Free Cognitive Capacity Assessed by the P300 Method During Manual Docking Training in Space.

INTRODUCTION: The classical P300 brain potential method was used to assess the cognitive capacity during training of manual docking in space. The aim of the study was to enhance the safety of this operation during a mission.METHODS: To examine this, N = 8 cosmonauts had to perform the manually controlled docking task simultaneously with an acoustic monitoring task. The P300 component was evoked by the acoustic stimuli of the secondary task. The docking task had to be executed at three difficulty levels: low (station not turning); medium (station turning around one axis); and difficult (station turning around three axes). In the secondary task, subjects had to discriminate between a low and a high tone, which occurred with a probability of 90% and 10%, respectively. Subjects had to count the high tones. After the 10th high tone, they had to inspect the power supply by giving an oral command.RESULTS: A methodology for event-related potentials was successfully demonstrated under space conditions. The P300 amplitude was largest and the latency shortest during the medium difficult task.DISCUSSION: The results suggest that P300 can be recorded during the complex manual docking task in space and could be used to assess individual available cognitive capacity of cosmonauts during a space mission.Bubeev JA, Johannes B, Kotrovska TI, Schastlivtseva D, Bronnikov S, Hoermann H-J, Gaillard AWK. Free cognitive capacity assessed by the P300 method during manual docking training in space. Aerosp Med Hum Perform. 2024; 95(4):187-193.

External to internal cranial perfusion shifts during simulated weightlessness: Results from a randomized cross-over trial.

The exact pathophysiology of the spaceflight-associated neuro-ocular syndrome (SANS) has so far not been completely elucidated. In this study we assessed the effect of acute head-down tilt position on the mean flow of the intra- and extracranial vessels. Our results suggest a shift from the external to the internal system that might play an important role in the pathomechanism of SANS.

Visual Attention Relates to Operator Performance in Spacecraft Docking Training.

BACKGROUND: Manually controlled docking of a spacecraft to a space station is an operational task that poses high demands on cognitive and perceptual functioning. Effective processing of visual information is crucial for success. Eye tracking can reveal the operator's attentional focus unobtrusively and objectively. Therefore, our aim was to test the feasibility of eye tracking during a simulation of manual docking and to identify links between visual information processing and performance.METHODS: We hypothesized that duration and number of gazes to specific regions of interest of the simulation (total dwell time and number of dwells) would be associated with docking accuracy. Eye movements were recorded in 10 subjects (30% women, M = 33.4 yr old) during the 6° head-down tilt bed rest study AGBRESA during 20 training sessions with the 6df learning program for spacecraft docking.RESULTS: Subjects' gaze was directed most frequently and longest to the vizor (185 dwells and 22,355 ms per task) followed by the two instrument displays (together 75 dwells and 4048 ms per task). We observed a significant positive relationship between number and duration of visual checks of speed and distance to the docking point and the accuracy of the docking maneuver.DISCUSSION: In conclusion, eye tracking provides valuable information related to docking accuracy that might prospectively offer the opportunity to improve docking training effectiveness.Piechowski S, Johannes B, Pustowalow W, Arz M, Mulder E, Jordan J, Wolf OT, Rittweger J. Visual attention relates to operator performance in spacecraft docking training. Aerosp Med Hum Perform. 2022; 93(6):480-486.

Operator's Reliability During Spacecraft Docking Training on Board Mir and ISS.

BACKGROUND: The experimental research PILOT on board the space stations aimed to assess cosmonauts expectable reliability in a mission relevant operation, the manual docking of Soyuz or Progress spacecrafts on the space stations Mir and International Space Station (ISS), respectively.METHOD: Therefore, a simulation of the docking of two space apparatuses was used for training and research. The methodological approach is described, taking into consideration the level of performance and the individual effort spent, the psychophysiological costs. In three decades altogether 32 cosmonauts took part.RESULTS: A significant increase of reliability was found from Mir (0.45 scores) to ISS missions (0.51). On ISS the reliability remained stable (0.50 0.1).DISCUSSION: Salnitskis model for the evaluation of operators reliability was further developed and tested, which turned out to be sensitive as well as robust enough for a practical application in this critical operational task.Johannes B, Bronnikov SV, Bubeev JA, Kotrovskaya TI, Shastlivtseva DV, Piechowski S, Hoermann H-J, Jordan J. Operators reliability during spacecraft docking training on board Mir and ISS. Aerosp Med Hum Perform. 2021; 92(7):541549.

