Effect of a helium and oxygen mixture on physiological parameters of rats with cerebral arterial air embolism.

Introduction: Cerebral arterial air embolism (CAE) is a serious and potentially dangerous condition that can interrupt the blood supply to the brain and cause stroke. One of the promising gas mixtures for emergency treatment of air embolism is an oxygen-helium mixture. Methods: We modeled CAE in awake rats by injecting air into the common carotid artery. Immediately after CAE, animals were either untreated or underwent hyperbaria, oxygen inhalation, heated air inhalation, or helium-oxygen mixture inhalation. Body temperature, locomotor activity, respiratory and cardiovascular parameters were monitored in the animals before CAE modeling, and 3 and 24 h after CAE modeling. Results: After 3 hours of CAE modeling in awake rats, depression of the nervous, cardiovascular and respiratory systems, as well as decreased body temperature were observed. 24 h after CAE modeling multifocal cerebral ischemia was observed. Normobaric helium-oxygen mixture inhalation, on par with hyperbaric treatment, restored body temperature, locomotor activity, respiratory volume, respiratory rate, and blood pressure 3 hours after CAE, and prevented the formation of ischemic brain damage lesions 24 h after CAE. Discussion: Thus, inhalation of a heated oxygen-helium gas mixture (O2 30% and He 70%) immediately after CAE improves the physiological condition of the animals and prevents the foci of ischemic brain damage formation.

Space Medicine: Scientific Foundations, Achievements, and Challenges.

This article, based on a report presented at the Scientific Session of the Russian Academy of Sciences, highlights the history of the formation of space medicine, its theoretical foundations, and the role of scientists of the Academy of Sciences in the preparation and implementation of the first manned flight into space. The achievements of domestic specialists in space physiology, biology, and medicine promoting the development of manned cosmonautics are considered. Examples are given of the implementation of the results of space research, as well as instruments and devices for medical support of space crews, into practical health care. The problems of medical support of future interplanetary flights and the ways of their solution are analyzed.

Effect of Simulated Microgravity and Lunar Gravity on Human Inspiratory Muscle Function: 'Selena-T' 2015 Study.

As a part of the multi-disciplinary "SELENA-T"-2015 Bed Rest Study, we investigated the pattern of inspiratory muscles fatigue in 22 healthy male subjects during incremental exercise test to exhaustion before and after 21 days of hypokinesia evoked by bed rest. Hypokinesia consisted of head-down bed rest (HDBR) at a minus 6° angle, simulating microgravity present on orbiting spacecraft, in 10 subjects. The remaining 12 subjects spent the first 5 days of hypokinesia in HDBR position and the subsequent 16 days in head-up bed rest (HUBR) at a plus 9.6° angle, as a presumed analog of lunar gravity that is six times less than Earth's gravity. Maximal inspiratory pressure (MIP) and electromyograms (EMG) of the diaphragm (D), parasternal (PS), sternocleidomastoid (SCM), and scalene (S) muscles served as indices of inspiratory muscle function. Before both HDBR and HUBR, exercise decreased MIP and centroid frequency (fc) of EMG (D, PS, SCM, and S) power spectrum (p < 0.05). After 3 weeks of HDBR, but not HUBR, inspiratory muscles fatigue was more expressed compared with control (p < 0.05). We conclude that HDBR lowers inspiratory muscles resistance to fatigue during high-intensity exercise while HUBR has no such effect. These changes may limit maximal ventilation and may contribute to exercise intolerance observed after prolonged simulated microgravity. The physiological mechanisms of respiratory muscle dysfunction after HDBR consist primarily of postural effects, and are not due only to hypokinesia.

A Method of Ground Simulation of Physiological Effects of Hypogravity on Humans.

A novel method of ground simulation in humans of physiological effects induced by the stay on the surface of celestial bodies with hypogravity was developed and successfully tested. This method is based on the change of gravity force angle, which decreases the gravitational component of the blood hydrostatic pressure characteristic of human vertical posture on the Earth and the load-weight onto the locomotor apparatus to the lower values expected at celestial bodies with hypogravity. The methodological requirements for ground simulation of the physiological effects of lunar gravity on human body are specified and substantiated by theoretical calculations. The experimental study revealed redistribution of liquid media in the human organism, functional changes in the cardiorespiratory system, and a decrease in the load-weight applied to the locomotor apparatus.

Intersystem relationships of respiration and hemodynamics in the initial period of postural effects.

