CHANGES IN MAIN VEIN CHARACTERISTICS OF COSMONAUT'S LOWER EXTREMITIES IN THE COURSE OF YEAR-LONG SPACE MISSIONS.

Leg venous measurements were performed in two cosmonauts during the 379-d "Mir" mission (K-1 and 340-d ISS mission (K-2). The paper presents individual changes in venous capacity, distention and filling rate in the legs of these two cosmonauts, and 23 cosmonauts on 6-mos. missions as controls. In the first half of the year-long missions, changes in venous characteristics showed similar trends though had different dimensions. For instance, in K-1 increases in capacity and distention were more pronounced than in K-2. In the second half of the missions, the cosmonauts again displayed different changes in venous characteristics. In K-1 they all were unstable with episodes of simultaneous increases in venous capacity, distention and filling rate that were unfavorable for orthostatic stability (OS). Changes in the K-2 leg veins were less dramatic and detrimental to OS. Recovery of the pre-flight status of leg veins following the year-long missions took a longer time as compared with 6-mos. missions; the process was still incomplete by day 8 after landing. We surmise that in future one-year and longer missions the majority of cosmonauts are likely to have favorable changes in leg veins; however, untoward venous developments and consequent OS impairment must not be excluded.

[Normal values of the major parameters of lower limb veins in Russian cosmonauts prior to flight and in healthy untrained subjects].

The article presents normal values of the major parameters of lower limb veins in cosmonauts during preparations for space flight and volunteers leading a common life. The authors report the results and discuss the causes for differences in normal leg venous parameters in these groups of subjects. Incomparability of measurements made in cosmonauts and common people is demonstrated. Changes in lower limb veins of a cosmonaut in microgravity can be evaluated only relative to his/her normal values of the major venous parameters (capacitance, compliance and filling) before flight.

[CHANGE IN THE CONDITION OF LOWER LIMB VEINS IN COSMONAUTS ON LONG-DURATION MISSIONS].

The paper reports changes in the main parameters of the lower limb veins in 36 cosmonauts in the course of 6-month space missions. Major reduction in the leg volume was shown in all cosmonauts, as well as a significant increase of venous capacity and compliance. Rate of vein filling exhibited different trends, i.e. decreased in the majority of cosmonauts (n = 26, 74%) and increased in the rest (n = 9, 26%). Increases in venous capacity, compliance and filling rate may impact orthostatic stability (OS). These changes are among the pathophysiological mechanisms of the OS loss in space flight.

[Developing the methodology of examining the lower limb veins in cosmonauts for the space medicine practice].

The article centres on development of a methodology for evaluating the function of lower limb veins of cosmonauts in microgravity. The whys and wherefores of the choice of occlusive plethysmography equipment and procedure are explained. Much place is given to arguments for the requisite body and limb positioning during venous plethysmography pre launch and on return from space flight. To minimize the gravity effect on venous blood flow, the body should be in the level position and the calf aligned with the hydrodynamically indifferent point. Determining the type of test occlusion, occlusion adjustments, venous parameters of interest, and data processing procedure constitute the methodology.

[Human venous hemodynamics in microgravity and prediction of orthostatic tolerance in flight].

The paper presents the results of investigating the lower limbs venous status in cosmonauts (n = 13) with the use of occlusion plethysmography in 6-month missions to the Russian segment of the International space station (ISS). An interrelation of shifts in venous capacitance, compliance and filling with orthostatic tolerance (OT) in the lower body negative pressure test (LBNP) was stated. OT predictability by the leg vein status in the course of space flight was demonstrated. The objective changes of veins predictive of OT reduction were identified. There are 3 levels of changes in venous capacitance, compliance and filling that prognosticate respective reductions in LBNP tolerance and were attested in 91% of the in-flight LBNP testing.

[The features of adaptation and disadaptation of the human cardiovascular system in the space flight conditions].

