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.

[Effect of geomagnetic activity on the human body in extreme conditions and correlation with data from laboratory observations]. / Vozdeistvie geomagnitnoi aktivnosti na organizm cheloveka, nakhodiashchegosia v ékstremal'nykh usloviiakh, i sopostavlenie s dannymi laboratornykh nabliudenii.

It was hypothesized based on previous laboratory observations and theoretical concepts that astronauts working at the "Mir" station under zero gravity conditions exhibit enhanced sensitivity to geomagnetic disturbances. The result of studies made it possible to reveal the dynamics of changes in cardiovascular characteristics separately in the main phase and the phase of storm restoration. A similar dynamics of cardiac activity was observed in experimental rabbits during geomagnetic storms.

[Autonomous nervous regulation of circulation during prolonged isolation studied with analysis of the cardiac rhythm variability]. / Issledovanie vegetativnoi reguliatsii krovoobrashcheniia vo vremia dlitel'noi izoliatsii na osnove analiza variabel'nosti serdechnogo ritma.

Adjusting reactions of human body were evaluated using mathematical analysis of the cardiac rhythm. Variability of cardiac intervals was reduced in consequence of an elevation of sympathetic tone within the autonomous nervous system. Analyzed were diurnal arrays of cardiac intervals derived from Holter monitoring data. Pulse rate and standard deviation of the cardiac interval length were calculated for each of the 5-minute periods of recording. These data were used to calculate values of the parameters per an hour, 8 hours, and 24 hours. The analysis revealed that generally the body stress-reaction to prolonged isolation consists of increased strain of regulating systems in an effort to mobilize functional reserves. Depending on individual characteristics and functional reserves, the regulating systems become overstrained at some time-point and higher level regulators may be involved in adaptation. Criteria of overstrain include exaggerated pulse rate versus rising standard deviation. Combination of these shifts during morning and night hours should be qualified as least favorable. Test-subject 003, in whom regulation overstrain has been never observed in the experiment, was distinguished by the largest functional reserve.

[Individual peculiarities of adaptation to long-term space flights: 24-hour heart rhythm monitoring]. / Individual'nye osobennosti adaptatsii k usloviiam dlitel'nogo poleta po dannym sutochnogo monitorirovaniia serdechnogo ritma.

Presented are results of studying 24-hr variability of the cardiac rhythm which characterizes individual difference in reactions of two crew members to the same set of stresses during a 115-day MIR mission. Spacelab (USA) cardiorecorders were used. Data of monitoring revealed significantly different baseline health statuses of the cosmonauts. These functional differences were also observed in the mission. In one of the cosmonauts, the cardiac regulation changed over to a more economic functioning with the autonomous balance shifted towards enhanced sympathetic activity. After 2-3 months on mission he had almost recovered pre-launch level of regulation. In the other, the regulatory system was appreciably strained at the beginning of the mission as compared with preflight baseline. Later on, on flight months 2-3, this strain kept growing till a drastic depletion of the functional reserve. On return to Earth, this was manifested by a strong stress reaction with a sharp decline in power of high-frequency and grow in power of very low frequency components of the heart rhythm. The data suggest that adaptation to space flight and reactions in the readaptation period are dependent on initial health status of crew members, and functional reserve.

[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.

Adaptive responses of the cardiovascular system to prolonged spaceflight conditions: assessment with Holter monitoring.

This article presents selected findings obtained with Holter monitoring from two crew members of the expedition, performed during a 175-day space mission on board orbital space station "MIR." Using mathematical processing of daily cardiointervals files, 5-minute sections of records were analyzed consecutively. Then, the average daily values of indices, the average-per-every-eight-hours values (morning, evening, night) and mean values per hour were computed. The results of analysis showed that prolonged exposure of man to microgravity conditions leads to important functional alteration in human neuroautonomic regulatory mechanisms. Both crew members had significant increase of heart rate, the rise of stress index, the decrease in power of the spectrum in the range of respiratory sinus arrhythmia. These marked signs of activation of the sympathetic section of the vegetative nervous system showed individual variations. The analysis of the daily collection of cardiointervals with Holter monitoring allows us to understand and forecast the functional feasibilities of the human organism under a variety of stress conditions associated with acute and chronic microgravity exposure.