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At least 919 records · Page 51Linked to original sources
PubMed2006

Gastric emptying effects of dietary fiber during 8 hours at two simulated cabin altitudes.

BACKGROUND: In a questionnaire survey, long-distance flying staff of a charter airline reported significantly more dyspeptic symptoms than did short-haul crewmember and ground personnel (belching: 57% vs. 37%, bloating: 51% vs. 36%). To elucidate the reason for increased frequency of gastrointestinal symptoms during long-distance flights, we investigated the effects of altitude and diet on gastric emptying, cardiovascular function, and bodily complaints. METHODS: In a 2 x 2 repeated measurement design we simulated an 8-h flight in a hypobaric chamber in 16 healthy men subjected to 2 meal conditions (high fiber vs. low fiber) on separate days, and assigned to either a flight altitude of 2500 m (8200 ft) or 1000 m (3280 ft). The subjects were blinded toward altitude. Heart rate and gastrointestinal symptoms were taken every hour, and gastric emptying was assessed by 13C-octanoic acid breath-test. In a separate experiment, we examined the effect of the two test meals (2 g vs. 20 g of fiber) in 30 healthy men under conventional laboratory conditions and found no significant differences. RESULTS: At an altitude of 2500 m, heart rate was significantly increased independent of the dietary condition. Gastric emptying (T1/2) was significantly delayed at 2500 m (8200 ft) when a high-fiber meal was given (146.3 +/- 58.4 min low fiber vs. 193.9 +/- 54.3 min high fiber). The symptom score for gastric distension (mean: 1.33 +/- 0.3 vs. mean: 1.07 +/- 0.15) and bloating (mean: 1.82 +/- 0.47 vs. mean: 1.34 +/- 0.35) were also significantly increased at 2500 m for the high-fiber meal compared with the low-fiber meal. CONCLUSIONS: Flight altitude is a physiological load. In combination with a high-fiber diet, this induces significant delays in gastric emptying that may explain symptoms of cabin and cockpit crew and passengers on long-distance flights.

Adult↗
PubMed2006

Effect of altitude on seasonal flight activity of Rhagoletis cerasi flies (Diptera: Tephritidae).

The effect of altitudinal variation on the seasonal flight activity of Rhagoletis cerasi (Linnaeus) flies was evaluated along an altitudinal gradient from 150 to 1170 m in Mount Uludag, northwestern Turkey. The predicted dates of fly emergence, flight duration and dates of 5%, 50% and 95% cumulative fly catches at various altitudes were estimated from a degree-day model. Degree-day predictions were compared with those obtained from observations made with yellow sticky traps. The observed and predicted dates of appearance of adults were delayed by 1.4 and 2.0 days for every 100 m increase in altitude, respectively. The delay in phenology events was less at high altitudes than postulated by Hopkins' bioclimatic law, whether observed or predicted. The average absolute difference in predicted and observed dates of cumulative percentage catch of adults was 4.9 and 3.0 days in 1997 and 1998, respectively, but these differences were not significant. Prolonged flight activity was predicted and observed at higher altitudes, but the flight period lasted significantly longer than predicted. The observed flight period varied from 29 to 43 days in 1997 and from 36 to 52 days in 1998 between the lowest and highest altitude on the transect. Altitudinal variation between geographically close locations should be taken into account to properly time monitoring activities and hence to manage R. cerasi populations more effectively.

Altitude↗
PubMed1991

[Structural adaptation of the placenta in natural hypoxia at moderate and high altitude].

26 placentas of Kirghiz women from the town of Narin situated at the altitude of 2020 m above the sea level (moderate altitude), 22 placentas of women from Murgab (3600-3800 m above the sea level, high altitude) and 22 placentas of Frunze city (760 m, control) women were studied by means of organo--and stereometry using a standardized schema. A body weight decrease of newborns and placentas was established in the rating: control--moderate--high altitude. "Miniaturization" of foetuses is a response to the natural deficiency of oxygen in the atmospheric air. Moderate hypoxia has a training effect on the placenta while hypoxia associated with high altitude is followed by its dysadaptation. The role of placenta in the mechanisms of the foetus development inhibition under the conditions of natural hypoxia is suggested.

