Effect of vault irritation on the bulbar respiratory neurons during hypoxia

Influence of the vault on the impulse activity of respiration center neurons in medulla oblongata and respiration was studied in the norm and during hypoxia. Hypoxia stages served as a test model for ensuing vault effect summation. In normoxia, electrical irritation of the vault had largely an activating effect. Moderate pO2 reduction with rising to the altitudes of 4000-5000 m activated pulsation of the respiratory neurons; influence of vault irritation was less evident than in normoxia even though it prevailed over inhibition. The respiratory neurons activity declined conspicuously at the peak altitude of 7500-8000 m and critical hypoxia; it was then that the facilitatory effect of vault irritation was especially strong. On "descent" to normal atmospheric pressure the spontaneous rhythmic activity of neurons and reaction to irritation returned gradually to baseline values.     

Various individual features of human adaptation to altitude

Two groups of young healthy men--natives of lowlands who for one year lived and worked in chronic hypoxia (Group 1 at an altitude of 1680 m with PO2 = 120 mm Hg and Group 2 at an altitude of 3650 with PO2 = 90 mm Hg) were examined. It was found that after this prolonged exposure the subjects showed a higher sensitivity of the respiration system to hypoxia, an enhanced lung ventilation and circulation, a lower gas exchange and physical work capacity. The concentration of lactic acid at rest in the Group 2 subjects was 47% higher than in the Group 1 subjects. The lactate/pyruvate ratio in the Group 2 subjects increased by 46% thus indicating an enhanced rate of anaerobic processes. A higher deficiency of buffer bases, a lower concentration of bicarbonates in blood at rest and during exercise tests of the Group 2 subjects pointed to metabolic acidosis. The subjects with a higher rate of anaerobic metabolism in a low PO2 environment displayed a diminished sensitivity of the hypoxic stimulation of respiration, an increased tolerance to the very low PAO2 and a reduced work capacity in chronic hypoxia.     

Effect of hypoxia on heart glycogen utilization during exercise

An investigation was made into the effects of physical exercise upon heart glycogen change in rats exposed to decreased barometric pressure in hypobaric chamber simulating the effects of 3,000 m and 5,000 m altitude. Blood and cardiac tissue samples were examined after 1 h and 5 h of treadmill running at sea level and at 3,000 m, and after 1 h at 5,000 m. At sea level, cardiac glycogen level showed a classic biphasic evolution which was not affected by running. At 3,000 m, 1 h of running promoted an initial increase of 16% from control values, while a secondary decrease of 15% was measured after 5 h of running. Running for 1 h at 5,000 m induced a total depletion in cardiac glycogen level, the latter being depressed by 90% from control values. Free fatty acid (FFA) plasma level was increased by physical exercise at all barometric pressures, but the response was gradually enhanced by hypoxia. These data indicate that heart glycogen utilization during prolonged physical exercise is stimulated by acute altitude exposure, which suppresses the sparing effect observed at sea level upon dependence of enhanced FFA availability. The great differences in cardiac glycogen utilization support the views that enhanced glycogenolysis during hypoxia is promoted by different parameters, thus affecting various pathways. The slight decrease at 3,000 m suggests a moderate increase in anaerobic metabolism while the exhaustion observed after 1 h of running at 5,000 m indicates a decrease in cellular respiration response and enhanced heart anaerobic metabolism.     

Respiratory control in residents at high altitude: physiology and pathophysiology

Highland population (HA) from the Andes, living above 3000 m, have a blunted ventilatory response to increasing hypoxia, breathe less compared to acclimatized newcomers, but more, compared to sea-level natives at sea level. Subjects with chronic mountain sickness (CMS) breathe like sea-level natives and have excessive erythrocytosis (EE). The respiratory stimulation that arises through the peripheral chemoreflex is modestly less in the CMS group when compared with the HA group at the same P(ET(O2)). With regard to CO(2) sensitivity, CMS subjects seem to have reset their central CO(2) chemoreceptors to operate around the sea-level resting P(ET(CO2)). Acetazolamide, an acidifying drug that increases the chemosensitivity of regions in the brain stem that contain CO(2)/H(+) sensitive neurons, partially reverses this phenomenon, thus, providing CMS subjects with the possibility to have high CO(2) changes, despite small changes in ventilation. However, the same type of adjustments of the breathing pattern established for Andeans has not been found necessarily in Asian humans and/or domestic animals nor in the various high altitude species studied. The differing time frames of exposure to hypoxia among the populations, as well as the reversibility of the different components of the respiratory process at sea level, provide key concepts concerning the importance of time at high altitude in the evolution of an appropriate breathing pattern.     

