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PubMed2004

Irreversible subcortical dementia following high altitude illness.

In this report, we present the cases of two 63-year-old women who developed high altitude cerebral edema complicated by the occurrence of permanent neuropsychiatric sequelae. They shared a similar clinical course, in that both developed disturbance of consciousness shortly after their arrival at Cuzco, Peru (3500 m), and both developed persistent neuropsychiatric symptoms after resolution of the acute illness. Interestingly, in case 2 there was a 1-month lucid interval between remission of high altitude illness and occurrence of the irreversible neuropsychiatric sequelae. Brain computerized tomography in case 1 and brain magnetic resonance imaging in case 2 disclosed lesions in the globus pallidus bilaterally, suggesting that the neuropsychiatric symptoms in these patients were manifestations of subcortical dementia. The development of high altitude illness was considered to be attributable to mild restrictive lung impairment in case 1 and to a deficient ventilatory response to hypoxia in case 2. It must therefore be borne in mind that irreversible subcortical dementia may be associated with high altitude cerebral edema.

Acute Disease↗
PubMed2005

Neutral endopeptidase null mice are less susceptible to high altitude-induced pulmonary vascular leak.

Hypoxia increases pulmonary vascular leak, which is regulated in part by neutral endopeptidase (NEP). NEP is a cell-surface metalloprotease that degrades several vasoactive peptides, including endothelin-1 (ET-1) and atrial natriuretic peptide (ANP). We therefore hypothesized that NEP attenuates high altitude-induced pulmonary vascular leak. Wild-type and NEP null mice were exposed to a simulated high altitude (HA) of 6,728 m (22,000 ft; P(B) = 328 mmHg) or remained at the relatively low altitude (LA) of 1,500 m (4,920 ft; P(B) = 640 mmHg) for 24 h. Plasma ANP and ET-1 concentrations, right ventricular pressure (P(RV)), and indexes of lung injury were recorded. At HA, lung wet weight-to-body weight increased in all animals, but was greatest in the NEP wild-type mice. Vascular leak, as measured by Evans blue dye, increased only in the NEP wild-type mice at HA. P(RV) increased in both genotypes at HA. Plasma ANP concentrations increased at HA in both genotypes, but plasma ET-1 concentrations were elevated only in the NEP null mice at HA. Correlations between lung wet weight-to-body weight versus P(RV) (r = 0.56; p = 0.0136) and ANP versus P(RV) (r = -0.54; p = 0.02) were noted. We conclude that NEP null mice exposed to HA have a greater rise in ANP versus ET-1 plasma concentration, decreased pulmonary vascular pressure, and reduced high altitude-induced pulmonary vascular leak.

Altitude Sickness↗
PubMed1998

Intakes of high fat and high carbohydrate foods by humans increased with exposure to increasing altitude during an expedition to Mt. Everest.

The objectives of the study were to determine total energy intakes, distribution of energy derived from the macronutrients, and the effects of increasing altitudes on energy and macronutrient consumption during exposure to high altitudes. High fat, low carbohydrate diets (35% and 50% of energy, respectively) or low fat, high carbohydrate diets (20% and 65% of energy, respectively) were provided to two groups of subjects for a 3-wk period. Groups then consumed the alternate diet for 3 wk, followed by a return to the original diet for the remaining 3 wk of the study. Free choice of individual items and amounts within each diet was permitted. Intake of food and fluid was determined by means of monitored entries in daily food records. Five subjects remained at Base Camp (5300 m) and 10 subjects climbed to altitudes up to and including the summit of Mt. Everest (8848 m). Subjects consumed an average of 10.22 +/- 4.57 MJ/d (2442 +/- 1092 kcal) energy while at Base Camp, with climbers consuming significantly more than Base Camp personnel [11.89 +/- 4. 88 vs. 7.87 +/- 2.98 MJ/d (2841 +/- 1167 vs. 1881 +/- 713 kcal/d), P </= 0.0001]. There was a significant decline in energy consumption at increasing altitudes (P = 0.022), but no shift in distribution of energy provided from fat, carbohydrate or protein (P > 0.05). Contrary to previous reports, subjects in this study did not shift their food selections away from the high fat items towards high carbohydrate items.

