Decrease In Barometric Pressure Research Articles

Sleep loss effects on physiological and cognitive responses to systemic environmental hypoxia.

In the course of their missions or training, alpinists, but also mountain combat forces and mountain security services, professional miners, aircrew, aircraft and glider pilots and helicopter crews are regularly exposed to altitude without oxygen supplementation. At altitude, humans are exposed to systemic environmental hypoxia induced by the decrease in barometric pressure (<1,013hPa) which decreases the inspired partial pressure of oxygen (PIO2), while the oxygen fraction is constant (equal to approximately 20.9%). Effects of altitude on humans occur gradually and depend on the duration of exposure and the altitude level. From 1,500m altitude (response threshold), several adaptive responses offset the effects of hypoxia, involving the respiratory and the cardiovascular systems, and the oxygen transport capacity of the blood. Fatigue and cognitive and sensory disorders are usually observed from 2,500m (threshold of prolonged hypoxia). Above 3,500m (the threshold for disorders), the effects are not completely compensated and maladaptive responses occur and individuals develop altitude headache or acute altitude illness [Acute Mountain Sickness (AMS)]. The magnitude of effects varies considerably between different physiological systems and exhibits significant inter-individual variability. In addition to comorbidities, the factors of vulnerability are still little known. They can be constitutive (genetic) or circumstantial (sleep deprivation, fatigue, speed of ascent.). In particular, sleep loss, a condition that is often encountered in real-life settings, could have an impact on the physiological and cognitive responses to hypoxia. In this review, we report the current state of knowledge on the impact of sleep loss on responses to environmental hypoxia in humans, with the aim of identifying possible consequences for AMS risk and cognition, as well as the value of behavioral and non-pharmacological countermeasures.

Foraging activity of leaf‐cutter ants is affected by barometric pressure

AbstractAmong all activities displayed by ant colonies, searching for food is essential for all individuals survival. However, many external activities are hazardous or restrictive for the entire society. Even though leaf‐cutter ants are highly successful insects, they are subject to extreme aspects of foraging, as raindrops and wind. Although recruitment and food exploitation are known to change with temperature and humidity, barometric pressure changes and how they affect ant behavior remain unknown. We aimed to determine how an increase or decrease in barometric pressure might modify foraging strategies of the leaf‐cutter ant Atta sexdens compared to steady pressure. The first modification observed in the workers behavior was the scouts greater promptness in leaving the nest when the barometric pressure decreased. Regard to the foragers, there was no difference in the number of individuals recruited for collecting leaves. However, it was cut and brought into the nest 1.5 and 2 times more leaves during the pressure drop, respectively. The reason for this foraging efficiency as a whole was ultimately the sum of the efficiency of each forager. The shifts in behavior, therefore, could be related to the indirect consequences of a pressure decrease, such as rainfall and strong winds, both strong constraints on ants on a trail. This is the first report of barometric pressure affecting the behavior of a social insect under controlled conditions.

Barometric-pumping controls fugitive gas emissions from a vadose zone natural gas release

Subsurface natural gas release from leaking oil and gas wells is a major environmental concern. Gas migration can cause aquifer contamination, explosive conditions in soil gas, and greenhouse gas emissions. Gas migration is controlled by complex interacting processes, thus constraining the distribution and magnitude of “fugitive gas” emissions remains a challenge. We simulated wellbore leakage in the vadose zone through a controlled release experiment and demonstrate that fugitive gas emissions can be directly influenced by barometric pressure changes. Decreases in barometric-pressure led to surface gas breakthroughs (>20-fold increase in <24 hours), even in the presence of low-permeability surficial soils. Current monitoring strategies do not consider the effect of barometric pressure changes on gas migration and may not provide adequate estimates of fugitive gas emissions. Frequent or continuous monitoring is needed to accurately detect and quantify fugitive gas emissions at oil and gas sites with a deep water table.

Transcriptional profiling in the livers of rats after hypobaric hypoxia exposure.