The work was aimed at analysis and generalization of the hemodynamic data collected over 20 years from 26 cosmonauts flown 8 to 438 days aboard orbital stations Salyut 7 and Mir. The paper presents the results of ultrasonic investigations of the heart, arterial and venous peripheral vessels in different parts of human body, and measurements of leg veins capacity with the use of occlusive plethysmograpy. It was shown that in the resting condition such prime hemodynamic parameters as the pumping function of the heart and blood supply of the brain, and integral parameters, i.e. arterial pressure and heat rate, were best "protected" as they demonstrated stability throughout long exposure in microgravity. In the absence of gravitational stimulation, arterial resistance went down in essentially all vascular regions below the heart level; to put it differently, the anti-gravity distribution of the vascular tone was annulled gradually as unneeded in microgravity. Compared with the data about arteries, venous hemodynamics was found to be particularly sensitive considering the early advent and significance of changes. Venous return slowed down, resistance of the lower body vessels declined and capacity of the leg venous net increased. Functional testing with the lower body negative pressure revealed degradation of the gravity-dependent reactions that became more conspicuous as flight duration extended further. Cardiovascular deconditioning showed itself clearly on return to Earth's gravity by decreased g-tolerance during re-entry and orthostatic instability post flight. These investigations provided objective evidence for multifactorial genesis of orthostatic instability during space flight including blood redistribution, altered tone regulation of leg's venous and arterial vessels and hypovolemia.

[Dynamics of human cardiovascular responses in different periods of long-term exposure in weightlessness].

Purpose of the work was to determine trends in the human cardiovascular function at rest and during LBNP in different periods of short- (8-25 d) and long-term (126-438 d) space flights (SF) using the data of USI and leg occlusive plethysmography. Due to blood redistribution and hypovolemia in the first week on SF, the cardiovascular system decreased the left heart filling and output without loss in myocardium contractility, weakened the renal artery resistance, and increased the maximum capacity of leg veins. In 30-40 days, these developments became more pronounced and were followed by a relative stabilization of hemodynamics at rest. Arterial circulation in the brain was stable; however, passive congestion in the region grew as SF duration extended. The most dramatic changes were observed in leg arteries (weakening of resistance) and veins (increase in maximum capacity). Venous changes were more distinct than arterial. Despite the relative stabilization at rest, LBNP showed a decline of the gravity-dependent reactions which was also a function of SF duration. In the first month of SF, the downward trend of femoral arteries vasoconstriction was not detrimental to cerebral circulation. SF extension impacted regulation of the vascular tone and caused cerebral circulation deficiency during LBNP. In several cases, the hemodynamic reaction to LBNP was affected to the extent which could be qualified as a failure to adapt to the orthostatic condition.

[Hemodynamic shifts in humans under the conditions of prolonged microgravity and the role of hypovolemia].

Purpose of this work was to elicit the role of hypovolemia in the development of hemodynamic shifts and loss of orthostatic tolerance in humans during prolonged space flights (PSF). Correlation analysis of the data of in-flight ultrasonic investigations of hemodynamics in resting cosmonauts and bio-impedance measurements of body liquids in different periods during PSF pointed out that changes in the left ventricle filling and renal artery resistance (Rren) reflect the degree of hypovolemia with r = 0.95. The dependence of orthostatic tolerance on hypovolemia fell short of this ambiguity. Lower body negative pressure tests (LBNP) performed by 15 cosmonauts in different periods of PSF typically correlated with the body hydration status at r = 0.94; however, several cosmonauts showed a substantial loss of LBNP tolerance despite a moderate hypovolemia. Therefore, we may hypothesize that hypovolemia is a significant yet not the sole factor in orthostatic disorders. Deconditioning, altered control of hemodynamics, decreased vasoconstriction of arterial vessels and increased compliance of the leg veins have an important, in some cases decisive role in degradation of orthostatic tolerance.

[Effect of prophylactic device "Braslet" on hemodynamic changes during long-term missions to orbital station Mir].

The benefit from occlusive cuffs (prophylactic device Braslet) to human hemodynamics was evaluated in seven cosmonauts on long-term Mir missions using the ultrasonic technique (Echography and Doppler). Braslet had a positive effect on cosmonauts" state of health during the first month of flight. Improvement of cerebral hemodynamics was attested objectively by reduction of venous congestion. However, the device did not produce a noticeable effect on the leg vein expansibility and capacity at the beginning of long-term mission. Starting on flight month 3, cumulation of the Braslet effect on the leg large veins resulted in progressive vein expansion. Regular wearing of the Braslet device produced changes in expansibility, capacity and elasticity of the veins in lower extremities. Extent of these changes was dependent on period of Braslet application and tightness of occlusion. Though the state of leg veins of the cosmonauts who had been favourable to Braslet during mission did not appear changed after landing, still we cannot make the conclusion that the occlusive cuffs do not bring harm if worn continuously, as their delayed effects have not been evaluated and remain unknown.

[Possibility to predict cosmonauts' orthostatic tolerance following short-and long-term space flights].

