Autonomic cardiovascular and respiratory control during prolonged spaceflights aboard the International Space Station.

Impaired autonomic control represents a cardiovascular risk factor during long-term spaceflight. Little has been reported on blood pressure (BP), heart rate (HR), and heart rate variability (HRV) during and after prolonged spaceflight. We tested the hypothesis that cardiovascular control remains stable during prolonged spaceflight. Electrocardiography, photoplethysmography, and respiratory frequency (RF) were assessed in eight male cosmonauts (age 41-50 yr, body-mass index of 22-28 kg/m2) during long-term missions (flight lengths of 162-196 days). Recordings were made 60 and 30 days before the flight, every 4 wk during flight, and on days 3 and 6 postflight during spontaneous and controlled respiration. Orthostatic testing was performed pre- and postflight. RF and BP decreased during spaceflight (P < 0.05). Mean HR and HRV in the low- and high-frequency bands did not change during spaceflight. However, the individual responses were different and correlated with preflight values. Pulse-wave transit time decreased during spaceflight (P < 0.05). HRV reached during controlled respiration (6 breaths/min) decreased in six and increased in one cosmonaut during flight. The most pronounced changes in HR, BP, and HRV occurred after landing. The decreases in BP and RF combined with stable HR and HRV during flight suggest functional adaptation rather than pathological changes. Pulse-wave transit time shortening in our study is surprising and may reflect cardiac output redistribution in space. The decrease in HRV during controlled respiration (6 breaths/min) indicates reduced parasympathetic reserve, which may contribute to postflight disturbances.     

Estimation and prediction of functional changes in organisms in space flight

The article is devoted to theoretical and applied problems of estimation of the organism functional state and a level of health. Transitive states between health and illness, between norm and a pathology, so-called prenosological states are considered. The level of health is determined by adaptable opportunities of an organism, a degree of regulatory systems tension and their functional reserve. As the basic methodical approach to an estimation of a degree of regulatory systems tension the method of heart variability analysis is described. The applied aspect of a considered problem is submitted by results of the researches which have been carried out in conditions of space flight. Changes of organism functional state at different stages of adaptation to conditions of long weightlessness are described. The mathematical model of functional states is submitted. Four types of the vegetative regulation, differing on the adaptive reactions in conditions of space flight are allocated. Results of researches of crew members of the International space station are submitted.     

Influence of moderate physical exercise on the cardiac rhythm parameters of elementary and junior high school children

To reveal the specific features of the influence of moderate exercise (running) on the autonomic regulation of the cardiac rhythm, changes in the heart rate variability (HRV) parameters have been analyzed during three months in 292 children aged 9–14, as dependent on the sex and the baseline autonomic tone estimated by means of cluster analysis. It has been shown that, in schoolchildren engaged in running for health, HRV changes give evidence for the optimization of the mechanisms of autonomic regulation. The HRV parameters in the girls were more resistant to muscular activity compared to boys. The data obtained indicate that running for health requires a differential approach to dosing of the exercise, taking into account the sex and the baseline autonomic tone.     

Effectiveness of a cytokine restraining agent (CRA (TM)) in attenuating disuse deconditioning induced by hindlimb unloading in rats

Spaceflight alters many immune responses and among the regulatory components of an organisms response system that have been to be affected by spaceflight is the cytokine network. Spaceflight, as well as ground-based model systems of spaceflight, have been shown to affect the production and activation of various cytokines including interleukins (IL) and tumor necrosis factor (TNF). Levels of urinary IL-2 are elevated on the first day of spaceflight and again after returning from space. Most results from ground-based studies in rodents indicate either no alterations in cytokines or decreased levels. Results from this experiment indicate that HP 228, a potent cytokine restraining agent (CRA (TM)) was effective in attentuating many of the disuse deconditioning changes induced by the ground-based hindlimb suspension model that simulates weightlessness in rats. HP 228 is a novel heptapeptide with unnatural amino acids and can effectively restrain lipopolysaccharide (LPS)-induced increased levels of several key cytokines, including plasma TNF alpha, IL-1 beta and IL-6. HP 228 has also been shown to be effective in several rodent models of pain, inflammation and LPS-induced lethality, as well as in reducing inducible nitric oxide synthase.     

