Interrelations of hypocapnia, hypoxia, cerebral blood flow and electrical activity of the brain under voluntary hyperventilation in humans

Changes of different physiological parameters in human caused by hyperventilation of 3-min and longer duration were investigated and correlated. It was found that during 3-min hyperventilation, resulting in 4.5-5 fold increase of the respiration velocity, similar phasing changes of the central and cerebral haemodynamics occurred. The blood flow velocity according to the rheographic data during the hyperventilation first increases, reaching maximum at 1st - 2nd min of the test, and then decreases, reaching minimum at 2nd - 3rd min after it's end, and then slowly increases. Cerebral blood flow velocity during all the 3 min of the hyperventilation in most of the subjects keeps being increased, and after the test - decreased. At the same time transcutaneous pressure of carbon dioxide changes differently - decreases to minimum (approximately 25 mmHg) at the end of the test and then increases, reaching approximately 90% of the background level, at 5th min after the end of the test. Oxygen saturation of the blood during the test is found to be 98-100% and decreases to 90% at 5th min after it's end, which in overall with cerebral blood flow decrease appears to be the factor of the brain's hypoxia. In different subjects "mirror" changes of the EEG spectral power of different EEG ranges in relation to transcutaneous pressure of carbon dioxide dynamics were revealed by the hyperventilation. Taking into account the factors of duration or recurrence of the hyperventilation is important for the understanding the interrelations of cerebral haemodynamics, hypocapnia, hypoxia and electrical activity of the brain. It was found that after the recurrent hyperventilation of increasing amount (several times in hour by 3 min) cerebral blood flow might decrease markedly against the background of relatively small changes of electrical activity of the brain. The discussing of the data presented in the paper is carried out from the point of view of important role of tissue oxygen utilization mechanisms of the brain in adaptation to hypoxia and hypocapnia.     

Electrical activity of the brain and oxygen supply for cognitive-mnestic activity in humans under different degrees of hypoxia

Comparative analysis of the indices of oxygen supply for the body and the brain and the functional state of the brain was carried out in three experimental situations: performance of cognitive-mnestic tests under normoxic (TN) and hypoxic conditions (TH) and exposure to hypoxia in the absence of cognitive tasks (H). Each subject participated in all of the experiments. Hypoxic conditions were created by breathing of a hypoxic gas mixture (HGM) consisting of oxygen and nitrogen for 25 min. The first group (eight subjects) was exposed to moderate hypoxia, with the gas mixture containing 12% O₂ (HGM-12); the second group (eight subjects) was exposed to severe hypoxia, with the gas mixture containing 8% O₂ (HGM-8). The cognitive-mnestic activity (CMA) under both normoxia and hypoxia was continuous and included the following tests: “Arithmetic calculations,” “Memory for numerals,” “Colored figures”, and “Sensorimotor response time.” The CMA efficiency was significantly impaired only under severe hypoxia (HGM-8). The CMA efficiency was higher in some subjects of the first group (HGM-12) in the TH series as compared to that in the TN series. The EEG spectral power (SP) during CMA was decreased as compared to the background in all subjects in the TN series and in most subjects of the first group, exposed to HGM-12, whereas it was increased in all subjects of the second group, exposed to HGM-8. The EEG SP was lower in most subjects of both groups studied in the TH series as compared to that found in the H series. The rheographic index of cerebral blood flow rate was not changed compared to the background in the TN series and was increased in the H and TH series during HGM-8 treatment. The increase in cerebral blood flow was less pronounced in the TH series as compared to the H series in most subjects of the second group (HGM-8). Oxygen consumption by the body was elevated by 10–20% in the TN series. A significant increase in oxygen consumption was found in the subjects of both groups studied during hypoxia treatment (H), and it was greater in HGM-12. The following differences were found between the subjects of the two experimental groups: the increase in oxygen consumption in most subjects of the first group (HGM-12) was higher in the TH series as compared to the H series, whereas, in most subjects of the second group (HGM-8), the increase in oxygen consumption was higher in the H series. The data are discussed from the point of view of synergic and concurrent relationships between different forms of energy expenditure on structural and functional reorganization and organ-specific functions.     