Limited Effect of 60-Days Strict Head Down Tilt Bed Rest on Vascular Aging.

BACKGROUND: Cardiovascular risk may be increased in astronauts after long term space flights based on biomarkers indicating premature vascular aging. We tested the hypothesis that 60 days of strict 6° head down tilt bed rest (HDTBR), an established space analog, promotes vascular stiffening and that artificial gravity training ameliorates the response. METHODS: We studied 24 healthy participants (8 women, 24-55 years, BMI = 24.3 ± 2.1 kg/m2) before and at the end of 60 days HDTBR. 16 subjects were assigned to daily artificial gravity. We applied echocardiography to measure stroke volume and isovolumetric contraction time (ICT), calculated aortic compliance (stroke volume/aortic pulse pressure), and assessed aortic distensibility by MRI. Furthermore, we measured brachial-femoral pulse wave velocity (bfPWV) and pulse wave arrival times (PAT) in different vascular beds by blood pressure cuffs and photoplethysmography. We corrected PAT for ICT (cPAT). RESULTS: In the pooled sample, diastolic blood pressure (+8 ± 7 mmHg, p < 0.001), heart rate (+7 ± 9 bpm, p = 0.002) and ICT (+8 ± 13 ms, p = 0.036) increased during HDTBR. Stroke volume decreased by 14 ± 15 ml (p = 0.001). bfPWV, aortic compliance, aortic distensibility and all cPAT remained unchanged. Aortic area tended to increase (p = 0.05). None of the parameters showed significant interaction between HDTBR and artificial gravity training. CONCLUSION: 60 days HDTBR, while producing cardiovascular deconditioning and cephalad fluid shifts akin to weightlessness, did not worsen vascular stiffness. Artificial gravity training did not modulate the response.

Cardiac adaptations to 60 day head-down-tilt bed rest deconditioning. Findings from the AGBRESA study.

AIMS: Reduced physical activity increases the risk of heart failure; however, non-invasive methodologies detecting subclinical changes in myocardial function are not available. We hypothesized that myocardial, left ventricular, systolic strain measurements could capture subtle abnormalities in myocardial function secondary to physical inactivity. METHODS AND RESULTS: In the AGBRESA study, which assessed artificial gravity through centrifugation as potential countermeasure for space travel, 24 healthy persons (eight women) were submitted to 60 day strict -6° head-down-tilt bed rest. Participants were assigned to three groups of eight subjects: a control group, continuous artificial gravity training on a short-arm centrifuge (30 min/day), or intermittent centrifugation (6 × 5 min/day). We assessed cardiac morphology, function, strain, and haemodynamics by cardiac magnetic resonance imaging (MRI) and echocardiography. We observed no differences between groups and, therefore, conducted a pooled analysis. Consistent with deconditioning, resting heart rate (∆8.3 ± 6.3 b.p.m., P < 0.0001), orthostatic heart rate responses (∆22.8 ± 19.7 b.p.m., P < 0.0001), and diastolic blood pressure (∆8.8 ± 6.6 mmHg, P < 0.0001) increased, whereas cardiac output (∆-0.56 ± 0.94 L/min, P = 0.0096) decreased during bed rest. Left ventricular mass index obtained by MRI did not change. Echocardiographic left ventricular, systolic, global longitudinal strain (∆1.8 ± 1.83%, P < 0.0001) decreased, whereas left ventricular, systolic, global MRI circumferential strain increased not significantly (∆-0.68 ± 1.85%, P = 0.0843). MRI values rapidly returned to baseline during recovery. CONCLUSION: Prolonged head-down-tilt bed rest provokes changes in cardiac function, particularly strain measurements, that appear functional rather than mediated through cardiac remodelling. Thus, strain measurements are of limited utility in assessing influences of physical deconditioning or exercise interventions on cardiac function.