Velocity of head movements and sensory-motor adaptation during and after short spaceflight

To investigate to time course of sensory-motor adaptation to microgravity, we tested spatially-directed voluntary head movements before, during and after short spaceflight. We also tested the re-adaptation of postural responses to sensory stimulation after space flight. The cosmonaut performed in microgravity six cycles of voluntary head rotation in pitch, roll and yaw directions. During the first days of weightlessness the angular velocity of head movements increased. Over the next days of microgravity the velocity of head movements gradually decreased. On landing day a significant decrease of head rotation velocity was observed compared to the head movement velocity before spaceflight. Re-adaptation to Earth condition measured by body sway on soft support showed similar time course, but re-adaptation measured by postural responses to vestibular galvanic stimulation was prolonged. These results showed that the angular velocity of aimed head movements of cosmonauts is a good indicator of sensory-motor adaptation in altered gravity conditions.     

Heart rate variability and short duration spaceflight: relationship to post-flight orthostatic intolerance

Background  

Upon return from space many astronauts experience symptoms of orthostatic intolerance. Research has implicated altered autonomic cardiovascular regulation due to spaceflight with further evidence to suggest that there might be pre-flight autonomic indicators of post-flight orthostatic intolerance. We used heart rate variability (HRV) to determine whether autonomic regulation of the heart in astronauts who did or did not experience post-flight orthostatic intolerance was different pre-flight and/or was differentially affected by short duration (8 – 16 days) spaceflight. HRV data from ten-minute stand tests collected from the 29 astronauts 10 days pre-flight, on landing day and three days post-flight were analysed using coarse graining spectral analysis. From the total power (P_TOT), the harmonic component was extracted and divided into high (P_HI: >0.15 Hz) and low (P_LO: = 0.15 Hz) frequency power regions. Given the distribution of autonomic nervous system activity with frequency at the sinus node, P_HI/P_TOT was used as an indicator of parasympathetic activity; P_LO/P_TOT as an indicator of sympathetic activity; and, P_LO/P_HI as an estimate of sympathovagal balance.     

Analysis of Heart Rate Variability in Space Medicine

Space medicine was one of the first fields of science and practice to use the analysis of the heart rate variability (HRV) for obtaining new scientific information and solving the tasks of exercising medical control over humans working under extreme conditions. The theoretical basis of HRV analysis and different approaches to the assessment of the data obtained are presented in the work. The technique for HRV analysis with regard to the specifics of space studies is described. The results of investigations at different stages of the space flight, including the use of Holter monitoring, are presented. Special attention is given to the results of the investigations in a long-term 14-month space flight. The adaptation to long-term weightlessness was shown to be of a multistep character with the gradual involvement of additional regulatory mechanisms.     

Comparison of two systems for long-term heart rate variability monitoring in free-living conditions - a pilot study

Objective  

A number of small portable systems that can measure HRV are available to address questions related to autonomic regulation in free-living subjects. However, ambulatory HRV measurements obtained through use of these systems have not previously been validated against standard clinical measurements such as Holter recordings. The objective of this study was to validate HRV obtained using a commonly used system, Actiheart, during occupational and leisure-time activities.     

Age-dependent heart rate variability in preschool children living under the conditions of the European Arctic region

The results of analysis of specific characteristics of the heart rate variability (HRV) regulation in preschool children living under the Arctic high-latitude conditions are presented. The principal ageand gender-specific differences in the HRV regulation have been inferred from the intergroup evaluations of the HRV indicators in boys and girls. A functional developmental delay has been shown in 2.5-year-old girls compared with boys of the same age group. The applied orthostatic test has shown lower reserve capacities in children of the senior group compared with the junior group. It has been shown that the mechanisms of the regulation of cardiac rhythm in girls experience higher strain during orthostasis as compared with boys. The division of children into age groups with an age difference of one year has allowed the detection of the tendency towards basically different responses to functional loads during orthostasis. The mean HRV values characteristic of four- to six-year-old children living in the Arctic are presented. It has been shown that the children living at middle latitudes have a higher adaptive potential compared with the children living in high-latitude Arctic areas.     

Phenotypic screening for heart rate variability in the mouse

We developed a technology for heart rate (HR) variability (HRV) analysis in the mouse for characterization of HR dynamics, modulated by vagal and sympathetic activity. The mouse is the principal animal model for studying biological processes. Mouse strains are now available harboring gene mutations providing fundamental insights into molecular mechanisms underlying cardiac electrical diseases. Future progress depends on enhanced understanding of these fundamental mechanisms and the implementation of methods for the functional analysis of mouse cardiovascular physiology. By telemetric techniques, standard time and frequency-domain measures of HRV were computed with and without autonomic blockade, and baroreflex sensitivity testing was performed. HR modulation in the high-frequency component is predominantly mediated by the parasympathetic nervous system, whereas the low-frequency component is under the influence of both the parasympathetic and sympathetic systems. The presented technology and protocol allow for assessment of autonomic regulation of the murine HR. Phenotypic screening for HR regulation in mice will further enhance the value of the mouse as a model of heritable electrophysiological human disease.     

