The physiological consequences of breath-hold diving in marine mammals: the Scholander legacy

Most of the physiological traits used by marine mammals to perform long and deep breath-hold dives were described in Scholander's seminal paper in 1940. Since then, several studies have provided an improved understanding of the mechanistic basis of the mammalian diving response (Scholander, 1940, 1963; Mottishaw et al., 1999; Fahlman et al., 2011), the aerobic dive limit (ADL) (Kooyman et al., 1980; Butler and Jones, 1997; Davis and Kanatous, 1999; Horning, 2012), and management of respiratory gases (Boutilier et al., 2001; Fahlman et al., 2008a; Hooker et al., 2009; Kvadsheim et al., 2012), but many questions remain. Some widely-accepted ideas actually lack experimental confirmation, and a variety of marine mammal species, potentially novel models for elucidating new diving adaptations, have not been adequately studied. The aim of this Frontiers Special Topic is to provide a synthesis of the current knowledge of the physiological responses that may explain the varied diving behavior of marine mammals. We strove to include contributions that challenge current ideas, and which propose new hypotheses, utilize new experimental approaches, and explore new model species

The use of diagnostic imaging for identifying abnormal gas accumulations in cetaceans and pinnipeds.

Recent dogma suggested that marine mammals are not at risk of decompression sickness (DCS) due to a number of evolutionary adaptations. Several proposed adaptations exist. Lung compression and alveolar collapse that terminate gas exchange before a depth is reached where supersaturation is significant and bradycardia with peripheral vasoconstriction affecting the distribution, and dynamics of blood and tissue nitrogen levels. Published accounts of gas and fat emboli and dysbaric osteonecrosis in marine mammals and theoretical modeling have challenged this view-point, suggesting that decompression-like symptoms may occur under certain circumstances, contrary to common belief. Diagnostic imaging modalities are invaluable tools for the non-invasive examination of animals for evidence of gas and have been used to demonstrate the presence of incidental decompression-related renal gas accumulations in some stranded cetaceans. Diagnostic imaging has also contributed to the recognition of clinically significant gas accumulations in live and dead cetaceans and pinnipeds. Understanding the appropriate application and limitations of the available imaging modalities is important for accurate interpretation of results. The presence of gas may be incidental and must be interpreted cautiously alongside all other available data including clinical examination, clinical laboratory testing, gas analysis, necropsy examination and histology results

Flerspråkig undervisning av nyanlända elever – transspråkande i en språkintroduktionskontext

Föreliggande studie undersöker transspråkande i undervisningen av flerspråkiga nyanlända elever på en gymnasieskolas Språkintroduktionsprogram med hjälp av följande frågor: Hur uppmuntras och används transspråkande av lärarna i undervisningen? På vilka sätt beskriver modersmålslärarna att flerspråkiga nyanlända elevers möjligheter till lärande påverkas av en undervisningspraktik som tillåter och uppmuntrar transspråkande? Forskning har visat att stöttning på modersmålet är en viktig faktor för nyanlända elevers skolframgång, samt har en positiv inverkan för andraspråkets utveckling. Modersmålslärarna blir därför betydelsefulla i undervisning som riktar sig till flerspråkiga nyanlända elever. På skolan där studien är genomförd har rektor organiserat undervisning i ämnet samhällskunskap så att fyra modersmålslärare och en ämneslärare, med svenska som modersmål, arbetar tillsammans i klassrummet och på så vis skapat förutsättningar för en flerspråkig undervisning. Det empiriska materialet består av fältanteckningar, som producerats genom deltagande observationer av undervisningen i praktiken, och av transkriberat material från enskilda kvalitativa intervjuer med modersmålslärarna. Resultatet visar att lärarna använder flera språk och multimodala resurser som stöttning i kommunikationsprocesserna och uppmuntrar och tillåter eleverna att använda sina olika språkliga resurser för att stötta varandra i planerade samarbetsinriktade aktiviteter. Modersmålslärarna beskriver att en flerspråkig undervisning kan påverka flerspråkiga nyanlända elevers lärande positivt eftersom eleverna blir mer delaktiga, intresserade av och motiverade till skolarbetet. Men, det framkommer även uppfattningar om att en transspråkande undervisning innebär utmaningar, såsom att samarbeta kring och att planera en sådan undervisning så att alla elever ges likvärdiga förutsättningar för kunskapsmässig och personlig utveckling, vilket uppfattas kunna påverka nyanlända elevers möjligheter att utveckla sina språk- och ämneskunskaper

Estimated tissue and blood N2 levels and risk of in vivo bubble formation in deep-, intermediate- and shallow diving toothed whales during exposure to naval sonar.

