Three dimensional Ballistocardiogram and Seismocardiogram: what do they have in common?

3D-body accelerations, i.e. Ballistocardiograms (BCG) and Seismocardiograms (SCG), ECG and Impedance-cardiograms (ICG) were recorded on healthy volunteers participating to the European Space Agency (ESA) 59th parabolic flight campaign. In the present paper we document the similarities and differences that can be seen in the seismo- and ballisto-cardiogram signals in different positions (standing and supine) under normal gravity condition as well as during the weightlessness phases (0G) of a parabolic flight. Our results demonstrate that SCG and BCG both present a similar three dimensional (3D) nature, with components of the BCG having lower frequency content than the SCG. The recordings performed in the 0G environment are the one with the smoothest shape and largest maximum magnitude of the Force vector. The differences seen between SCG and BCG stress further the importance for the need of using different nomenclature for the identification of peaks in both signals.

Cardiovascular changes in parabolic flights assessed by ballistocardiography.

This paper presents a comparison of the cardiovascular changes observed in microgravity as compared to ground based measurements. The ballistocardiogram (BCG), the electrocardiogram (ECG) and the transthoracic impedance cardiogram (ICG) were recorded on five healthy subjects during the 57th-European Space Agency (ESA) parabolic flight campaign. BCG is analyzed though its most characteristic wave, the IJ wave complex that can be identified along the longitudinal component of BCG and which has been demonstrated to be linked to cardiac ejection. The timings between the contraction of the heart and the ejection of blood in the aorta are analyzed via the time delay between the R-wave of the ECG and the I and J-waves of BCG (RI and RJ intervals respectively). Our results show that the IJ complex presents a larger amplitude in weightlessness and suggest that stroke volume (SV) increases in microgravity. We assume that ballistocardiography is an efficient method to assess the ventricular performance.

3D-ballistocardiography in microgravity: comparison with ground based recordings.

3D-Ballistocardiograms ECG and Impedancecardiograms (ICG) were recorded on 5 healthy volunteers participating to the European Space Agency (ESA) 57(th) parabolic flights campaigns. Comparisons are made between the baseline recordings performed on the ground and the recordings made during the microgravity phases of a parabolic flight. The spatial curves of the displacement, velocity and acceleration vectors, instead of their individual components are used to compute the magnitude of the force vector, kinetic energy and work during the cardiac cycle. Our hypothesis is that the 3D-BCG provides parameters correlated with the timings of ejection (PEP, LVET). Although our subject population is limited (N=5), this is the first study of BCG to be performed with N>1. Our results suggest that microgravity decrease the complexity of the 3D displacement curve and that peaks in curvature are consistently present in microgravity and on the ground. However they do not seem to be perfectly related to the classical cardiac ejection timings from ICG.

Timing and source of the maximum of the transthoracic impedance cardiogram (dZ/dt) in relation to the H-I-J complex of the longitudinal ballistocardiogram under gravity and microgravity conditions.

The transthoracic impedance cardiogram (ICG) and the acceleration ballistocardiogram (BCG) measured close to the center of mass of the human body are generated by changes of blood distribution. The transthoracic ICG is an integrated signal covering the whole thorax and spatial resolution is poor. Comparison between both signals can be used to elucidate the source of the ICG signal. We recorded the ECG, ICG, and BCG simultaneously in healthy subjects under resting and microgravity conditions during parabolic flights. The time interval between the R-peak of the ECG and the maximum of the ICG (R-dZ/dtmax) and the time interval between the R-peak of the ECG and the I-peak in the BCG (R-I) differed significantly (p<0.0001). The I-peak in the BCG always occurred earlier during systole than dZ/dtmax. The delay of dZ/dtmax ranged between 23 and 28 ms at rest and was lowest under microgravity conditions (12 ± 4 ms, p<0.02). Our results suggest that both signals have different sources. Combination of modern imaging techniques with classical non invasive approaches to detect changes of blood distribution may provide new insights into the complex interaction between blood flow and mechanocardiographic signals like the BCG.

[Researches of autonomic regulation of blood circulation in the condition of long-term space flight].