Adaptation, Physiological↗
PubMed1991

Medical consequences of acute exposure to high altitude.

People who ascend rapidly to altitudes greater than 3,000 meters (10,000 ft) may become ill; rarely, some may die from an inability to adapt to hypoxia. Age, pre-existing cardiopulmonary or hematologic disease, and the rate and degree of ascent are known to limit man's adaptation to high altitudes. Other factors, such as blunted hypoxic respiratory drive and sublinical disease of the pulmonary vascular bed are probably also important. Pre-exposure with acetozolamide (Diamox) helps, but once symptoms of high altitude pulmonary edema (HAPE) occur, supplemental oxygen and rapid descent to lower altitudes are the only known remedies. In view of the steady increase in the number of people who work and play at high altitudes, physicians must understand the pathophysiologic mechanisms involved in order to treat properly and to counsel patients.

Altitude Sickness↗
PubMed1990

Effects of burnrate, wood species, altitude, and stove type on woodstove emissions.

During the winter of 1986-87, the U.S. Environmental Protection Agency (EPA) conducted an emission measurement program in Boise, ID, as part of the Integrated Air Cancer Project (IACP). This program was designed to identify the potential mutagenic impact of residential wood burning on ambient and indoor air. One facet of this field sampling effort involved obtaining emission samples from chimneys serving wood burning appliances in Boise. As a companion to the field source sampling, a parallel project was undertaken in an instrumented woodstove test laboratory to quantify woodstove emissions during operations typical of Boise usage. Two woodstoves were operated in a test laboratory over a range of burnrates, burning either eastern oak or white pine from the Boise, ID, area. A conventional stove, manufactured in the Boise area, was tested at altitudes of 90 and 825 m. A catalytic stove was tested only at the high altitude facility. All emission tests were started with kindling a fire in a cold stove using black and white newsprint. Emissions were collected using the wood stove dilution sampling system (WSDSS) for a continuous period of about 8 hours, encompassing start-up and several wood additions. The results showed wide variability probably due primarily to the difficulty in duplicating conditions during start-up. Total WSDSS emissions showed the expected inverse correlations with burnrate for the conventional stove and nearly flat for the catalytic stove. While there appeared to be little or no correlation of total WSDSS emissions with altitude, the sum of the 16 polynuclear aromatic hydrocarbons (PAHs) quantified showed an inverse correlation with altitude: higher PAH emissions at the lower altitude.

Air Pollutants↗
PubMed1990

Vascular response of retinal arteries and veins to acute hypoxia of 8,000, 10,000, 12,500, and 15,000 feet of simulated altitude.

Computerized scanning microdensitometry of fundus photographs was used to study the effect of acute hypoxia on vessel diameters of 238 retinal arteries and 227 veins in 40 men aged 18-23 years. Fundus photography was performed at sea level and at simulated altitudes in a low-pressure chamber, randomly selecting 10 men to each of four altitudes--8,000, 10,000, 12,500, and 15,000 ft (2,400, 3,000, 3,800, and 4,500 m). After 15 min of hypoxic exposure, the caliber of small arteries (less than 75 microns) increased 4% (p less than 0.01) and that of large arteries (greater than or equal to 75 microns) 7% (p less than 0.05), already at 8,000 ft (2,400 m). The caliber of large veins did not change until an increase of 6% (p less than 0.01) was observed at 15,000 ft (4,500 m). Although large arteries increased 7% (p less than 0.05) and 8% (p less than 0.01) in diameter at 10,000 ft (3,000 m) and 15,000 ft and small veins 9% (p less than 0.05) and 12% (p less than 0.01) at the same altitudes, respectively, no change was observed at 12,500 ft (3,800 m). Thus, the dilating effect of hypobaric hypoxia was nonlinear from sea level to 15,000 ft of simulated altitude. As an overall response to the four simulated altitudes the vasodilation was negatively correlated to the vessel diameter at sea level (r = -0.20) in both arteries and veins (p less than 0.01). The variability of hypoxic vascular response was as great within different parts of individual retinas as between different retinas.

Adolescent↗
PubMed1975

Analysis of gases and pH of blood at altitude.

