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At least 1,495 records · Page 83Linked to original sources
PubMed2003

Change in serum sodium concentration during a cold weather ultradistance race.

OBJECTIVE: To investigate change in serum sodium concentration and its potential causes during a cold weather ultradistance race. DESIGN: Descriptive research. SETTING: A 100-mile (161-km) race over a snow-packed course in the Alaskan wilderness. Athletes competed in 1 of 3 divisions: foot, bike, or ski. PARTICIPANTS: Twenty athletes (11 runners, 6 cyclists, 3 skiers) volunteered for the study. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Subjects were weighed and had blood drawn for hematocrit, serum sodium, serum aldosterone, and plasma arginine vasopressin concentrations pre- and postrace. Fluid and sodium intake were determined by race dietary analysis. RESULTS: Serum sodium concentration decreased significantly prerace (140.8 +/- 1.2 mmol/L) to postrace (138.4 +/- 2.2 mmol/L), although no athletes were classified as hyponatremic. Mean weight loss was significant during the race (-1.2 kg), although 1 athlete maintained his weight, and 3 athletes gained small amounts of weight (0.2 kg, 0.2 kg, and 0.5 kg, respectively). Hematocrit decreased significantly prerace (42.2 +/- 3.5) to postrace (40.3 +/- 4.1). Plasma arginine vasopressin and serum aldosterone increased significantly during the race (2.6 +/- 0.7 to 6.0 +/- 4.6 pg/mL and 5.1 +/- 2.6 to 40.8 +/- 25.1 ng/dL, respectively). Fluid consumption was 300 +/- 100 mL/h, and sodium intake was 310 +/- 187 mg/h. CONCLUSIONS: Decreased serum sodium concentration after a cold weather ultradistance race was due to fluid overload caused by excessive fluid consumption. Current recommendations that ultradistance athletes consume 500 to 1000 mL/h may be too high for athletes competing in the extreme cold.

Adaptation, Physiological↗
PubMed2005

An unusual fracture of the talus in a snowboarder.

Fractures of the talus are uncommon. However, snow- boarding and skateboarding are 2 activities that are specifically associated with talus fractures. These patients sustain occult lateral talus process fractures that present as a severe ankle injury. The diagnosis is difficult because of subtle clinical and plain radiographic findings. Computed tomography is a very useful tool for the assessment of these injuries. Although the majority of these athletes have lateral sided talus fractures, there are variants. We present an unusual case of a displaced intra-articular fracture of the subtalar joint involving the middle articular facet of the talus with extension of the fracture into the talar head. This highlights the importance of carefully assessing snowboarders' "ankle injuries."

Adult↗
PubMed2004

Injuries among skiers and snowboarders in Quebec.

BACKGROUND: Snow sports such as skiing and snowboarding are recognized as hazardous, but population-based injury rates or specific risk factors have been difficult to estimate as a result of a lack of complete data for both numerator and denominator. METHODS: We used data from 3 surveys to estimate the number of participants and annual number of outings in Quebec by age, sex, activity, and calendar year. Injuries reported by ski patrollers were used to estimate injury rates among skiers and snowboarders for the head and neck, trunk, upper extremity, and lower extremity. RESULTS: Head-neck and trunk injury rates increased over time from 1995-1996 to 1999-2000. There was a steady increase in the rate of injury with younger age for all body regions. The rate of head-neck injury was 50% higher in snowboarders than in skiers (adjusted rate ratio [ARR] = 1.5; 95% confidence interval = 1.3-1.8). Women and girls had a lower rate of head-neck injury (0.73; 0.62-0.87). Snowboarders were twice as likely as skiers to have injuries of the trunk (2.1; 1.7-2.6), and more than 3 times as likely to have injuries of the upper extremities (3.4; 2.9-4.1). Snowboarders had a lower rate of injury only of the lower extremities (0.79; 0.66-0.95). Snowboarder collision-related injury rates increased substantially over time. CONCLUSIONS: Except for lower extremity injuries, snowboarders have a higher rate of injuries than skiers. Furthermore, collision-related injury rates have increased over time for snowboarders. Targeted injury prevention strategies in this group seem justified.

Adolescent↗
PubMed2005

Pediatric closed head injuries treated in an observation unit.