Adult↗
PubMed1999

Oxidative stress in humans during work at moderate altitude.

Increased oxidative stress has been associated with work at high altitude; however, it is not known whether oxidative stress is a significant problem at moderate altitudes. The oxidative stress indicators, breath pentane (BP), 8-hydroxydeoxyguanosine (8-OHdG), oxygen radical absorption capacity (ORAC), 4-hydroxynonenal (4-HNE), malondialdehyde (MDA), and lipid peroxides (LPO) were measured in breath, blood and urine samples of U.S. Marines engaged in moderate altitude ( approximately 3000 m) cold weather field training. The test subjects were divided into a placebo and four antioxidant supplement groups (n = 15/group) and received the following supplements for 28 d: 1) vitamin E, 440 alpha-tocopherol equivalents (alpha-TE); 2) vitamin A, 2000 retinol equivalents (RE) of beta-carotene; 3) vitamin C, 500 mg ascorbic acid; 4) a mixture of 440 alpha-TE, 2000 RE of beta-carotene, 500 mg ascorbic acid, 100 microg selenium and 30 mg zinc daily. Strenuous work ( approximately 23 MJ/d) in cold weather at moderate altitude was accompanied by increases in several indicators of oxidative stress that were not effectively controlled by conventional antioxidant supplements. The group receiving the antioxidant mixture exhibited lower BP (P < 0. 05) compared with those receiving single antioxidant supplements; however, not all markers of oxidative stress responded like BP. Because these markers did not respond in the same manner, it is important to include markers from more than one source to assess the effect of supplemental dietary antioxidants.

Adult↗
PubMed2006

Explorative genome scan to detect candidate loci for adaptation along a gradient of altitude in the common frog (Rana temporaria).

Today, with the rapid development of population genomics, the genetic basis of adaptation can be unraveled directly at the genome level, without any prerequisites about the selectively advantageous genes or traits. For nonmodel species, it is now possible to screen many markers randomly scattered across the genome and to distinguish between the neutral genetic background and outlier loci displaying an atypical behavior (e.g., a higher differentiation between populations). This study investigated the genetic frame of adaptation to a gradient of altitude in the common frog (Rana temporaria) by means of a genome scan based on 392 amplified fragment length polymorphism markers. Using two outlier detection methods never applied to dominant data so far, we sought for loci with a genetic differentiation diverging from neutral expectations when comparing populations from different altitudes. All the detected loci were sorted out according to their most probable cause for outlier behavior and classified as false positives, outliers due to local effects, or outliers associated with altitude. Altogether, eight good candidate loci were identified as potentially involved in adaptation to altitude because they were picked out in several independent interaltitude comparisons. This result illustrated the potential of genome-wide surveys to reveal selection signatures along selection gradients, where the association between environmental variables and fitness-related traits may be complex and/or cryptic. In this article, we also underlined the need for confirmation of the selection footprints for the outlier loci. Finally, we provided some preliminary insights into the genetic basis of adaptation along an altitudinal cline in the common frog.

Adaptation, Physiological↗
PubMed2001

Effect of altitude training on the peroxidation and antioxidant enzymes in sportsmen.