Cognition Test Battery Performance Is Associated with Simulated 6df Spacecraft Docking Performance.

INTRODUCTION: Environmental and operational stressors commonly encountered in spaceflight can affect astronaut cognitive performance. It is currently unclear how performance decrements on test batteries that assess individual cognitive domains translate to complex operational performance.METHODS: N 30 healthy adults (mean SD age 33.5 7.1 yr, range 2548 yr; 16 men) with demographic characteristics similar to astronauts performed all 10 tests of the Cognition test battery as well as a simulated 6 degrees-of-freedom (6df) spacecraft docking task 15 times. Performance on 60 Cognition outcome variables was rank-correlated with 6df docking performance individually as well as in models containing up to 12 predictors after accounting for sex, age, and study design effects.RESULTS: Average response time on the Digit Symbol Substitution Test (DSST)a measure of processing speed requiring complex scanning, visual tracking, and working memorywas the best individual predictor of 6df docking performance (unadjusted r 0.550; semipartial cross-validated R² 0.244). Furthermore, higher levels of spatial orientation efficiency and vigilant attention, lower levels of impulsivity, and faster response speed were associated with higher 6df performance, while sensorimotor speed, memory, and risk decision making were less relevant. After semipartial cross-validation, a model with three Cognition outcomes (DSST average response time, Abstract Matching accuracy, and conservative response bias on the Fractal 2-Back test) explained 30% of the variance in 6df performance.CONCLUSIONS: This study demonstrates direct links between performance on tests designed to assess specific cognitive domains and complex operational docking performance.Basner M, Moore TM, Hermosillo E, Nasrini J, Dinges DF, Gur RC, Johannes B. Cognition test battery performance is associated with simulated 6df spacecraft docking performance. Aerosp Med Hum Perform. 2020; 91(11):861867.

Operational and Experimental Tasks, Performance, and Voice in Space.

BACKGROUND: Voice analysis offers an unobtrusive approach for psychological monitoring. We demonstrate the relationship between voice parameters and cognitive performance in: 1) a task with psychological test character, and 2) performance in an operational, mission-relevant task. The central methodological aim was to verify the usefulness of voice commands and counting in providing anchor values for the step-function model of voice pitch.METHODS: During a 22-yr period, 42 cosmonauts participated in the Russian space experiment "Pilot", which was a hand-controlled docking maneuver. As reference the experiment included the cognitive task "Manometer." This task was controlled through voice commands. These voice commands were stored and are the basis for the present analysis.RESULTS: Cosmonauts differed in their working style and respective performance during the Manometer task. Clustered groups can be assumed to represent different effort. Importantly, these groups differed in the changes of voice pitch among mission phases and among task repetitions. However, there were no differences between these motivation groups and performance in the professional task.DISCUSSION: The differing effort is the effect of different motivation of cosmonauts for experimental test tasks vs. mission-relevant professional tasks. Latter ones provide a more reliable chance to assess the real actual state and skills of a cosmonaut. Voice pitch measurement seems to be reliable and useful under space conditions for monitoring this volitional effort.Johannes B, Bronnikov SV, Bubeev JA, Kotrovskaya TI, Shastlivtseva DV, Piechowski S, Hoermann H-J, Rittweger J, Jordan J. Operational and experimental tasks, performance, and voice in space. Aerosp Med Hum Perform. 2019; 90(7):624-631.

Sleep Is Compromised in -12° Head Down Tilt Position.

