squats. The mean standing relative foot forces at 3.0 Gz were 2.3 and 2.4 for the male and female subjects, respectively. The work rate required to power the space cycle was a linear function of Gz, and is well within the aerobic scope of untrained individuals. The findings of this study demonstrate that hypergravity can be used as an effective modality for loading skeletal muscle and that subjects can perform squat resistance exercise without developing motion sickness or illusory motion.

Hypergravity resistance exercise: the use of artificial gravity as potential countermeasure to microgravity

The aims of this study were to 1) determine if hypergravity (HG) squats can produce foot forces similar to those measured during 10-repetition maximum (10RM) squats using weights under normal 1-G(z) condition, and 2) compare the kinematics (duration and goniometry) and EMG activities of selected joints and muscles between 10RM and HG squats of similar total foot forces. Eight men and six women [27 yr (SD 4), 66 kg (SD 10)] completed ten 10RM [83 kg (SD 23)] and 10 HG squats (2.25-3.75 G(z)). HG squats were performed on a human-powered short-arm centrifuge. Foot forces were measured using insole force sensors. Hip, knee, and ankle angles were measured using electrogoniometers. EMG activities of the erector spinae, biceps femoris, rectus femoris, and gastrocnemius were also recorded during both squats. All subjects were able to achieve similar or higher average total foot forces during HG squats compared with those obtained during 10RM squats. There were no differences in total duration per set, average duration per repetition, and goniometry and EMG activities of the selected joints and muscles, respectively, between 10RM and HG squats. These results demonstrate that HG squats can produce very high foot forces that are comparable to those produced during 10RM squats at 1 G(z). In addition, the technique and muscle activation are similar between the two types of squats. This observation supports the view that HG resistance training may represent an important countermeasure to microgravity.

Hypergravity squat as an alternative to classical squat and potential countermeasure to microgravity

The aims of this study were to determine if hypergravity squats can produce foot forces similar to those measured while performing 10-repetition maximum (10-RM) squats under normal 1 Gz condition, and compare the integrated EMG (iEMG) and goniometry of selected muscles and joints, respectively between hypergravity and 10-RM squats of similar foot forces. Six healthy young men [25 ± 2 yr (mean ± SD), 76± 5 kg] completed ten 10-RM squats (97 ± 12 kg) and 10 hypergravity squats (3.2 ± 0.3 Gz; range of 3–3.75 Gz) under similar average total foot force conditions (104% 10-RM) in the same visit. Hypergravity squats were performed on a human powered short-arm centrifuge. Foot forces were monitored using insole force sensors. Hip and knee flexion/extension, plantar/dorsi flexion, and EMG of the erector spinae, bicep femoris, rectus femoris and gastrocnemius were also monitored during the squats. There were no differences in average total foot forces, average duration per repetition, and iEMG and range of motion of the selected muscles and joints, respectively between hypergravity and 10-RM squats except a 60% greater iEMG of the gastrocnemius muscles during hypergravity squats (P < 0.05). These results suggest that hypergravity squats are comparable to squats performed at 1 Gz, and may represent an important countermeasure to microgravity. Supported by NSBRI through NASA MA00403 and UCI, grant M01 RR00827 from the GCRC, NIH.

Dynamic Biomechanical Model of Foot Forces During Hypergravity Resistance Training