According to the analysis of the data of active and passive orthostatic tolerance (OST) testing before and after 67 short- (SSF) and 53 long-term (LSF) space flights OST declined in all the cosmonauts regardless of flight length. Active testing on R+1 after SSF (7 to 25 d) and LSF (49 to 438 d) attested OST loss by 33% and 48%, respectively. Full OST recovery following SSF and LSF was observed in a week and 1.5-2 months, respectively. A correlation was established (r = 0.81) between the post-flight OST loss and pre-flight baseline value. Depending on whether the pre-flight OST value was very good, good or satisfactory, its loss on R+1 after LSF can make up 20-30%, 30-50% and 55-65%, respectively. Consequently, data of preflight OST testing can be used for prediction of its decline post normal space flight.

[Shifts in human venous hemodynamics in long-term space flight].

Veins and venous hemodynamics before, during and after long-term space flights (SF) were evaluated with the ultrasonic (B-scan, Doppler) techniques and occlusion plethysmography. Fifteen cosmonauts were investigated in eight SFs of about 6 months in duration. In three SFs, 30 investigations of the main veins in different parts of the body were fulfilled with participation of 7 cosmonauts. In five SFs, 48 investigations of venous distensibility in legs were fulfilled with occlusion plethysmography with participation of 8 cosmonauts. Femoral veins tended to increase distension throughout SF. Exaggerated leg veins distensibility and compliance was persistently observed during application of occlusion from the early period of SF (wks 1-2) which, in our opinion, extenuates the reduction in LBNP tolerance and post-flight degradation of orthostatic stability. These shifts were growing markedly till months 2-3 of exposure to microgravity and tended to stabilize at the worst (as compared with prelaunch values) level at the end of six-month SFs.

[Correlation of the cosmonauts' physiological reactions to +Gx loads during deorbit with the hemodynamic shifts in the period of short-term microgravity].

Physiological reactions of four cosmonauts to +Gx during the descent after short-term (less than 30 d) space flights were correlated with the hemodynamic shifts developed previously during the LBNP test and occlusive plethysmography in microgravity. The cosmonauts who had exhibited a sharp decrease in cerebral circulation during the in-flight LBNP tests showed signs of deteriorated cerebral blood flow (vertigo, weakness, hyperhydration) at the attempt to assume the vertical posture and to climb out of the landing module. Also, the cosmonauts found to have the arterial and venous tone significantly dropped in microgravity, suffered petechial hemorrhages in the back integument during the exposure to +Gx. These data suggest a correlation between the physiological reactions of cosmonauts to +Gx at the end of short-term space flight and the shifts in hemodynamics earlier in microgravity.

[Rearrangement of the hemodynamic mechanisms of orthostatic tolerance of humans on long-term space missions].

Orthostatic tolerance (OT) was evaluated in 25 cosmonauts using the traditional standing test before and after space fights of about six months in length; 15 cosmonauts of this group were also subjected to ultrasonic investigation during the lower body negative pressure test before, during and after long-term SF. Efficiency of the OT vascular mechanisms was gradually falling and stabilized at the end of six-month SF at a level significantly below pre-flight level. Post-flight OT recovery took longer time as compared with short-term SF suggesting more profound shifts in the vascular control system. Ultrasonic monitoring of blood flow along the aorta, medial cerebral artery and femoral artery enabled more comprehensive and reliable evaluation of the vascular tone and circulation control and appeared more informative than the traditional recording of integral indices, i.e. HR and BP.

[Relationship between the hemodynamic disorders in cosmonauts on short-term space flights and orthostatic stability].

Comparative investigation of the hemodynamic responses of cosmonauts at rest, during occlusive leg plethysmography, and LBNP in relatively short (less than a month) space flights were performed to tie up these measurements with post-landing orthostatic stability (OS). The decreased LBNP tolerance in flight that correlated later on with impaired reactions to both active and passive orthostatic testing are attributed, among other reasons, to deficient vasoconstriction of the main arteries and over-extendibility of veins in the lower extremities. Results of ultrasonic investigations of hemodynamics during LBNP tests before and after space flight and data of leg venous extension in SF can and should be used in predicting cosmonaut's orthostatic status post flight.

Ultrasound techniques in space medicine.

