Changes in the autonomic reactivity pattern to psychological load under long-term microgravity--twelve men during 6-month spaceflights

A complex psychophysiological test battery was applied to twelve subjects during long-term spaceflights. This experiment was designed to assess the psychophysiological reactivity to acute psychological stressors. A set of noninvasive physiological measurements (electrocardiogram, electromyogram, blood pressure, skin conductance, peripheral skin temperature) was used to describe the reactivity of the autonomic nervous system and the cardiovascular system to an induced series of changes between mental activity load and quiet relaxation. It could be shown that under space conditions the subjects react differently than on earth. On the basis of significantly lower heart rates we concluded that an extended parasympathetic cardial influence is present during later periods of long-term space flights. The peripheral skin conductance reactivity, however, indicated a tendency to higher peripheral sympathetic tonus under microgravity. Assuming individually different pathways of sympathetic-parasympathetic traffic under psychological stress, the whole set of data could be classified into autonomic outlet types (AOT) based on clinical reference data. Most of the subjects changed their AOT during flight. After flight the subjects eventually fell back into their pre-flight patterns, but seven of twelve subjects showed a significantly different autonomic system reactivity at least once after landing that was similar to that of hypertensive patients, indicating an extended sympathetic overshoot directly post-flight. In conclusion it is assumed that sympathetic effects in one measurement do not exclude less sympathetic or even parasympathetic effects in others during adaptation to extreme environments.

Human thermohomeostasis onboard "Mir" and in simulated microgravity studies

Significant changes of thermogomeostatic parameters was obtained by thermotopometric method using the techniques simulate of microgravity effects: bed rest, pressurized isolation, suit immersion (SI). However, each of ground models made rectal temperature (T) trend downward. The autothermometric study (24 and 12 sessions, 2-13th and 6-174th flight days) was carried out onboard "Mir" by two flight engineers who had preliminary tested at SI (1-2 days). Studies of German investigators onboard "Mir" confirmed: rectal T must be higher in space flight as compared to the normal environment (n=4). Comparative studies suggest that microgravity is a key factor for the human body surface T raise and abolishment of the external/internal T-gradient. T-homeostasis was not really changing during missions and could be regarded as acute effect of microgravity. After delineation of changes in body surface T--by Carnot's thermodynamic law--rectal T raise should have been anticipated. Facts pointing to the excess entropy of human body must not be passed over.

Human responses to propionic acid. II. Quantification of breathing responses and their relationship to perception

In 20 normal and four anosmic participants, instantaneous inhalation and exhalation flow rates were recorded in response to 15 s stimulations with clean air or propionic acid concentrations (0.16, 1.14, 8.22 and 59.15 p.p.m., v/v) that ranged from peri-threshold for normals to clearly supra-threshold for anosmics. Each odorant/irritant delivery to the face-mask began with an exhalation. This allowed concentration to reach full value before stimulus onset, defined as the point where the participant began to bring the stimulus into the nose by inhalation. Two seconds after this stimulus onset, normals exhibited cumulative inhaled volume (CIV) declines of 39 and 14%, and latencies of 500 and 710 ms, with presentations of 59.15 and 8.22 p.p.m., respectively. With anosmics, 59.15 p.p.m. caused a 19% decline in CIV that began at 730 ms. Examination of the first inhalation after stimulus onset shows that the CIV declines in normals were achieved by a progressive decline in volume (InVol), beginning with a slight drop at 1.14 p.p.m., and a marked decline in duration (InDur) with only the highest concentration. Anosmics exhibited declines in InDur and InVol with only the 59.15 p.p.m. stimulus, and these declines were much more modest than the changes seen in normals. Comparison of these breathing results with perceptual responses from this same experiment demonstrates that: (i) in normals, odor perception rises slightly, but breathing does not change, with the lowest concentration; (ii) the higher breathing sensitivity (declines in InVol) of normals is paralleled by both the higher nasal irritation of these individuals and the presence of odor sensation; (iii) InDur declines in normals only with a stimulus concentration sufficient to cause marked nasal irritation in anosmics; and iv) in anosmics, modest but reliable declines in both InDur and InVol mirror the marked elevation in nasal irritation magnitude seen with only the highest concentration. In view of the failure of prior work to provide evidence that olfactory activation alone can cause any of the breathing changes we observed, we conclude that some breathing parameters are quite useful as rapid and sensitive measures of nasal irritation that arises from activation of nasal trigeminal afferents alone or in combination with the olfactory nerve.