We studied the dependence of parameters of lung volumes and the elastic properties of the lungs on changes in the central hemodynamics occurring in the initial period of passive postural changes in cats. It was found that transition from the horizontal to head-up and head-down tilting was accompanied by opposite hemodynamic changes in the cranial and caudal parts of the body. Changes in lung compliance and functional residual capacity of the lungs were opposite and linearly depended on the intensity of hemodynamic shifts, which indicates passive character of the primary disorders primarily determined by a physical factor, gravity-dependent redistribution of body fluids.

Effect of long-term simulated weightlessness on surfactant and water balance in mouse lungs.

Weightlessness produces adaptive and maladaptive changes in the respiratory system. We assessed the effects of 30-day antiorthostatic hanging as a model of microgravity on the water balance in the lungs and surface activity and phospholipid composition of pulmonary surfactant in C57Bl/6 mice. Long-term antiorthostatic hanging increased water content in the lungs and reduced surface-active properties of the surfactant. This was accompanied by an increase in the content of alveolar phospholipids and changes in their fractional composition (increase in the relative content of lysophosphatidylcholine and phosphatidylethanolamine).

[Stress-resistance and the condition of surfactant system and water balance in the lung of suspended rats].

White male rats with the body mass of 180-220 grams were distributed into the open-field active (presumably stress-resistant) and open-field inactive (presumably stress vulnerable) groups for a 10-day experimental suspension with the purpose to evaluate the surfactant activity in bronchoalveolar lavages, total phospholipids and their fractions, and water balance in the lung. In modeled microgravity, augmented blood filling of the rat's lung increases the alveolar phospholipid content and alters the phospholipid fractional composition in the pulmonary surfactant. Ten-day suspension raises pulmonary surfactant activity to a greater extent in stress-resistant animals rather than in their stress vulnerable peers.

Influence of space flight factors on the ultrastructure of rat diaphragm muscle.

Analysis of ultrastructural changes in diaphragm muscle and synaptic apparatus after 7- and 14-day biosatellite spaceflight showed destructive and atrophic changes that developed starting from in the early terms of exposure. Structural alterations of different severity were revealed in all elements of the muscle (muscle fibers, neuromuscular junctions, intramuscular nerves, and blood vessels) and were paralleled by activation of regeneration processes.

[Morphofunctional study of antiortostatic hipokinesia action in the case of focal ischemic brain cortex damage].

It was investigated the influence of antiortostatic hipokinesia (ANOC) with different combinations with photothrombosis of prefrontal cortex of rat brain by quantitative measures of passive avoidance reflex and reparative processes on the creation of dikaryons in cortex. Recieved data let to suppose, that ANOC increase ischemic damages and decrease quantity of dikaryons in cortex.

[The regeneratory potential of platelet in local brain inflammation under microgravity].

A hemorrhagic stroke model that provides the long-term presence of test materials in the focus has been constructed. A lesion is induced in the motor cerebral cortical region. The lesion location and locomotor dysfunction are reproducible. The presence of platelets in the focus reduces the extent and volume of hemorrhages, increases the number and diameter of newly formed vessels, and attracts a macrophage population not found in the control, which is identified from green granules and perivascular location. Motor function is restored more rapidly than in the control. The impact of microgravity is opposite to that of platelets. There are increases in blood congestion, hemorrhage area and postoperative mortality and a reduction in the population of macrophages with green granules. No motor function recovery was observed during a 7-day follow-up.

[Change in sensitivity of the central respiration mechanism in the 21-hour bedrest conditions].

The investigation was aimed at studying the mechanisms for change in the respiration center sensitivity in consequence of 21-hr bed rest with head-end tilted at -15 degrees combined with liquid loss (lasix, 20 ml) and recovery (IV infucol and glucose). Time of maximal breath-holding, capillary and venous O2 and CO2 pressure values were measured in the baseline data collection period, during and shortly after BR. Data analysis showed that extension of the maximal breath-holding time both during inspiration and expiration was statistically significant in the initial 10 minutes of tilting. Comparison of the breath-holding test data between the experimental series demonstrated that infusion of equally glucose and infucol did not affect voluntary apnea during inspiration or expiration. From BR hour 17, partial pressure of venous O2 showed a significant rise, while venous CO2 pressure decreased, also significantly. It is hypothesized that degradation of the respiration center sensitivity was connected most likely with blood pooling in the upper body and altered pressure on the baroreceptors.

[Structural and functional features of the rats' prefrontal cortex following 14-day suspension].

Effects of 14-d suspension on the processes of rats' nervous cells conjugation in the brain cognitive cortex were studied. Signs of cognitive functions degradation and decrease of the number of conjugated nervous cells were found in the experimental group after suspension. This evidence are qualified as a negative effect of suspension on memory and physiological regeneration of neurons.

