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.

Central and regional hemodynamics in prolonged space flights.

This paper presents the results of measuring central and regional (head, forearm, calf) hemodynamics at rest and during provocative tests by the method of tetrapolar rheography in the course of Salyut-6-Soyuz and Salyut-7-Soyuz missions. The measurements were carried out during short-term (19 man-flights of 7 days in duration) and long-term (21 man-flights of 65-237 days in duration) manned missions. At rest, stroke volume (SV) and cardiac output (CO) as well as heart rate (HR) decreased insignificantly (in short-term flights) or remained essentially unchanged (in long-term flights). In prolonged flights CO increased significantly in response to exercise tests due to an increase in HR and the lack of changes in SV. After exercise tests SV and CO decreased as compared to the preflight level. During lower body negative pressure (LBNP) tests HR and CO were slightly higher than preflight. Changes in regional hemodynamics included a distinct decrease of pulse blood filling (PBF) of the calf, a reduction of the tone of large vessels of the calf and small vessels of the forearm. Head examination (in the region of the internal carotid artery) showed a decrease of PBF of the left hemisphere (during flight months 2-8) and a distinct decline of the tone of small vessels, mainly, in the right hemisphere. During LBNP tests the tone of pre- and postcapillary vessels of the brain returned to normal while PBF of the right and left hemisphere vessels declined. It has been shown that regional circulation variations depend on the area examined and are induced by a rearrangement of total hemodynamics of the human body in microgravity. This paper reviews the data concerning changes in central and regional circulation of men in space flights of different duration.

Medical problems of manned space flights onboard orbital stations.

Medical aspects of crew safety and life support as well as biomedical investigations form part and parcel of the preparation and conduct of manned space programs. The list of biomedical problems related to these programs is very long. The present paper concentrates on some of them.

Cardiovascular changes in prolonged space flights.

In prolonged manned space flights, the cardiovascular function was examined at rest and during provocative tests. As compared to the preflight data the following changes were seen: higher heart rate at rest and during LBNP tests, decrease of stroke volume at rest and during LBNP test and a less marked increase (or decrease) during exercise tests, symptoms of a greater heart load which transformed to the syndrome of myocardial hypodynamics (preload) during LBNP tests or to the syndrome of myocardial hyperdynamics (afterload) during exercise tests (with other than preflight ratios of systolic and diastolic time intervals). The above cardiovascular changes did not, as a rule, aggravate with flight time and can be viewed as adaptive reactions to microgravity. The above cardiovascular changes were primarily produced by fluid redistribution in the cranial direction, diminished participation of the muscle system in circulation, and involvement of unloading reflexes from the cardiopulmonary receptor zones.

Human adaptation to simulated gravitational fields.

We present the resuIts of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the role of functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g.

Human adaptation to simulated gravitational fields.

We present the results of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g.

Physiological reactions during acute adaptation to reduced gravity.

Experiments were carried out on healthy volunteers exposed to a 7-day water immersion. The subjects were kept dry by use of a water proof, highly elastic cloth. During the experiment different cardiovascular, fluid-electrolyte and biochemical parameters were recorded. During the 7-day immersion, physiological parameters changed on a phasic basis. An acute period of adaptation began within the first minutes of immersion and ended by the third day. Later some of the parameters showed relative normalization. The experimental results suggest that the hypophyseal-adrenal system and renal function are closely coupled regulatory mechanisms for adaptive reactions of the cardiovascular system and for fluid-electrolyte metabolism during acute adaptation of the human body to reduced gravity.

Comparison of physiological effects of head-down tilting and immersion on the human body.

Among the methods simulating weightlessness, effects on the human body, head-down tilting and water immersion are very useful. The purpose of the present investigation was to carry out a comparative study of water balance and water-protein composition of the blood using the above two methods to simulate the physiological effects typical of an acute stage of weightlessness adaptation. The results of the 7-d head-down tilting and immersion experiments allow the following conclusions: More pronounced changes in water balance and water-protein composition of the blood during immersion seem to indicate that immersion produces a greater effect on the human body; The pattern of changes during immersion and tilting suggests that the adaptation period to immersion takes a longer time; These findings give evidence that immersion, compared with head-down tilting, reproduces more closely effects of acute adaptation to simulated weightlessness.

Prophylactic [correction of prophylatic] effects of intermittent acceleration against physiological deconditioning in simulated weightlessness.