Ascent to high altitude feels uncomfortable in part because of a decreased partial pressure of oxygen due to the decrease in barometric pressure. The molecular mechanisms causing injury in liver tissue after exposure to a hypoxic environment are widely unknown. The liver must physiologically and metabolically change to improve tolerance to altitude-induced hypoxia. Since the liver is the largest metabolic organ and regulates many physiological and metabolic processes, it plays an important part in high altitude adaptation. The cellular response to hypoxia results in changes in the gene expression profile. The present study explores these changes in a rat model. To comprehensively investigate the gene expression and physiological changes under hypobaric hypoxia, we used genome-wide transcription profiling. Little is known about the genome-wide transcriptional response to acute and chronic hypobaric hypoxia in the livers of rats. In this study, we carried out RNA-Sequencing (RNA-Seq) of liver tissue from rats in three groups, normal control rats (L), rats exposed to acute hypobaric hypoxia for 2 weeks (W2L) and rats chronically exposed to hypobaric hypoxia for 4 weeks (W4L), to explore the transcriptional profile of acute and chronic mountain sickness in a mammal under a controlled time-course. We identified 497 differentially expressed genes between the three groups. A principal component analysis revealed large differences between the acute and chronic hypobaric hypoxia groups compared with the control group. Several immune-related and metabolic pathways, such as cytokine-cytokine receptor interaction and galactose metabolism, were highly enriched in the KEGG pathway analysis. Similar results were found in the Gene Ontology analysis. Cogena analysis showed that the immune-related pathways were mainly upregulated and enriched in the acute hypobaric hypoxia group.

Lowering barometric pressure induces neuronal activation in the superior vestibular nucleus in mice.

Weather changes accompanied by decreases in barometric pressure are suggested to trigger meteoropathy, i.e., weather-related pain. We previously reported that neuropathic pain-related behavior in rats is aggravated by lowering barometric pressure, and that this effect is abolished by inner ear lesions. These results suggest that mechanisms that increase vestibular neuronal activity may parallel those that contribute to meteoropathy generation. However, it remains unknown whether changes in barometric pressure activate vestibular neuronal activity. To address this issue, we used expression of c-Fos protein as a marker for neural activation. Male and female mice were placed in a climatic chamber, and the barometric pressure was lowered by 40 hPa, from 1013 hPa, for 50 min (LP stimulation). The total number of c-Fos-positive cells in the vestibular nuclei was counted bilaterally after LP stimulation. We also video-recorded mouse behaviors and calculated the total activity score during the LP stimulation. LP stimulation resulted in significant c-Fos expression in the superior vestibular nucleus (SuVe) of male and female mice. There was no effect of LP stimulation on the total activity score. These data show that distinct neurons in the SuVe respond to LP stimulation. Similar mechanisms may contribute to the generation of meteoropathy in humans.

Continuous monitoring of soil CO2 flux at Aso volcano, Japan: the influence of environmental parameters on diffuse degassing

Continuous measurements of soil CO2 flux are useful for understanding degassing processes and for monitoring volcanic activities. Recent studies at many volcanoes have revealed that soil CO2 flux variations are significantly influenced by environmental parameters as well as volcanic processes. In this study, we conducted continuous monitoring of soil CO2 flux in the flank of Nakadake cone, Aso volcano, Japan, from January 2016 to November 2017. The results of our observations during an active period before and after a large phreatomagmatic eruption on 8 October 2016 and during a calm period from 2017 showed variations in soil CO2 flux due to oscillations in environmental parameters. Excluding these variations from the raw time series by multivariate linear regression analysis, the time series of soil CO2 flux presented some anomalous peaks in both the active and calm periods. Careful comparison of the anomalous peaks with the environmental parameters revealed that most of the anomalous peaks were likely due to an increase in wind speed and/or a decrease in barometric pressure. However, the anomaly after the 8 October 2016 eruption was not completely explicable by the variations in the environmental parameters and coincided with increases in seismic amplitude and plume SO2 flux. This anomaly was possibly attributed to an increase in magmatic CO2 flux. These findings emphasized the importance of careful statistical treatment of the soil CO2 flux data after excluding the influences of the environmental parameters at each measurement site. These statistical treatments will contribute to a better understanding of the degassing processes and monitoring of volcanic activities, including phreatic or phreatomagmatic eruptions.