Heart period and heart period variability during sleep on the MIR space station

The long-term acclimation of cardiac rhythms to microgravity was studied in four astronauts aboard the Russian space station MIR during wakefulness and sleep. Sleep polygraphies were obtained between the third and the 30th day in space and, in addition, prior to mission on the ground. From each of the sleep polygraphies, beat-to-beat intervals of cardiac rhythms were determined. The response of heart period and heart period variability to the stimulus microgravity was tested during sleep across sleep stages and during waking. A lengthening of heart period by about 100 ms was found in space compared to measurements on the ground. The slowing of heart rate was more pronounced for non-REM sleep than for REM sleep. A systematic change in heart period in relation to the duration of the stay in space could not be detected. An analysis of heart period variability in the high frequency (respiratory sinus arrhythmia) band supports the hypothesis that the decrease of heart rate under microgravity is produced by an increase in parasympathetic activity. Testing the response of cardiac rhythms to microgravity across distinct behavioural states seems to be a powerful tool to investigate the cardiovascular system.

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.

On the contribution of space medicine in the public health care

With the beginning of space era, a new branch of medicine has arisen and has been developing along with human exploration of outer space. And even though space medicine mainly faces the same problems as traditional medicine--cosmonauts health care and their high efficiency--this branch, has its own features, associated with the unusual factors of space flight, of which weightlessness is the major one. During the development of manned cosmonautics (duration of a human stay in space has reached already 438 days), methods of cosmonauts medical support and monitoring of their condition have been developed, knowledge of human possibilities and methods of process of organism adaptation to various and frequently severe conditions of external environment have increased. All this led to the fact that nowadays space medicine can become useful for improvement of human health care not only in space but also on the Earth. Moreover, the problem of implementation of cosmonautics achievements, and in particular of space medicine, in practice of public health care presents one of the most important issues concerning human health care. It is also connected with public opinion which is more and more concerned about the efficiency of significant expenses on space activities, especially lately. People often are set by the questions: what has space given, what fruits has space research provided to mankind, which results of this research can be used on the Earth already today for improvement of their life, for discussion of many difficult earthly problems? In terms of using cosmonautics possibilities, its achievements for health care and treatment, it is possible to define a few branches, in which purposeful studies are carried out.

Diminished plasma cGMP during weightlessness

We performed an experiment within the project "RLF" (Russian long-term flight) on a cosmonaut onboard the space station MIR. For creating an analogue to orthostatic stress, we used lower body negative pressure (LBNP) as stimulus. Decrease in central and peripheral baroreceptor load by LBNP can be used as a cardiovascular countermeasure in cosmonauts or for inducing endocrine responses. Altered steady-state plasma concentration values of volume sensitive hormones have been observed inflight as well as postflight. Within this project we measured plasma ANP and cGMP as second messenger. Changes in plasma cGMP concentration are generally considered to be a good indicator of those in ANP activity. However, in our experiments depression of cGMP during space flight was more impressive than ANP decline. We are not aware of previous measurements of plasma cGMP under these conditions, and believe to be the first to report complete suppression of plasma cGMP during long-term stay in space.