Spaceflight has been shown to cause atrophy, reduced functional capacity, and increased fatigue in limb skeletal muscles, with the greatest change observed in antigravity muscles. The mechanisms of these losses are not fully understood but can be attributed to altered gene expression of myofibrillar proteins that is closely related to the muscle usage. During long duration space flight, periods of hypergravity may induce heightened G-like forces that could prevent muscle atrophy. PURPOSE: Determine if hypergravity is an effective resistive load to create significant ground reaction forces when performing squats in microgravity. METHODS: The Space Cycle is a human powered short arm centrifuge that can generate varying levels of hypergravity. The Space Cycle is configured with two arms, and active arm and passive arm, vertically hanging from a rotational axel. When a rider on the active arm peddles, the rotational rate of the centrifuge increases causing both arms swing upward towards a horizontal orientation. The hanging-arm design allows a subject standing in the passive arm (gondola) to experience hypergravity along their Gz axis. Experimental testing with this ground based Space Cycle has allowed the comparison of foot forces between squats performed in hypergravity and in earth gravitation. To test the effectiveness of the induced hypergravity in a microgravity environment a dynamic biomechanical model has been developed representing the mechanical Space Cycle and human subject. The subject is modeled using 12 rigid bodies with specified inertial properties representing different limb segments. Joints were modeled with kinematic constraints and viscoelastic properties. Input torques were prescribed for both the rotational speed of the Space Cycle and subject joint trajectories such that the rotational velocity and joint angles matched measured values. RESULTS: During squats on ground and while riding the Space Cycle: insole pressure sensors recorded foot forces, goniometers recorded the subject joint angles and hall-effect sensors recorded rotational velocity. Foot forces were simulated for squats performed on the Space Cycle both in microgravity (0G) and on earth (1G) environments. CONCLUSIONS: The dynamic model of the Space Cycle captures the major characteristics of the foot forces during squats performed in hypergravity on earth and significant foot forces have been predicted for squats in microgravity.

Some approaches to medical support for Martian expedition

Medical support in a Martian expedition will be within the scope of crew responsibilities and maximally autonomous. Requirements to the system of diagnostics in this mission include considerable use of means and methods of visualization of the main physiological parameters, telemedicine, broad usage of biochemical analyses (including “dry” chemistry), computerized collection, measurement, analysis and storage of medical information. The countermeasure system will be based on objective methods of crew fitness and working ability evaluation, individual selection of training regimens, and intensive use of computer controlled training. Implementation of the above principles implies modernization and refinement of the countermeasures currently used by space crews of long-term missions (LTM), and increases of the assortment of active and passive training devices, among them a short-arm centrifuge. The system of medical care with the functions of prevention, clinical diagnostics and timely treatment will be autonomous, too. The general requirements to medical care during the future mission are the following: availability of conditions and means for autonomous urgent and special medical aid and treatment of the most possible states and diseases, “a hospital”, and assignment to the crew of one or two doctors. To ensure independence of medical support and medical care in an expedition to Mars an automated expert system needs to be designed and constructed to control the medical situation as a whole.

CARDIOPULMONARY RESPONSES TO SUPINE CYCLING DURING SHORT-ARM CENTRIFUGATION

PURPOSE: To investigate cardiopulmonary responses to supine cycling with concomitant +Gz (head to foot) acceleration using the Ames human powered short-arm centrifuge (HPC). METHODS: Eight males (mean ± SD, age: 32 ± 5 y; height: 178 ± 5 cm; weight: 86.1 ± 6.2 kg) completed two maximal exercise tests supine on the HPC, with and without acceleration, within a three day period. A one-tailed t-test for dependent samples (experiment-wise error rate: 0.1; adjusted α: 0.025) was used to compare treatments. RESULTS: Peak acceleration was +3.4 ± 0.1 Gz. Peak oxygen uptake (VO2 peak) was not different between treatment groups (3.1 ± 0.1 L • min−1 stationary, and 3.2 ± 0.1 L • min−1 acceleration). Peak heart rate (HRpeak) and pulmonary minute ventilation (VEBTPSpeak) were elevated (P ≥ 0.025) for acceleration trials (182 ± 3 b • min−1; 132 ± 9.0 L • min−1) when compared to stationary trial data (175 ± 3 b • min−1; 115.5 ± 8.5 L • min−1). Ventilatory threshold (Tvent), expressed as a percent VO2 peak, was not different for stationary and acceleration trials (72 ± 2% vs. 68 ± 2%). CONCLUSIONS: Results suggest that concomitant +3.4 Gz acceleration does not alter VO2 peak response to supine cycling. However, HRpeak and VEBTPSpeak responses are increased while Tvent, expressed as a function of VO2 peak, expressed as a function of VO2 peak, is unaffected. Thus, traditional methods of exercise prescription based on VO2 response are appropriate for this mode of exercise, but exercise prescription based on HR response require modification.