In the article is presented five-year experience of experimentation in autonomic regulation of blood circulation onboard the International space station. The heart rate variability (HRV) analysis was the basic methodical approach in the researches. We described probabilistic approach created on the basis of HRV analysis to an estimation of risk of pathology development in the conditions of long space flight. The individual type of autonomic regulation had essential value during the analysis of results. It is shown that the type of regulation, which is inherent in every cosmonaut in the conditions of weightlessness, remains even during following flights. We obtained the new scientific data on connection of character of adaptable reaction of an organism to the space flight factors with individual type of autonomic regulation. It is shown that staying in weightlessness is connected with changeover of regulatory systems and with transition in a zone of prenosological states. Adaptable reactions in weightlessness are characterized by tension growth of regulatory systems at preservation of sufficient functional reserves. The mobilization of additional resources after returning to the Earth is required and consequently functional reserve of mechanisms of regulation decreases. Cosmonauts with vagotonic and normo-sympatotonic types of autonomic regulation appear to be the most resistant. Knowing the type of autonomic regulation we will be able to foresee possible reaction of the cosmonaut to the factors of space flight. As a result of HRV analysis during the flight of the past few months likelihood estimations were calculated and risk categories were defined. Consequently, 3 groups of risk of pathology development were distinguished. In conclusion, theoretical and applied relevance of the conducted experiments were considered.

Three dimensional ballisto- and seismo-cardiography: HIJ wave amplitudes are poorly correlated to maximal systolic force vector.

Ballistocardiography was recorded in 3-D on a free floating astronaut in space as well as on healthy volunteers participating to the ESA 55(th) and DLR 19(th) parabolic flights campaigns. In this paper we demonstrate further the usefulness of recording and analyzing ballistocardiograms (BCG) in three dimensions. The spatial curves of the displacement, velocity and acceleration vectors are analyzed instead of their individual 2-D components. The maximum magnitude of the force vector is shown to be poorly correlated to the HI and IJ wave amplitude traditionally computed on the longitudinal (feet-to-head) component of acceleration (uni-dimensional BCG). We also suggest that kinetic energy and work are useful parameters to consider for a physiological interpretation of the 3D-BCG. The technique presented is invariant from the axis of representation and provides important novel physiological information. We stress further the need of 3D recordings and analysis techniques for Ballisto- and Seismo-cardiography.

Three dimensional ballistocardiography: methodology and results from microgravity and dry immersion.

Balistocardiography was recorded in 3-D on a free floating astronaut in space as well as on healthy volunteers participating to a dry immersion study in a terrestrial laboratory. We demonstrate a new technique suitable for the analysis of 3-D BCG. The spatial curve of the displacement vector is analyzed instead of the three components of acceleration. The technique presented is invariant from the axis of representation and provides important novel physiological information.

[Potentiality of building-up the medical operations system for long-duration space missions by noncontact physiological functions recording during sleep time].

Methods of investigating the physiological functions in space crews on extended missions during night sleep are of much fundamental and practical substance. The design of experiment "Sonocard" utilizes the method of seismocardiography. Purpose of the experiment is to validate the procedures of noncontact in-sleep physiological data recoding which are potent to enhance the space crew medical operations system. The experiment was performed systematically by ISS Russian crew members starting from mission-16. The experimental procedure is easy and does not cause discomfort to human subjects. Results of the initial experimental sessions demonstrated that, as on Earth, sleep in microgravity is crucial for the recovery of body functional reserves and that the innovative technology is instrumental in studying the recovery processes as well as person unique patterns of adaptation to extended space mission. It also allows conclusions about sleep quality, mechanisms of recreation, and body functionality. These data may enrich substantially the information used by medical operators of the space missions control centers.

[Software for polygraphs used in scientific research].

Polygraphs--devices for simultaneous detection of several physiological parameters--are currently used in medicine in psychology. Special polygraphs are also used in scientific research. The process of data acquisition and processing in such polygraphs is usually computer-controlled. The goal of this work was to describe software for detection of polygraph signals used in cardiorespiratory system research. The software supports the experiment script language, allows hyperventilation testing, and makes it possible for the examination subject to control the data detection process.

[Assessment and prediction of health status of the Mars mission crew members].

The scientific concept of health assessment and prediction in a piloted mission to Mars has been built on the principles of pre-nosologic diagnostics, i.e., identification of the norm-pathology borderline states. The article deals with the medical care policy for the mission, and specific techniques and technologies. A three-level system of health assessment and prediction is proposed. Innovative approaches to evaluation of the body control systems during long exposure in microgravity have a footing of ground-based and space experimental investigations. Namely, these include evaluation of the cardiorespiration autonomous regulation and body functional reserve assessment by noninvasive recording of physiological signals in sleeping crewmembers before and after mission.

Periodic structures and diurnal variation in blood pressure and heart rate in relation to microgravity on space station MIR.