模拟高原缺氧不同时间对大鼠心肌线粒体功能的影响及其在习服—适应中的意义

目的：观察模拟高原缺氧不同时间对心肌线粒体的影响,探讨模拟高原缺氧对机体影响的细胞机制以及线粒体功能改变在机体对缺氧习服—适应中的意义,为高原缺氧性疾病的防治提供理论基础。方法：观察急性连续缺氧（模拟５ ０００ｍ 高原）３、１２、３６ 和７２ 小时以及慢性间断缺氧１４、２８ 和４２天对大鼠心肌线粒体的影响。测定了线粒体呼吸控制率、琥珀酸脱氢酶及细胞色素氧化酶活性和线粒体丙二醛含量。结果：各时间点的线粒体呼吸控制率比对照组都显著降低,急性缺氧的下降程度较慢性组为甚,其中急性缺氧３ 小时组抑制程度最显著。细胞色素氧化酶活性在急性缺氧３ 小时末显著降低,随后有所回升,而慢性缺氧则使细胞色素氧化酶活性升高。琥珀酸脱氢酶活性在急性缺氧组升高。线粒体丙二醛含量在急性与慢性缺氧各时间点均显著升高,其中以３ 小时组的丙二醛值为最高。结论：急性缺氧、尤其是在最初３ 小时心肌线粒体呼吸功能受抑制较严重,线粒体细胞色素氧化酶和琥珀酸脱氢酶活性升高可能有一定的代偿适应意义。     

长时间缺氧对大鼠脑皮质线粒体细胞色素氧化酶活性及亚基I、Ⅳ蛋白表达的影响

目的：通过观察缺氧过程中大鼠脑皮质线粒体细胞色素氧化酶（COX）活性、亚基COX I、Ⅳ的蛋白量的变化，探讨COX活性改变及其调节的可能机制。方法：成年雄性Wistar系大鼠随机分为平原对照组，缺氧2、5、15和30d组。缺氧大鼠于低压舱内模拟海拔5000m高原连续减压。氧电极法测量脑皮质线粒体COX活性，Western blot分析线粒体COX I、Ⅳ蛋白。结果：缺氧15d内，COX活性持续下降，与对照组差异有显著性意义；缺氧30d时，COX活性较缺氧15d时显著升高，但仍低于平原水平，差异有显著性意义。各组线粒体COXI、Ⅳ蛋白量差异无显著性意义。结论：缺氧可影响脑皮质线粒体COX活性，这可能是缺氧导致线粒体氧化磷酸化功能改变的在因之一；COXI、Ⅳ蛋白表达不是影响酶活性的主要因素。     

高原低氧研究中小型代用低压舱实验技术改良

本文以小型真空干燥箱代用低压舱进行了技术改良，达到了置入单只小型动物模拟高原低压性低氧环境无舱内或动物体内二氧化碳贮留且低氧效果理想的要求，同时实现了准确、安全可靠地在低压环境条件下动物血样采集和生命状态变化动态连续监测技术，为同行低氧研究提供了即准确可靠又经济实用的实验技术。     

Reduced systolic blood pressure elevations during maximum exercise at simulated altitudes

Ten healthy female subjects performed maximum exercise on a bicycle in an altitude chamber during normoxia and hypobaric hypoxia simulating altitudes of 2,450, 3,700 and 4,600 m. The increases in systolic blood pressure responses were reduced with the degree of hypobaric hypoxia, whereas heart rate and diastolic pressure responses were unchanged. The increases in blood levels of aldosterone, plasma renin activity, adrenaline, noradrenaline, neuropeptide-Y and vasoactive intestinal peptide were similar at the different simulated altitudes. Angiotensin-converting enzyme and vasoactive intestinal peptide levels were not affected by hypoxia or maximum exercise. The present results suggest that the decreases in systolic blood pressure responses during hypobaric hypoxia could not be explained by altered responses of the measured vasoactive substances from the renin-angiotensin, gastrointestinal, and autonomic nervous systems.     

