急性轻、中度缺氧对人的短时记忆能力的影响

目的 研究急性轻,中度缺氧对人的短时记忆能力绩效的影响。方法 利用低压舱模拟２８００ｍ、３６００ｍ及４４００ｍ高度缺氧暴露１ｈ,考察１８名健康男性青年的记忆长廊、记忆扫描,连续识别记忆和空间记忆测验绩效的变化。     

急性轻、中度缺氧暴露对心理运动及反应时的影响

目的：研究急性轻,中度缺氧暴露对人的心理运动及视觉反应时的影响。方法 利用低压舱模拟300m（对照高度）,2800m,3600m,4400m高度缺氧暴露1h,考察了18名健康男性青年被试者指82％和74％,2800m缺氧暴露1h心理运动绩效的各个参数并无显著改变（P＞0．05）,3600米缺氧步加重（P＜0．01）。而简单反应时和指测验的绩效暴露于4400米时仍无显著改变（P＞0．05）,结论 以上高度时会对选择反应时等复杂反应产生负面影响,且随着主度的增加而加重。     

急性中度缺氧对人计算能力影响的研究

为观察急性中度缺氧对人计算能力的影响，利用低压舱模拟３００ｍ（对照），３６００ｍ，４４００ｍ，５０００ｍ高度的缺氧暴露，考察１６名健康男性青年的连续计算，系列加减及心算测验综合绩效的变化，结果显示，３６００ｍ缺氧暴露１ｈ，连续计算测验的错误率增加，系列加减运算的反应时延长，综合绩效下降，均达到显著水平（Ｐ〈０．０５），４４００ｍ缺氧暴露各测验的绩效均明显下降（Ｐ〈０．０５），５０００ｍ暴露时各项测     

Cognitive and emotional processing at high altitude

INTRODUCTION: Exposure to altitude reduces oxygen supply to the central nervous system and may cause a variety of neuropsychological impairments. We investigated the relationship between certain cognitive functions and cardiovascular and respiratory variables during acute hypobaric hypoxia. METHODS: There were three groups of seven men who were each exposed to a 2-h altitude profile (AP) involving 30 min at each of the following simulated altitudes (m): AP1, 450-1500-3000; AP2, 450-1500-4500; Control 450-650-650. The neuropsychological tests included word fluency and three word-association tasks tapping processes of cognitive flexibility and emotion regulation. A lateralized tachistoscopic lexical decision task with high and low emotional target words was also administered to assess possible shifts in hemispheric superiorities for positive and negative affect. RESULTS: No significant differences in word fluency, word association, or lateralized lexical decision performances were found, despite a significant oxygen desaturation and a drop in diastolic BP at 4500 m, indicating the beginning of central hypoxia in terms of a functional impairment of the vasomotor center. CONCLUSION: During acute exposure to hypobaric hypoxia, selected cognitive and affective functions mediated by the frontal lobe were preserved. Functional hemispheric asymmetries for emotional processes remained unchanged.     

Persistent memory impairment after high altitude climbing

High altitude climbing without supplementary oxygen is a common sporting practice and athletes have been extensively evaluated with respect to possible brain functional impairment during its performance. Little is known on the contrary about long-term effects of hypoxia on the central nervous system. We evaluated, at sea level, a group of 10 high-altitude climbers with a battery of neuropsychological tests before and 75 days after the ascent. Our results suggest the occurrence of an impairment of memory performance after return to sea-level at least in some subjects, while speech and certain practical abilities were unchanged.     

Brain perfusion abnormalities in chronic obstructive pulmonary disease: comparison with cognitive impairment

OBJECTIVES: To clarify cerebral perfusion distribution and cognitive functions in patients with chronic obstructive pulmonary disease (COPD) according to the hypoxia levels and to assess if there is a relationship between cognitive impairment and cerebral perfusion index. Patients and METHODS: Eight patients with stable hypoxemic COPD (HC), 10 patients with stable nonhypoxemic COPD (NHC), and 10 age-matched healthy volunteers participated in the study. All subjects underwent a complete neuropsychological assessment with the mental deterioration battery (MDB), Wechsler memory scale-revised (WMS-R), color trail test (CCT), and grooved pegboard test (GPT). SPECT examination with Tc-99m HMPAO was performed in all patients and controls. Quantitative analysis was performed by a region of interest (ROI)-based method. RESULTS: The scores of verbal memory, delayed recall and attention were significantly lower in COPD patients (p < 0.01). The scores of other subtests were similar in patients and controls. Comparing NHC patients to HC groups showed that verbal memory was impaired in both groups, but delayed recall and attention scores were significantly worse in HC patients than NHC patients. Perfusion indexes on frontal ROIs in NHC patients and frontal and parietal ROIs in HC patients showed significant decreases. Our scintigraphic findings were correlated with the results of neuropsychological tests. CONCLUSIONS: Our results demonstrate that cerebral perfusion is significantly altered in COPD patients. Hypoxemic patients showed more deterioration in cerebral perfusion and cognitive performance than nonhypoxemic patients. The relationship between decreased perfusion and cognitive impairment and the clinical significance of these results require further studies in larger populations.     