The prophylactic effect on adult human males of intermittent acceleration against physiological deconditioning in weightlessness simulated by water immersion was studied at +0.8, +1.2, and +1.6 g. These prophylactic exposures reduced renal excretion of fluid and plasma volume changes, and increased venous compliance and the time at which the subjects could tolerate an acceleration field of +3 g.

Preliminary results of medical investigations during manned flights of the Salyut 4 orbital station.

In 1975 the Soviet Union performed two manned flights on board the orbital station Salyut 4. The first mission of 30 days was flown by A. A. Gubarev (Commander) and G. M. Grechko (Flight Engineer) and the second mission of 63 days by P.I. Klimuk (Commander) and V.I. Sevastyanov (Flight Engineer). The present paper gives preliminary data on the general health and cardiovascular investigations of the crew members during and after flight. The clinical and physiological examinations of the cosmonauts showed that the work-rest cycles and counter-measures used helped to maintain their good health and high performance in flight, to alleviate adverse reactions and to facilitate readaptation post-flight. Medical results of the post-flight investigations revealed no changes that may detract from further increasing the duration of manned space missions.

Prevention of human deconditioning during prolonged immersion in water.

A 56-day immersion experiment in which two subjects participated was carried out. During the experiment the preventive effect of periodic acceleration combined with exercise and water-salt intake was assessed. Simulating an increased gravitational field, exposure to acceleration increased the static component of the load upon the musculo-skeletal system, increased the gradient of the blood hydrostatic pressure, activated mechanisms responsible for the venous return to the heart, stimulated systems regulating antidiuretic and antisodiumdiuretic reflexes. Involvement of these mechanisms restored haemodynamic parameters, fluid-electrolyte balance and blood coagulability. The prophylactic effect of acceleration was enhanced if combined with exercise and supplemented water-salt intake.

[Complex apparatus for remote study of external respiration]. / Kompleks apparatury dlia distantsionnogo issledovaniia vneshnego dykhaniia

A complex set of instruments ensuring telerecording of the basic ventilation and gas exchange values is described. The set provides for the possibility of delivering various gas mixtures to the examinee. The set was mounted, tested and operated with a centrifuge under radial overloads of up to 12Gx. A six-year experience of its operation demonstrated its reliability, accuracy and reproducibility of the results obtained.

Deconditioning during prolonged immersion and possible countermeasures.

Test subjects covered with a waterproof highly elastic cloth were exposed to 13-day water immersion up to the neck. They were divided into two groups. The first (control) group consisting of six persons was exposed to immersion alone and the second (experimental) group was exposed daily to accelerations of 0.6-2 Gz for 60-90 min during the last 6 days of immersion. Before and after immersion all the test subjects were exposed to +3 Gz for 5 min which served as a provocative test. These experiments give evidence that the use of dry immersion allows experimentation during prolonged immersion without concomitant complications. Variations in the physiological parameters (cardiovascular system, fluid-electrolyte balance, blood-coagulatory system) are indicative of the preventive effect of periodic accelerations during 13-day immersion.

A study of the cumulative effects of repeated exposures to radial accelerations.

After exposure to transverse accelerations of 4-10 g changes in the vascular system of the eye and immunobiological resistance of the body persisted from 5 to 15 days. The data give evidence that the state of retinal vessels is the most informative index of the cumulative effect on the body and its recovery.

Human sensitivity to gravity (on the problem of gravipreferendum).

Experiments were carried out in a centrifuge with an arm of 7.25 m, the cabin being equipped with a self-contained system of control. During an exposure to head-to-feet accelerations (+gz) of 2 g and an onset rate of 0.1 g s-1 the test subject controlled the centrifugation himself and selected the acceleration values he was instructed to attain. The subjects were shown to be capable of assessing integrally the value of accelerations and estimating it with an error of 0.1-0.12 g. During an exposure to chest-to-back accelerations (+gx) limited to a value of 12 g and a gradient of 0.3 g s-1 the ability to select actively the rate of an acceleration increase was studied. Repeated centrifugations resulted in the formation and strengthening of the skill of maintaining a physiologically optimal rate of an acceleration increase. Onset rates were determined for every level of acceleration. When calculated as a mean, physiologically optimal values of the onset rate for 12 g were 0.16-0.18 g s-1. The findings give insight into important properties of the physiological structure of "gravipreferendum", which is the capability of man to differentiate between gravity levels and to select actively optimal rates of an increase in acceleration.