Relationships between Cerebral Blood Flow Dynamics and Bioelectric Activity of the Human Brain in Experimental Acute Hypoxia

The relationships between the parameters of oxygen content in the body (hemoglobin saturation with oxygen and trancutaneous oxygen tension), central hemodynamics (cardiac output), and cerebral hemodynamics (cerebral blood flow rate) were studied during a hypoxic test (inhalation of an oxygen–nitrogen mixture containing 8% oxygen for 15 min). Special attention was paid to the relationships between the dynamics of cerebral blood flow and cerebral bioelectric activity measured by EEG parameters. It was demonstrated that the trancutaneous oxygen tension decreased to a greater extent than the hemoglobin saturation with oxygen and the cerebral blood flow increased to a greater extent than the cardiac output. The increase in cerebral blood flow and the increase in the indices and power of and EEG waves in the course of hypoxia were strongly positively correlated with each other in most subjects. However, if these parameters were considered in the series of subjects, the degree of the increase in the indices and power of and waves in different subjects was negatively correlated with the increase in the cerebral blood flow. The results are explained in terms of redistribution of blood flow in the body to provide a better oxygen supply to the brain and optimization of the ratios between the cerebral oxygen consumption and the functional load on the system of oxygen supply.     

Relations of the EEG local and spatialtemporal spectral characteristics changes under hypoxia in humans

Spatial temporal and local EEG characteristics were studied in healthy subjects during inhalation of hypoxic oxygen-nitrogen gas mixture with 8 % content of oxygen. Analysis of spectra power density, coherence, phase shift, similarity of dominant frequencies in the EEGs of different derivations was performed separately for the EEG epochs with and without visually detected patterns of spatial synchrony of the EEG. Apart from this, a fact of dominance of the frequency in the EEG spectra of corresponding derivation was taken into account when estimating spectral parameters. Results of the study showed that, in general, under hypoxia, the EEG coherence in alpha- and delta-frequency range decreases as compared to the background level, in beta-range growth of this parameter is observed, in theta-range ambiguous changes occur: in the epochs with patterns of spatial synchrony--growth, in other epochs--lowering. Under hypoxia, also occurs growth of frontal and temporal EEGs' phase shift (corresponding to EEGs other derivations) in delta- and theta-range. In beta-range, on the contrary, average level of the phase shift decreases. It was revealed that taking into account the fact of dominance of frequency in the local EEG spectra is necessary for correct interpretation of the EEG spatial and temporal parameter analysis' results. A mathematical model of interaction between processes with different frequency characteristics is suggested, which explains some facts obtained in the study.     

Differences in the strategies and potentials of human adaptation to hypoxia

The general patterns and individual specific features of human adaptation to acute hypoxic hypoxia caused by breathing a hypoxic oxygen-nitrogen gas mixture containing 8.0% oxygen have been studied. It was found that, at the initial stage of hypoxia, all examined subjects demonstrated a reduced oxygen consumption as compared to normoxia; then, this parameter increased and, beginning from a certain moment (after 5–15 min of exposure), exceeded the baseline level by 10–40%. Hypotheses explaining the mechanisms of this growth in oxygen consumption during hypoxia are considered. It has been found that the roles of the cardiovascular system and mechanisms of the tissue and cellular utilization of oxygen in the growth of the rate of oxygen consumption caused by hypoxia vary in different subjects. The hypothesis is put forward that the relatively low potential for rearrangement of the biological oxidation system at the cellular level, aimed at increasing the rate of oxygen consumption, predetermines a need to increase the rate of oxygen supply by the blood and, therefore, a greater strain of the cardiovascular system. In many cases, this strain can cause failure of adaptation to hypoxia. Other parameters that can serve as characteristics of a subject’s resistance to hypoxia, such as the intensity of EEG slow waves and the level of blood oxygenation, are also considered.     