Brain magnetic resonance imaging (MRI) and neurological changes after a single high altitude climb.

PURPOSE: Neurological impairment, mental dysfunction, and brain imaging changes caused by severe hypoxia have been described by several authors. However, the occurrence of transitory, long lasting, or permanent brain damage has been debated. Although climbing to 8000 m is reserved to a small number of climbers, there are hundreds of lowlanders spending relatively short holidays climbing peaks up to 6000 m in the Andes or in the Himalayas. They are usually not well acclimated and often suffer from acute mountain sickness (AMS). The aim of this study was to examine the effect of a single high altitude exposure on the changes in brain MRI and neuropsychological testing in climbers. METHODS: Brain MRI, medical history, and a battery of neuropsychological tests were obtained in eight male climbers between 31 and 48 yr of age a few days before and between 5 and 10 d after returning to sea level following ascent to altitudes of over 6000 m without oxygen. RESULTS: The mean AMS symptom score recorded at 5500 m was three in all climbers, headache being the predominant symptom. CONCLUSION: We did not observe the changes in brain imaging and in neuropsychological testing observed by other authors. The residual central nervous system impairment following return from high altitude was not observed in our study, and the good results in neuropsychological testing were well correlated with the unchanged brain MRI imaging.     

Acute hypoxia and related symptoms on mild exertion at simulated altitudes below 3048 m

INTRODUCTION: Helicopter aircrew have reported features of hypoxia below 3048 m (10,000 ft). The aim of this study was to examine the effect of physical activity below 3048 m on the development of hypoxia. METHODS: Six subjects exercised at 30 W and 60 W for 4 min at sea level, 610 m, 2134 m, and 2743 m (2000 ft, 7000 ft, and 9000 ft). RESULTS: There was an abrupt decrease in Spo2 once physical activity was commenced. This was small at sea level (1%) and 610 m (2.2%), however, the Spo2 fell by 4.3% at 2134 m and 5.5% at 2743 m (to Spo2 88.1% and 85.7%, respectively). Spo2 returned to near-resting values within 3 min of stopping exercise. Symptoms of hypoxia were reported significantly more frequently during activity than rest at each of the altitudes. DISCUSSION: Helicopter aircrew should be aware that physical activity as low as 2134 m can produce hypoxemia and symptoms of hypoxia similar to that which would normally be expected in a person resting at approximately 3658-4572 m (12,000-15,000 ft).     

No evidence of impaired neurocognitive performance in collegiate soccer players

A high incidence of cerebral concussion has been reported among soccer players. We studied whether long-term or chronic neuropsychological dysfunction was present in collegiate soccer players. Two hundred forty subjects from a National Collegiate Athletic Association division I institution were stratified into three groups: soccer athletes (91), nonsoccer athletes (96 women's field hockey, women's lacrosse, and baseball players), and controls (53 college students). Subjects completed a concussion history questionnaire and underwent preseason baseline neuropsychological testing before the start of either the freshman or sophomore year. Data were collected on the results of six neuropsychological tests and from a concussion history questionnaire for number of previous concussions, Scholastic Aptitude Test results, and exposure to soccer and heading. Despite an average of 15.3 seasons of soccer exposure and a higher prevalence of previous concussions, the soccer athletes did not demonstrate impaired neurocognitive function or scholastic aptitude when compared with the nonsoccer athletes or the student nonathletes. Additionally, there was no significant relationship between a history of soccer-related concussion and either neurocognitive performance or scholastic aptitude. Neither participation in soccer nor a history of soccer-related concussions was associated with impaired performance of neurocognitive function in high-level United States soccer players.     