Effects of mountaineering training at high altitude (4,350 m) on physical work performance of women

BACKGROUND: Little is known about work performance of women in hypobaric hypoxia. Moreover, whether native women of moderate altitude (2,000-2,100 m) differ from their lowland counterparts in their ability to adjust to hypobaric hypoxia is also not known. Hence, physiological alterations on work performance due to mountaineering training with altitude adaptation was evaluated in two groups of women and compared to the differences in the responses of the native women of moderate altitudes (Highlanders-HL) with those of the plains (Lowlanders-LL). METHODS: Pre-training tests were conducted at 2,100 m, then during sojourn to 4,350 m and re-tested again after return to 2,100 m. Physical work performance was assessed following standard step-test-exercise on a 30 cm stool with 24 cycles x min(-1) for 5 min. Heart rate, BP, ventilation, oxygen consumption and oxygen saturation were monitored at rest and during exercise followed by 5 min recovery in all three situations. RESULTS: During initial assessment, HL showed higher cardiovascular efficiency with faster recovery of exercise heart rate. Both groups showed significant improvement in physical performance due to mountaineering training at high altitude (HA). The difference in performance between two groups narrowed down at 4,350 m and further reduced during re-test with maintenance of initial superiority of the HL. CONCLUSIONS: a) Native women of moderate altitude (HL) are more fit compared with their plains counterparts (LL); b) All women achieved marked improvement in cardiovascular and respiratory efficiency as well as the step-test score due to intense mountaineering training at HA, and the rate of improvement in physical performance was higher in LL; c) Further, induction by trekking under progressive hypoxia coupled with rigorous mountaineering activity at HA merits in understanding better acclimatization and improved physical performance.     

Effect of acute normobaric hypoxia on peripheral sweat rate

Peripheral sweat rate was measured to determine if acute normobaric hypoxia exerted a local inhibition on sweat gland function. It was hypothesized that peripheral sweat rate would be reduced during hypoxia, following cholinergic stimulation. Nineteen subjects (24 +/- 3 yr; 177 +/- 9 cm; 75.5 +/- 20.1 kg), 8 females and 11 males, were tested once during normobaric hypoxia, simulating an altitude of approximately 3050 m (P(O2) = 13.9%; P(B) approximately 730 mmHg), and once at sea level (200 m; P(O2) = 20.9%; P(B) approximately 730 mmHg). While seated at rest, a approximately 7-cm(2) area of the anterior forearm was stimulated using pilocarpine iontophoresis to produce localized sweating at the site. Following stimulation, sweat was collected from the area for 15 min using a Macroduct Sweat Collection System. One-way repeated measures ANOVA indicated a significantly lower sweat rate during normobaric hypoxia (4.6 +/- 2.6 g x m(-2) x min(-1)) compared to sea level (5.5 +/- 3.0 g x m(-2) x min(-1); p = 0.006). Because sweating was initiated directly at the sweat gland, thus bypassing central nervous system input, changes in sweat rate were likely due to peripheral alterations. Although these peripheral mechanisms warrant further investigation, the results of this study suggest a direct hypoxic influence on sweat gland function as evidenced by a decrease in sweat rate.     

Adrenocortical activity and urinary cyclic AMP levels: effects of hypobaric hypoxia.