The functional state of microcirculation and autonomic regulation in young subjects with different levels of subjectively experienced psychological stress

A comprehensive comparative analysis of hemodynamics, microcirculation (the method of laser Doppler flowmetry with an occlusion test and the optical tissue oxymetry), blood circulation neurohumoral regulation (analysis of heart rate variability, HRV) in apparently healthy young subjects with different levels of subjectively experienced emotional stress has been performed. Depending on the degree of everyday stress (acute and/or chronic), the character of the autonomic regulation of blood circulation, as well as the state of the microcirculation and its regulation substantially vary. Moderate stress is accompanied by coactivation of sympathetic-parasympathetic regulatory mechanisms with augmented HRV baroreflex regulation circuits, which compensates for hemodynamic changes and is not accompanied by hypotensive reactions. An increase in the activity of neurogenic and myogenic tones of microhemodynamics in the subjects with moderate stress, which determines a high probability of blood shunting in tested tissue and decrease in relative oxygen extraction, has been discovered. Moderate levels of stress are also associated with an increase in the latency of postocclusive vasoreactive hyperemia, which is considered to be an early sign of the endothelium-mediated dysfunction of microcirculation.     

Heart rate dynamics in iNOS knockout mice

Nitric oxide has both an inhibitory and excitatory role in the regulation of pre-ganglionic sympathetic neurons, involving the iNOS and nNOS systems respectively. The aim of the present study was to examine cardiovascular autonomic activity in iNOS knockout mice using spectral analysis of heart rate variability (HRV), and to determine the role of iNOS in altered HRV in endotoxaemia. Electrocardiograms were recorded in anaesthetised mice, and the R-R intervals digitized for spectral analysis of HRV and cardiac rhythm regularity using sample entropy analysis. The basal heart rate was higher in iNOS knockout mice compared with controls (465+/-8 vs 415+/-13 beat/min P<0.05), with a significant increase in the low frequency power of HRV spectra in iNOS knockout mice compared with controls (49.4+/-4.3 vs 33.8+/-5.6 normalized units, P<0.05), consistent with increased cardiac sympathetic activity. Endotoxaemia is known to decrease HRV, but the role of iNOS is unknown. LPS (20 mg/kg i.p) increased basal heart rate in both wild type and iNOS knockout mice, but caused a depression of HRV and sample entropy in both groups. Studies in isolated beating atria showed that the changes of HRV under basal or post-LPS conditions disappeared in vitro, suggesting that the autonomic system is responsible for altered HRV. We conclude that disruption of iNOS gene leads to an increase in the low frequency power of HRV consistent with increased cardiac sympathetic activity. These data also demonstrate that LPS-induced decrease of HRV is independent of iNOS.     

Integrated assessment of neurodynamic and autonomic indicators in adolescents: Age-specific,gender-specific,and typological characteristics

The results of investigations carried out in school students aged 11–16 years (n = 930) have allowed us to determine some gender- and age-specific features in the neurodynamic and autonomic indicators of adolescents and identify the factors determining the formation of their psychophysiological state. The analysis of associations between the characteristics recorded in adolescents and a specific type of autonomic regulation has led to the conclusion about the predictive significance shown by the assessment of their functional constitution as an individual’s adaptation and resource characteristics.     

Behavioural and functional vestibular disorders after space flight: 2. Fish,amphibians and birds

The review presents data on functional changes in fish, amphibians and birds associated with otolith organ activity after exposure to weightlessness during spaceflight. These data are of importance both for solving some fundamental problems of vestibulology and for practice. In the latter case, lower vertebrates are considered as a convenient and, most importantly, adequate model to unravel the mechanisms of vestibular disorders in humans. Analysis of the experimental results shows that weightlessness exerts no substantial effect on the formation and functional state of the otolith system in embryos of fish, amphibians and birds developing during spaceflight. Moreover, they even promote faster embryonic development of fish and amphibians as shown for mammalian fetuses. The experiments show that both in lower and higher vertebrates weightlessness brings about similar functional and behavioral changes. For example, in fish hatchlings and amphibian tadpoles (without lordosis) the vestibulo-ocular reflex was more pronounced immediately after orbital spaceflight than in control. An analogous alteration in the otolith reflex was observed in most cosmonauts after short-time space missions. In adult terrestrial vertebrates, as well as in humans, immediately after landing there was found a drop in the level of activity and deterioration of the equilibrium function and motor coordination. Another interesting finding was an unusual looping behavior when fish and tadpoles swam in loops post landing. Presumably, unusual motor activity of animals, as well as illusions arising in cosmonauts and astronauts during the transition from 1 to 0 g, have the same background being associated with changes in the stimulation pattern of the otolith organs. Considering the similarity of vestibular responses, the use of animal models seems very promising as allowing different invasive techniques.     