Effect of normobaric hypoxia on sound localization

BACKGROUND: Three-dimensional (3D) audio displays have considerable potential for conveying spatial information in the aviation environment. How reliably these displays will function in that environment will depend in part on the extent to which sound localization is affected by hypoxia. Many aircraft systems operators are routinely exposed to mild hypoxia, and all are at risk of exposure to more severe hypoxia. METHODS: We have examined hypoxia's effect on localization by measuring the localization performance of four subjects exposed to simulated altitudes of 0, 1200, 2400 and 3700 m above sea level for about 30 min. Sounds to be localized were presented from a free-field source at locations covering 360 degrees of azimuth and extending from -47.6 to + 80 degrees elevation. RESULTS: Localization performance was statistically indistinguishable across the altitudes tested. Average localization errors ranged from 12.6 degrees +/- 0.7 SE at 2400 m to 14 degrees +/- 0.84 SE at 0 m. CONCLUSION: The finding that hypoxia induced by exposure to simulated altitudes as high as 3700 m has no effect of sound localization is encouraging with respect to the continued development of 3D audio displays for use in the aviation environment.     

Investigation of the combined effects of bedrest and mild hypoxia

Subjects were exposed to an 8-h mild hypoxia exposure (8000 ft. equivalent, 2438 m) with and without a 28-h period of 6 degrees headdown bedrest. Anticipated responses to the bedrest and the hypoxia were observed. There was no indication that bedrest affected the arterial oxygenation or the oxygen gradient across the lungs of the subjects undergoing mild hypoxia. It is concluded that there is no evidence that would preclude an alveolar O2 pressure as low as 69 torr during contingency spacecraft operation.     

Differential neuropsychological effects of diving to 350 meters

Six divers were compressed on heliox to 350 m. Repeated neuropsychological and neurological tests were conducted during the dive. Averaged increased tremor during the compression was found. Two divers had major EEG changes, while two divers had a completely normal EEG. Memory was most impaired among the cognitive variables. At 350 m there was some normalization in the EEG, and the tremor levels returned to normal. Memory impairment, however, was sustained. Three months later nine divers performed an open sea dive to 300 m. Whereas minor fatigue effects were found for the experimental dive, examinations after the open sea dive indicated more specific cerebral after effects. An increased tremor, reduced hand grip strength and foot tapping speed, lowered autonomic reactivity, and memory problems were found. Some divers had unequivocal asymmetrical plantar responses and unilateral weak abdominal reflexes, accompanied by EEG changes with corresponding laterality. In three of the divers these signs were not present 1 month later.     

Neuropsychological sequelae of 50 Hz magnetic fields

Purpose : The effects of occupational levels of 50 Hz magnetic fields on cognitive function were studied on 30 human volunteers. Materials and methods : The exposure system consisted of Merrit-type modified Helmholtz coils forming a 2 m cube, employing two orthogonal sets of coils producing a 28 μ T (resultant) circularly polarized 50 Hz magnetic field. Subjects sat at a desk within the coils where they undertook a series of verbal and written tests of cognitive function. After these tests were concluded (~30min) subjects were either exposed or sham-exposed to fields (double-blinded) for 50min. A second set of tests (employing alternate versions) was administered 20min from the start of this period. Each subject returned after 7 days to repeat the sequence, but with the opposite field/sham status. Results and conclusions : The majority of the results indicated no significant effect of exposure on cognition. However, verbal recall of a list of 15 words after an interference (the different list) was significantly impaired in the 'field on' condition. This is indicative of a reduction in short-term memory of words. The mean baseline score was somewhat higher in the 'field on' condition. However, this difference is within the parameters of normal variation. The other significant result occurred during performance of a trail-making task (alternating 1-A-2-B-3-C, etc.), with a decrease in performance as a result of exposure to the 50 Hz field. This task requires executive functioning with a working memory load, involving parietal spatial processing coordinated by prefrontal executive processing. In summary, the data are suggestive of detrimental effects on cognitive processes, particularly short-term learning and executive functioning. However, larger sample sizes are required to demonstrate statistically a more specific pattern of cognitive effects.     