PURPOSE: The aim of this work was an evaluation of the influence of physical exercise in high-altitude conditions (about 2000 m above sea level) on thiobarbituric acid reactive substances (TBARS) and superoxide dismutase (SOD) and catalase (CAT) activities in 10 kayakers and 10 rowers. METHODS: During their training, the sportsmen performed different kinds of static and dynamic efforts. The blood samples were taken from the cubital vein on the control day at low altitude and at high altitude, and on the 4th, 10th, and 18th days of the training camp before and after exercise. The TBARS and lactic acid concentrations in blood plasma and SOD and CAT activities in erythrocytes were measured. RESULTS: A statistically significant increase of SOD and CAT activities in erythrocytes after exercise on the 4th, 10th, and 18th days of training was found. The TBARS concentration in erythrocytes decreased in a statistically significant way after the end of the 10th day of exercise (P < 0.01), and on 18th day it more than doubled (P < 0.001) when preexercise values were compared with postexercise values of each day. A statistically significant increase of TBARS concentration in blood plasma was observed only after the end of exercise on the 10th day-using the same comparison as above. A statistically significant increased lactic acid concentration in blood plasma was noticed both on 4th or 18th days of training. CONCLUSIONS: The results obtained show the increasing generation of oxygen-derived free radicals and the compensatory intensification of SOD and CAT activities after training in altitude (high mountain) conditions.

Adult↗
PubMed1994

Intraocular gas and low-altitude air flight.

BACKGROUND: Air travel has been contraindicated for patients with intraocular gas on the basis of experimental studies, because of the risk of elevated intraocular pressure during atmospheric depressurization. METHODS: A clinical study of gas bubble volume and intraocular pressure rise during a low-altitude air flight was performed on a patient with a gas bubble volume of 65% after retinal detachment surgery. RESULTS: The flight was well tolerated, and the patient did not experience pain or decreased vision. The maximum altitude of the flight was 3,000. Maximum intraocular pressure was 49 mmHg, with a baseline of 16 mmHg. Increases in intraocular pressure and bubble volume were instantaneous with changes in altitude. Implications for pressurized flight situations are discussed. CONCLUSION: Low-altitude air flight can be well tolerated by patients with intraocular gas, even with a relatively large vitreous cavity gas fill. Decisions about when to let patients with intraocular gas fly should be made on an case-to-case basis, depending on ocular factors and the planned flight characteristics.

Aerospace Medicine↗
PubMed1984

Failure of long-term acclimatization in smokers moving to high altitude.

It was found that several foreign experts recruited for an irrigation project in southern Peru could not cope with their work at an altitude of 3 200 m. When we analyzed the haematological acclimatization to high altitude in 109 adult males, we found that the moderate differences in haematocrit level (0.9) and haemoglobin concentration (0.2 g/100 ml) between male smokers and non-smokers at low altitude were almost quadrupled at 3 200 m height. The haemoglobin concentration increased in both groups during the first month, after which it remained constant. Of 51 Swedish employees, 25 smokers and 26 non-smokers, 14 were obliged to terminate their contracts. All 10 who had failed to cope with their work for other than purely medical reasons were smokers. This group of smoking men also had an overconsumption of alcohol. We therefore conclude that life style determines long-term acclimatization to high altitude.

Adaptation, Physiological↗
PubMed2005

Adaptive changes in cardiac myosin heavy chain and creatine kinase isozymic profiles in rats native of altitude.

AIM: The developmental changes in the myosin heavy chain (MHC) profile, creatine kinase (CK) and lactate dehydrogenase (LDH) activities and isozyme expression occurring in heart were examined in rats born and living at altitude (La Paz, Bolivia, 3700 m, H(LP)) for 16 generations. We hypothesized that H(LP) rats respond differently to hypoxia than rats born and living at sea level, and secondarily exposed to altitude during 3 weeks (H(3W)). METHODS: The cardiac expression of MHC, CK and LDH was studied in left (LV) and right ventricle (RV) of H(LP) animals 1, 2, 3, 4 and 18 weeks after birth, and compared with control normoxic (C groups) and H(3W) animals. RESULTS: Rats secondarily exposed to hypoxia showed a lower alpha-MHC content than C or H(LP) rats in both LV and RV, 3 weeks after birth (P < 0.05), consistent with a delay in the maturation of the heart contractile phenotype. A global increase in the total CK activity was observed in the LV of H(3W) animals in comparison with C rats (P < 0.05), while no change was reported in H(LP) animals. In both ventricles, M-LDH activity was higher in H(3W) than in H(LP) and C rats (P < 0.05). The relative amount of alpha-MHC decreased by 20% in RV of 18-week-old H(LP) and H(3W) rats in comparison with C animals, consistent with the hypoxia-induced ventricular enlargement (P < 0.01). An increased activity of the foetal B-CK subunit was observed in both LV and RV of H(3W) rats in comparison with H(LP) and C animals (P < 0.05). CONCLUSION: This study demonstrates that rats native and living at altitude for several generations present some features relevant to genetic selection to altitude.

