1988. Forced and voluntary diving in ducks: cardiovascular adjustments and their control. Can. J . Zool . 66: 75 -83. Diving ducks submerge voluntarily for less than 1 min yet, in forced dives in the laboratory, redhead ducks can endure at least 8 min underwater. This is much longer than a dabbling duck of the same body mass can endure and is a result of the quicker onset of oxygen-conserving cardiovascular responses in divers. Oxygen conservation during forced dives is indicated by a profound bradycardia as blood flow is restricted to cerebral and central cardiovascular areas. In voluntary dives, on the other hand, heart rate is frequently above resting rates, and blood flow is preferentially directed to the working muscles of the hind limbs. Profound bradycardia only occurs in unrestrained ducks when they are trapped underwater. Since leg movements cease within 30 s after ducks are trapped, blood flow must at that time be directed away from the working muscles, as in the "classical" oxygen-conserving dive response. Cardiovascular adjustments to forced diving are caused by stimulation of nasal receptors in diving ducks. In dabblers, arterial chemoreceptor stimulation is crucial to the response, although an intact barostatic system may be necessary for development of profound bradycardia. Baroreceptors are essential for the cardiac response observed when dabblers are trained to dive for food, although neither baro-, chemo-, nor naso-receptors appear to have much to do with the cardiac adjustments to voluntary submergence in diving ducks. Nevertheless, in divers, cardiac adjustments to dabbling and forced, voluntary, and trapped dives are linearly related on a plot of dive (trapped) against the logarithm of predive (pretrap) heart rate. This relationship is due to a similar increase in vagal activity, of some 50% of maximum, in all types of diving manoeuvers. Phychogenic factors, long thought to be important in cardiac responses to forced diving, would appear to underpin this relationship. JONES, D. R., FURILLA, R. A., HEIEIS, M. R. A., GABBOTT, G. R. J., et SMITH, F. M. 1988. Forced and voluntary diving in ducks: cardiovascular adjustments and their control. Can. J. Zool. 66 : 75 -83. Les plongCes volontaires des canards plongeurs ne durent pas plus de 1 min et pourtant, en laboratoire, Aythya americana peut supporter des plongCes forcCes d'au moins 8 min.Ces durCes sont beaucoup plus longues que chez les canards de surface de meme masse, grice a la mise en place plus rapide des mCcanismes cardiovasculaires conservateurs d'oxygkne. La conservation d'oxygkne se manifeste par une profonde bradycardie, alors que le debit sanguin est circonscrit dans les rCgions cCrCbrales et cardiovasculaires centrales. Au cours des plongCes volontaires, au contraire, la frkquence cardiaque est souvent supkrieure la frkquence de repos et le debit sanguin est orient6 de fagon prkfCrentielle vers les muscles actifs des pattes. Chez les canards plongeurs libres, la bradycardie profonde ne se produit que s'ils sont piCgCs sous l'eau. Co...
HEIEIS, M. R. A., and JONES, D. R. 1988. Blood flow and volume distribution during forced submergence in Pekin ducks (Anas platyrhynchos). Can. J. Zool. 66: 1589 -1596. Blood is the major oxygen store in ducks forced to dive, and underwater endurance depends on how much of this store can be used by oxygen-sensitive tissues such as the heart and brain. Arterial injection of macroaggregated albumin labelled with technetium-99m, which is trapped and held by capillaries, showed that circulation in dives was restricted to the thoracic and head areas. However, tracing red blood cells labelled with technetium-99m as they were injected during dives showed not only that the time required for the activity to reach equilibrium was 4-10 times longer than when labelled cells were injected into resting ducks but also that blood flow continued in the leg and visceral regions. Tracing red blood cells, labelled with technetium-99m and mixed in the circulation before a dive, during the dive showed that labelled red blood cells were redistributed from the peripheral and visceral areas to the central cardiovascular area. Measurement of circulating red blood cell volume during and after diving showed that, on average, 75.24 f 4.56% of the total red blood cell volume was circulated during forced submergence. Hence, in forced dives, red blood cell volume is positioned in such a manner that the heart and brain have access to the oxygen stored there, and the residual blood flow in the periphery ensures that most of the red blood cell volume is circulated.HEIEIS, M. R. A., et JONES, D. R. 1988. Blood flow and volume distribution during forced submergence in Pekin ducks (Anas platyrhynchos). Can. J. Zool. 66 : 1589 -1596. Le sang est la principale source d'oxygttne durant la plongie forcCe chez le canard. L'endurance a la submersion depend de la proportion d'oxygttne utilisCe par les tissus sensibles a l'hypoxie, tels le cerveau et le coeur. Des injections arterielles de macro-agrkgats d'albumine marques au technetium-99 m et retenus dans les capillaires semblent montrer que la circulation durant la plongee est restreinte aux regions thoraciques et cerebrales. Cependant, l'observation suivie des erythrocytes marques au technCtium-99 m et inject& au cours de la plongee montre, non seulement que le temps requis pour que leur activite atteigne un equilibre est 4 a 10 fois plus long que lorsque les agrkgats sont injectes chez les canards au repos, mais aussi que le sang continue de circuler dans les pattes et les rCgions viscCrales. L'observation suivie des erythrocytes marques au technetium-99 m et integres a la circulation avant la plongee montre que ces Crythrocytes sont redistribuks des regions peripheriques et viscCrales a la region cardiovasculaire durant la plongee. La mesure du volume des erythrocytes en circulation durant et aprks les submersions forcies indique qu'en moyenne 75,24 f 4,56% du volume total des Crythrocytes circule durant la plongie forcCe. Durant la plongee forcee, le volume d'Crythrocytes est donc reparti de manikre a...
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