Neuropsychological sequelae of 50 Hz magnetic fields

PURPOSE: The effects of occupational levels of 50 Hz magnetic fields on cognitive function were studied on 30 human volunteers. MATERIALS AND METHODS: The exposure system consisted of Merrit-type modified Helmholtz coils forming a 2 m cube, employing two orthogonal sets of coils producing a 28 microT (resultant) circularly polarized 50 Hz magnetic field. Subjects sat at a desk within the coils where they undertook a series of verbal and written tests of cognitive function. After these tests were concluded (approximately 30 min) subjects were either exposed or sham-exposed to fields (double-blinded) for 50 min. A second set of tests (employing alternate versions) was administered 20 min from the start of this period. Each subject returned after 7 days to repeat the sequence, but with the opposite field/sham status. Results and conclusions: The majority of the results indicated no significant effect of exposure on cognition. However, verbal recall of a list of 15 words after an interference (the different list) was significantly impaired in the 'field on' condition. This is indicative of a reduction in short-term memory of words. The mean baseline score was somewhat higher in the 'field on' condition. However, this difference is within the parameters of normal variation. The other significant result occurred during performance of a trail-making task (alternating 1-A-2-B-3-C, etc.), with a decrease in performance as a result of exposure to the 50 Hz field. This task requires executive functioning with a working memory load, involving parietal spatial processing coordinated by prefrontal executive processing. In summary, the data are suggestive of detrimental effects on cognitive processes, particularly short-term learning and executive functioning. However, larger sample sizes are required to demonstrate statistically a more specific pattern of cognitive effects.     

Loss of cabin pressurization in U.S. Naval aircraft: 1969-90.

During the 22-year period from 1 January 1969 to 31 December 1990, there were 205 reported cases of loss of cabin pressure in US Naval aircraft; 21 were crew-initiated and 184 were deemed accidental. The ambient altitudes varied from 10,000 ft (3048 m) to 40,000 ft. (12192 m). The most common reason for crew-initiated decompression was to clear smoke and fumes from the cockpit/cabin (95%). The most common cause for accidental loss of cabin pressure was mechanical (73.37%), with aircraft structural damage accounting for the remaining 26.63%. Serious physiological problems included 1 pneumothorax, 11 cases of Type I decompression sickness, 23 cases of mild to moderate hypoxia with no loss of consciousness, 18 cases of hypoxia with loss of consciousness, and 3 lost aircraft with 4 fatalities due to incapacitation by hypoxia. In addition, 12 ejections were attributed to loss of cockpit pressure. Nine of the ejections were deliberate and three were accidental, caused by wind blast activation of the face curtain. Three aviators lost their lives following ejection and seven aircraft were lost. While the incidence of loss of cabin pressure in Naval aircraft appears low, it none-the-less presents a definite risk to the aircrew. Lectures on the loss of cabin/cockpit pressurization should continue during indoctrination and refresher physiology training.     

Short-term intermittent normobaric hypoxia-haematological, physiological and mental effects

Effects on erythropoiesis and blood pressure as well as physical performance and mental effects were studied in 15 healthy subjects during intermittent exposure to normobaric hypoxia corresponding to either 2000 m (6 persons) or 2700 m (9 persons) above sea level; another group (5 persons) also served as controls at normoxia. The concept "live hightrain low" was used for 10 d consecutively and the exposure to hypoxia was 12 h/d. Blood pO₂ and oxygen saturation were significantly decreased during the 10 d at hypoxia. [Hb] and Hct decreased significantly after 2 d in hypoxia and then returned to pre-study levels. Erythropoietin was significantly elevated in both hypoxia groups during the initial 3–5 d. Reticulocytes were significantly increased during 7 d of hypoxia. Submaximal and maximal oxygen uptake, blood pressure at rest and during exercise and the profile of mood states (POMS test) did not change during the study. In conclusion, intermittent normobaric hypoxia for 10 d resulted in a significant stimulation of erythropoiesis. Staying at normobaric hypoxia may serve as a complement to an ordinary altitude level sojourn.     

Effect of high terrestrial altitude and supplemental oxygen on human performance and mood.

Sustained exposure to high terrestrial altitudes is associated with cognitive decrement, mood changes, and acute mountain sickness (AMS). Such impairment in aviators could be a safety hazard. Thirteen male soldiers, ages 19-24, ascended in 10 min from sea level to 4,300 m (simulated), and remained there 2.5 d. Four times per day, subjects completed a test battery consisting of nine cognitive tests, a mood scale, and an AMS questionnaire. During one test session per day, subjects breathed 35% oxygen instead of ambient air. Analysis revealed transient deficits on altitude day 1 for three cognitive tasks. Most tasks displayed a persistent training effect. Sick subjects' moods were more negative and their performance improvement less. On altitude day 1, oxygen administration improved performance on two cognitive tests and one mood subscale. Following rapid ascent to 4,300 m, performance is most affected during the first 8 h. Individuals affected by AMS tend to improve more slowly in performance and have more negative moods than those who feel well.     