Age dependency and correlation of heart rate variability,blood pressure variability and baroreflex sensitivity

Simultaneous analysis of heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) with different types of measures may provide non-duplicative information about autonomic cardiovascular regulation. Therefore, a multiple signal analysis of cardiovascular time series will enhance the physiological understanding of neuro cardiovascular regulation with deconditioning in bedrest or related gravitational physiological studies. It has been shown that age is an important determinant of HRV and BRS in healthy subjects. Whereas in the case of BPV, the effect of aging seems to depend upon the activity status of the subjects. In view of the facts that most of the previous works were dealing with only the variability of one kind of cardiovascular parameters in one study with conventional time-domain and/or frequency-domain analysis, we therefore designed the present work to compare the HRV, BPV and BRS between young and middle-aged male healthy subjects in one study with the same subjects using various techniques, including the approximate entropy (ApEn) measurement, a statistic quantifying HRV "complexity" derived from non-linear dynamics.     

Management of athletic training taking into account individual heart rate variability characteristics

This article presents a new approach to planning and timely adjusting athletic trainings according to the data of the quick analysis of heart rate variability. It has been shown that individual types of regulation are different not only in the autonomic balance, but also in the degree of endurance of training and competition loads.     

Gravitropically-stimulated seedlings show autotropism in weightlessness

In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed.     

The variability of the heart rhythm and the nature of the feedback as a result of operator activity in man]

In a memory task which required sustained attention, the positive or negative emotional state of an operator was created by introduction of two different types of feedback in accordance with the number of correct or wrong solutions. Standard and original indices were used for evaluation of the short-term variability of the heart rate (HRV) during performance. Changes in the HRV were observed only in the periods of performance with the failure type of the feedback. These changes reflected stabilization of heart bit-to-bit intervals. The original index of the fast HRV turned to be the most sensitive for testing HRV changes. Human autonomic reactions of such a kind during operator-like activity are known as a predictor for the functional state of dissatisfaction. This confirms the practical importance of application of the HRV indices for testing the ergonomic properties of the systems which control the operator-computer interaction.     

Welfare implication of measuring heart rate and heart rate variability in dairy cattle: literature review and conclusions for future research

Heart rate (HR) measurements have been used to determine stress in livestock species since the beginning of the 1970s. However, according to the latest studies in veterinary and behaviour–physiological sciences, heart rate variability (HRV) proved to be more precise for studying the activity of the autonomic nervous system. In dairy cattle, HR and HRV indices have been used to detect stress caused by routine management practices, pain or milking. This review provides the significance of HR and HRV measurements in dairy cattle by summarising current knowledge and research results in this area. First, the biological background and the interrelation of the autonomic regulation of cardiovascular function, stress, HR and HRV are discussed. Equipment and methodological approaches developed to measure interbeat intervals and estimate HRV in dairy cattle are described. The methods of HRV analysis in time, frequency and non-linear domains are also explained in detail emphasising their physiological background. Finally, the most important scientific results and potential possibilities for future research are presented.     

Characteristics of the autonomic regulation in humans with different susceptibility to cold

To determine the strained adaptation to cold, the cardiovascular reactivity under local cold exposure and the characteristics of regulation of the circulatory system in persons with high individual susceptibility to cold was studied. It was shown that the subjective characteristics of high susceptibility to cold in the form of initial symptoms of Raynaud’s phenomenon correlated with the symptoms of aggravated and generalized cold-induced vasoconstriction (CIV) during the local cold test. The analysis of the heart rate variability (HRV) in persons with aggravated CIV revealed a decrease in the parameters of the time-domain characteristics of HRV (RRNN, SDNN, RMSSD, pNN₅₀, and coefficient of variation) as well as a decrease in the total power (TP) of the frequency-domain characteristics and the absolute values of the frequency bands (VLF, LF, and HF) with a relative increase of the LF component. This reflects possible changes in the autonomic regulation of the cardiovascular system, which manifest themselves in a reduced contribution of reflectory mechanisms to the heart rate regulation followed by relative predominance of baroreflex regulation. The diagnostic value of aggravated cold-induced vasoconstriction in identifying disorders of adaptation to cold or premorbid state of the cardiovascular system is discussed.