The Influence of Weak Geomagnetic Disturbances on the Rat Cardiovascular System under Natural and Shielded Geomagnetic Field Conditions

Abstract—This work was aimed at studying the effects of weak geomagnetic disturbances on systolic blood pressure, the R–R interval, the low-frequency and high-frequency components, and its ratio of heart rate variability spectrum under natural and shielded geomagnetic field conditions. All tests were performed with male Wistar rats placed in simulation and shielded chambers. In the simulation chamber, significant shifts in the parameters under study were observed on the days of geomagnetic disturbances: an increase in systolic blood pressure, as well as in the ratio of low- to high frequency components of the heart rate variability spectrum. In the shielded chamber, the parameters were not considerably different under quiet and disturbed geomagnetic field. In addition, in the stimulation chamber, the value of the mean daily barometric pressure was inversely correlated with systolic blood pressure; this relationship was significantly weakened under shielded geomagnetic field conditions. It was concluded that weak geomagnetic disturbances affect cardiovascular and autonomic nervous system functions. The authors hypothesize that the enhanced effect of a slight decrease in barometric pressure on systolic blood pressure in the natural geomagnetic field could be associated with the effect of geomagnetic activity on the mechanisms of blood oxygenation.

Impact of Hypobaric Hypoxia on Repeated Sprint Performance

PURPOSE: To investigate the impact of hypobaric hypoxia on sprint performance and metabolic recovery after repeated sprint bouts. METHODS: Six men (20±3yrs; 77±13kg; 181±12cm) performed three familiarization sprint sessions (decrease learning effects) at sea level (SL). Sprint sessions consisted of repeated high intensity exercise bouts (30 sec all-out sprint: 1min rest) on a self-propelled treadmill. Following familiarization, volunteers performed one sprint session per week at 250m, 2000m, and 3000m (random order) carrying a load (30% body mass) in a hypobaric chamber. Sprints were repeated until peak velocity decreased by 20% of that established during familiarization. Pre- and post sprint arterial oxygen saturation (SaO2), heart rate (HR), rate of perceived exertion (RPE), and blood lactate (Hla) were measured. RESULTS: There was no difference (P > 0.05) in the # of sprints completed at SL, 250m, 2000m, and 3000m (5±3, 5±2, 4±2, 4±1, respectively). Post sprint session SaO2 values were lower (P < 0.05) as altitude increased (96±2%, 250m; 90±5%, 2000m; 82±4%, 3000m). Post session HR, RPE, and blood Hla were elevated (P < 0.05) vs. pre- session values, but were not different (P > 0.05) among altitudes. CONCLUSIONS: While repeated sprint performance was not affected due to hypobaric hypoxia, post session SaO2 was reduced with each decrease in barometric pressure. It appears that the lower SaO2 values associated with the simulated altitudes tested did not alter the aerobic recovery of anaerobic pathways used during sprinting as the SaO2 values were not low enough to be a limiting factor. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.

Shamals and climate variability in the Northern Arabian/Persian Gulf from 1973 to 2012

ABSTRACTThis paper presents key results from analysis of surface meteorological observations collected in the Northern Arabian/Persian Gulf (N Gulf; Kuwait, Bahrain, and NE Saudi Arabia), which spans a 40‐years period (1973–2012). The first part of this study analyzes climate variability in the N Gulf, and relates them to teleconnection patterns (North Atlantic Oscillation, El Nino Southern Oscillation, and Indian Ocean Dipole). Results of the analysis indicate that during the study period the climate in the region experienced a general trend of increase in temperature (0.8°C), decrease in barometric pressure (1 mbar), reduction in humidity (6%), and decrease in visibility (9%). Significant correlations were found between the three teleconnection patterns and the meteorological conditions suggesting that seasonal variabilities in air temperature, barometric pressure, and precipitation are closely related to the teleconnection patterns. The second part of this study examines the 40‐year variability of Shamal events (strong NW winds that commonly generate significant dust storms). The data suggests that on average Shamal events occur at a rate of 10 events year–1 with 85% of the events occurring during the summer and winter. The number of these events has increased in the past 14 years of the study period. These events resulted in abrupt changes in meteorological conditions: an increase in wind speed of 2.7 m s–1, a decrease in visibility of 1.7 km, and reduction in humidity of 4.3%. Seasonal variations in temperature (an increase in temperature during summer of 0.8°C, and a decrease of 1.5°C during winter) and barometric pressure (a decrease in barometric pressure during summer of 0.6 mbar and an increase of 7.8 mbar during winter) were observed during Shamal events.