Compensatory and adaptive rearrangement in the human respiratory system under acute hypoxic conditions

Relationships between the parameters of external respiration (minute volume and respiration rate) and those of internal, tissue respiration (oxygen consumption, arteriovenous oxygen difference and efficiency of oxygen uptake) were studied during a period of acute hypoxia and upon its completion. The subjects were exposed to hypoxia for 25 min using oxygen-nitrogen hypoxic gas mixtures (HGMs) differing in oxygen content (8 and 12%, HGM-8 and HGM-12, respectively). From the third to the fifth minutes of exposure to HGM-8, the respiration minute volume (RMV) was found to increase by 51 ± 33% as compared to the background value; however, the body’s oxygen consumption (OC) was 35 ± 22% reduced. Afterwards, OC grew to reach, from the 20th to the 25th min of hypoxia, 108 ± 21% of the background value and 181% of the value determined from the third to the fifth minutes of hypoxia. OC growth was accompanied by an insignificant RMV increase (by 12%) as compared to the level determined from the third to the fifth minutes of hypoxia, whereas the efficiency of oxygen uptake from the arterial blood increased by 75% for the same period. RMV growth from the third to the fifth minutes of hypoxia occurred as expense result of a higher breathing depth; at the same time, the respiration rate decreased as compared to the background value. By the period from the 20th to the 25th min of exposure to HGM-8, the respiration rate increased by 21% as compared to the period from the third to the fifth minutes of hypoxia. The efficiency of oxygen uptake from the arterial blood remained higher than the background value for at least 5 min after completion of the exposure to HGM-8. During the same period, the ventilation equivalent, an indicator of the efficiency of external respiration, i.e., of oxygen supply to the body, was significantly lower than the background value. During the exposure to HGM-12, RMV increased to a lesser extent than on exposure to HGM-8, however, the efficiency of oxygen uptake was higher during exposure to HGM-12; therefore, OC was also higher in the latter case. Therefore, the assumption that, during hypoxia, intensified external respiration (ventilatory response) itself compensates oxygen deficiency in inhaled air is revised. Ventilatory response is only a portion of the entire functional system of respiration (both external and tissue respiration). The role of ventilatory response is important for conditioning the tissue respiration rearrangement to eliminate deficiency of oxygen consumption during hypoxia. The retained higher oxygen uptake from the arterial blood during the period after completion of hypoxic treatment testifies to the adaptive implication of changes in tissue respiration; the same is confirmed by a reduced ventilation equivalent after hypoxia, which is indicative of the growing efficiency of external respiration, i.e., of an improved oxygen supply to the body.     

Individual specifics of oxygen consumption by the human organism in hypoxia

Influence of hypoxia on a human organism was studied with the help of hypoxic gas mixtures (HGM) in the first series with 14 % content of oxygen in nitrogen (n = 6), in the second one--with 12 % (n = 10) in the third one--with 8 % (n = 14). Hypoxic exposition in all the series was 25 min. In 6 subjects engaged in all the 3 series, physical working capacity was assessed in two-step test on a veloergometer. In all the 3 series, oxygen consumption by the organism some time after the start of the hypoxic action exceeded the background normnoxic level. Maximal value of this excess on the average was the highest in HGM-12 series--40 +/- 12 %. Maximal increase of the respiration and central blood circulation velocity was the highest in HGM-8 series, 90 +/- 24 and 25 +/- 16 % respectively. Analysis of the EEG parameters, oxygen saturation and rheoencephalographic data indicates the probability of the cerebral metabolic rate of oxygen during hypoxia to beein normal (in most subjects) and even increased (in some subjects). In 3 subjects of 6, whose physical working capacity was assessed, maximal increase of oxygen consumption was observed in HGM-8 series--105 +/- 34 %. Their physical working capacity was higher than of those subjects, who showed maximal increase of oxygen consumption in HGM-12 series. Analysis of increase in oxygen consumption (paradoxical under hypoxic conditions) doesn't allow to ascribe it wholly to an increase of the respiration and central blood circulation. Obviously, the increase of oxygen and energy expenditures for biochemical adaptation to hypoxia, which has common features with adaptation to physical activity plays an important role under hypoxia.     

