Seven-day dry immersion: Interrelationship between the changes in the water-electrolyte balance and cardiovascular responses

The results of an experiment with a seven-day dry immersion are presented. Eight healthy men were examined before, during, and after the exposure. It was shown that the primary response involved hemodynamic and water-electrolyte changes. The mechanisms of cardiovascular adaptation to the immersion conditions were revealed. In particular, some electrophysiological shifts in the propagation of myocardial excitation were found, leading to an increase in the variance of natural small oscillations of the electric potential of the heart. The revealed significant reduction of the functional reserves of the cardiovascular regulatory mechanisms during adaptation to dry immersion is of great practical importance. The results suggest that the water-electrolyte balance shifts induced by dry immersion are the basis and the first phase of further changes in the autonomic regulation and functional state of the myocardium.     

The water-salt balance and renal function in space flights and in model experiments

Study of a condition of mineral and water-electrolyte metabolism, function of kidneys, and their hormonal regulation during model experiments (hypokinesia, bed rest, immersion etc.), and also in space flights and in readaptation period, has shown a major role of water-electrolyte homeostasis during general adaptation of humans and animals to new conditions of life and to conditions of weightlessness in particular. The change in regulation of volumes of fluid milieu in an initial period of weightlessness was shown to be the consequence of redistribution of blood and hemodynamics of the shifts resulting in change of production of volume-regulation hormones, formation of negative water balance, and redistribution of fluid in the organism among various fluid compartments. At later stages of flight or long-term hypokinesia, a change of water-electrolyte homeostasis occurs with a decrease in the kidneys excretion of sodium, and diuresis, but with an increased excretion of calcium and production of ADH and RAAS hormones. Following returning to earth gravitation, the majority of astronauts have adaptive reactions, compensating for the loss extracellular fluid and mineral substances and formation of "earth" water-electrolyte homeostasis. For estimation of water-electrolyte homeostasis and the functions of kidneys in astronauts, various functional loading tests have been developed. The developed system of preventive maintenance is successfully used for abolition of adverse changes at various stages of space flight and in readaptation period.     

Functional load tests in the assessment of the state of the kidneys and water-electrolyte metabolism

The use of functional load tests to assess the specific features of water-electrolyte metabolism under extreme conditions is considered, with special emphasis on their implications for space physiology and medicine. Water and mineral metabolism, the kidney function, and their hormonal regulation during simulation experiments, as well as in spaceflights and in the readaptation period, play an important role in human adaptation to new conditions of vital activity. In order to assess the state of the kidneys and water-electrolyte metabolism in cosmonauts and investigators, functional load tests were developed. They enabled us not only to gain insight into the mechanisms of osmotic and volumetric regulation but also to develop countermeasures to correct unfavorable shifts in water-salt homeostasis.     

Vertical and horizontal posture during suited immersion: similarity and differences according to some body functions

The role of axial body orientation was weighed during acute adaptation to suit immersion (SI) in 3 hr vertical (SIv, n=4) exposure series, and 3 d experiments in which six volunteers participated in both SIv and SIh. Various types of SI recruited different hormonal mechanisms to induce similar reactions of the water-electrolyte metabolism (WEM). Changes in the body position relative to the gravity vector modified equally strength and dynamics of the WEM regulation. The experimental data suggest that osmo- and volume-regulation reactions to SIv shown the response to the actual volumetric stimulus against the "distributed" weight-bearing reaction. They are less vigorous as compared to SIh and do not reach maximum within 3 hrs. Physiological reactions to SIh were marked by greater effects of ADH on the kidney when compared with dry immersion, and an additional stimulation of aldosterone secretion by the sympathetic nervous system and/or ACTH. SIh caused rapid and more heavy symptoms of motion sickness that correlated with body mass reduction, negative water balance, degradation of tolerance of classic physical tests executed after SI. Three-days SIv, as opposed to SIh, resulted in more profound hypervolemia in the upper body of the test-subjects.     

Physiological [correction of Physilogical] cost of standard physical load after 7-day dry immersion

Working capacity and cardiovascular response to exercise were studied in men subjected to 7-days of dry immersion. Heart rate, ventilation, and oxygen uptake and consumption were measured before immersion and on the 4th and 7th days of immersion. No significant changes in heart rate were found, but some changes in ventilation and oxygen uptake dynamics indicate that gas exchange may be altered during immersion. Physiological adaptation and individual differences are discussed.     

