Operation Everest II: pulmonary gas exchange during a simulated ascent of Mt. Everest

Eight normal subjects were decompressed to barometric pressure (PB) = 240 Torr over 40 days. The ventilation-perfusion (VA/Q) distribution was estimated at rest and during exercise [up to 80-90% maximal O2 uptake (VO2 max)] by the multiple inert gas elimination technique at sea level and PB = 428, 347, 282, and 240 Torr. The dispersion of the blood flow distribution increased by 64% from rest to 281 W, at both sea level and at PB = 428 Torr (heaviest exercise 215 W). At PB = 347 Torr, the increase was 79% (rest to 159 W); at PB = 282 Torr, the increase was 112% (108 W); and at PB = 240 Torr, the increase was 9% (60 W). There was no significant correlation between the dispersion and cardiac output, ventilation, or pulmonary arterial wedge pressure, but there was a correlation between the dispersion and mean pulmonary arterial pressure (r = 0.49, P = 0.02). When abnormal, the VA/Q pattern generally had perfusion in lung units of zero or near zero VA/Q combined with units of normal VA/Q. Alveolar-end-capillary diffusion limitation of O2 uptake (VO2) was observed at VO2 greater than 3 l/min at sea level, greater than 1-2 l/min VO2 at PB = 428 and 347 Torr, and at higher altitudes, at VO2 less than or equal to 1 l/min. These results show variable but increasing VA/Q mismatch with long-term exposure to both altitude and exercise. The VA/Q pattern and relationship to pulmonary arterial pressure are both compatible with alveolar interstitial edema as the primary cause of inequality.     

Ophthalmodynamometry for ICP prediction and pilot test on Mt. Everest

Background  

A recent development in non-invasive techniques to predict intracranial pressure (ICP) termed venous ophthalmodynamometry (vODM) has made measurements in absolute units possible. However, there has been little progress to show utility in the clinic or field. One important application would be to predict changes in actual ICP during adaptive responses to physiologic stress such as hypoxia. A causal relationship between raised intracranial pressure and acute mountain sickness (AMS) is suspected. Several MRI studies report that modest physiologic increases in cerebral volume, from swelling, normally accompany subacute ascent to simulated high altitudes.     

Surpassing Mt. Everest: extreme flight performance of alpine bumble-bees

Animal flight at altitude involves substantial aerodynamic and physiological challenges. Hovering at high elevations is particularly demanding from the dual perspectives of lift and power output; nevertheless, some volant insects reside and fly at elevations in excess of 4000 m. Here, we demonstrate that alpine bumble-bees possess substantial aerodynamic reserves, and can sustain hovering flight under hypobaria at effective elevations in excess of 9000 m, i.e. higher than Mt. Everest. Modulation of stroke amplitude and not wingbeat frequency is the primary means of compensation for overcoming the aerodynamic challenge. The presence of such excess capacity in a high-altitude bumble-bee is surprising and suggests intermittent behavioural demands for extreme flight performance supplemental to routine foraging.     

Operation Everest II: plasma lipid and hormonal responses during a simulated ascent of Mt. Everest

To examine the effect of hypobaric hypoxia on plasma lipid profiles, fasting blood samples were collected from six men (21-31 yr) at 760 Torr and periodically during a 40-day exposure to decreasing barometric pressure culminating in a final ambient pressure of 282 Torr. Preascent plasma total cholesterol concentration ([TC]) was decreased by 25% after the 40-day exposure (P less than 0.01). High-density lipoprotein concentrations ([HDL-C]) decreased 32% (P less than 0.001) with no alteration in the TC-to-HDL-C weight ratio. Plasma triglyceride concentration increased twofold during this period (P less than 0.01). There were no significant differences in fasting plasma free fatty acid concentrations or free fatty acid-to-albumin molar ratio throughout the study. Fasting plasma insulin levels were increased approximately twofold with no significant changes in glucagon concentration or the insulin-to-glucagon molar ratio. Plasma norepinephrine concentrations were increased threefold on reaching 282 Torr (P less than 0.01), with no significant changes in plasma epinephrine concentrations. Mean energy intake (kcal/day) decreased 42%, whereas mean body weights decreased by 8.9 +/- 0.8% (P less than 0.01) with exposure. Increased concentrations of insulin may lead to increased hepatic production of triglyceride-rich lipoproteins, thus eliciting metabolic changes independent of weight loss and dietary intake.     

Barometric pressures on Mt. Everest: new data and physiological significance.