The accuracy of a system for measuring pH and gas in blood in a changing-altitude environment was studied. No problems were encountered when arterial blood was measured, provided the instrument was properly calibrated. Failure to calibrate to the correct altitude settings caused major variations in measuring oxygen levels in blood. Standard gases used for calibrating were measured at altitude without recalibrating the system; approximately 80% of the oxygen and 90% of the carbon dioxide partial-pressure values were within 3 mm Hg of their expected value. More deviation occurred for Po2 values as the altitude increased. Frequently, the Po2 electrode malfunctioned, particularly above 8000 ft (2438 m). The Corning Blood Gas System, which was used in this study, was capable of making accurate determinations of gas in blood if properly operated and calibrated to specific altitude levels.

Altitude↗
PubMed1989

Reticuloendothelial phagocytic activity in high-altitude acclimatized rats.

Experiments were undertaken with rats to determine the effects of chronic exposure to a simulated high altitude of 5,000 m on phagocytic activity of the reticuloendothelial system (RES). Phagocytic index (K) was determined by measuring the rate of blood clearance of colloidal carbon given intravenously. K value of the chronically altitude exposed rats was found to be greater than that of the sea level control animals (p less than 0.02), indicating that acclimatization to high altitude stimulated the RES phagocytosis. On analysis of the weights of the liver and spleen, the corrected phagocytic index (alpha) of the high altitude-acclimatized rats was also found to be higher than that of the sea level control animals (p less than 0.05) while the weights of the liver and spleen expressed in percent body weight were not affected by high altitude exposure. The increased number of carbon-containing Kupffer cells in the liver and the increased phagocytic indices (both K and alpha values) suggested that most of the increase in RES phagocytic activity was due to increased RES tissue activity per unit mass of tissue rather than tissue hypertrophy.

Acclimatization↗
PubMed1989

Increase in Hb-O2-affinity at moderate altitude (2000 m) in patients on maintenance hemodialysis.

Oxygen transport by erythrocytes was studied in eight patients on maintenance hemodialysis before, during and after a 2-week stay at an altitude of 2000 m. Dialysis was continued at that altitude. In all tests, blood samples were collected one or two days following hemodialysis. Pre-altitude tests: The patients exhibited anemia (hemoglobin concentration, Hb = 97.4 +/- 17 g/l). Due to an elevated red cell 2,3-diphosphoglycerate concentration (2,3-DPG) and mild metabolic acidosis, elevated standard and in vivo P50 values (pO2 at 50% oxygen saturation of hemoglobin, sO2) were measured. Altitude: Upon ascent, arterial pO2 decreased from 82 +/- 4 torr to about 60 torr, sO2 was lowered by 5%. After 2 weeks sojourn, pO2 and sO2 increased towards normal values. In contrast to healthy subjects, dialysis patients developed respiratory alkalosis (blood pH: +0.074) upon ascent. This caused a significant shift to the left of the oxygen dissociation curve (ODC), indicated by lowered in vivo P50-values (P50,vv,-2 torr). Red cell 2,3-DPG, P50,st (P50 at a blood pH = 7.4 and pCO2 = 40 torr), hemoglobin concentration and hematocrit showed a high day-to-day variability and did not change because of the altitude exposure. We interpret the increase of the oxygen affinity of hemoglobin in patients with renal anemia as beneficial, as it favors oxygen loading of hemoglobin in the lung during exposure to a hypoxic environment.

2,3-Diphosphoglycerate↗
PubMed1989

[A comparison of cyclists' time records according to altitude and materials used].