Adaptation, Physiological↗
PubMed2004

Problems with capnography at high altitude.

The aim of this study was to investigate why capnographs malfunction at high altitude, in order to suggest ways of improving instrument reliability. Four machines were decompressed to simulated high altitude and measurements taken. The study showed that the reduced air density at altitude has effects upon the pump, causing difficulty in entraining gas, and that high altitude has additional effects upon calibration of the instruments.

Altitude↗
PubMedDate not supplied

Hormone profiles at high altitude in man.

Altitude induced alterations in circulatory levels of PRL, LH, FSH and testosterone were studied in seven eugonadal men at sea level (SL), during their stay at high altitude (HA, 3500 m) and a week after return to SL. The mean plasma PRL level at SL was 5.83 +/- 1.7 SE ng/ml. On day one and seven of arrival at HA, the PRL values of 7.81 +/- 1.81 and 9.21 +/- 1.64 ng/ml respectively were not significantly different (p greater than 0.05) than the initial SL values. However, on day 18 of stay at HA, PRL levels were significantly increased (p less than 0.01) to 17.68 +/- 1.82 ng/ml and returned to initial SL values within seven days of return to SL. A significant decrease (p less than 0.01) in LH and testosterone was observed on seventh day of stay at HA and the decreased levels were maintained till day 18 of observations. Plasma testosterone returned to the initial SL values within a week of return to SL, whereas LH levels remained significantly lower (p less than 0.01). The FSH levels did not show any significant change during their stay at HA or after return to SL. These observations suggest that exposure to altitude is associated with hyperprolactenemia and an impaired pituitary gonadal function. The decreased levels of LH and testosterone at HA could either be due to hypoxic stress per se or secondary to altitude induced hyperprolactenemia.

Adult↗
PubMed2005

Symptomatic portal system thrombosis in soldiers due to extended stay at extreme altitude.

BACKGROUND: With induction of Indian Army to heights over 5000 m above mean sealevel (MSL), several new complications of long-term stay at extreme altitude have come to light. The authors' experience with soldiers who developed symptomatic portal system thrombosis (SPST) is described here. METHODS: Clinical data were prospectively collected between April 1998 and April 2003, on all patients hospitalized for SPST from high-altitude areas (HAA, >3000 m above MSL) and those from non-high-altitude areas (NHAA). Site of thrombosis was confirmed by imaging and included splenic, portal, superior mesenteric, or inferior mesenteric vein thrombosis. Patients were investigated to rule out known predisposing factors and prothrombotic conditions. RESULTS: A total of 37 cases of SPST were seen during the study period, of which 26 were from HAA. Mean age of cases from HAA was 27 +/- 4.6 years and all were male. Mean stay at high altitude was 11.7 +/- 6.2 months. First symptom was pain in abdomen in almost all the cases, later followed by gastrointestinal bleeding and fever in 14 each, and vomiting in 19. Clinical examination showed ascites (81%), splenomegaly (76.9%), and hepatomegaly (69.2%). Diagnosis was made by imaging scans (23 cases) and on surgery in three cases. A known prothrombotic state was detected in five cases from HAA and in eight cases from NHAA (P < or = 0.01). Ultrasound Doppler scan picked up collaterals as early as 12-45 days after onset of symptoms. CONCLUSIONS: Extended stay at HAA may be a risk factor for development of symptomatic portal system thrombosis.