Recent studies are elucidating the interrelation between sleep, cranial perfusion, and cerebrospinal fluid (CSF) circulation. Head down tilt (HDT) as a simulation of microgravity reduces cranial perfusion. Therefore, our aim was to assess whether HDT is affecting sleep (clinicaltrials.gov; identifier NCT02976168). 11 male subjects were recruited for a cross-over designed study. Each subject participated in two campaigns each comprising 3 days and 2 nights. Intervention started on the second campaign day and consisted of maintenance of horizontal position or -12° HDT for 21 h. Ultrasound measurements were performed before, at the beginning and the end of intervention. Polysomnographic measurements were assessed in the second night which was either spent in horizontal posture or at -12° HDT. Endpoints were sleep efficiency, sleep onset latency, number of sleep state changes and arousals, percentages of N3, REM, light sleep stages and subjective sleep parameters. N3 and REM sleep reduced by 25.6 and 19.1 min, respectively (P = 0.002, g = -0.898; P = 0.035, g = -0.634) during -12° HDT. Light sleep (N1/2) increased by 33.0 min at -12° HDT (P = 0.002, g = 1.078). On a scale from 1 to 9 subjective sleep quality deteriorated by 1.3 points during -12° HDT (P = 0.047, g = -0.968). Ultrasonic measurement of the venous system showed a significant increase of the minimum (P = 0.009, P < 0.001) and maximum (P = 0.004, P = 0.002) cross-sectional area of the internal jugular vein at -12° HDT. The minimum cross-sectional area of the external jugular vein differed significantly between conditions over time (P = 0.001) whereas frontal skin tissue thickness was not significantly different between conditions (P = 0.077, P = 0.811). Data suggests venous congestion at -12° HDT. Since subjects felt comfortable with lying in -12° HDT under our experimental conditions, this posture only moderately deteriorates sleep. Obviously, the human body can almost compensate the several fold effects of gravity in HDT posture like an affected CSF circulation, airway obstruction, unusual patterns of propioception and effects on the cardiovascular system.

Galanin and Adrenomedullin Plasma Responses During Artificial Gravity on a Human Short-Arm Centrifuge.

Galanin and adrenomedullin plasma responses to head-up tilt and lower body negative pressure have been studied previously. However, to what extent short-arm human centrifugation (SAHC) affects these responses is not known. In this study, we assessed how the application of variable gradients of accelerations (ΔGz ) via shifting of the rotation axis during centrifugation affects selected hormonal responses. Specifically, we tested the hypothesis, that cardiovascular modulating hormones such as galanin and adrenomedullin will be higher in non-finishers (participants in whom at least one of the pre-defined criteria for presyncope was fulfilled) when compared to finishers (participants who completed the entire protocol in both sessions) during SAHC exposure. Twenty healthy subjects (10 women and 10 men) were exposed to two g-levels [1 Gz and 2.4 Gz at the feet (Gz_Feet)] in two positions (axis of rotation placed above the head and axis of rotation placed at the heart level). Elevated baseline levels of galanin appeared to predict orthostatic tolerance (p = 0.054) and seemed to support good orthostatic tolerance during 1 Gz_Feet SAHC (p = 0.034). In finishers, 2.4 Gz_Feet SAHC was associated with increased galanin levels after centrifugation (p = 0.007). For adrenomedullin, the hypothesized increases were observed after centrifugation at 1 Gz_Feet (p = 0.031), but not at 2.4 Gz_Feet, suggesting that other central mechanisms than local distribution of adrenomedullin predominate when coping with central hypovolemia induced by SAHC (p > 0.14). In conclusion, baseline galanin levels could potentially be used to predict development of presyncope in subjects. Furthermore, galanin levels increase during elevated levels of central hypovolemia and galanin responses appear to be important for coping with such challenges. Adrenomedullin release depends on degree of central hypovolemia induced fluid shifts and a subject's ability to cope with such challenges. Our results suggest that the gradient of acceleration (ΔGz ) is an innovative approach to quantify the grade of central hypovolemia and to assess neurohormonal responses in those that can tolerate (finishers) or not tolerate (non-finishers) artificial gravity (AG). As AG is being considered as a preventing tool for spaceflight induced deconditioning in future missions, understanding effects of AG on hormonal responses in subjects who develop presyncope is important.

Microcirculation in open vs. minimally invasive dorsal stabilization of thoracolumbar fractures.