Can daily centrifugation prevent the haematocrit increase elicited by 6-degree, head-down tilt?

A measure to counteract the effects of low or zero gravity is required for long-term space flight, such as the manned Mars mission scheduled by the National Aeronautics and Space administration (NASA) for 2014. We conducted a series of centrifugation experiments with humans, using a short-arm centrifuge (radius 1.8 m, made by First Medical Co., Tokyo, Japan). We employed 6-degree, head-down tilt (HDT) for 4 days to simulate space flight. Ten healthy male volunteers underwent 4-day HDT and a 2-G daily centrifuge load for 60 min in the +Gz direction and measurements, such as haematocrit, 24-h urine volume, body weight and electrocardiogram (ECG) were made. There was no significant increase in the haematocrit during the HDT period, although our previous studies had shown a significant increase during HDT. A 60-min daily load of +2 Gz appears to be effective in reversing the haematocrit increase due to 4-day HDT.

Comparison of gradual and rapid onset runs in a short-arm centrifugation

A gradual onset run (GOR) in a short-arm centrifugation was performed on ten healthy students. The centrifuge had a 1.8 m radius, and the subjects sat on a chair in a cabin. The Gz force increased to 2.2 Gz at 0.1 °/sec 2 for 32 min. and the same Gz-level was maintained for 20 min. Three out of ten subjects completed the whole protocol; the load on the others was terminated because of symptoms or increased heart rate. There were few symptoms such as vertigo, that was a common problem with a rapid onset run (ROR) in former experiments, due to the short-arm centrifugation. The changes of the flicker test after the load were much less in the GOR protocol than in the ROR protocol, even in the terminated group. GOR seemed preferable to ROR in preventing vertigo even though it took longer to reach the necessary G load.

Human cardiovascular and vestibular responses in long minutes and low +Gz loading by a short arm centrifuge

1.4 G, 1.7 G, and 2.0 G of +Gz and 60 minutes centrifugation was adopted to 20 healthy male subjects using 1.8 m radius centrifuge equipped to Nihon University School of Medicine. G was applied from lower G, considering G training effect for the subjects. Effects on performance decline and side effects of such a short-arm centrifugation were especially observed in the experiments, because this size of centrifuge could be used in space station in future for a strong countermeasure of cardiovascular deconditioning, demineralization from bone, etc. G training effect was observed same as higher and rapid G acceleration in fighter pilot. Subjects suffered from many types of discomfort; such as sensation of heaviness of diaphragm, cold sweat, nausea, irritable feeling, arrhythmia, tachycardia, rapid decrease of blood pressure, which sometimes caused interruption of G load. As 2.0 G and 60 minutes centrifugation seemed very tough load to the subjects, there should be necessary some G suit or other countermeasure, if we apply a higher G and/or longer G duration. Performance decline due to the load commonly continued for 1 hour or so. Side effects were observed in relation to neuro-vestibular, cardio-vascular, and autonomic nervous system.

Principle approaches to selection of the short-arm centrifuge regimens for extended space flight

Eight +Gz regimens on the SAC varying in their values (within 0.8 to 1.6 G), exposures, schedules, etc. were analyzed. Some regimens were combined with water-salt supplements (WSS) or veloergometer training (VE). Weightlessness was simulated by 3- to 28-day water immersion. +3 Gz loads on the centrifuge with the radius of 7.5 m were applied prior to and post immersion. Regimens for human runs on the SAC as a novel, perspective countermeasure for interplanetary expeditions should be selected with due regard of the human tolerance, their efficiency, and subsequent verification and specification in orbital flights. These approaches showed that 3 days of exposure to 1.2 G combined with WSS and 6 days of exposure to G-loads from 0.8 to 1.6 G together with VE were most optimal.