BACKGROUND: Closed head injury (CHI) is common in childhood and frequently results in hospital admission for observation and treatment. Observation units (OUs) have shown significant benefits for patients and physicians. At our institution, a level 1 pediatric trauma center, patients with CHI are often admitted to an OU for up to 24 hours of observation and treatment. STUDY OBJECTIVES: To describe characteristics of patients with a CHI admitted to a pediatric OU and to identify demographic, historical, clinical, and radiographic factors associated with the need for unplanned inpatient admission (UIA) after OU management. METHODS: Retrospective cohort review of all OU admissions for CHI at Primary Children's Medical Center (PCMC) from August 1999 through July 2001. Data collected included age, gender, mechanism of injury, presenting symptoms, physical examination findings, head computed tomography (CT) results, diagnosis, length of stay, outcome of the injury, and need for UIA. RESULTS: During the study period, 827 patients were seen in the ED for CHI. Two hundred eighty-five patients (34%) were admitted to the OU, 273 (33%) were admitted to an inpatient service, and 269 (33%) were discharged home. OU patients had a median age of 5.2 years, ranging from 2 weeks to 17 years. Sixty-one percent were male. The median admission length of stay was 13 hours. Common mechanisms of injury included: falls (60%), motor vehicle accidents (12%), bicycle accidents (10%), impacts from objects (9%), auto-pedestrian accidents (4.6%), and snow-related accidents (4.6%). Presenting symptoms in the ED included vomiting (39%), loss of consciousness (26%), amnesia to event (19%), persistent amnesia (5%), and seizures (4%). Physical examination findings noted in the ED included altered mental status (45%), facial abnormalities (43%), scalp abnormalities (38%), and neurologic deficits (9%). Two hundred eighty patients (98%) admitted to the OU had a head CT performed. Skull fractures were present in 109 patients (39%) and intracranial pathology (ie, epidural hematoma, subdural hematoma, or intraparenchymal contusion) was present in 38 patients (13%). Only 13 patients (5%) required admission to an inpatient service from the OU for the following reasons: continued need for intravenous (IV) fluids (n = 5), venous thrombosis (n = 2), persistent CSF leakage (n = 3), decreased level of consciousness (n = 1), pain management (n = 1), and clearing of the patient's cervical spine (n = 1). No patient deteriorated or required neurosurgery. Patients with basilar skull fractures, a head laceration (scalp or facial), and patients that needed IV fluids in the ED were more likely to need inpatient admission after a 24-hour observation stay. Logistic regression analysis identified basilar skull fractures (OR 11.61), face/scalp lacerations (OR 7.52), and the need for ED IV fluid administration (OR 4.26) to be associated with UIA. Most children with these findings were successfully discharged within 24 hours, however. Age, sex, loss of consciousness, seizure, vomiting, amnesia, altered mental status, neurologic deficits, intracranial pathology, and skull fractures (aside from basilar skull fractures) were not related to UIA. CONCLUSION: The vast majority (96%) of pediatric OU patients with CHI such as small intracranial hematomas, skull fractures, and concussions were discharged safely within 24 hours without serious complications. The presence of a basilar skull fracture, head laceration, and the need for ED IV fluids were associated with increased risk of UIA. OU admission is an efficient and effective management setting for children with stable intracranial pathology, skull fractures, and concussions.

Adolescent↗
PubMed2005

Severe inbreeding depression in a wild wolf (Canis lupus) population.

The difficulty of obtaining pedigrees for wild populations has hampered the possibility of demonstrating inbreeding depression in nature. In a small, naturally restored, wild population of grey wolves in Scandinavia, founded in 1983, we constructed a pedigree for 24 of the 28 breeding pairs established in the period 1983-2002. Ancestry for the breeding animals was determined through a combination of field data (snow tracking and radio telemetry) and DNA microsatellite analysis. The population was founded by only three individuals. The inbreeding coefficient F varied between 0.00 and 0.41 for wolves born during the study period. The number of surviving pups per litter during their first winter after birth was strongly correlated with inbreeding coefficients of pups (R2=0.39, p<0.001). This inbreeding depression was recalculated to match standard estimates of lethal equivalents (2B), corresponding to 6.04 (2.58-9.48, 95% CI) litter-size-reducing equivalents in this wolf population.

Animals↗
PubMed2006

Predicting the consequences of carry-over effects for migratory populations.

Migratory animals present a unique challenge for predicting population size because they are influenced by events in multiple stages of the annual cycle that are separated by large geographic distances. Here, we develop a model that incorporates non-fatal carry-over effects to predict changes in population size and show how this can be integrated with predictive models of habitat loss and deterioration. Examples from Barn swallows, Greater snow geese and American redstarts show how carry-over effects can be estimated and integrated into the model. Incorporation of carry-over effects should increase the predictive power of models. However, the challenge for developing accurate predictions rests both on the ability to estimate parameters from multiple stages of the annual cycle and to understand how events between these periods interact to influence individual success.

Animal Migration↗
PubMed1995

Mechanisms for dynamic stereomotion respond selectively to horizontal velocity components.

When dynamic visual noise such as the 'snow' on a detuned television receiver is inspected with a delay between the signals in the two eyes, the noise appears to rotate in depth around a vertical axis. We propose that this dynamic noise stereophenomenon arises because channels tuned jointly to depth and motion respond selectively to horizontal motion components in the noise. We used spatially filtered stimuli to reduce the strength of vertically oriented Fourier components in the noise, and found that this reduced the strength of the stereophenomenon. Reducing the strength of horizontally oriented components had a lesser effect. Our evidence is consistent with the conclusion that stereo-motion is predominantly detected by oriented receptive fields with an aspect ratio similar to those of cortical simple cells.