Thyroidal handling of radioiodine in sea level residents exposed to hypobaric hypoxia

In the present investigation thyroidal accumulation of radioiodine and its release were assessed by direct testing of thyroid function using radioactive iodine, in vivo, in sea level residents intermittently exposed to hypobaric hypoxia. Thyroidal accumulation of radioiodine and its turnover were examined daily for 14 days. Twelve healthy human male volunteers were divided into three groups, with an equal number of individuals in each group. A decompression chamber was used to expose each group of subjects to hypoxic conditions at a simulated altitude of 3810 m for 8 h/day for 14 days. An oral dose of 25Ci iodine-131 was administered to each individual of the first group immediately before the initiation of intermittent hypoxia. The second group of subjects received a tracer dose at the beginning of the 4th day of the 14 days, intermittent exposure to hypoxia, while the third group received the tracer dose 1 week after the completion of the exposure. Control studies were carried out on the subjects before they were subjected to the experimental conditions. Thyroidal accumulation of¹³¹I in experimental subjects during the hypoxic state and in the post-hypoxic state was higher than in the control studies. The pattern of accumulation during exposure to hypoxia and in the post-hypoxic state showed multiple peaks of radioactive iodine uptake (PRAIU), a unique feature. The multiple PRAIU by the thyroid in experimental subjects were sharp and of short duration, reflecting an increased rate of¹³I release from the thyroid. Control subjects had a single PRAIU by the thyroid 24 h after the administration of tracer.     

Conjunctival oxygen tension at high altitude

Transconjunctival oxygen tension (PcjO2) was studied using a hypobaric chamber and during mountaineering excursions. Measurements obtained during acute chamber exposures (15-20 min) at sea level, 1829 m (6,000 ft), 3048 m (10,000 ft), 4267 m (14,000 ft) and return to sea level were (means +/- SEM): 60.1 +/- 2.7, 49.1 +/- 1.8, 38.3 +/- 2.4, 27.4 +/- 1.5, and 61.1 +/- 2.8 mm Hg, respectively (n = 13). The ratio of PcjO2 to arterial blood oxygen tension (PaO2) did not change in a consistent manner between sea level and 4267 m; PcjO2 was 74 +/- 6.9% of PaO2. The 16 subjects participating in the mountaineering phase of the study revealed similar means at sea level and 1829 m (57.4 +/- 2.4 and 46.3 +/- 1.9 mm Hg respectively), but a smaller decrement was observed at 3048 m (43.0 +/- 1.6 mm Hg). The difference between mountain and chamber values may be accounted for by a partial acclimatization to altitude brought about by longer exposure on the mountain excursions. A comparison between PcjO2 and transcutaneous oxygen tension during the chamber study suggests that a greater precision and sensitivity is obtained with measurement of oxygen tension at the conjunctival site. PcjO2 measurement is a non-invasive reflection of PaO2 which is suitable for continuous monitoring during hypoxia studies.     

Are effort measures sensitive to cognitive impairment?

The basic premise of symptom validity tests (SVTs) is that appropriate effort can be assessed because the designs of SVT measures are thought to be insensitive to all but the most extreme forms of impairment of memory. In patients with mild traumatic brain injury in particular, it is thought that failure on effort measures consistently reflects poor effort or even conscious exaggeration of symptoms. This study examines the issue of SVT failure as a reflection of cognitive impairment and/or neuropsychiatric impairment by presenting cases of three patients who were given full neuropsychological batteries but in each case failed the Word Memory Test (WMT), a verbal recognition SVT measure. One patient who failed the WMT was probably in the early stages of dementia. The WMT fit the "Genuine Memory Impaired Profile". Two mild traumatic brain injury patients failed the WMT but their patterns of performance suggested that cognitive deficits influenced WMT performance. In determining the validity of neuropsychological test data in the individual case, it is recommended that the examiner consider whether cognitive impairment could affect performance on effort measures and the recommended cut score. Also, it is recommended that examiners use multiple indicators of effort.