Standard open and percutaneous minimally invasive surgical procedures co-exist in the treatment of fractures of the thoracolumbar spine. Shorter skin incisions just above the pedicles are used in minimally invasive procedures. Full-length skin incisions and invasive preparations are applied in the standard open approach. While both methods show equivalent rates of intraoperative surgical complications and comparable clinical and radiological outcomes, blood loss and operation time have shown to be decreased in minimally invasive treatment. However, no study so far has investigated differences in microcirculation. This study hypothesized less impairment of microcirculation in the minimally invasive approach compared to the open approach and an improvement of microcirculation over time. A prospective cohort study was conducted using non-invasive laser-Doppler spectrophotometry (an O2C "oxygen to see" device) for measurement of cutaneous and subcutaneous blood oxygenation (SO2), haemoglobin concentration (Hb), and blood flow at depths of 2, 8, and 15 mm at six locations on the skin. Measurements were performed before surgery, 8 and 24 h after surgery, and 2, 4, 7, 12 and 20 days after surgery, however the number of patients measured decreased towards the later time points. Forty patients were included in the study, 20 with each approach (18 females and 22 males). Pair-wise comparison of the types of surgical procedure for each measurement point revealed a significantly higher flow value in the minimally invasive group at one of the measurement points located between the incisions (P = .041). The point-wise analyses of SO2 and Hb did not show significant differences between the approaches. In conclusion, significantly albeit moderately higher flow values could be found in minimally invasive procedures compared to open operations of thoracolumbar fractures in the area of skin that is spared by the incisions.

Psychophysiological Assessment in Pilots Performing Challenging Simulated and Real Flight Maneuvers.

BACKGROUND: The objective assessment of psychophysiological arousal during challenging flight maneuvers is of great interest to aerospace medicine, but remains a challenging task. In the study presented here, a vector-methodological approach was used which integrates different psychophysiological variables, yielding an integral arousal index called the Psychophysiological Arousal Value (PAV). METHODS: The arousal levels of 15 male pilots were assessed during predetermined, well-defined flight maneuvers performed under simulated and real flight conditions. RESULTS: The physiological data, as expected, revealed inter- and intra-individual differences for the various measurement conditions. As indicated by the PAV, air-to-air refueling (AAR) turned out to be the most challenging task. In general, arousal levels were comparable between simulator and real flight conditions. However, a distinct difference was observed when the pilots were divided by instructors into two groups based on their proficiency in AAR with AWACS (AAR-Novices vs. AAR-Professionals). AAR-Novices had on average more than 2000 flight hours on other aircrafts. They showed higher arousal reactions to AAR in real flight (contact: PAV score 8.4 ± 0.37) than under simulator conditions (7.1 ± 0.30), whereas AAR-Professionals did not (8.5 ± 0.46 vs. 8.8 ± 0.80). DISCUSSION: The psychophysiological arousal value assessment was tested in field measurements, yielding quantifiable arousal differences between proficiency groups of pilots during simulated and real flight conditions. The method used in this study allows an evaluation of the psychophysiological cost during a certain flying performance and thus is possibly a valuable tool for objectively evaluating the actual skill status of pilots.Johannes B, Rothe S, Gens A, Westphal S, Birkenfeld K, Mulder E, Rittweger J, Ledderhos C. Psychophysiological assessment in pilots performing challenging simulated and real flight maneuvers. Aerosp Med Hum Perform. 2017; 88(9):834-840.

Short-Term Effects of Lupin vs. Whey Supplementation on Glucose and Insulin Responses to a Standardized Meal in a Randomized Cross-Over Trial.