Four Russian crew members were studied on space station MIR, and blood pressure (BP) and heart rate (HR) data were continuously collected. BP and HR data were collected on earth 1 day before orbital flight to the space station, then at weeks 8, 16 and 24 during space flight, and again 1 or 2 days after returning to earth. Time serial data for BP and HR were analyzed by spectral analysis with the MemCalc system (Suwa Trust, Sapporo, Japan). Periodic structures of diurnal variation in systolic blood pressure (SBP), diastolic blood pressure (DBP) and HR were compared at 24-hour, 12-hour and 8-hour intervals, these being determined as the main periodic components for the assessment of BP and HR variability. The 24-h mean levels of SBP and HR during space flight were unchanged. Waking SBP was not different from pre-flight values. During sleep, in-flight changes in HR did not differ from pre-flight values. SBP during sleep in orbit increased to over pre-flight values. Waking DBP was reduced during flight. The SBP and HR phases over a 24-hour cycle were shortened with a more pronounced shortening in weeks 8 and 16 compared with pre-flight values, and at week 24 recovered to preflight values. The 12, 8-hour-cycle remained unchanged, and were similar to pre-flight values. At the space station, the astronauts' mission was carried out under strict control of sleeping and waking hours; therefore, their 24-hour schedule is an artificially constructed situation. Main periodicity structures were maintained by strict control of lifestyle during long-term space flight. The conclusions reached were as follows: 1) SBP levels during sleep in a space environment increased compared with those on earth; 2) the periodicity phase of BP and HR shifted toward to 24-hour cycle as a result of long-term space flight, even though these periods shortened after a few months compared with pre-space flight values.

The autonomous regulation system functional reserves evaluation in 7-day head down bedrest.

The heart rate variability estimation was used for autonomous regulation diagnostic in the 7-day head down bedrest experiment (HDBR). The new device "Pneumocard" and the fix respirations test were applied. The growth of sympathetic activity of autonomous nervous system and reduction of functional reserves of regulation mechanisms were observed in the microgravity modeling by HDBR. The analysis of the individual data had shown, that at two volunteers with most significant growth of SI after the experiment the orthostatic intolerance was observed. The data received in experiment confirm a hypothesis that growth of sympathetic activity in microgravity is accompanied by reduction of regulation mechanisms functional reserves is prognostic unfavorable.

Blood pressure variability during 120-day head-down bed rest in humans.

Influence of physical inactivity and microgravity to periodic structure of blood pressure was studied. Six healthy males were kept under head-down bed rest (HDBR) for 120 days. Blood pressure and heart rate (HR) were recorded by a portable sphygmomanometer and a Holter electrocardiogram, respectively. The results were analyzed by spectrum analysis. Phase, amplitude and acrophase of systolic blood pressure (SBP) by approximately 24, 12 and 8 h were measured before, 60, 120 day and after HDBR. The phase at 24, 12 and 8 h did not show significant changes during HDBR, and acrophase showed a tendency to shift to 14:00 after HDBR. Amplitude for 24 h tended to attenuate during bed rest (BR), and significantly increased after BR. The results of this study suggest that the circadian rhythm of SBP and HR were maintained by strict control of sleep, awakening and food intake in microgravity model of a long-term BR state. However, the tendency to decrease 24-h cyclic amplitude of SBP appeared to be the rhythmic modulation related to cardiovascular deconditioning.

[The adaptation of the blood circulation to the long-term microgravity: ballistic-cardiographic investigation during 14 month space flight]. / Adaptatsiia sistemy krovoobrashcheniia k usloviiam dlitel'noi nevesomosti: ballistokardiograficheskie issledovaniia vo vremia 14-mesiachnogo kosmicheskogo poleta.

Specificity of the use of ballistocardiography (BCG) in space flight is considered. In particular, the contactless method makes it possible to continue recording during the night hours and study the ultradian rhythms reflective of the state of higher autonomous centers. As was stated, on months 7 to 8 of the mission by cosmonaut-physician Polyakov the BCG amplitude rose in concert with activation of the higher autonomous centers that were apparently involved in maintaining the established cardiovascular homeostasis. By months 11 to 13 on mission, the BCG amplitude decline resulted in an increase in the SCG/BCG index representing the amount of myocardium energy spent on blood transport.

Autonomic regulation of circulation and cardiac contractility during a 14-month space flight.