生境异质度对稻田捕食性天敌及水稻害虫的生态调节有效性

【目的】探索生境高异质度对稻田捕食性天敌及水稻害虫的生态调节有效性,了解这种策略是否会引起其他植食性昆虫成为水稻重要害虫的风险。【方法】2017-2018年连续2年种植单季稻,在稻田边缘种植花生与大豆,构建高异质性边缘生境稻田(rice paddy with high heterogeneous marginal habitats, HHR),调查HHR稻田与简单低异质性边缘生境稻田(rice paddy with low heterogeneous marginal habitats, LHR)中捕食性天敌与水稻害虫功能团的发生规律与相关性,计算益害比。【结果】2017年在HHR稻田中采集到捕食性天敌40种,1 667头;在LHR稻田中采集到捕食性天敌30种,991头。2018年在HHR稻田中采集到捕食性天敌33种,1 384头;在LHR稻田中采集到捕食性天敌34种,1 031头。HHR与LHR两类稻田中获得的捕食性天敌群落重要值P_i≥0.01的物种相似度很高,优势种相似。2017年HHR稻田的捕食性天敌物种丰富度明显高于LHR稻田,这种差异主要由群落重要值P_i<0.01的种类引起。2018年两类稻田的捕食性天敌物种丰富度没有差异。单位样方面积内的捕食性天敌个体数量,HHR中明显高于LHR,这种差异在2017年的分蘖期与成熟期达显著水平(P<0.05),在2018年的开花期极显著(P<0.01)。2017年在HHR中采集到水稻害虫22种,637头;在LHR中采集到水稻害虫19种,743头;物种相似性系数0.88。2018年在HHR中采集到水稻害虫16种,1 011头;在LHR中采集到水稻害虫16种,2 014头;物种相似性系数0.75;主要害虫物种组成结构相同。水稻害虫数量发生的时间动态分析表明,在分蘖期,虽然HHR稻田中的水稻害虫数量明显高于LHR(P<0.05),但此期害虫的数量不多,发生较轻。在孕穗期、开花期与成熟期,HHR稻田中的水稻害虫数量明显低于LHR稻田,这种差异在2017年的成熟期与2018年的孕穗期极显著(P<0.01),在2018年的成熟期差异显著(P<0.05)。2017年HHR和LHR中个体数量益害比N_pi值分别为2.62和1.33;2018年分别为1.37和0.51。【结论】具有高异质性边缘生境的稻田,能提高系统对捕食性天敌物种的涵养潜力,显著提高稻田捕食性天敌个体数量,提高益害比,具有更好的控制害虫的物质基础,促进捕食性天敌对水稻害虫的生态控制效能,不会引起其他植食性昆虫演变为水稻重要害虫风险,可为保护稻田生态系统天敌发挥生态效能提供可借鉴的策略与方法。     

CEREBRAL ENERGY STATE IN INSULIN-INDUCED HYPOGLYCEMIA, RELATED TO BLOOD GLUCOSE AND TO EEG

—Concentrations of phosphocreatine, creatine, ATP, ADP and AMP were measured in the cerebral cortex of rats during insulin-induced hypoglycemia. Blood glucose concentrations were related to clinical symptoms in unanaesthetized animals and to the EEG pattern in paralysed and lightly anaesthetized animals. There was an excellent correlation between blood glucose concentration and EEG pattern. In animals showing a pronounced slowing of the EEG or convulsive polyspike activity for up to 20 min, there were no changes in any of the phosphates. However, after prolonged convulsive activity some animals showed clear signs of energy failure, and in all animals with an isoelectric EEG there was a major derangement of the energy state. Since the majority of those animals did not show signs of cerebral hypoxia or ischemia it is concluded that hypoglycemic coma is accompanied by substrate deficiency of a degree sufficient to induce energy depletion of brain tissue.     

Cerebral blood flow in the fetal guinea-pig

To measure brain blood flow in the fetal guinea-pig, radioactive microspheres were injected in the lateral saphenous vein whilst a reference sample of blood was withdrawn from the right axillary artery. Measurements were made near term of pregnancy, on the 60th-66th day, during anaesthesia with pentobarbitone and diazepam. Fetal blood pressure was 4.25 +/- 0.12 kPa and fetal heart rate was 250 +/- 7 beats per min. The arterial oxygen content varied between 1.9-5.1 mmol 1(-1). Blood flow to the whole brain (mean 1.13 +/- 0.14 ml min-1 g-1) was significantly correlated to the reciprocal of arterial oxygen content (r = 0.84). Four regions of the brain were examined: the cerebral hemispheres, the cerebellum, the thalamus and midbrain, and the pons and medulla. In each region blood flow was inversely related to arterial oxygen content (r = 0.80-0.83) but the rate of perfusion of the brain stem was greater than that of the cerebral hemispheres or cerebellum.     