Background: Whey protein is known to reduce postprandial glycaemia in people with type 2 diabetes mellitus. Lupin as a vegetable source of protein could be considered as an alternative, as the percentage of vegetarian and vegan consumers is raising. The present study compares the acute glycemic effects of whey and lupin in healthy volunteers following a carbohydrate-rich reference meal. Methods In cross-over design, three standardized meals (reference meal; reference meal + whey; reference meal + lupin) were provided to 12 healthy male and female volunteers, aged between 23 and 33, in a balanced, randomized order. Volunteers' blood glucose and insulin concentrations were analyzed at baseline and at seven time points following the ingestion of the meals. Results: The supplementation of whey or lupin significantly blunted the postprandial increase in blood glucose concentrations compared to the reference meal (p < 0.001). In the overall statistical analysis, this effect was comparable for whey and lupin [Δ AUC whey-lupin = 8%, 0-60 min area under the curve (0-60 min AUC), p = 0.937], with a blunting effect of -46% by whey (p = 0.005, 0-60 min AUC) and of -54% by lupin (p < 0.001, 0-60 min AUC). When comparing whey and lupin data only, the insulin increase was found to be more pronounced for whey protein than for lupin supplementation (Δ AUC whey-lupin = 39%, 0-60 min AUC, p = 0.022). However, when comparing the insulin response of each supplementation to the one of the reference meal, no differences could be detected (whey p = 0.259, 0-60 min AUC; lupin p = 0.275, 0-60 min AUC). Conclusions: Results suggest that lupin and whey can both lower the increase of postprandial blood glucose concentrations to a comparable extent, implying the usability of lupin to reduce postprandial glycaemia. However, the insulin response following the supplementations to a carbohydrate-rich meal seems to differ for these two protein sources.

Increased salt consumption induces body water conservation and decreases fluid intake.

BACKGROUND: The idea that increasing salt intake increases drinking and urine volume is widely accepted. We tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions. METHODS: Over the course of 2 separate space flight simulation studies of 105 and 205 days' duration, we exposed 10 healthy men to 3 salt intake levels (12, 9, or 6 g/d). All other nutrients were maintained constant. We studied the effect of salt-driven changes in mineralocorticoid and glucocorticoid urinary excretion on day-to-day osmolyte and water balance. RESULTS: A 6-g/d increase in salt intake increased urine osmolyte excretion, but reduced free-water clearance, indicating endogenous free water accrual by urine concentration. The resulting endogenous water surplus reduced fluid intake at the 12-g/d salt intake level. Across all 3 levels of salt intake, half-weekly and weekly rhythmical mineralocorticoid release promoted free water reabsorption via the renal concentration mechanism. Mineralocorticoid-coupled increases in free water reabsorption were counterbalanced by rhythmical glucocorticoid release, with excretion of endogenous osmolyte and water surplus by relative urine dilution. A 6-g/d increase in salt intake decreased the level of rhythmical mineralocorticoid release and elevated rhythmical glucocorticoid release. The projected effect of salt-driven hormone rhythm modulation corresponded well with the measured decrease in water intake and an increase in urine volume with surplus osmolyte excretion. CONCLUSION: Humans regulate osmolyte and water balance by rhythmical mineralocorticoid and glucocorticoid release, endogenous accrual of surplus body water, and precise surplus excretion. FUNDING: Federal Ministry for Economics and Technology/DLR; the Interdisciplinary Centre for Clinical Research; the NIH; the American Heart Association (AHA); the Renal Research Institute; and the TOYOBO Biotechnology Foundation. Food products were donated by APETITO, Coppenrath und Wiese, ENERVIT, HIPP, Katadyn, Kellogg, Molda, and Unilever.

Ultra-long-term human salt balance studies reveal interrelations between sodium, potassium, and chloride intake and excretion.

