Changes of external respiration, brain circulation and the EEG in acute hypoxia in the subjects with different hypoxic resistance

Two groups of individuals were distinguished in experiments with acute hypoxic action (respiration of oxygen-nitrogen mixture with 8 % oxygen content) - with low (LHR) and high (HHR) resistance to hypoxia. In subjects of the LR group, slowing down of the pulse rate and lowering of arterial pressure in the shoulder artery were observed on the 5th-10th minute of hypoxia. In the HHR subjects, primary growth of the pulse rate was followed by its stabilization; no significant changes of the arterial pressure were observed. In LHR subjects, in the first 5-10 min of the hypoxia, a significantly lower level of the blood oxygen saturation was observed in comparison to the HHR. In the LHR group, there was a higher increment of amplitude-frequency index of the rheoencephalogram in comparison to the HHR, indicating a higher increment of the cerebral blood flow. The slowing down of the pulse rate in the LHR subjects was accompanied with increasing cerebral pulse volume, so that in spite of the pulse rate slowing, the minute volume of cerebral circulation increased. In the LHR subjects, two-phased dynamics of the EEG was observed: in the first phase there was a slow growth of theta- and delta-band EEG spectral power, in the second phase (on the 5th-10th min of hypoxia), sharp (200-300 % of the background level) growth of the EEG spectral power in those bands was observed. In the HHR subjects, gradual growth of EEG spectral power occurred with relative stabilization on the 10th-12th min of hypoxia. Possible role of the stress in the collapse-like reaction during acute hypoxia is analysed, which might cause increase of the oxygen request of the brain, higher growth of cerebral blood flow and more pronounced lowering of functional activity of the brain in the LHR subjects.     

Changes in the sympathetic-adrenal system during stress in rats with high and low resistance to acute hypoxia

Quantitative luminescent microscopy was used to examine the sympathetic system of cardiac ventricles (SSCV) and the adrenal medulla (AM) of adult Wistar male rats high-resistant (HRH) and low-resistant (LRH) to acute hypoxia and exposed norepinephrine (NE) stress. The relative area of fluorescence adrenergic terminals (RAFAT) of the ventricles and AM catecholamine levels (CL) were shown to be equal in control HRH and LRH rats. The LRH rats displayed a two-phase SSCV response in the first 6 hours of NE stress. Their RAFAT rose an hour later and their RAFAT in the basal zone of the left ventricle insignificantly exceeded that of HRH rats, RAFAT in the latter being unchanged by that time. At hour 6, the heart RAFAT decreased as compared to 1-hour and control levels in LRH and HRH rats and became equal in the two groups. The AM CL in LRH and HRH rats remained unaltered within the whole period of the examination. Despite the profound differences in the resistance of HRH and LRH rats to hypoxia, the responsiveness of their sympathoadrenal system (SAS) to stress is rather homogeneous. With stress, the sympathetic link of SAS is more labile than the adrenal one.     

Changes in autonomic response and resistance to acute graded hypoxia during intermittent hypoxic training

A placebo-controlled study was performed to examine the effects of intermittent normobaric hypoxic preconditioning on the autonomic regulation of blood flow, as well as on heart rate variability (HRV) response and resistance to acute hypoxia, in healthy male volunteers. Intermittent hypoxic training (IHT) increased the efficiency of the mechanisms of autonomic regulation of heart rate (HR) at rest by increasing the parasympathetic control and optimized changes in HRV during simulated acute hypoxia. The hypoxic preconditioning contributed to increased resistance of the body to simulated acute hypoxia, as reflected by less marked hemoglobin desaturation and a smaller increase in the HR. The training effects of the IHT were more pronounced in the subjects with an initially low resistance to a hypoxic factor as compared to those resistant to acute hypoxia.     

Changes in tissue monoamine oxidase activity and resistance to acute hypoxia in rats during stress

Male Wistar rats exposed to different stresses developed shifts in the brain and liver monoaminoxidase activity. In the so called "cognitive" stimulation, the activity was enhanced in the brain and reduced in liver. Mild stresses also enhanced the activity in the brain. Extreme stimulation (starch peritonitis) caused a significant diminishing of the activity in the brain. All the stress schedules accompanied by enhancement of the brain monoaminoxidase activity increased the rats' tolerance of acute hypoxic hypoxia. Negative correlations between the blood lactic acid contents and the brain monoaminoxidase activity were revealed in rats of both the control and the "cognitive" groups. The findings suggest a direct interrelationship between post-stress shifts of the brain monoaminoxidase activity and the hypoxia tolerance.     

Effects of pyrazidol on resistance of animals to hypobaric hypoxia]

The influence of monoamine oxidase type A inhibitor pyrazidol on rats sensitivity to hypobaric hypoxia was investigated. Preliminary pyrazidol administration shows evident protective effect under hypoxia. It increases animals survival at the altitude of 12,000 m above the sea level, prevents lungs affection and erythrocyte membrane destabilization at the altitude of 9,000 m during 3 hours. Plasma total peroxidase activity, extraerythrocyte hemoglobin concentration and free iron content were used as the indexes of erythrocyte membrane stability reflecting the organism state under stress effects.     

Morpho-functional study of the brain of animals with different types of individual resistance to hypoxia

The experiments on white rats have shown that animals with distinct tolerance to hypoxia were characterized by individual metabolic changes in phylogenetically different brain structures. Adaptation to hypoxia in animals with high tolerance was associated with metabolic changes in the reticular formation and in animals with low tolerance with changes in the cerebral cortex. The experiments have shown that white rats with distinct individual tolerance to hypoxia are characterized by an inherent level of plastic metabolism in different brain structures. A correlation between brain tissue metabolism and individual tolerance of animals to hypoxia is suggested.     

Age-related ultrastructural characteristics of various cells in acute hypoxia

Ultrastructural peculiarities, concerning reaction of cells in various populations brain-sensorimotor cortex, mammillary nuclei, vascular plexus; myocardium; liver; jejunum) in mature (6-8 months) and old (24-30 months) male white Wistar rats have been studied at an experimental acute hypobaric hypoxic hypoxia. Both general changes, that are manifested in various degree in different cell groups and organo-specific ones are noted. The manifestation degree of the reactive changes is evidently connected with certain metabolic and functional peculiarities, as well as with the character of cell restoration. In the old animals hypoxic hypoxia produces more profound destructive processes in all cell populations studied. This is accompanied with a restriction in ability to adaptation.     

Changes in the rat lymphoid organs in acute hypoxia

Changes occurring in the rat thymus, spleen, mesenteric lymph nodes have been studied by means of some histological and cytofluorimetrical methods under the effect of an acute hypoxia that imitates the rise to 7,000 m above the sea level for 1 h and to 6,500 m for 6 h. Under the effect of hypoxia, migration of differentiated lymphocytes out of the lymphoid organs is increasing, certain essential shifts in temporal parameters take place in the mitotic cycle of the lymphocytes, contents of nucleic acids in the lymphoid cells change. The phenomena mentioned demonstrate that under the acute hypoxic stress, intensified differentiation processes of the lymphocytes in the thymus, spleen and the lymph node take place and the lymphoid tissue functional activity increases.     

Sexual cycle period and resistance of mice to acute experimental hypoxia]

Variations of survival to an acute hypoxia (nitrogen) were studied, in 200 females, OF1, SPF mice, 72 days old, in groups of 10, at different periods of their estrus cycle, which were evidenced by vaginal smears. In mice which were in diestrus since 3-4 following days, the hypoxic survival (27.27%) was statistically less than in mice which were in estrus (58.00 %) or at the beginning of the diestrus (53.85 %).