Adult↗
PubMed2001

The re-establishment of the normal blood lactate response to exercise in humans after prolonged acclimatization to altitude.

1. One to five weeks of chronic exposure to hypoxia has been shown to reduce peak blood lactate concentration compared to acute exposure to hypoxia during exercise, the high altitude 'lactate paradox'. However, we hypothesize that a sufficiently long exposure to hypoxia would result in a blood lactate and net lactate release from the active leg to an extent similar to that observed in acute hypoxia, independent of work intensity. 2. Six Danish lowlanders (25-26 years) were studied during graded incremental bicycle exercise under four conditions: at sea level breathing either ambient air (0 m normoxia) or a low-oxygen gas mixture (10 % O(2) in N(2), 0 m acute hypoxia) and after 9 weeks of acclimatization to 5260 m breathing either ambient air (5260 m chronic hypoxia) or a normoxic gas mixture (47 % O(2) in N(2), 5260 m acute normoxia). In addition, one-leg knee-extensor exercise was performed during 5260 m chronic hypoxia and 5260 m acute normoxia. 3. During incremental bicycle exercise, the arterial lactate concentrations were similar at sub-maximal work at 0 m acute hypoxia and 5260 m chronic hypoxia but higher compared to both 0 m normoxia and 5260 m acute normoxia. However, peak lactate concentration was similar under all conditions (10.0 +/- 1.3, 10.7 +/- 2.0, 10.9 +/- 2.3 and 11.0 +/- 1.0 mmol l(-1)) at 0 m normoxia, 0 m acute hypoxia, 5260 m chronic hypoxia and 5260 m acute normoxia, respectively. Despite a similar lactate concentration at sub-maximal and maximal workload, the net lactate release from the leg was lower during 0 m acute hypoxia (peak 8.4 +/- 1.6 mmol min(-1)) than at 5260 m chronic hypoxia (peak 12.8 +/- 2.2 mmol min(-1)). The same was observed for 0 m normoxia (peak 8.9 +/- 2.0 mmol min(-1)) compared to 5260 m acute normoxia (peak 12.6 +/- 3.6 mmol min(-1)). Exercise after acclimatization with a small muscle mass (one-leg knee-extensor) elicited similar lactate concentrations (peak 4.4 +/- 0.2 vs. 3.9 +/- 0.3 mmol l(-1)) and net lactate release (peak 16.4 +/- 1.8 vs. 14.3 mmol l(-1)) from the active leg at 5260 m chronic hypoxia and 5260 m acute normoxia. 4. In conclusion, in lowlanders acclimatized for 9 weeks to an altitude of 5260 m, the arterial lactate concentration was similar at 0 m acute hypoxia and 5260 m chronic hypoxia. The net lactate release from the active leg was higher at 5260 m chronic hypoxia compared to 0 m acute hypoxia, implying an enhanced lactate utilization with prolonged acclimatization to altitude. The present study clearly shows the absence of a lactate paradox in lowlanders sufficiently acclimatized to altitude.

Acclimatization↗
PubMed2001

Maternal plasma glucose at high altitude.

OBJECTIVE: To compare plasma glucose in pregnant women living at very high altitude; pregnant women living at sea level; non-pregnant women living at very high altitude; and non-pregnant women living at sea level. DESIGN: Cross-sectional study. PARTICIPANTS: Ninety-four pregnant women attending for routine antenatal care at 8-42 weeks of gestation in Cerro de Pasco, Peru which is situated 4370 m above sea level; 122 pregnant women in Lima, which is at sea level; 22 non-pregnant women in Cerro de Pasco; and 31 non-pregnant women in Lima. METHODS: Plasma glucose concentrations were measured in samples obtained from the antecubital vein between 8 am and 10 am after an overnight period of fasting for at least 10 hours. RESULTS: Fasting plasma glucose was lower in women at high altitude than in those at sea level, and in both groups the level was lower in pregnant women than in non-pregnant controls. The body mass index was not significantly different between all four groups, and it did not have a significant independent contribution in explaining the variance in fasting plasma glucose. CONCLUSION: Women native at high altitude have lower plasma glucose concentrations before and during pregnancy than those at sea level.