Six highly motivated and trained military test subjects were exposed to a simulated altitude of 4267 m (477 torr) for 48 hours, prededed and followed by sea level runs lasting 32 hours. During each scenario tests subjects were required to perform their respective military tasks on a continual basis with sporadic rest not exceeding several hours. Extremely high levels of plasma cortisol prior to the start of each session and persistently elevated concentrations of urinary 17-OH corticosteroids at sea level were consistently observed. (This observation probably explains the relatively minor changes in adrenocortical output noted during acute exposure to hypobaric hypoxia. Analogous results were obtained for urinary cyclic AMP, i.e. elevated baseline levels and minimal response to high altitude. The results indicate an attenuated response as well as an association between urinary measures of adrenocortical activity and cyclic AMP excretion.     

Cardiopulmonary transition in the high altitude infant

The perinatal cardiopulmonary transition at high altitude differs from that at sea level because oxygen plays a fundamental role in the developmental changes from fetus to newborn infant. Under conditions of high altitude hypoxia, arterial oxygen saturations are lower, breathing patterns and maturation of respiratory control reflexes differ, and regression of fetal characteristics of the pulmonary vasculature proceeds more slowly. Several aspects of transition vary not only with postnatal age and altitude, but also with population group, suggesting an effect of genetic adaptation on perinatal physiology. Exposure to chronic high altitude hypoxia during the perinatal transition also results in apparent lifelong alterations in respiratory reflex responses and pulmonary vasoreactivity. Disruption of the normal process of cardiopulmonary transition can result in symptomatic high altitude pulmonary hypertension. The exaggerated hypoxemia associated with acute respiratory infections in young infants still undergoing transition contributes to infant mortality at high altitude.     

Reduced tolerance of simulated altitude (4200 m) in young men with borderline hypertension

BACKGROUND: Primary hypertensives who are acutely exposed to hypoxic hypoxia show an enhanced reactivity of arterial chemoreceptors as well as an exaggerated response of the sympathetic nervous system. Since these phenomena could influence their ability to tolerate sustained hypoxic hypoxia, this study was performed to determine whether persons predisposed to hypertension have a normal tolerance of simulated high altitude. METHODS: Subjects were 18 young men with a family history of hypertension (sons of hypertensives, SOHT) whose BP values were in the upper normal or borderline hypertensive range. Controls were 15 young men without parental hypertension (sons of normotensives, SONT) who had normal BP values. Each subject underwent both a control and an altitude experiment. The latter consisted of an 8-h exposure to hypobaric hypoxia (equivalent to 4200 m) while resting supine in an altitude chamber. Fluids were administered by mouth and by intravenous line to produce sustained diuresis. Variables measured included heart rate, BP, respiratory rate, O2 saturation, urine flow rate, and sodium excretion. RESULTS: All subjects tolerated the control experiment and all SONT also completed altitude exposure. However, 8 of 18 SOHT developed antidiuresis and had to leave the chamber early due to symptoms of mild acute mountain sickness. Compared with SONT, SOHT exhibited more stable cardiorespiratory parameters at altitude. CONCLUSIONS: The data support the hypothesis that borderline hypertensives have stronger cardiorespiratory responses to altitude than controls, a response that is compatible with higher excitability of their arterial chemoreceptors. However, their altitude tolerance is reduced even at rest, probably because of the renal effects of an exaggerated response in the sympathetic nervous system.     

轻、中度缺氧对事件相关电位的影响及不同刺激模式的比较

目的 观察轻、中度缺氧对脑事件相关电位（ＥＲＰ）的影响,比较不同刺激模式发的ＥＲＰ对缺氧的敏感性,方法１２名受试者在地面、２５００ｍ和４３００ｍ匠心同度（吸放低氧混合气）分别进行视觉Ｏｃｄｄｂａｌｌ、Ｓｔｅｒｎｂｅｒｇ记忆量（ＭＳＥＴ）为１ 和ＭＳＥＴ为３的任务测试,记录ＥＲＰ的Ｐ３潜伏期、波幅和反应时（ＲＴ）及反应错误率（ＥＲ）。结果 ４３００ｍ高度缺氧时Ｐ３潜伏期显著延长,任务难度较大时ＥＲ增     