Barometric pressure influences host-orientation behavior in the larva of a dipteran ectoparasitoid

Rain and temperature have been awarded as the most important weather factors that influence insect behavior. Barometric pressure studies have been relegated to a secondary place mainly because most studies deal with adult insects where temperature and water availability are the main environmental factors that influence behavior. We studied the influence of barometric pressure on the host orientation behavior in Mallophora ruficauda, an ectoparasitoid with an active host-seeking larval stage. Our results show that a steeper decrease in barometric pressure than expected by regular variation reduced orientation to host chemical cues. This study is the first to show a correlation between changes in the barometric pressure and the seeking behavior of parasitoid soil-dwelling larvae. Our results show that in this kind of insects, ambient factors other than temperature, water availability and light, can influence and have a profound impact on the process of parasitism. We discuss the influence of this behavior on a task so important for parasitoids as host location, and highlight the importance of including such information in parasitoid foraging ecology and climatic change studies.

Transcriptional downregulation of sterol metabolism genes in murine liver exposed to acute hypobaric hypoxia

Ascent to high-altitude results in decreased inspired partial pressure of oxygen because of a decrease in barometric pressure. Altitude acclimatization requires physiological and metabolic changes to improve tolerance to altitude hypoxia. Cellular response to hypoxia results into changes in the profile of gene expression and the present study explored the same in murine model. Liver being the largest metabolic organ, the molecular details of acute hypobaric hypoxia (AHH) induced transcriptional changes in the tissue were investigated. Swiss albino mice were exposed to hypobaric hypoxia (∼426 mmHg) in a decompression chamber and cDNA microarray was used to study the transcriptional profile in liver. Notably, by the tenth hour several of the genes involved in sterol metabolism such as SREBF1, INSIG1, HMGCS1, FDFT1, SQLE, and HSD3B4 were downregulated more than 2-fold suggesting that AHH suppresses sterol biosynthesis in the liver. Real-time PCR helped validate the downregulation of SREBF1, HMGCS1, FDFT1, and HSD3B4 genes. However, no significant change was observed in the serum cholesterol levels throughout the AHH exposure. The findings are indicative of transcriptional downregulation of SREBP target genes as a part of acclimatization response to hypoxia. The study highlights the significance of SREBP in the regulation of sterol metabolism under the acute hypoxic response.

Relation of Atmospheric Pressure Changes and the Occurrences of Acute Myocardial Infarction and Stroke

Previous studies have demonstrated variation in vascular events with respect to season and time of day. Changes in barometric pressure display daily and seasonal variations and could modulate the occurrence of vascular events. The objective of this study was to determine whether a relation exists between changes in barometric pressure and occurrence of stroke or acute myocardial infarction (AMI). A retrospective analysis of hospital admissions for AMI and stroke from 1993 to 1996 in central Texas was related to changes in atmospheric pressure that were obtained from the National Climatic Data Center. Patients who had AMI (n = 1,327) or stroke (n = 839) were identified from a computerized hospital database. Mean atmospheric pressure, greatest change in pressure, and rate of change in pressure per 24-hour period were computed. One-, 2-, and 3-day and seasonal groupings of cardiovascular events were related to corresponding changes in barometric pressure. The fall and winter seasons had the highest variability in atmospheric pressure readings. There was a significant correlation (p = 0.0083) between a decrease in atmospheric pressure and the occurrence of AMI the day after a pressure decrease, especially during the fall and winter seasons. No relation between stroke and atmospheric pressure was demonstrated. In conclusion, we conclude that rapid decreases in barometric pressure are associated with the occurrence of AMI but not of stroke.