Adult↗
PubMed1990

Limiting factors for exercise at extreme altitudes.

Man can only survive and do work in the severe oxygen deprivation of great altitudes by an enormous increase in ventilation which has the advantage of defending the alveolar PO2 against the reduced inspired PO2. Nevertheless the arterial PO2 on the summit of Mt Everest at rest is less than 30 Torr, and it decreases with exercise because of diffusion limitation within the lung. One of the consequences of the hyperventilation is that the marked respiratory alkalosis increases the oxygen affinity of the haemoglobin and assists in loading of oxygen by the pulmonary capillary. Although ventilation is greatly increased, it is a paradox that cardiac output for a given work level is the same in acclimatized subjects at high altitude as at sea level. Stroke volume is reduced but not because of impaired myocardial contractility because this is preserved up to extreme altitudes. Indeed the normal myocardium is one of the few tissues whose function is unimpaired by the very severe hypoxia. There is evidence that oxygen delivery to exercising muscle is diffusion limited along the pathway between the peripheral capillary and the mitochondria. At the altitude of Mt Everest, maximal oxygen uptake is reduced to 20-25% of its sea level value, and it is exquisitely sensitive to barometric pressure. Seasonal variations of barometric pressure affect the ability of man to reach the summit without supplementary oxygen. In spite of the greatly reduced aerobic capacity, anaerobiosis is greatly curtailed, and it is predicted that above 7500 m, there is no rise in blood lactate on exercise. The paradoxically low lactate is possibly related to plasma bicarbonate depletion.

Air Pressure↗
PubMed1995

Aerobic exercise capacity at sea level and at altitude in Kenyan boys, junior and senior runners compared with Scandinavian runners.

The aim of this study was to characterize Kenyan runners in regard to their oxygen uptake and blood and ammonia responses when running. Untrained Kenyan boys (14.2 +/- 0.2 years) and Scandinavian runners were included for comparison. The studies were performed at altitude (approximately 2.000 m.a.s.l.) and, for several Kenyan and Scandinavian runners, at sea level as well. At altitude sedentary adolescent Kenyan boys had a mean maximal oxygen uptake (VO2max) of 47 (44-51) ml.kg-1.min-1, whereas similarly aged boys regularly walking or running but not training for competition reached above 62 (58-71) ml.kg-1.min-1 in VO2max. Kenyan runners in active training had 68 +/- 1.4 ml.kg-1.min-1 at altitude and 79.9 +/- 1.4 ml.kg-1.min-1 at sea level, with individuals reaching 85 ml.kg-1.min-1. The best Scandinavian runners were not significantly different from the Kenyan runners in VO2max both at altitude and at sea level, but none of the Scandinavians reached as high individual values as observed for some Kenyan runners. The running efficiency, determined as the oxygen cost at a given running speed, was less in the Kenyan runners, and the difference became more pronounced when body weight was expressed in ml.kg-0.75 min-1. Blood lactate concentration was in general lower in the Kenyan than in the Scandinavian runners, and the Kenyans also had extremely low ammonia accumulation in the blood even at very high exercise intensities. It is concluded that it is the physical activity during childhood, combined with intense training as teenagers that brings about the high VO2max observed in some Kenyan runners. Their high aerobic capacity, as well as their good running economy, makes them such superior runners. In addition, their low blood lactate and ammonia accumulation in blood when running may also be contributing factors.

Adolescent↗
PubMed1999

Trends in the workload of the two high altitude aid posts in the Nepal Himalayas.