The space flight of physician cosmonaut V.V. Polyakov, the longest to date (438 days), has yielded new data about human adaptation to long-term weightlessness. Autonomic regulation of circulation and cardiac contractility were evaluated in three experiments entitled Pulstrans, Night, and Holter. In the Pulstrans experiment electrocardiographic (ECG), ballistocardiographic (BCG), seismocardiographic (SCG), and some other parameters were recorded. In the Night experiment, only the ballistocardiogram was recorded, but a special feature of this experiment is that the BCG records were obtained with a contactless method. This method has several advantages, the most important of which are the possibility of studying slow-wave variations in physiologic parameters (ultradian rhythms) on the basis of recordings made under standard conditions over a prolonged period. The Holter experiment (24-hour electrocardiographic monitoring) used a portable cardiorecorder (Spacelab, USA). The obtained electrocardiographic data were used to analyze heart rate variability. In the first 6 months of the 14-month flight, the dynamics of cardiovascular parameters in V.V. Polyakov was virtually the same as in the other cosmonauts. The data obtained after the first 6 months of Polyakov's sojourn in space are unique and mention should be made of at least three important aspects: (1) activation of a new, additional adaptive mechanism in the 8th-9th months of flight, as is evidenced by alterations in the periodicity and power of superslow wave oscillations (ultradian rhythms) reflecting the activity of the subcortical cardiovascular centers and of the higher levels of autonomic regulation; (2) growth of cardiac contractility accompanied by a decrease in heart rate during the last few months of flight; (3) a considerable increase in the daily average values of absolute power of heart rate's variability MF component, which reflects the activity of the vasomotor center. Specific mechanisms of adaptation to weightless conditions appear to be associated with activation of higher autonomic centers. The hypothesis that central levels of circulation regulation are activated in a long-term space flight was investigated by analyzing of ultradian rhythms in nighttime. The data, received during the flight of V. V. Polyakov, show, that the process of human adaptation to long influence of weightlessness consists of a number of consecutive stages, during which the activation of more and more high levels of control system of physiological functions occurs.

Assessment of electrophysiological state of heart in astronauts in terms of decartographic and conventional electrocardiographic characteristics.

Long-term observation of the heart state during specialized professional activities plays an important part in preventive medicine. This study is aimed at assessment of electrophysiological state of heart in astronauts by common electrocardiography, vectorcardiography, and dipole electrocardiotopography (DECARTO technique). The subjects observed were two astronauts performing a long-term flight at the Mir orbital station. DECARTO technique was used to obtain an intelligible-pictorial representation of the data in the form of so-called decartograms for visual and quantitative analysis. The observations showed rather stable chronotopography of the heart depolarization process. However, there was an increase of the maximal magnitude of the electric heart vector and a decrease of the ventricular gradient vector in the middle part of the flight. Just upon landing, a pronounced decrease of the ventricular gradient magnitude, followed by a fast restoration of its value was observed in both subjects. The DECARTO technique used in combination with vectorcardiography facilitated the detailed visual analysis of the electrocardiographic data. (Fig. 3, Ref. 3.)

[Problem of automated evaluation of the functional state of the body in current aerospace and preventive medicine]. / Problema avtomatizirovannoi otsenki funktsional'nogo sostoianiia organizma v kosmonavtike i profilakticheskoi meditsine na sovremennom étape.

The methodology of evaluating the health status of the normal man is discussed. Special attention is given to the boundary states between the norm and pathology, i.e. ++pre-nosological and premorbid states. The development of automatic systems for evaluating the functional state of the human body is described. A motor-borne automatic system "Autosan-82" is described as a ground-based analog of a space system of medical monitoring. Also, a description of present-day automatic systems "Control", "Vita", and "Rhythm" is given. They can provide health evaluation at three levels: 1) preliminary assessment and identification of subjects in different health conditions; 2) diagnosis of functional states, identification of risk factors, and potential profiles of pathology; 3) medical examinations by specialists in different medical disciplines of subjects with potential pathologies or detailed evaluation of reserve capabilities of health subjects.

[Evaluation of physical work capacity of the astronauts on Saliut-6]. / Otsenka fizicheskoi rabotosposobnosti kosmonavtov na stantsii "Saliut-6".

Electrocardiograms of Salyut-6 prime crew-members recorded during their exercises on a bicycle ergometer and treadmill are presented. ECG were recorded by a portable tape recorder Cardiocassette and transmitted to the Earth via the radiocommunication channel. This procedure helped to better understand cardiovascular adaptation to different workloads, including submaximal, as well as reserve abilities of the body at various flight stages. This can be used advantageously to correct and control the training process as well as to predict the cardiovascular status at the final flight stage.