Electroencephalograms and cerebral blood flow in carp, Cyprinus carpio, subjected to acute hypoxia

Changes in electroencephalogams (EEG) and cerebral blood flow were examined in carp immobilized with a muscle relaxant during 60 min hypoxia (water Po ₂ of approximately 20 mmHg) and subsequent 30 min normoxia. The amplitude of EEG waves recorded from the telencephalon decreased gradually but slightly with the progression of hypoxia, whereas the telencephalic blood flow increased mainly due to an increased blood velocity. These findings suggested that cerebral activity during hypoxia was compensated to some degree by increased cerebral blood flow. However, carp showed large variations in the patterns of EEG responses and cerebral blood flow.     

Characteristics of the human EEG during cognitive-mnemenic activity under hypoxic conditions

The amplitude-frequency and spatiotemporal characteristics of the EEGs of subjects performing various cognitive-mnemenic activities under the conditions of graduated hypoxia were studied. The quickness and correctness of test performance were significantly decreased beginning from the sixth minute of hypoxia as compared to normoxic conditions. The amplitude and mean period of the dominant EEG activity in this functional state were higher than in the same tests performed under normoxic conditions and lower than in the case of hypoxia not accompanied by the performance of tests. The spatiotemporal characteristics of the EEG under hypoxic conditions displayed both the characteristics typical of hypoxia (a decrease in EEG cross-correlation within anterior cortical regions) and those typical of cognitive-mnemenic activity (an increase in the correlation between the EEGs of distant zones of anterior and posterior cortical regions). It is assumed that the “intermediate” EEG pattern observed in subjects performing cognitive-mnemenic tests under hypoxic conditions reflects opposite effects of hypoxia and intellectual effort on the functional activity of brain neurons.     

急性高原低氧环境对不同情绪状态脑电功率的影响*

目的: 探讨急性高原低氧环境对不同情绪状态脑电功率的影响。方法:本研究为双因素多水平试验设计(氧气环境2个水平×情绪类型4个水平)。通过编写情绪图片诱导12名年龄在20～25岁之间的男性被试产生四类不同情绪:低效价低唤醒(LVLA)、高效价低唤醒(HVLA)、低效价高唤醒(LVHA)、高效价高唤醒(HVHA) ,分别近似于沮丧、轻松、恐惧、快乐四类情绪,并使用Brain Products 32导脑电采集设备采集不同情绪状态下的脑电信号;次日,采用常压低氧舱模拟4 300 m的高原低氧环境,同一批被试在低氧10 h 后使用相同试验范式采集脑电信号。对采集来的脑电信号进行功率谱分析(FFT),同时对额叶(F3\Fz\F4)脑电的五个频段(delta、theta、alpha、beta、gamma)进行两因素重复测量方差分析。结果:功率谱分析发现:急性低氧前后,四类情绪状态下alpha波的全脑分布差异主要集中在额叶、顶叶及部分颞叶;HVLA情绪状态下alpha波全脑分布差异最小。两因素重复测量方差分析结果发现:①delta、beta频段功率受氧气环境影响显著(P＜0.05),低氧环境下功率增强。②theta、alpha频段功率指标上,氧气环境和情绪类型交互作用显著(P＜0.05),低氧环境下除HVLA情绪状态外,theta、alpha频段功率皆出现了显著增强。③两因素对gamma频段影响都不显著(P＞0.05)。结论:在四类情绪状态下,氧气环境的变化对大脑活动的影响差异区域主要集中在额叶、顶叶及部分颞叶;低氧环境对沮丧、恐惧、快乐情绪状态有明显影响,低氧与情绪类型对于theta及alpha频段功率的改变具有协同作用。     

Effect of sojourn at 4,300 m altitude on electroencephalogram and visual evoked response.