Barometric pressures (PB) near the summit of Mt. Everest (altitude 8, 848 m) are of great physiological interest because the partial pressure of oxygen is very near the limit for human survival. Until recently, the only direct measurement on the summit was 253 Torr, which was obtained in October 1981, but, despite being only one data point, this value has been used by several investigators. Recently, two new studies were carried out. In May 1997, another direct measurement on the summit was within approximately 1 Torr of 253 Torr, and meteorologic data recorded at the same time from weather balloons also agreed closely. In the summer of 1998, over 2,000 measurements were transmitted from a barometer placed on the South Col (altitude 7,986 m). The mean PB values during May, June, July, and August were 284, 285, 286, and 287 Torr, respectively, and there was close agreement with the PB-altitude (h) relationship determined from the 1981 data. The PB values are well predicted from the equation PB = exp (6.63268 - 0.1112 h - 0.00149 h2), where h is in kilometers. The conclusion is that on days when the mountain is usually climbed, during May and October, the summit pressure is 251-253 Torr.     

Energy expenditure cutting supercane.

VO2 VE, and heart rates (fH) were measured in 61 Colombian sugarcane cutters while harvesting cane in the AM and PM and in the laboratory during a VO2max test. Productivity and sweat rates were also measured in the field. The subjects had an estimated dietary intake of 2,970 kcal/day, which was lower than calculated daily energy expenditure. During the work measurements the VO2 was 1.5 1/min, VE 48 1/min, and fH 135 beats/min; there were no differences between AM and PM values. The subjects sustained about 35% of VO2max during the 8 h workday, but worked at 57% of VO2max during the tests. Measured energy cost was 7.4 +/- 1.5 kcal/min during the workday. Sweat rates were higher PM than AM (5 KG/8 h day). Grouping of the men according to productivity demonstrated that taller, heavier men were better producers and had lower calculated heart rates at VO2 1.51/min. Efficiency of cane cutting was higher (9%) PM.     

喜马拉雅山珠峰段蚂蚁物种的分布格局

为了揭示喜马拉雅山蚂蚁物种的分布规律,采用样地调查法研究了珠峰段蚂蚁物种的分布格局。合计发现蚁科Formicidae 3亚科13属23种,蚂蚁物种的分布主要受气温因素制约。大多数物种分布范围狭窄,对高山环境的适应性较弱,适应性强的物种较少。珠峰段北坡分布有4个物种,山间谷地仅分布有3个物种,而南坡分布有22个物种。蚂蚁物种对植被类型的选择受气温和植物丰富度的共同影响,在8类生境中,中山阔叶林的物种最丰富。在9类场所中,以石下筑巢和地表觅食的物种最丰富。西藏盘腹蚁Aphaenogaster tibetana Donisthorpe是珠峰段分布范围最广、占据生境类型最多的物种,其分布上限高达4980 m,是目前已知西藏境内分布最高的物种。     

A strategy for determining arterial blood gases on the summit of Mt. Everest

Background  

Climbers on the summit of Mt. Everest are exposed to extreme hypoxia, and the physiological implications are of great interest. Inferences have been made from alveolar gas samples collected on the summit, but arterial blood samples would give critical information. We propose a plan to insert an arterial catheter at an altitude of 8000 m, take blood samples above this using an automatic sampler, store the samples in glass syringes in an ice-water slurry, and analyze them lower on the mountain 4 to 6 hours later.     

Asynchronous recruitment history of Abies spectabilis along an altitudinal gradient in the Mt. Everest region

Aims Forest growth and recruitment and their relationships to climate are complex. The aims of our study are (i) to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt. Everest region and (ii) to identify the climatic factors that are responsible to the observed patterns in tree growth and recruitment.Methods Four plots, each 30 × 60 m in size, were established from the lower to upper limits of the eastern Himalayan fir forest in Dingjie County of the Mt. Everest Nature Reserve, China. Dendrochronological techniques were applied to obtain information about the radial growth and age of the trees in the plots. Correlation analysis was used to identify the relationships between radial growth and recruitment of trees and climatic variables, i.e. monthly mean temperature and Palmer Drought Severity Index (PDSI). The population age structure was analyzed to investigate the recruitment history.Important findings The timberline plot was characterized by significant tree recruitments in the recent three decades and sporadic recruitments in earlier periods. The other three plots showed recruitment pulses during 1880–1910 in Plot 3?700 m, during 1870–80 and 1920–30 in Plot 3?520 m and during 1900–40 in Plot 3?410 m. The recruitment of fir trees in the timberline was sensitive to summer (June–September) temperatures, but it was mainly controlled by episodic disturbances in lower altitudes. Fir radial growth in the upper two plots was positively correlated with previous winter and current August temperature. Fir radial growth at the two lower plots was positively correlated with PDSI from previous September to current September.     