Peak heart rate decreases with increasing severity of acute hypoxia.

The purpose of the present study was to investigate the degree to which peak heart rate is reduced during exhaustive exercise in acute hypoxia. Five sea-level lowlanders performed maximal exercise at normobaric normoxia and at three different levels of hypobaric hypoxia (barometric pressures of 518, 459, and 404 mmHg) in a hypobaric chamber and while breathing 9% O(2) in N(2). These conditions were equivalent to altitudes of 3300, 4300, 5300, and 6300 m above sea level, respectively. At 4300 m, maximal exercise was also repeated after 4 and 8 h. Peak heart rate (HR) decreased from 191 (182-202) (mean and range) at sea level to 189 (179-200), 182 (172-189), 175 (166-183), and 165 (162-169) in the acute hypoxic conditions. Peak HR did not decrease further after 4 and 8 h at 4300 m compared to the acute exposure at this altitude. Between barometric pressures of 518 and 355 mmHg (approximately 3300 and 6300 m), peak HR decreased linearly: peak HR(hypobaria) = peak HR(sea level) - 0.135 x [hypobaria(3100) - hypobaria (mmHg)]; or peak HR(altitude) = peak HR(sea level) - 0.15 x (altitude - 3100 m). This corresponds to approximately 1-beat x min(-1) reduction in peak HR for every 7-mmHg decrease in barometric pressure below 530 mmHg (approximately 130 m of altitude gained above 3100 m). At termination of exercise, maximal plasma lactate and norepinephrine concentrations were similar to those observed during maximal exercise in normobaric normoxia. This study clearly demonstrates a progressive decrease in peak HR with increasing altitude, despite evidence of similar exercise effort and unchanged sympathetic excitation.

Association between significant decrease in barometric pressure and onset of labor

To determine whether there is any correlation between sudden decrease in barometric pressure and onset of labor, a non-experimental, retrospective study at a 948-bed tertiary care hospital was done. Pregnant patients of 36 weeks gestation or more who presented with spontaneous onset of labor during the 48 hours surrounding the 12 occurrences of significant drop in barometric pressure in 1992 were included in the study. Significantly more occurrences of onset of labor were identified in the 24 hours after a drop in barometric pressure than were identified in the 24 hours prior to the drop in barometric pressure ( P < 0.05). Therefore, the overall number of labor onsets increased in the 24 hours following a significant drop in barometric pressure.

Effect of Altitude on Hand-held Peak Flowmeters

To quantify the effect of altitude on the operational characteristics of hand-held peak flowmeters. Altitude simulation within a hypobaric chamber combined with five constant simulated peak flows delivered from a computerized pump were used to test commercially available peak flowmeters. F.G. Hall Hyperbaric/Hypobaric facilities located at Duke University School of Medicine. Two each of nine models of commercially available hand-held peak flowmeters and a volume spirometer were tested at six simulated altitudes (100, 500, 1,000, 1,500, 2,000, and 3,000 m) using five target peak flows. Each peak flow was injected into each meter twice. Forward stepwise regression was used to check for nonlinear relationships between altitude and peak expiratory flowmeter readings. Linear regression equations were fit to the data at each target flow across altitude. Effect of absolute peak flow was tested by analysis of covariance. For these altitudes, linear relationships were found between altitude and measured peak flow. For all meters tested, the average decrease in peak flow ranged from -8.7% at the lowest target flow (123 L/min) to -6.5% at the highest target flow (702 L/min) for each 100 mm Hg decrease in barometric pressure (PB). Individual meters ranged from -12.3% at the lowest target flow to -4.4% at the highest target flow for 100 mm Hg decrease in PB. The spirometer had no significant changes associated with changes in PB. In all cases, the magnitude of the altitude effect, measured by percent change, decreased with increasing peak flow. Peak expiratory flowmeters underread PEF as a function of both increasing altitude and increasing target peak flow.