Adaptation of the water-electrolyte metabolism to space flight and at its imitation

A fifty-year study of water-electrolyte metabolism, the condition of the water medium of the body, and hormonal regulation during space flights and the postflight period or their on-ground modeling (hypokinesia, bed rest, immersion, etc.) has shown the important role of water-salt homeostasis in adaptation of the human and animal body to weightlessness. It has been revealed that, in weightlessness, the conditions for the development of a negative balance of a liquid (hydrohydration) and basic electrolytes are created. After termination of long space flights, attributes of the development of adaptive reactions, compensating for the loss of extracellular liquid volume come to light. In order to assess the state of the kidneys and water-electrolyte metabolism in cosmonauts and investigators, functional load tests, and special methods of diagnostics were developed. This is the basis for the research aimed at improving the scheme of correction of the water balance of the body of cosmonauts at different stages of a flight.     

Adaptations of heart activity to physical exercise in female physical education teachers in the European North

Characteristics of heart activity were studied in female residents of the European North with ages between 25 and 59 years who were adapted to physical exercise. The results of studies of the biological age and the degree of training are presented. The mechanisms of adaptation and the specific features of the cardiovascular system (CVS) response to physical exercise depending on the duration of professional experience of subjects were determined. The greatest changes in the functional CVS characteristics were observed in the youngest (25–35 years) and oldest (46–59 years) subjects. This was shown to depend on the type of adaptation, age-specific characteristics, and moderately severe climatic conditions. Comparison of groups of subjects with different durations of professional experience showed that the speed of nervous processes decreased, the regulation of blood circulation became inert, and age-related shifts in some of the variables accelerated. These changes are considered to be the result of an increased expenditure of the physiological reserves of the body under different environmental conditions.     

Identification of proteins of cardiovascular system in healthy subjects’ urine during “dry” immersion

We analyzed the urine proteome in 14 healthy volunteers who were subjected to 5-day dry immersion using proteomic analysis methods and bioinformatics approach. We identified nine proteins related to the cardiovascular system. It was shown that 5-day dry immersion modifies the urine proteomic profile, indicating renal, endocrine, circulatory, and metabolic changes. Most of these changes are characterized by both a very rapid development and very rapid restoration within return to normal conditions.     

Fundamental and applied objectives of investigation in dry immersion

The results of extended comparative research in the effect of hypogravity on the motor system in space flights and ground-based experiments have shown that “dry” immersion (DI) is the most adequate model of microgravity—the time of development, and the volume and depth of structural and functional motor disorders in DI are very close to what is observed in real microgravity. The high intensity and speed of development of hypogravity effects during immersion hypokinesia in comparison with bed rest hypokinesia, differing from DI only by the level of support deafferentation, promoted an insight into the leading (triggering) role of support lessness in the genesis of microgravity-induced syndromes of muscular deconditioning and hypogravitational ataxia. The involvement and pathways of support afferentation within the muscular system were experimentally studied and verified. The mechanisms of the development of changes in the activity of the system mechanisms remain much less investigated. These issues, as well as some new approaches for the elimination of the negative effects of hypogravity, were the subjects of investigation in the program of a complex dry immersion experiment, the results of which are presented in this issue of the journal.     

Effect of the mineral water naftusy on some indices of water-electrolyte metabolism in man]

The clinic-physiological examination of patients with urolithiasis has revealed that single and course taking of medicinal water Naftusya induces shifts of water-electrolyte exchange in the organism, their expressivity and direction are determined, as a rule, by the initial value of indices. As a whole, the effect of water Naftusya can be characterized as "equilibratory" one effecting by the "law of the initial value".     

The dynamics of blood biochemical parameters in an experiment with seven-day immersion

In an experiment with seven-day immersion, blood samples were taken from eight volunteers (21 to 26 years old) seven days prior to immersion, on days 3 and 7 of immersion and on days 1 and 8 of recovery. Blood serum was analyzed for 38 biochemical markers of the functional state of the myocardium, skeletal muscles, hepatobiliary system, kidneys, pancreas, gastrointestinal tract, prostate, and protein-nucleic, carbohydrate, electrolyte, and mineral metabolisms. Seven-day immersion was shown to alter the biochemical parameters within the range of the physiological norm. The observed changes included lower activities of enzymes associated with muscular and myocardial constellation, shifts in electrolytes (K, Na, Mg), and an increase in the biliary function parameters. Increased concentrations of the parameters of lipid metabolism suggest a higher risk of atherogenesis. Biochemical parameters of bone tissues and erythrocyte activity were practically unchanged. Most of the parameters returned to the preexperimental values by day 8 of recovery.     

Immune system parameters of healthy humans in a chamber experiment with hyperbaric oxygen—nitrogen—argon air

Data on the immune system state during nine-day isolation in a pressurized compartment with normoxic or hypoxic oxygen-nitrogen-argon air (ONAA) are presented. The results showed that adaptation of the immune system of healthy humans to isolation effects is accompanied by changes in a number of parameters of innate and adaptive immunity. The time course and intensity of shifts caused by the set of experimental factors are likely to be dependent on the hereditary mechanisms of the immunological reactivity. To prevent adaptation failure of the immune system, monitoring of immune homeostasis is necessary.     