BACKGROUND: The intake of sodium, chloride, and potassium is considered important to healthy nutrition and cardiovascular disease risk. Estimating the intake of these electrolytes is difficult and usually predicated on urine collections, commonly for 24 h, which are considered the gold standard. We reported on data earlier for sodium but not for potassium or chloride. OBJECTIVE: We were able to test the value of 24-h urine collections in a unique, ultra-long-term balance study conducted during a simulated trip to Mars. DESIGN: Four healthy men were observed while ingesting 12 g salt/d, 9 g salt/d, and 6 g salt/d, while their potassium intake was maintained at 4 g/d for 105 d. Six healthy men were studied while ingesting 12 g salt/d, 9 g salt/d, and 6 g salt/d, with a re-exposure of 12 g/d, while their potassium intake was maintained at 4 g/d for 205 d. Food intake and other constituents were recorded every day for each subject. All urine output was collected daily. RESULTS: Long-term urine recovery rates for all 3 electrolytes were very high. Rather than the expected constant daily excretion related to daily intake, we observed remarkable daily variation in excretion, with a 7-d infradian rhythm at a relatively constant intake. We monitored 24-h aldosterone excretion in these studies and found that aldosterone appeared to be the regulator for all 3 electrolytes. We report Bland-Altman analyses on the value of urine collections to estimate intake. CONCLUSIONS: A single 24-h urine collection cannot predict sodium, potassium, or chloride intake; thus, multiple collections are necessary. This information is important when assessing electrolyte intake in individuals.

Performance Assessment in the PILOT Experiment On Board Space Stations Mir and ISS.

BACKGROUND: The aim of this investigation into the performance and reliability of Russian cosmonauts in hand-controlled docking of a spacecraft on a space station (experiment PILOT) was to enhance overall mission safety and crew training efficiency. The preliminary findings on the Mir space station suggested that a break in docking training of about 90 d significantly degraded performance. METHODS: Intensified experiment schedules on the International Space Station (ISS) have allowed for a monthly experiment using an on-board simulator. Therefore, instead of just three training tasks as on Mir, five training flights per session have been implemented on the ISS. This experiment was run in parallel but independently of the operational docking training the cosmonauts receive. RESULTS: First, performance was compared between the experiments on the two space stations by nonparametric testing. Performance differed significantly between space stations preflight, in flight, and postflight. Second, performance was analyzed by modeling the linear mixed effects of all variances (LME). The fixed factors space station, mission phases, training task numbers, and their interaction were analyzed. Cosmonauts were designated as a random factor. All fixed factors were found to be significant and the interaction between stations and mission phase was also significant. DISCUSSION: In summary, performance on the ISS was shown to be significantly improved, thus enhancing mission safety. Additional approaches to docking performance assessment and prognosis are presented and discussed.

Agreement between 24-hour salt ingestion and sodium excretion in a controlled environment.

Accurately collected 24-hour urine collections are presumed to be valid for estimating salt intake in individuals. We performed 2 independent ultralong-term salt balance studies lasting 105 (4 men) and 205 (6 men) days in 10 men simulating a flight to Mars. We controlled dietary intake of all constituents for months at salt intakes of 12, 9, and 6 g/d and collected all urine. The subjects' daily menus consisted of 27 279 individual servings, of which 83.0% were completely consumed, 16.5% completely rejected, and 0.5% incompletely consumed. Urinary recovery of dietary salt was 92% of recorded intake, indicating long-term steady-state sodium balance in both studies. Even at fixed salt intake, 24-hour urine collection for sodium excretion (UNaV) showed infradian rhythmicity. We defined a ±25 mmol deviation from the average difference between recorded sodium intake and UNaV as the prediction interval to accurately classify a 3-g difference in salt intake. Because of the biological variability in UNaV, only every other daily urine sample correctly classified a 3-g difference in salt intake (49%). By increasing the observations to 3 consecutive 24-hour collections and sodium intakes, classification accuracy improved to 75%. Collecting seven 24-hour urines and sodium intake samples improved classification accuracy to 92%. We conclude that single 24-hour urine collections at intakes ranging from 6 to 12 g salt per day were not suitable to detect a 3-g difference in individual salt intake. Repeated measurements of 24-hour UNaV improve precision. This knowledge could be relevant to patient care and the conduct of intervention trials.

Wireless Monitoring of Changes in Crew Relations during Long-Duration Mission Simulation.