Landfill Gas Migration—Field Investigations At Skellingsted Landfill, Denmark

The background for a landfill gas explosion accident which happened at Skellingsted Landfill in Denmark was investigated. To understand the behaviour of the lateral migrating landfill gas in the area where the accident occurred, an intensive investigation was carried out after the explosion accident measuring time-series of gas composition in 30 wells over a 35-day period. The changes in gas composition in selected wells following a decrease in barometric pressure were measured over a 33-h period. The maximal distance for measured methane concentrations above 5% (vol.) in the pore gas was 90 m. The investigations showed that changes in barometric pressure have a great impact on the pore gas composition. Indications of methane oxidation were observed down to 2 m below ground in distances of more than 60 m from the landfill.

Landfill gas migration—Field investigations at Skellingsted landfill, Denmark

The background for a landfill gas explosion accident which happened at Skellingsted Landfill in Denmark was investigated. To understand the behaviour of the lateral migrating landfill gas in the area where the accident occurred, an intensive investigation was carried out after the explosion accident measuring time-series of gas composition in 30 wells over a 35-day period. The changes in gas composition in selected wells following a decrease in barometric pressure were measured over a 33h period. The maximal distance for measured methane concentrations above 5% (vol.) in the pore gas was 90 m. The investigations showed that changes in barometric pressure have a great impact on the pore gas composition. Indications of methane oxidation were observed down to 2 m below ground in distances of more than 60 m from the landfill.

Meteorologic influences on the frequency of pulmonary embolism.

Reports published earlier this century suggested that meteorologic factors influence the incidence of pulmonary embolism. These observations were based on few patients and often lacked rigorous standards of evidence. In the current study, the authors evaluate the association between barometric pressure changes and pulmonary embolism using radionuclide ventilation-perfusion (V/Q) scan data. Daily interpretation data for V/Q lung scans were correlated retrospectively with daily local barometric pressure changes over a 7-year period. The incidence of pulmonary embolic disease was significantly related to a decrease in barometric pressure during the 3 days preceding clinical presentation. Meteorologic factors are less important than better-known risk factors for pulmonary embolism; however, their effect is demonstrable in a large data sample. This work confirms previously published associations between barometric pressure changes and the incidence of pulmonary embolism.

Avian Reproduction over an Altitudinal Gradient: Incubation Period, Hatchling Mass, and Embryonic Oxygen Consumption