Naval sonar has been accused of causing whale stranding by a mechanism which increases formation of tissue N2 gas bubbles. Increased tissue and blood N2 levels, and thereby increased risk of decompression sickness (DCS), is thought to result from changes in behavior or physiological responses during diving. Previous theoretical studies have used hypothetical sonar-induced changes in both behavior and physiology to model blood and tissue N2 tension PN2, but this is the first attempt to estimate the changes during actual behavioral responses to sonar. We used an existing mathematical model to estimate blood and tissue N2 tension PN2 from dive data recorded from sperm, killer, long-finned pilot, Blainville’s beaked, and Cuvier’s beaked whales before and during exposure to Low- (1–2 kHz) and Mid- (2–7 kHz) frequency active sonar. Our objectives were: (1) to determine if differences in dive behavior affects risk of bubble formation, and if (2) behavioral- or (3) physiological responses to sonar are plausible risk factors. Our results suggest that all species have natural high N2 levels, with deep diving generally resulting in higher end-dive PN2 as compared with shallow diving. Sonar exposure caused some changes in dive behavior in both killer whales, pilot whales and beaked whales, but this did not lead to any increased risk of DCS. However, in three of eight exposure session with sperm whales, the animal changed to shallower diving, and in all these cases this seem to result in an increased risk of DCS, although risk was still within the normal risk range of this species. When a hypothetical removal of the normal dive response (bradycardia and peripheral vasoconstriction), was added to the behavioral response during model simulations, this led to an increased variance in the estimated end-dive N2 levels, but no consistent change of risk. In conclusion, we cannot rule out the possibility that a combination of behavioral and physiological responses to sonar have the potential to alter the blood and tissue end-dive N2 tension to levels which could cause DCS and formation of in vivo bubbles, but the actually observed behavioral responses of cetaceans to sonar in our study, do not imply any significantly increased risk of DCS.Publisher PDFPeer reviewe

Gas bubble disease in the brain of a living California sea lion (Zalophus californianus)

A yearling California sea lion (Zalophus californianus) was admitted into rehabilitation with signs of cerebellar pathology. Diagnostic imaging that included radiography and magnetic resonance imaging (MRI) demonstrated space-occupying lesions predominantly in the cerebellum that were filled partially by CSF-like fluid and partially by gas, and cerebral lesions that were fluid filled. Over a maximum period of four months, the brain lesions reduced in size and the gas resorbed and was replaced by CSF-like fluid. To test the animal in this study for motor memory deficits, an alternation task in a two-choice maze was utilized. The sea lion performed poorly similar to another case of pneumocerebellum previously reported, and contrary to data acquired from a group of sea lions with specific hippocampal injury. The learning deficits were attributed to the cerebellar injury. These data provide important insight both to the clinical presentation and behavioral observations of cerebellar injury in sea lions, as well as providing an initial model for long-term outcome following cerebellar injury. The specific etiology of the gas could not be determined. The live status of the patient with recovery suggests that the most likely etiologies for the gas are either de novo formation or air emboli secondary to trauma. A small air gun pellet was present within and was removed from soft tissues adjacent to the tympanic bulla. While no evidence to support the pellet striking bone was found, altered dive pattern associated with this human interaction may have provided the opportunity for gas bubble formation to occur. The similarity in distribution of the gas bubble related lesions in this case compared with another previously published case of pneumocerebellum suggests that preferential perfusion of the brain, and more specifically the cerebellum, may occur during diving events

Inflation and deflation pressure-volume loops in anesthetized pinnipeds confirms compliant chest and lungs

We examined structural properties of the marine mammal respiratory system, and tested Scholander’s hypothesis that the chest is highly compliant by measuring the mechanical properties of the respiratory system in five species of pinniped under anesthesia (Pacific harbor seal, Phoca vitulina; northern elephant seal, Mirounga angustirostris; northern fur seal Callorhinus ursinus; California sea lion, Zalophus californianus; and Steller sea lion, Eumetopias jubatus). We found that the chest wall compliance (CCW) of all five species was greater than lung compliance (airways and alveoli, CL) as predicted by Scholander, which suggests that the chest provides little protection against alveolar collapse or lung squeeze. We also found that specific respiratory compliance was significantly greater in wild animals than in animals raised under human care. While differences in ages between the two groups may affect this incidental finding, it is also possible that lung conditioning in free-living animals may increase pulmonary compliance and reduce the risk of lung squeeze during diving. Overall, our data indicate that compliance of excised pinniped lungs provide a good estimate of total respiratory compliance