Group structure and cohesion along with their changes over time play an important role in the success of missions where crew members spend prolonged periods of time under conditions of isolation and confinement. Therefore, an objective system for unobtrusive monitoring of crew cohesion and possible individual stress reactions is of high interest. For this purpose, an experimental wireless group structure (WLGS) monitoring system integrated into a mobile psychophysiological system was developed. In the presented study the WLGS module was evaluated separately in six male subjects (27-38 years old) participating in a 520-day simulated mission to Mars. Two days per week, each crew member wore a small sensor that registered the presence and distance of the sensors either worn by the other subjects or strategically placed throughout the isolation facility. The registration between two sensors was on average 91.0% in accordance. A correspondence of 95.7% with the survey video on day 475 confirmed external reliability. An integrated score of the "crew relation time index" was calculated and analyzed over time. Correlation analyses of a sociometric questionnaire (r = .35-.55, p< .05) and an ethological group approach (r = .45-.66, p < 05) provided initial evidence of the method's validity as a measure of cohesion when taking behavioral and activity patterns into account (e.g. only including activity phases in the afternoon). This confirms our assumption that the registered amount of time spent together during free time is associated with the intensity of personal relationships.

Muscular forces affect the glycosaminoglycan content of joint cartilage: unloading in human volunteers with the HEPHAISTOS lower leg orthosis.

BACKGROUND AND PURPOSE: Unloading alters the thickness of joint cartilage. It is unknown, however, to what extent unloading leads to a loss of glycosaminoglycans (GAGs) in the cartilage tissue. We hypothesized that muscle forces, in addition to axial loading, are necessary to maintain the joint cartilage GAG content of the knee and the upper and lower ankle. PATIENTS AND METHODS: The HEPHAISTOS orthosis was worn unilaterally by 11 men (mean age 31 (23-50) years old) for 56 days. The orthosis reduces activation and force production of the calf muscles while it permits full gravitational loading of the lower leg. MRI measurements of the knee and ankle were taken before the intervention, during the intervention (on day 49), and 14 days after the end of the intervention. Cartilage segmentation was conducted semiautomatically for the knee joint (4 segments) and for the upper (tibio-talar) and lower (subtalar) ankle joints (2 segments each). Linear mixed-effects (LME) models were used for statistical analysis. RESULTS: 8 volunteers completed the MRI experiment. In the lower ankle joint, differences in ΔT1 were found between the end of the intervention and 14 days after (p = 0.004), indicating a decrease in GAG content after reloading. There were no statistically significant differences in ΔT1 values in the knee and upper ankle joints. INTERPRETATION: Our findings suggest that in addition to gravitational load, muscular forces affect cartilage composition depending on the local distribution of forces in the joints affected by muscle contraction.

Magnetic resonance-determined sodium removal from tissue stores in hemodialysis patients.

We have previously reported that sodium is stored in skin and muscle. The amounts stored in hemodialysis (HD) patients are unknown. We determined whether (23)Na magnetic resonance imaging (sodium-MRI) allows assessment of tissue sodium and its removal in 24 HD patients and 27 age-matched healthy controls. We also studied 20 HD patients before and shortly after HD with a batch dialysis system with direct measurement of sodium in dialysate and ultrafiltrate. Age was associated with higher tissue sodium content in controls. This increase was paralleled by an age-dependent decrease of circulating levels of vascular endothelial growth factor-C (VEGF-C). Older (>60 years) HD patients showed increased sodium and water in skin and muscle and lower VEGF-C levels compared with age-matched controls. After HD, patients with low VEGF-C levels had significantly higher skin sodium content compared with patients with high VEGF-C levels (low VEGF-C: 2.3 ng/ml and skin sodium: 24.3 mmol/l; high VEGF-C: 4.1 ng/ml and skin sodium: 18.2 mmol/l). Thus, sodium-MRI quantitatively detects sodium stored in skin and muscle in humans and allows studying sodium storage reduction in ESRD patients. Age and VEGF-C-related local tissue-specific clearance mechanisms may determine the efficacy of tissue sodium removal with HD. Prospective trials on the relationship between tissue sodium content and hard end points could provide new insights into sodium homeostasis, and clarify whether increased sodium storage is a cardiovascular risk factor.