-Embryonic oxygen consumption, incubation period, and hatchling mass do not vary significantly among populations of Red-winged Blackbirds (Agelaius phoeniceus) breeding over a 2,900-m altitudinal gradient, despite a 28% decrease in oxygen tension from the lowest to the highest altitude. Calculations suggest that embryos develop normally at 2,900 m at air-cell 02 tensions of 7.1 kPa. The regulation of loss of water vapor or CO2 by a reduction of eggshell conductance appears to have been more important for populations breeding in montane environments than maximizing 02 availability to the embryo. The superior tolerance to hypoxia demonstrated by embryos of wild birds, compared to that of embryos of domestic chickens, may relate to the modification of the diffusive resistance of 02 inside the shell. Received 28 September 1981, accepted 24 April 1982. THE ability of a species to invade a new habitat and to establish permanent residency there depends importantly upon successful reproduction. Avian species have exploited a remarkable diversity of habitats. This success is particularly striking in view of the potential vulnerability of avian embryos to environmental stresses. Because avian embryos develop externally from the body of the adult, they are less protected by the homeostatic systems of the adult than are embryos of viviparous vertebrates. Although the physiology of avian embryos has received considerable attention during the last decade, embryonic tolerances of and adaptations to harsh environments have received little study. Avian embryos exchange gases with the environment by diffusion (Wangensteen et al. 1970/71). The diffusive flux of 02 into the egg, and CO2 and water vapor outwards, is described by a modification of the Fick equation (Wangensteen et al. 1970/71, Paganelli et al. 1975): M = (DIRT) (ApIL) -AP (1) Present address: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721 USA. where M = gas flux (cm3 STPD * s-1), D = diffusion coefficient (cm2 * s-1), Ap = effective pore area (cm2), L = length of diffusion path or shell thickness (cm), RT = gas constant and absolute temperature (cm3 STPD cm-3 kPa-'), and AP = partial pressure difference of gas across shell (kPa). The terms (DIRT)(ApIL) are often combined into the term G (cm-3 s-l kPa-1), representing the conductance of the eggshell to each gas (Ar et al. 1974). The progressive decrease in barometric pressure, PB, in montane habitats is an environmental gradient that poses distinct problems for diffusive respiratory systems. Equation 1 suggests two factors that should become progressively more important to avian development as PB falls with increasing altitude. First, 02 flux (MC2) is influenced by the Po2 difference across the eggshell (AP02). Because ambient Po2 falls as PB decreases, the driving force for 02 diffusion will decrease unless internal P02 is lowered commensurately. Therefore, an embryo may not obtain sufficient 02 above certain altitudes to sustain normal metabolism and growth. Second, theoretical predictions and empirical results show that D is inversely proportional to PB (Reid and Sherwood 1966, Paganelli et al. 1975). Therefore, gases exchanged between the embryo and the environment will diffuse more rapidly as PB decreases with al710 The Auk 99: 710-718. October 1982 This content downloaded from 157.55.39.187 on Wed, 30 Mar 2016 05:48:07 UTC All use subject to http://about.jstor.org/terms October 1982] Avian Reproduction and Altitude 711 titude, if all other factors in Eq. 1 are constant. The enhanced diffusion of 02 into the egg may compensate in part for the detrimental effects of hypoxia on metabolism (Visschedijk et al. 1980), but augmented rates of diffusion of CO2 and water vapor from the egg during incubation may prove harmful to normal embryonic growth (Rahn et al. 1977, Carey 1980). Therefore, successful breeding by montane populations of birds has undoubtedly required that the resistant properties of the eggshell to gaseous diffusion be designed to meet the demands for maximizing 02 supply and minimizing excessive losses of CO2 and water vapor at high elevations. Tolerance to hypoxia has been studied thus far only in embryos of domestic fowl (Gallus domesticus). They are unable to maintain normal levels of metabolism or growth when subjected acutely or for the duration of incubation to moderate hypoxia (Visschedijk et al. 1980). Growth and metabolism of embryos obtained from a colony of chickens raised for more than 15 yr at 3,800 m were significantly reduced below control levels (Wangensteen et al. 1974). These results raise interesting questions concerning the abilities of embryos of wild birds breeding at high altitudes to obtain sufficient 02 for normal metabolism and growth. The purpose of this study was to evaluate 02 Uptake directly by measuring embryonic metabolic rate and indirectly by studying incubation period, hatchling mass, and embryonic mortality in Red-winged Blackbirds (Agelaius phoeniceus) breeding over a 2,900-m altitudinal gradient.

Electrocardiographic observations in high altitude residents of Nepal and Bolivia

Parameters computed from electrocardiographic recordings (mean frontal QRS axis, â QRS, positive (R-S) difference in lead V1, incidence of atypical conduction pattern in V1) were compared: (1) in two populations residing at the same altitude (3 800 m) but in different geographical sites: Aymaras in Bolivia and Tibetans in Nepal, (2) in three groups of Bolivians dwellers, ethnically similar and fully acclimatized, at three altitudes (4 780 m, 3 800 m, 400 m). This work involved 661 subjects. Results: (a) The mean â QRS value in highlanders is shifted to the right when compared to that of lowlanders: the right axis deviation increases with altitude, (b) The mean â QRS value is identical in Bolivian and Tibetan groups living at the same altitude, (c) The axis deviates to the left with aging in all the environmental conditions. This migration is accompanied by a lower incidence of positive (R-S) difference in adults compared to younger subjects, (d) The mean â QRS value of the females is always situated to the left of that males for all age groups. This difference receives a possible confirmation by the lower incidence of atypical complexes in V1 in females, (e) The present values of â QRS as well as others found in the litterature and those of mean pulmonary arterial pressure reported by different authors have been plotted, both as a function of elevation: The two relationships can be described by two linear functions with a point of intersection. Such points suggest an altitude threshold above which a further decrease in barometric pressure results in marked cardiovascular responses. They are both located in the vicinity of 2 500 m.