Adaptation and selective information transmission in the cricket auditory neuron AN2

Sensory systems adapt their neural code to changes in the sensory environment, often on multiple time scales. Here, we report a new form of adaptation in a first-order auditory interneuron (AN2) of crickets. We characterize the response of the AN2 neuron to amplitude-modulated sound stimuli and find that adaptation shifts the stimulus-response curves toward higher stimulus intensities, with a time constant of 1.5 s for adaptation and recovery. The spike responses were thus reduced for low-intensity sounds. We then address the question whether adaptation leads to an improvement of the signal's representation and compare the experimental results with the predictions of two competing hypotheses: infomax, which predicts that information conveyed about the entire signal range should be maximized, and selective coding, which predicts that "foreground" signals should be enhanced while "background" signals should be selectively suppressed. We test how adaptation changes the input-response curve when presenting signals with two or three peaks in their amplitude distributions, for which selective coding and infomax predict conflicting changes. By means of Bayesian data analysis, we quantify the shifts of the measured response curves and also find a slight reduction of their slopes. These decreases in slopes are smaller, and the absolute response thresholds are higher than those predicted by infomax. Most remarkably, and in contrast to the infomax principle, adaptation actually reduces the amount of encoded information when considering the whole range of input signals. The response curve changes are also not consistent with the selective coding hypothesis, because the amount of information conveyed about the loudest part of the signal does not increase as predicted but remains nearly constant. Less information is transmitted about signals with lower intensity.     

Proteomics of ischemia/reperfusion injury in rabbit myocardium reveals alterations to proteins of essential functional systems

Brief periods of myocardial ischemia prior to timely reperfusion result in prolonged, yet reversible, contractile dysfunction of the myocardium, or "myocardial stunning". It has been hypothesized that the delayed recovery of contractile function in stunned myocardium reflects damage to one or a few key sarcomeric proteins. However, damage to such proteins does not explain observed physiological alterations to myocardial oxygen consumption and ATP requirements observed following myocardial stunning, and therefore the impact of alterations to additional functional groups is unresolved. We utilized two-dimensional gel electrophoresis and mass spectrometry to identify changes to the protein profiles in whole cell, cytosolic- and myofilament-enriched subcellular fractions from isolated, perfused rabbit hearts following 15 min or 60 min low-flow (1 mL/min) ischemia. Comparative gel analysis revealed 53 protein spot differences (> 1.5-fold difference in visible abundance) in reperfused myocardium. The majority of changes were observed to proteins from four functional groups: (i) the sarcomere and cytoskeleton, notably myosin light chain-2 and troponin C; (ii) redox regulation, in particular several components of the NADH ubiquinone oxidoreductase complex; (iii) energy metabolism, encompassing creatine kinase; and (iv) the stress response. Protein differences appeared to be the result of isoelectric point shifts most probably resulting from chemical modifications, and molecular mass shifts resulting from proteolytic or physical fragmentation. This is consistent with our hypothesis that the time course for the onset of injury associated with myocardial stunning is too brief to be mediated by large changes to gene/protein expression, but rather that more subtle, rapid and potentially transient changes are occurring to the proteome. The physical manifestation of stunned myocardium is therefore the likely result of the summed functional impairment resulting from these multiple changes, rather than a result of damage to a single key protein.     

Dry immersion effects on the mechanisms of metaboreflex regulation of hemodynamics during exercise

The effects of four-day dry immersion on metaboreflex regulation of hemodynamics were evaluated during local static exercise (30% of the maximum voluntary contraction) of the calf plantar flexors. One group of immersed subjects received low-frequency electrostimulation of their leg muscles to decrease the immersion effect on the EMG of exercising muscles. Metaboreflex regulation was evaluated by comparison of cardiovascular responses to physical loads with and without post-exercise circulatory occlusion. Immersion slightly increased the heart rate (HR) and reduced the systolic blood pressure in resting subjects; however, it did not have a distinct effect on blood pressure (BP) and HR during exercise or metaboreflex potentiation of hemodynamic shifts.     

Biomechanics and regulation of external respiration under conditions of five-day dry immersion

The functional state of external respiration and the features of its regulation in healthy persons were studied under conditions of microgravity simulated using dry immersion. The lung volume, the ratio of thoracic and abdominal components during quiet breathing and performing various respiratory maneuvers, as well as the parameters that characterize the regulation of breathing (the duration of breath holding and the ability to voluntarily control respiratory movements), were recorded during the baseline period, on days 2 and 4 of dry immersion, and after the end of the dry immersion. It has been shown that the breathing pattern did not significantly change under conditions of dry immersion compared to the baseline period; however, the inspiratory reserve volume increased (p < 0.05), while the expiratory reserve volume decreased (p < 0.01). Dry immersion did not alter pulmonary ventilation, yet most of the subjects trended toward an increase in the contribution of the abdominal component of breathing movements during quiet breathing and demonstrated a statistically significant increase in this parameter during the lung vital capacity maneuver. The durations of the inspiratory and expiratory maximal breath holding under conditions of immersion did not differ from the background values. During the immersion, the accuracy of voluntary control of breathing increased. We believe that immersion, similar to microgravity, leads to changes in the reserve lung volume, which are partly because of changes in the body position; changes in relative contributions of the thoracic and abdominal components in the breathing movements; and changes in voluntary breath regulation.     