BACKGROUND: Acute mountain sickness (AMS), High altitude pulmonary edema (HAPE) and High Altitude Cerebral Edema (HACE) are well known problems in the high altitude region of the Nepal Himalayas. To assess the proportion of AMS, HAPE, and HACE from 1983 to 1995 in the Himalaya Rescue Association (HRA) aid posts' patients at the Everest (Pheriche 4,243 m) and Annapurna (Manang 3,499 m) regions, the two most popular trekking areas in the Himalayas. A retrospective study was conducted at the HRA medical aid posts in Manang (3,499 m) and Pheriche (4,243 m) in the Himalayas, where 4,655 trekkers (tourists, mostly Caucasians) and 4,792 Nepalis (mostly porters and villagers) were seen at the two high-altitude clinics from 1983 to 1995, for a variety of medical problems, including AMS. METHODS: The number of trekking permits issued for entering the two most popular regions in the Himalayas was calculated and referenced to the proportion of trekkers with medical conditions. Well established guidelines like the Lake Louise Diagnostic Criteria were used in the assessment of AMS, HAPE and HACE. Linear regression analyses were performed on data collected from the two aid posts to determine the effect of time on each variable. For comparison between the aid posts, angular transformation (arcsine) and analysis of variance (ANOVA) were performed on all proportional (incidence) data. RESULTS: Approximately 20% of all visitors (Nepali plus trekkers) who visited the higher Pheriche aid post were diagnosed with AMS compared to around 6% at the lower Manang aid post. There was a linear increase over time in the number of trekkers entering the Everest (r=0.904, p<.001) and the Annapurna (r=0.887, p<.001) regions. The proportion of trekker patients with any medical condition visiting the two HRA aid posts at Manang and Pheriche, expressed as a function of the total number of trekkers entering the Everest and Annapurna regions, was not significantly different between Pheriche (average 4%) and Manang (average 1%). However, the proportion of AMS, HAPE and HACE in patients (Nepali plus trekkers) to the aid posts was greater in those visiting the higher Pheriche aid post compared to the lower Manang aid post (f=56.74, n=13; p<. 001). Importantly, only the proportion of AMS (r=0.568; p<.05) and not HAPE or HACE increased over time in Pheriche, alongside an unchanged proportion of trekker patients, amongst all Pheriche aid post patients. There was no increase of AMS, HAPE or HACE in Manang. CONCLUSIONS: HAPE and HACE are the life-threatening forms of AMS and although there is a linear increase of trekkers entering the Himalayas in Nepal, the findings revealed that HAPE and HACE have not increased over time. One possible explanation may be that awareness drives by organizations like the Himalayan Rescue Association may be effective in preventing the severe forms of AMS.

Altitude Sickness↗
PubMedDate not supplied

A statistical estimator of the spatial distribution of the water-table altitude.

An algorithm was designed to statistically estimate the areal distribution of water-table altitude. The altitude of the water table was bounded below by the minimum water-table surface and above by the land surface. Using lake elevations and stream stages, and interpolating between lakes and streams, the minimum water-table surface was generated. A multiple linear regression among the minimum water-table altitude, the differerence between land-surface and minimum water-table altitudes, and the water-level measurements from surficial aquifier system wells resulted in a consistently high correlation for all groups of physiographic regions in Florida. A simple linear regression between land-surface and water-level measurements resulted in a root-mean-square residual of 4.23 m, with residuals ranging from -8.78 to 41.54 m. A simple linear regression between the minimum water table and the water-level measurements resulted in a root-mean-square residual of 1.45 m, with residuals ranging from -7.39 to 4.10 m. The application of the multiple linear regression presented herein resulted in a root-mean-square residual of 1.05 m, with residuals ranging from -5.24 to 5.63 m. Results from complete and partial F tests rejected the hypothesis of eliminating any of the regressors in the multiple linear regression presented in this study.

Algorithms↗