The purpose of this study was to re-assess the energy cost of track cycling in order (a) to compare the one-hour world records at sea-level and altitude with classical bicycles or with modern bicycles including aerodynamic components, and (b) to estimate the optimal altitude to set a new one-hour world record. Energy cost of track cycling with a classical or aerodynamic bicycle was estimated according to the equation developed by di Prampero et al. (1979) using data from Davies (1980) for the rolling resistance coefficient and from Gross et al. (1983) for the aerodynamic resistance coefficient for each type of bicycle. When compared to the classical track-bicycle, and to the bicycle studied by di Prampero et al. (1979), the aerodynamic track-bicycle reduces the resistance coefficient by 11.7 and 16.9% respectively. According to these estimations the cyclists sustain 87-95% of maximal aerobic power over one hour, which is a likely value for a 60 min exercise period for top-level athletes. When the reduction of air density and of maximal aerobic power with altitude are taken into account, equivalences between performances achieved at different altitudes and with the two types of track-bicycles, can be computed. The best overall performance appears to be the current one-hour record at sea-level using an aerodynamic bicycle (Moser: 50.644 km.h-1). This performance is equivalent to 53.5 km.h-1 in Mexico City (2230 m), 54.4 km.h-1 in La Paz (3417 m) and 54.5 km.h-1 at 3843 m (472 mmHg), which would be the optimal altitude to set the record.

Air Pressure↗
PubMed1987

Increased affinity to substrate in sarcolemmal ATPases from hearts acclimatized to high altitude hypoxia.

It has been well documented that acclimatization to chronic high altitude hypoxia involves a complex of adaptation changes which are capable of protecting the myocardium in diverse situations such as in acute hypoxia, coronary occlusion-induced ischaemia or isoprenaline-induced calcium overload. Since many of the former changes concern membrane functions, namely those of the sarcolemma, the activities and kinetic properties of sarcolemmal Mg2+-, Ca2+- and (Na+ + K+)-ATPase were investigated in right heart ventricles of rats acclimatized to intermittent high altitude hypoxia simulated in a barochamber. In the course of the experiment, the ventricles were subjected to a special anoxic test in vitro. The high altitude induced increase in cardiac tolerance to anoxia was not accompanied by any preservation of the sarcolemmal ATPase activities. On the contrary, membrane preparations obtained from the right ventricles of hearts acclimatized to high altitude exhibited significantly lower ATPase activities in comparison to non-acclimatized controls. The significant diminution in Km values of ATPases established in acclimatized hearts points to an increase in the affinity of their active sites to ATP. The latter effect is in agreement with the lowered rate of both the decrease in ATPase activities and the reduction of contractility in acclimatized hearts during the anoxic test, as well as with the considerably improved postanoxic reparability of contractions as compared to the controls. It is being concluded that the sarcolemmal changes at the level of ATPases involved in ionic transport processes represent an integral part of the adaptation complex to chronic high altitude hypoxia.

Acclimatization↗
PubMed1989

High-altitude mountaineering and brain function: neuropsychological testing of members of a Mount Everest expedition.

Concern has been raised regarding the possibility that hypoxic conditions encountered during high-altitude mountaineering may have lasting harmful effects on the human brain. Members of an expedition to Mount Everest completed a series of neuropsychological tests before and after the expedition. Exposure to altitudes above 7,200 m was limited to a maximum of four consecutive nights, separated by rest periods at lower altitudes. No significant decline in performance was observed on any test. The subjects also completed a short series of tests at different altitudes during the expedition. No significant deterioration was observed at altitudes up to 7,500 m. There do not appear to be lasting harmful effects on brain function under these conditions.

Altitude↗
PubMedDate not supplied

[Hemorrhage and hemostasis in guinea pigs irradiated under high altitude conditions].

Hemorrhagic intensity, hemostasis and blood vessel wall resistance to mechanical effects were studied in guinea-pigs exposed to whole-body irradiation (3.0 Gy). The animals were irradiated at low altitude (760 m above sea level) and at high altitude (3200 m above sea level) after 1 and 31 day of adaptation. It was demonstrated that hemorrhagic intensity in both groups of guinea-pigs irradiated at high altitude was significantly reduced in comparison with that at low altitude. The decrease of radiation-induced hemorrhages at high altitude is associated with less severe changes in thrombopoiesis, blood vessel wall and blood coagulation.

Altitude↗
PubMed1986

[Dynamics of various characteristics of the sympathetic ganglia of animals subjected to chemical sympathectomy at high altitude].