Ultrasound examinations have been performed on 15 cosmonauts who have remained in orbit for flights ranging from 2.5 to 8 months in duration. Soviet researchers have combined hemodynamic assessments with parallel attempts to develop improved ultrasound techniques and equipment for use onboard space stations. These techniques and equipment are reviewed, as are findings relative to exercise effects on hemodynamic changes. In general, longitudinal echocardiographic studies have suggested that 1) few differences exist between resting preflight and on-orbit cardiac contractility measures; 2) declines in orthostatic stability after long-term flights are not due to deterioration of the myocardial functional state; and 3) lower stroke volumes and heart rate increases occurring during exertion may be considered compensatory hemodynamic resettings rather than indications of disturbed left ventricular contractility.

[Myocardial contractility during angina pectoris attack in ischemic heart disease]. / Sokratitel'naia funktsiia miokarda pri pristupe grudnoi zhaby u bol'nykh ishemicheskoi bolezn'iu serdtsa

The myocardial contractility function was studied with the aid of echocardiography in 42 male patients during dosaged physical exercises. The patients were selected so that at the peak of the exercises they developed an angina pectoris attack documented by ischaemic ECG changes. In some of the patients the changes were also observed during attacks of angina decubitus. Anginal attacks are accompanied by a reduction of the myocardial function. Haemodynamic reactions of two types were noted with myocardial ischaemia: type I reaction was observed in patients with ischaemic heart disease and practically normal values of the initial heart volume, and consisted in an increasing end-systolic and end-diastolic volumes, with the stroke volume remaining unchanged, and the ejection fraction somewhat decreasing; type 2 reaction was observed in patients with initially increased heart volumes, and consisted in a decreasing end-diastolic and stroke volumes, with an insignificant alteration of the end-systolic volume. The ejection fraction, being initially insignificantly decreased, tends to decrease further during the attack.

[Mechanism of nitroglycerin action]. / O mekhanizme deistviia nitroglitserina.

Data are presented on the effect of nitroglycerin upon the intracardiac haemodynamics studied by means of echocardiography in normal individuals and in patients with ischaemic heart disease. Three types of changes in the intracardiac haemodynamics under the effect of the drug were revealed. The possible mechanism of action of nitroglycerin is discussed in the light of the obtained data.

[Effects of occlusive cuffs "Braslet" on crew hemodynamics in short space flights and orthostatic stability post flight]. / Vliianie perezhimnykh manzhet "Braslet" na izmeneniia gemodinamiki v kratkovremennykh kosmicheskikh poletakh i poslepoletnuiu ortostaticheskuiu ustoichivost' kosmonavtov.

Effects of prophylactic device Braslet (occlusive cuffs wrapped around the calf) on hemodynamics were studied at rest and during the LBNP test during and on orthostatic stability post short (one-month) space flights. The ultrasonic procedure was applied to seven cosmonauts who had and six cosmonauts who had not worn the cuffs while in orbit. The device markedly alleviated the subjective feeling of discomfort caused by blood shift toward the cranial end at the beginning of adaptation to microgravity. Reductions in the central and peripheral hemodynamics, cervico-cephalic venous plethora specifically, were sequel to staying in microgravity. Testing of the hemodynamic reactions to LBNP during and after shortflights failed to discover noticeable deltas among the cosmonauts who had and had not worn the cuffs. The first analysis of objective in- and postflight data did not suggest any determent in orthostatic stability of cosmonauts due to application of the Braslet cuffs.

[Respiration and cardiovascular mechanisms of hypobaric correction of the head-down redistribution of local blood volumes]. / Respiratornye i serdechno-sosudistye mekhanizmy gipobaricheskoi korrektsii antiortostaticheskogo pereraspredeleniia regional'nykh ob"emov krovi.

The focus was placed on the physiological mechanisms of correction of the blood redistribution during the head-down tilt (HDT) with a discrete or complex use of the methods of negative pressure respiration (NPR) and lower body negative pressure (LBNP). It was evidenced that rise in the intracranial hydrostatic pressure in HDT (-6 degrees) can be compensated by NPR within a range of -10 to -15 cm of water column causing decrease in the intrasternal pressure from -5.04 to -7.74 cm w.c. Bioimpedance and ultrasonic investigations led to the conclusion that the decreased transpulmonary pressure is responsible for blood outflow from the intracranial venous system till the level adequate to the horizontal position of the body. The results were verified in experiments with unconscious cats: pressure in the exterior jugular vein and v. cava superior during HDT (-30 degrees) with NRP at -5 cm w.c. decreased by 3.2. and 4.3. w.c., respectively. Experiments with human subjects also demonstrated that the complex use of NPR and LBNP produces an additive hemodynamic effect and can be considered a new method for correcting the adverse consequences of redistribution of the local blood volumes toward the head end.