Depth Perception↗
PubMed2005

Evidence of a shift in the cyclicity of Antarctic seabird dynamics linked to climate.

Ecosystems and populations are known to be influenced not only by long-term climatic trends, but also by other short-term climatic modes, such as interannual and decadal-scale variabilities. Because interactions between climatic forcing, biotic and abiotic components of ecosystems are subtle and complex, analysis of long-term series of both biological and physical factors is essential to understanding these interactions. Here, we apply a wavelet analysis simultaneously to long-term datasets on the environment and on the populations and breeding success of three Antarctic seabirds (southern fulmar, snow petrel, emperor penguin) breeding in Terre Adélie, to study the effects of climate fluctuations on Antarctic marine ecosystems. We show that over the past 40 years, populations and demographic parameters of the three species fluctuate with a periodicity of 3-5 years that was also detected in sea-ice extent and the Southern Oscillation Index. Although the major periodicity of these interannual fluctuations is not common to different species and environmental variables, their cyclic characteristics reveal a significant change since 1980. Moreover, sliding-correlation analysis highlighted the relationships between environmental variables and the demography of the three species, with important change of correlation occurring between the end of the 1970s and the beginning of the 1980s. These results suggest that a regime shift has probably occurred during this period, significantly affecting the Antarctic ecosystem, but with contrasted effects on the three species.

Animals↗
PubMed2005

A window on the genetics of evolution: MC1R and plumage colouration in birds.

Melanins are a ubiquitous component of plumage colouration in birds and serve a wide variety of functions. Although the genetic control of melanism has been studied in chickens and other domestic species, little was known about the molecular genetics of melanin distribution in wild birds until recently. Studies have now revealed that a single locus, the melanocortin-1 receptor (MC1R) locus, is responsible for melanic polymorphisms in at least three unrelated species: the bananaquit, the snow goose and the arctic skua. Results show that melanism was a derived trait and allow other evolutionary inferences about the history of melanism to be made. The role of MC1R in plumage patterning is surprisingly diverse among different species. The conserved molecular basis for the evolution of melanism in birds and several other vertebrates is probably related to low pleiotropic effects at the MC1R.

Animals↗
PubMed2005

Fading out of vole and predator cycles?

Northern voles and lemmings are famous for their spectacular multiannual population cycles with high amplitudes. Such cyclic vole populations in Scandinavia have shown an unexpected and marked long-term decline in density since the early 1970s, particularly with a marked shift to lower spring densities in the early 1980s. The vole decline, mainly characterized by a strongly decreased rate of change in numbers over winter, is associated with an increased occurrence of mild and wet winters brought about by a recent change in the North Atlantic Oscillation. This has led to a decrease in winter stability and has shortened the period with protective snow cover, the latter considered as an important prerequisite for the occurrence of multiannual, high-amplitude cycles in vole populations. Although the vole decline is predicted to be negative for predators' reproduction and abundance, empirical data showing this are rare. Here we show that the dynamics of a predator-prey system (Tengmalm's owl, Aegolius funereus, and voles), have in recent years gradually changed from 3-4 yr, high-amplitude cycles towards more or less annual fluctuations only.

Animals↗
PubMed2005

Geophysical granular and particle-laden flows: review of the field.

An introduction is given to the title theme, in general, and the specific topics treated in detail in the articles of this theme issue of the Philosophical Transactions. They fit into the following broader subjects: (i) dense, dry and wet granular flows as avalanche and debris flow events, (ii) air-borne particle-laden turbulent flows in air over a granular base as exemplified in gravity currents, aeolian transport of sand, dust and snow and (iii) transport of a granular mass on a two-dimensional surface in ripple formations of estuaries and rivers and the motion of sea ice.

Complex Mixtures↗
PubMed2005

Rapid motions of free-surface avalanches down curved and twisted channels and their numerical simulation.

This paper presents a new model and discussions about the motion of avalanches from initiation to run-out over moderately curved and twisted channels of complicated topography and its numerical simulations. The model is a generalization of a well established and widely used depth-averaged avalanche model of Savage & Hutter and is published with all its details in Pudasaini & Hutter (Pudasaini & Hutter 2003 J. Fluid Mech. 495, 193-208). The intention was to be able to describe the flow of a finite mass of snow, gravel, debris or mud, down a curved and twisted corrie of nearly arbitrary cross-sectional profile. The governing equations for the distribution of the avalanche thickness and the topography-parallel depth-averaged velocity components are a set of hyperbolic partial differential equations. They are solved for different topographic configurations, from simple to complex, by applying a high-resolution non-oscillatory central differencing scheme with total variation diminishing limiter. Here we apply the model to a channel with circular cross-section and helical talweg that merges into a horizontal channel which may or may not become flat in cross-section. We show that run-out position and geometry depend strongly on the curvature and twist of the talweg and cross-sectional geometry of the channel, and how the topography is shaped close to run-out zones.