The alteration of human sleep and circadian rhythms during spaceflight

Numerous anecdotes in the past suggest the concept that sleep disturbances in astronauts occur more frequently during spaceflight than on ground. Such disturbances may be caused in part by exogenous factors, but also an altered physiological state under microgravity may add to reducing sleep quality in a spacecraft. The present investigation aims at a better understanding of possible sleep disturbances under microgravity. For the first time, experiments were conducted in which sleep and circadian regulation could be simultaneously assessed in space. Four astronauts took part in this study aboard the Russian MIR station. Sleep was recorded polygraphically on tape together with body temperature. For a comparison, the same parameters were measured during baseline periods preceding the flights. The circadian phase of body temperature was found to be delayed by about 2 h in space compared with baseline data. A free-run was not observed during the first 30 d in space. Sleep was shorter and more disturbed than on earth. In addition, the structure of sleep was significantly altered. In space, the latency to the first REM episode was shorter, and slow-wave sleep was redistributed from the first to the second sleep cycle. Several mechanisms may be responsible for these alterations in sleep regulation and circadian phase. Most likely, altered circadian zeitgebers on MIR and a deficiency in the process S of Borbély's sleep model cause the observed findings. The change in process S may be related to changes in physical activity as a result of weightlessness.

Main medical results of extended flights on space station Mir in 1986-1990

During 1986-1990 seven prime spacecrews (16 cosmonauts) have flown on-board the Mir orbital complex. The longest space mission duration was 366 days The principal objectives of the medical tasks were the maintenance of good health and performance of the spacecrews and conducting medical research programs which included study of the cardiovascular, motor, endocrine, blood, immune, and metabolic systems. Results obtained point to the ability of humans to readily adapt to a year-long stay in space and maintain good health and performance. Readaptation had a similar course as after other previous long-term space flights of up to 8 months in duration. Primary body system changes were not qualitatively different from findings after flights aboard the Salyut 6 and 7 space stations. In this case, during and after an 11-12 month flight, body system alterations were even less severe which was a result of adequate countermeasure use, their systematic and creative employment and maintenance of required environments to support life and work in space.

Long-term space flights--personal impressions

During a final 4-month stage of a 1-year space flight of cosmonauts Titov and Manarov, a physician, Valery Polyakov was included on a crew for the purpose of evaluating their health, correcting physical status to prepare for the spacecraft reentry and landing operations. The complex program of scientific investigations and experiments performed by the physician included an evaluation of adaptation reactions of the human body at different stages of space mission using clinicophysiological and biochemical methods; testing of alternative regimes of exercise and new countermeasures to prevent an unfavourable effect of long-term weightlessness.

Modifications of spontaneous oculomotor activity in microgravitational conditions

Investigations on spontaneous oculomotor activity were carried out prior to and after (five cosmonauts) and during space flight (two cosmonauts) on the 3rd, 5th and 164th days of the space flight. Recording of oculomotor activity was carried out by electrooculography on automated data acquisition and processing system "Zora" based on personal computers. During the space flight and after it all the cosmonauts with the eyes closed or open and dark-goggled showed an essential increase of the movements' amplitude when removing the eyes into the extreme positions especially in a vertical direction, occurrence of correcting saccadic movements (or nystagmus), an increase in time of fixing reactions.

Preliminary medical results of the Mir year-long mission

The basic goal of medical investigations during and after the 366-day mission was to accumulate data about physiological responses to such a long exposure to microgravity. In flight, cardiovascular and other systems were examined in detail and the efficacy of countermeasures used was assessed. After flight, physiological systems were also followed very carefully. According to the preliminary data, the medical results obtained during and after flight give evidence that man can well adapt to a year-long space flight, maintaining good health and adequate work capacity. The readaptation process was very similar to that observed after shorter flights (6-11 months). As compared to former flights, no new or qualitatively different changes in the vital systems of the body were seen. The observations indicate that the duration of manned space missions can be further increased.

The physician-cosmonaut tasks in stabilizing the crew members health and increasing an effectiveness of their preparation for returning to Earth

During a final 4-month stage of 1-year space flight of cosmonauts Titov and Manarov, a physician, Valery Polyakov was included on a crew for the purpose of evaluating their health, correcting physical status to prepare for the spacecraft reentry and landing operations. The complex program of scientific investigations and experiments performed by a physician included an evaluation of adaptation reactions of the human body at different stages of space mission using clinicophysiological and biochemical methods; testing of alternative regimes of exercises and new countermeasures to prevent an unfavorable effect of long-term weightlessness.