Changes in muscle proteomics in the course of the Caudwell Research Expedition to Mt. Everest

This study employed differential proteomic and immunoassay techniques to elucidate the biochemical mechanisms utilized by human muscle (vastus lateralis) in response to high altitude hypoxia exposure. Two groups of subjects, participating in a medical research expedition (A, n = 5, 19d at 5300 m altitude; B, n = 6, 66d up to 8848 m) underwent a ≈ 30% drop of muscular creatine kinase and of glycolytic enzymes abundance. Protein abundance of most enzymes of the tricarboxylic acid cycle and oxidative phosphorylation was reduced both in A and, particularly, in B. Restriction of α‐ketoglutarate toward succinyl‐CoA resulted in increased prolyl hydroxylase 2 and glutamine synthetase. Both A and B were characterized by a reduction of elongation factor 2alpha, controlling protein translation, and by an increase of heat shock cognate 71 kDa protein involved in chaperone‐mediated autophagy. Increased protein levels of catalase and biliverdin reductase occurred in A alongside a decrement of voltage‐dependent anion channels 1 and 2 and of myosin‐binding protein C, suggesting damage to the sarcomeric structures. This study suggests that during acclimatization to hypobaric hypoxia the muscle behaves as a producer of substrates activating a metabolic reprogramming able to support anaplerotically the tricarboxylic acid cycle, to control protein translation, to prevent energy expenditure and to activate chaperone‐mediated autophagy.     

Energy expenditure during bicycling

This study was designed to measure the O2 uptake (VO2) of cyclists while they rode outdoors at speeds from 32 to 40 km/h. Regression analyses of data from 92 trials using the same wheels, tires, and tire pressure with the cyclists riding in their preferred gear and in an aerodynamic position indicated the best equation (r = 0.84) to estimate VO2 in liters per minute VO2 = -4.50 + 0.17 rider speed + 0.052 wind speed + 0.022 rider weight where rider and wind speed are expressed in kilometers per hour and rider weight in kilograms. Following another rider closely, i.e., drafting, at 32 km/h reduced VO2 by 18 +/- 11%; the benefit of drafting a single rider at 37 and 40 km/h was greater (27 +/- 8%) than that at 32 km/h. Drafting one, two, or four riders in a line at 40 km/h resulted in the same reduction in VO2 (27 +/- 7%). Riding at 40 km/h at the back of a group of eight riders reduced VO2 by significantly more (39 +/- 6%) than drafting one, two, or four riders in a line; drafting a vehicle at 40 km/h resulted in the greatest decrease in VO2 (62 +/- 6%). VO2 was also 7 +/- 4% lower when the cyclists were riding an aerodynamic bicycle. An aerodynamic set of wheels with a reduced number of spokes and one set of disk wheels were the only wheels to reduce VO2 significantly while the cyclists were riding a conventional racing bicycle at 40 km/h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Microrefugia and Shifts of Hippophae tibetana (Elaeagnaceae) on the North Side of Mt. Qomolangma (Mt. Everest) during the Last 25000 Years

Microrefugia at high altitudes or high latitudes are thought to play an important role in the post-glacial colonization of species. However, how populations in such microrefugia have responded to climate changes in alternating cold glacial and warm interglacial stages remain unclear. Here we present evidence to indicate the Rongbuk Valley of the Mt. Qomolangma (Mt. Everest) area, the highest region on earth, had microrefugia for Hippophae tibetana and discuss how this low shrub was adapted to the extreme climate fluctuations of the last 25,000 years by shifts. By integrating geological, glaciological, meteorological, and genetic information, we found that the Rongbuk Valley was not only a glacial microrefugium but also an interglacial microrefugium for H. tibetana: the former was located on the riverbank below 4800 m above sea level (asl) or lower area and the latter at ∼5000 m asl. Our results show that after the Last Glacial Maximum (LGM), H. tibetana in the valley has undergone upward and downward migrations around ∼5000 m driven by climate fluctuations and the population in the glacial microrefugium has suffered extinction or extreme contraction. Moreover, with the rise of temperature in the last four decades, the upper limit of H. tibetana has shifted at least 30 m upward. Combining population history and recent range shift of this species is important in predicting the fate of this endemic species to future climate changes.     

Energy expenditure during simulated rowing

Metabolic function was measured by open-circuit spirometry for 310 competitive oarsmen during and following a 6-min maximal rowing ergometer exercise. Aerobic and anaerobic energy contributions to exercise were estimated by calculating exercise O2 cost and O2 debt.O2 debt was measured for 30 min of recovery using oxygen consumption (Vo2) during light rowing as the base line. Venous blood lactates were analyzed at rest and at 5 and 30 min of recovery. Maximal ventilation volumes ranged from 175 to 22l 1/min while Vo2 max values averaged 5,950 ml/min and 67.6 ml/kg min. Maximal venous blood lactates ranged from 126 to 240 mg/100 ml. Average O2 debt equaled 13.4 liters. The total energy cost for simulated rowing was calculated at 221.5 kcal assuming 5 kcal/l O2 with aerobic metabolism contributing 70% to the total energy released and anaerobiosis providing the remaining 30%. Vo2 values for each minute of exercise reflect a severe steady state since oarsmen work at 96-98% of maximal aerobic capacity. O2 debt and lactate measurements attest to the severity of exercise and dominance of anaerobic metabolism during early stages of work.