Complex Mixtures↗
PubMed2006

The environment and evolution of the West Antarctic ice sheet: setting the stage.

The West Antarctic ice sheet is the last ice sheet of the type cradled in a warm, marine geologic basin. Its perimeter stretches into the surrounding seas allowing warmer ocean waters to reach the undersides of its floating ice shelves and its relatively low surface elevation permits snow-carrying storms to extend well into its interior. This special environment has given rise to theories of impending collapse and for the past quarter-century has challenged researchers who seek a quantitative prediction of its future behaviour and the corresponding effect on sea level. Observations confirm changes on a variety of time scales from the quaternary to less than a minute. The dynamics of the ice sheet involve the complex interaction of ice that is warm at its base and cold along the margins of ice streams; subglacial till that is composed of a combination of marine sediment and eroded sedimentary rocks; and water that moves primarily between the ice and bed, but whose flow direction can differ from the direction of ice motion. The pressure of the water system is often sufficient to float the ice sheet locally and small changes in the amount of water in the till can cause it to rapidly switch from very weak to very stiff.

Journal Article↗
PubMed2006

Changes in ice dynamics and mass balance of the Antarctic ice sheet.

The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 degrees C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

Journal Article↗
PubMed2006

Determining the contribution of Antarctica to sea-level rise using data assimilation methods.

The problem of forecasting the future behaviour of the Antarctic ice sheet is considered. We describe a method for optimizing this forecast by combining a model of ice sheet flow with observations. Under certain assumptions, a linearized model of glacial flow can be combined with observations of the thickness change, snow accumulation, and ice-flow, to forecast the Antarctic contribution to sea-level rise. Numerical simulations show that this approach can potentially be used to test whether changes observed in Antarctica are consistent with the natural forcing of a stable ice sheet by snowfall fluctuations. To make predictions under less restrictive assumptions, improvements in models of ice flow are needed. Some of the challenges that this prediction problem poses are highlighted, and potentially useful approaches drawn from numerical weather prediction are discussed.

Journal Article↗
PubMed1975

The jumping mechanism of Xenopsylla cheopis. I. Exoskeletal structures and musculature.

The jumping apparatus of the flea, which includes highly modified direct and indirect flight muscles, is described: attention is drawn to the various specializations of the exoskeleton which stiffen the thorax and also provide the 'click' mechanism triggering take-off. A finger-like invagination of tall cells within the cavity of the developing pleural arch of the pharate adult secretes the resilin pad. This is illustrated with coloured photographs. It is suggested that winglessness of a Mecopteran-like ancestor pre-adapted fleas to a parasitic life-style, and that a jumping mode of progression was a primitive feature of the whole Order. Scattered throughout the Siphonaptera today are species which have secondarily lost the pleural arch and with it the power to execute large jumps. These are usually found among fleas parasitizing mammals inhabiting caves, subterranean burrows and runs, high aerial nests and snow or ice-bound habitats. Large pleural arches are associated with fleas infesting large mobile hosts.

Animals↗
PubMed1998

Motion perception: from phi to omega.

When human observers view dynamic random noise, such as television 'snow', through a curved or annular aperture, they experience a compelling illusion that the noise is moving smoothly and coherently around the curve (the 'omega effect'). In several series of experiments, we have investigated the conditions under which this effect occurs and the possible mechanisms that might cause it. We contrast the omega effect with 'phi motion', seen when an object suddenly changes position. Our conclusions are that the visual scene is first segmented into objects before a coherent velocity is assigned to the texture on each object's surface. The omega effect arises because there are motion mechanisms that deal specifically with object rotation and these interact with pattern mechanisms sensitive to curvature.

Humans↗
PubMed2004

A novel psychrotolerant member of the hymenomycetous yeasts from Antarctica: Cryptococcus watticus sp. nov.

Soil, snow and organic material, collected in November 1997 from the Vestvold Hills, Davis Base, Antarctica, were screened for yeasts. Two isolates, which were shown to be indistinguishable by rDNA sequencing and protein analysis by SDS-PAGE, are described in this communication as a novel species, Cryptococcus watticus sp. nov. (type culture, CBS 9496T=NRRL Y-27556T). Sequence analyses of the 26S rDNA D1/D2 region placed C. watticus in the hymenomycetous yeasts in a cluster with Holtermannia corniformis and Cryptococcus nyarrowii. This species has been allocated to the genus Cryptococcus on the basis of physiological and morphological characteristics.

Antarctic Regions↗