The purpose of the present study was to determine the effect of sojourn at high altitude on cerebral electrical activity. Electroencephalographic (EEG) and visual evoked responses (VER) were recorded from seven healthy males under the following conditions: 1) during the first 2-3 h at 4,300 m altitude when Pao2 was maintained at 90 mmHg (control condition), 2) during the first 2-3 h of hypoxia (Pao2 = 40 mmHg), and 3) at 24- to 48-h intervals during the first 9-12 days of hypoxia. Electrode placement was according to the 10-20 International Electrode System. The VER was recorded from an electrode at the inion referred to the left ear. We found no significant changes from control cerebral electrical activity during the first 2-3 h of hypoxia. One subject's VER amplitude was greater than control on the 2nd and 3rd days of hypoxia and a similar change from control was consistently evident in a second subject beginning the 5th day of hypoxia. These changes suggest cortical depression. After the 5th day changes occurred in the remaining subjects which would be consistent with cortical excitation. In three subjects, EEG frequency was increased, amplitude decreased, and/or spiking became evident. In four subjects VER amplitude was reduced. Our findings provide support for the hypothesis that certain behavioral and physiological changes induced by sojourn at altitude could be caused by alterations in central nervous system function.     

Change in the content of ATP and 2,3-diphosphoglycerate in the erythrocytes of rats adapted to hypoxia]

It was shown that on the 30th-60th days of training rats to hypoxia under conditions of pressure chamber there was an increase in ATP and 2,3-diphosphoglycerate content in erythrocytes. By changing the affinity of hemoglobin to oxygen the mentioned shifts could play an important role in the improvement of oxygen supply to the tissues.     

Progressive hypoxia until brain electrical silence: a useful model for studying protective interventions

Anesthetized spontaneously breathing rats, fitted with epicortical electrodes and catheters for sampling arterial, venous, and cerebral venous blood, were exposed to standardized progressive hypoxia. Three minutes of hypoxia sequentially caused hyperpnea, hypopnea, apnea, and cessation of electrocorticogram "spiking," of synchronization, and of background in electroencephalogram (EEG). Blood data and cerebral blood flow and metabolism were measured throughout and at "insults," i.e., at apnea and cessation events, to clarify their interdependence. Arterial and brain venous PO2 fell linearly with inspired oxygen (final value of 2% at 280 s). Hyperpnea induced arterial alkalosis; subsequent hypopnea led to near-normal PCO2 and pH when EEG ceased. Hypercapnia was more pronounced in cerebral than in systemic venous blood; time courses of pH changes were similar. Sagittal sinus blood pressure and outflow were linearly related and resembled the time course of local cerebral blood flow. Blood flow increased by 25% at apnea and only 60% at EEG silence. Cerebral metabolic rate of O2 rose during the hyperpnea phase and fell exponentially thereafter. Cerebral glucose uptake and lactate release increased within the first 3 min but fell abruptly when cortico-electric spiking ceased. Time courses of cerebral O2 consumption and spike rate were linearly related; both showed inverse linear relations to cerebral perfusion. The hypoxic insults were well defined by blood data; critical PO2 values were lower than previously assumed. This model is proving to be a useful, controlled method by which mechanisms of cerebral hypoxia tolerance may be studied in vivo.     