Comparison of exercise responses of males and females during acute exposure to hypobaria

Seventeen male and 20 female college students were tested on a bicycle ergometer in a hypobaric chamber to determine whether both sexes had similar submax and max exercise responses to acute hypoxia. Initial testing was at a terrestrial altitude of 1576 m, to which the subjects were acclimated; subsequent tests were at simulated altitudes of 2743 m and 3962 m. Analysis of covariance showed that inspired V was the only variable during submaximal work (50% max) to exhibit a significant difference in altitude response between males and females; women had a smaller increase than men. During max work, V and O2 pulse increased less in women. At 2743 m, max VO2 decreased more in females whereas, at 3962 m, no difference was noted. It was concluded that during both submaximal and maximal work with acute altitude exposure, women would demonstrate smaller relative increases in ventilation than would men.     

Functional and metabolic changes in the heart during the adaptation of the body to high altitude hypoxia

The study was carried out using 140 rabbits adapted to different altitudes (1000 m, 2000 m and 3250 m above sea level) for various times (from 2 days to 2 months). In the course of adaptation to high altitude hypoxia immediate adaptive changes (systemic, central hemodynamics, coronary circulation, cardiac electrical stability) and profound structural changes that formed the foundation of long-term adaptation (metabolic and structural changes) developed. The degree of adaptive changes was correlated with the altitude and time of exposure to hypoxia. High mountain adaptation developed in stages to sustain body requirements.     

Everest nails: a prospective study on the incidence of Beau's lines after time spent at high altitude

Beau's lines are transverse grooves seen in the nails that appear after a period of disruption in nail matrix formation. The fall in atmospheric pressure at high altitude causes hypobaric hypoxia in individuals spending time at high altitude, which may result in disruption of nail matrix formation and the appearance of Beau's lines. Members of an expedition to a research base camp at 5000 m in the Nepal Himalayas were contacted 4 and 8 weeks after returning to low altitude to report on the appearance of new transverse grooves in their nails. During the expedition, data on altitude, acute mountain sickness score, oxygen saturation, and the use of medications were collected by each individual in a twice-daily log book. Fifty-nine individuals consented to enroll in the study, with 52 (88%) contacted at follow-up at 8 weeks. The incidence of Beau's lines was 33%. There was no relationship to maximum altitude reached, minimum oxygen saturation, duration of various levels of hypoxia, worst AMS score, or length of stay above 4000 m (p = 0.118). The hypoxia associated with the hypobaric environment at high altitude could be sufficient to cause a disruption in nail matrix formation.     

青年士兵进驻不同海拔高度血液生化全项的改变

目的：研究进驻不同海拔高度青年士兵生化全项的变化;方法：随机挑选进入高原士兵20名,在海拔1300m,2900m和4400m处空腹静脉取血,进行血液生化全项检测。随海拔升高,心肌酶谱增加,海拔2900m和130m,4400m和2900m比较呈非常显著性差异性或显著性差异（P＜0．01或P＜0．05）;结论：随海拔升高对人体血液生化指标显示心肌酶轻度升高,而肝功、肾功、电解质及血糖无明显异常变化。     

高原缺氧对正常人血浆心钠素的影响

目的 :心钠素是近年来发现从心脏分泌的一种新激素 ,具有强大的利尿、排钠、扩张血管作用。本文观察高原缺氧对人体心钠素含量水平的影响。方法 :血液标本分别取自三个不同海拔地区正常人的空腹静脉血 ,北京地区 (海拔 31m) ;青海省西宁市地区 (海拔 2 2 6 0m) ;青海省果洛州 (海拔 3719m) ;用直接放免法测定血浆中心钠素的含量。结果 :低海拔组 (北京地区 )正常人血浆心钠素含量明显低于中等海拔组 (西宁地区 )及高海拔组 (果洛地区 )正常人 ;其 (P <0 .0 0 1)。结论 :不同海拔高度对正常人体血浆心钠素水平有一定的影响 ,缺氧可能是不同海拔正常人血浆心钠素水平发生的主要原因