[The physiological analysis of the possible reasons of hypoxemia in weightlessness].

In spaceflight at cosmonauts decrease of oxygen partial pressure in capillary blood on 12-30% in comparison with preflight values is revealed. The analysis of the possible reasons and mechanisms of hypoxemia in weightlessness is carried out. On the basis of this analysis the conclusion becomes that the principal cause of oxygen partial pressure decrease in blood of cosmonauts at microgravity, with the big degree of probability, is venoarterial bypassing. It is connected with increasing of venous blood passage through lungs, without full gas exchange in capillaries of small circulation circle.

[Optimization of directed training loads on the respiratory system].

Potentiality of an increased elastic resistance to respiratory movements in improving the functional conditioning of young athletes was evaluated. Training with increased elastic resistance to respiration brought about gains in strength and endurance of the respiratory muscles, growth of the maximal oxygen consumption, work ability, and special physical fitness of athletes.

[The ventilatory response to isocapnic hypoxia during head-down tilt].

The ventilatory response to isocapnic hypoxia was studied using rebreathing techniques in anesthetized and tracheostomized rats both in supine and in head-down tilt position (HDT-30 degrees). Hypoxic responses were calculated by the slope of ventilation against end tidal P(A)O2. The end-tidal P(A)CO2 was kept constant by varying expired gas flow through a CO2-absorbing bypass. The rebreathing was continued until P(A)O2 had fallen to between 70 +/- 3 and 50 +/- 2 mm Hg. The obtained results demonstrated that the maximal minute lung ventilation was 269 +/- 30 % during rebreathing test in supine position and 117 +/- 21% in the head-down tilt. It was also shown that the slopes of the relationship between minute ventilation and the decrease of end tidal P(A)O2 was 3-fold greater in supine than in HDT. The body position seems to affect the ventilatory response to isocapnic progressive hypoxia. In general, it may be a result of hemodynamic conditions alteration which increased respiratory resistive loads, changed the functional condition of carotid hemoreceptors and baroreceptor activity that modulate ventilatory response to chemoreceptor stimulation.

[The role of lung afferent system in respiratory control during head-down tilt].

The role of lung receptors in respiratory control during acute head-down tilt (AHDT, -30 degrees) was investigated in anesthetized, tracheostomized rats. The results show that AHDT increased the mechanical respiratory load, slowed inspiratory flow, reduced the end expiratory lung volume, tidal volume and minute ventilation. On the other hand, during AHDT a significant rise in inspiratory swings of oesophageal pressure was recorded indicated a compensatory increase in inspiratory muscle contraction force. These effects were reduced after transaction of the vagus nerve. It was also shown that respiratory response on added mechanical load was reduced during AHDT as compared with the value in horizontal position. This deference disappeared after vagotomy. The data obtained suggested that afferent information from lung receptors take part in compensation of respiratory effects of AHDT. The cause of reduction in respiratory response to loading during AHDT involves weakness of lung reflexes evoked by volume changes.

[Main results of the Biorisk experiment on the International Space Station].

To get better appreciation of the margins of phenotypic adaptation and genotypic changes in bacteria-fungi associations within the typical microbiota residing on structural materials of space-flown equipment, developed were a program and hardware for a series of experiments under the general name BIORISK. Protocol of each experimental cycle is based on the well-proven method of exposure of "passive" samples of materials (Biorisk-KM), microorganisms-materials systems inside the ISS service module (Biorisk-MSV), and microorganisms-materials systems on the outside of the ISS SM (Biorisk-MSN). Each six months the samples are returned to the laboratory in conjunction with crew rotation. Already the first in-hand data from the experiment point to the dramatic effect of space flight on growth, reproduction, and biological properties of test microbes and fungi. Thus, the activity of enzymes that characterize the pathogenic potential (RNA-ase and DNA-ase), and resistance of microorganisms to aseptic agents were found increased.

[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.

[The dynamic of breathing biomechanics and intrathoracic hemodynamics parameters during microgravity modeling].

In ground-based model of the hemodynamics effects of weightlessness, the intersystem relation of breathing and circulation was investigated during inspiration and expiration separately in anesthetized catz. It's shown that the dynamics of central venous pressure, esophageal pressure and filling pressure of the heart during inspiration in supine and head-down tilt position has obvious similarity to those which hypothetically can be present in microgravity. The results suggest that intrathoracic hemodynamics during inspiration in supine and head-down position may be an adequate ground model for investigation of weightlessness influences on intrathoracic circulation.