EEG markers of the disturbed systemic brain activity in hypoxia

Specific rearrangements of the brain bioelectric potential field and the structures where the components (waves) of the main EEG rhythms interact, as well as the stereotactic location and power of the equivalent electrical dipole sources (EEDSs), were studied at various stages of acute experimental hypoxia (breathing for 15–30 min a hypoxic gas mixture containing 8% oxygen in nitrogen). The disrupted intercentral relationships that ensure the formation of the dynamic “morphological equivalent” to support the integrative brain activity, rearrangements of this activity, and the adaptive functions of the whole brain proved to account for partial or complete disintegration of systemic brain activity during acute hypoxia. EEDS tomography showed that EEDSs responsible for the generation of the basic brain rhythmic pattern are normally located in the thalamic structures. At the initial stages of hypoxia, the distribution of the EEDS foci is changed so that the density of EEDSs is increased on the sections that include the hypothalamic region structures, basal nuclei of the forebrain, and the limbic system; the basal, frontal, and medial regions of the temporal lobes of both hemispheres are also involved. With increasing hypoxia, EEDSs appeared in the basal and medial regions of the frontal lobes. At this time, both the surface and deep regions of the frontal lobes of the brain hemispheres are the major targets of the hypoxic effect. At the stages of severe hypoxia, pronounced functional changes in the CNS are observed, including the phenomenon of movement of multiple EEDS foci primarily through the basal and mediobasal regions of the frontal and temporal lobes and in the limbic system structures. Thus, despite the generalized high-amplitude paroxysmal activity that is observed in EEG, a functional disintegration (disruption) of interactions between individual brain regions appears and leads to disturbed regulation of the brain and systemic brain activity. Spatiotemporal EEG markers have been identified that make it possible to assess the individual sensitivity and resistance to hypoxia, as well as the degree of disintegration of his systemic brain activity at different stages of hypoxia.     

EEG spectral characteristics at different stages of the unconscious visual set in two motivation conditions

Multichannel EEG were recorded in young healthy subjects in two series of experiments during formation, actualization, and extinction of the visual unconscious set to the perception of unequal circles under conditions of increased motivation of subjects to the result of their performance. In the first series of experiments, subjects were promised to be rewarded (a small money price) for each correct response (the "general" rise of motivation). In the second series, subjects were promised to be rewarded for correct responses only in cases when one of the circles was larger than the other one (the "directed" rise of motivation). The dynamics of the EEG spectral power derived under these two conditions was compared with similar indices obtained earlier during formation of the same set without any special motivation of subjects (control). In all experimental conditions, before the presentation of the stimuli the EEG power in the alpha range was higher in subjects with the stable set. The dynamics of changes in the alpha power at set stages was principally similar in all conditions. In all the experimental conditions, in subjects with unstable set the EEG power in the delta range was highest at the stage of set actualization. The most pronounced generalized changes in the EEG power in the theta-range during the "general" rise of motivation in subjects with stable and unstable forms of set and greater variability of the reaction time to the probe stimulus suggest that the task performance under these conditions required greater tension than under conditions of the "directed" rise of motivation.     

Nitric oxide metabolites level in human serum in acute normobaric hypoxia

The influence of acute normobaric hypoxia on NO metabolites level of the blood serum in volunteers at respiration of hypoxic gas mixture containing 8 % of O2 during 25 min was investigated. Health status of participants and the hypoxia intensity were monitored with a complex of indexes: EEC, ECG, blood pressure, oxygen saturation of haemoglobin, cardiac output, gas composition of exhaled air. Cluster analysis (k-means clustering) conducted among volunteers that have successfully passed the test has shown presence of two groups differing in NO metabolites level during experiment. Statistically significant differences on NO metabolites level between groups were observed before hypoxia exposure, on 10th minute of acute hypoxia (maximum difference) and on 5th minute of recovery. Differences on NO metabolites level between groups have been caused by changes in nitrates concentration whereas nitrites level did not differ. The least NO and nitrates levels have been revealed in volunteers that have been in volunteers that had interrupted performance of the test after 10 minutes of respiration of hypoxic gas mixture. Thus the moderate increase of NO metabolites level due to accumulation of nitrates at acute hypoxia testifies to good adaptive reserves of system of nitric oxide generation in organism.     

Normative EEG spectral characteristics in healthy subjects aged 7 to 89 years

The EEGs of 885 healthy subjects of both sexes aged 7 to 89 years were recorded in two modes: with the subjects’ eyes closed and with the eyes open. The subjects were divided into 20 age groups, for each of which the normative values of the EEG spectral characteristics were determined: the total EEG power spectra and the EEG independent component power spectra in the Δ, ϑ, α, and β frequency bands. Tables of confidence intervals with a level of confidence of 0.95 were constructed for each electrode channel in the case of the EEG power spectra and for each component in the case of the EEG independent component power spectra. The normative values obtained may provide EEG specialists with objective criteria for assessing cerebral dysfunction.