The effect of high altitude hypoxia on the sympathetic nervous system was studied on desympathized rats. The degree of the sympathetic ganglion neurons destruction and catecholamine fluorescence were determined. The investigation showed an increase of catecholamine fluorescence in sympathetic ganglia in high altitude adaptation. 30-day administration of sympatholytic guanethidine at high altitude results in destruction of less ganglion neurons than at low altitude. At high altitude the rate of fluorescence of biogenic amines in unaffected cells remains high. After partial desympathization (7 days), the rate of neuron destruction diminishes and biogenic amines fluorescence increases along with the duration of preliminary adaptation.

Adaptation, Physiological↗
PubMed1985

High-altitude pulmonary edema with absent right pulmonary artery.

High-altitude pulmonary edema potentially is fatal. Adults with unilateral absence of a right pulmonary artery are particularly susceptible to high-altitude pulmonary edema. The occurrence of high-altitude pulmonary edema was documented in a child with congenital absence of the right pulmonary artery. Improvement occurred only upon descent to low altitude. Physicians should be aware of this life-threatening condition in children ascending to high altitude, particularly in individuals with unilateral absence of a pulmonary artery.

Acute Disease↗
PubMed1985

Analyses of maximum cardiopulmonary performance during exposure to acute hypoxia at simulated altitude--sea level to 5000 meters (760-404 mm Hg).

The maximum cardiopulmonary performance of seven healthy male subjects was studied repeatedly in graded hypoxia at ambient pressures ranging from 760 to 404 mm Hg (sea level to 5000 m of simulated altitude). Using this approach it has been possible to not only establish a reproducible value for VO2max, but to determine an equation which may be used to predict the VO2 at altitude for healthy, unacclimatized males exercising to exhaustion. Moreover, we have attempted to explain the limits to pulmonary ventilation at decreasing levels of PO2 by comparing a given VO2max (STPD) to the corresponding VEmax (BTPS), showing that any further increase in the latter is impossible when a certain level of altitude has been reached. Finally, our series of experiments indicates that the HRmax falls at altitude. Although statistically significant, this decrement is not conspicuous. Thus, when used with the VO2max to calculate the number of ml of O2 consumed per beat of the heart, the "oxygen pulse" turns out to be more sensitive to the fall in VO2max at altitude than to the corresponding decrease in the HRmax.

Adult↗
PubMed1974

Fibrinolytic activity at high altitude and sodium acetate buffer.

At high altitude there is a tendency for fibrinolytic activity to be enhanced depending, perhaps, on the duration of exposure and this seems to be a protective mechanism against the development of high altitude pulmonary oedema which is associated with diminished fibrinolytic activity. The fibrinolytic response at high altitude seems to be fluctuated during the process of acclimatisation though being maintained at a plateau higher than that in the plains. It apparently results from hypoxic stress but more likely reflects the physiological response to the hypercoagulable state at high altitude. As clot lysis times in high altitude pulmonary oedema are unusually prolonged an attempt at shortening their observation in the test system is desirable. Sodium acetate, 0.12 M solution with pH 7.4 as a diluent in the low temperature technique of dilute clot lysis time is potentially effective to accelerate the lysis time by approximately 33% compared to phosphate buffer solution of similar pH and molarity. Also the end point of disintegration of clot is more abrupt and sharply defined. Sodium acetate buffer can advantageously replace phosphate buffer as a diluent in this technique.

Acetates↗
PubMed1979

High altitude medical problems.

Increased travel to high altitude areas by mountaineers and nonclimbing tourists has emphasized the clinical problems associated with rapid ascent. Acute mountain sickness affects most sojourners at elevations above 10,000 feet. Symptoms are usually worse on the second or third day after arrival. Gradual ascent, spending one to three days at an intermediate altitude, and the use of acetazolamide (Diamox) will prevent or ameliorate symptoms in most instances. Serious and potentially fatal problems, such as high altitude pulmonary edema or cerebral edema, occur in approximately 0.5 percent to 1.0 percent of visitors to elevations above 10,000 feet-especially with heavy physical exertion on arrival, such as climbing or skiing. Early recognition, high flow oxygen therapy and prompt descent are crucially important in management. Our knowledge of the causes of these and other high altitude problems, such as retinal hemorrhage, systemic edema and pulmonary hypertension, is still incomplete. Even less is known of the effect of high altitudes on medical conditions common at sea level or on the action of commonly used drugs.

Adolescent↗