Visual cells remember earlier applied target: plasticity of orientation selectivity

Background

A canonical proposition states that, in mature brain, neurons responsive to sensory stimuli are tuned to specific properties installed shortly after birth. It is amply demonstrated that that neurons in adult visual cortex of cats are orientation-selective that is they respond with the highest firing rates to preferred oriented stimuli.

Methodology/Principal Findings

In anesthetized cats, prepared in a conventional fashion for single cell recordings, the present investigation shows that presenting a stimulus uninterruptedly at a non-preferred orientation for twelve minutes induces changes in orientation preference. Across all conditions orientation tuning curves were investigated using a trial by trial method. Contrary to what has been previously reported with shorter adaptation duration, twelve minutes of adaptation induces mostly attractive shifts, i.e. toward the adapter. After a recovery period allowing neurons to restore their original orientation tuning curves, we carried out a second adaptation which produced three major results: (1) more frequent attractive shifts, (2) an increase of their magnitude, and (3) an additional enhancement of responses at the new or acquired preferred orientation. Additionally, we also show that the direction of shifts depends on the duration of the adaptation: shorter adaptation in most cases produces repulsive shifts, whereas adaptation exceeding nine minutes results in attractive shifts, in the same unit. Consequently, shifts in preferred orientation depend on the duration of adaptation.

Conclusion/Significance

The supplementary response improvements indicate that neurons in area 17 keep a memory trace of the previous stimulus properties, thereby upgrading cellular performance. It also highlights the dynamic nature of basic neuronal properties in adult cortex since repeated adaptations modified both the orientation tuning selectivity and the response strength to the preferred orientation. These enhanced neuronal responses suggest that the range of neuronal plasticity available to the visual system is broader than anticipated.     

Evolutionary Aspects of Cardioprotection

The review addresses the mechanisms of adaptation of the myocardium and cells of the cardiovascular system to hypoxia and ischemia as well as biochemical mechanisms of cardioprotection in animals of different phylogenetic levels. A special focus is placed on general adaptive strategies developed by evolutionarily distant animals in response to hypoxia and ischemia and on preconditioning and myocardial hibernation phenomena.     

Beneficial effects of Provinols: cardiovascular system and kidney

Red wine polyphenols have been reported to exert beneficial effects in preventing cardiovascular diseases but their molecular mechanisms of hemodynamic effects on functional cardiovascular and renal changes were studied much less. The review is focused on in vitro as well as in vivo effects of red wine extract containing polyphenolic compounds (Provinols) on cardiovascular systems and kidney in relation to the molecular and biochemical mechanisms of these compounds. This review provides the evidence that Provinols is able to produce ex vivo endothelium-dependent relaxation as a result of enhanced NO synthesis. Administration of Provinols partially prevents the development of hypertension during NO deficiency and accelerates the decrease of blood pressure in already established hypertension. The effects of Provinols include prevention and/or attenuation of myocardial fibrosis, reduction of aortic wall thickening and improvement of vascular functions. These functional and structural alterations are associated with significant augmentation of NO production, seen as the increase of NO synthase activity and eNOS protein expression. Moreover, it has been documented that Provinols decreased the oxidative stress within the cardiovascular system and kidney.     

Maternal inflammation, growth retardation, and preterm birth: insights into adult cardiovascular disease

The "fetal origin of adult disease Hypothesis" originally described by Barker et al. identified the relationship between impaired in utero growth and adult cardiovascular disease risk and death. Since then, numerous clinical and experimental studies have confirmed that early developmental influences can lead to cardiovascular, pulmonary, metabolic, and psychological diseases during adulthood with and without alterations in birth weight. This so called "fetal programming" includes developmental disruption, immediate adaptation, or predictive adaptation and can lead to epigenetic changes affecting a specific organ or overall health. The intrauterine environment is dramatically impacted by the overall maternal health. Both premature birth or low birth weight can result from a variety of maternal conditions including undernutrition or dysnutrition, metabolic diseases, chronic maternal stresses induced by infections and inflammation, as well as hypercholesterolemia and smoking. Numerous animal studies have supported the importance of both maternal health and maternal environment on the long term outcomes of the offspring. With increasing rates of obesity and diabetes and survival of preterm infants born at early gestational ages, the need to elucidate mechanisms responsible for programming of adult cardiovascular disease is essential for the treatment of upcoming generations.