Pflügers Archiv : European journal of physiology
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In this study we have investigated the effects of breath holding and of the physical properties of gases on four different respiratory dead spaces (VD): the Fowler, the physiological, the washout and the inert gas dead space. The experiments were performed with dogs which were ventilated artificially with breathing patterns with different post-inspiratory breath holding times (ta) of 0, 0.5, 1.0 and 2.0 s. Tracer amounts of acetone, ether and enflurane were infused continuously into a peripheral vein and a bolus of a mixture of krypton, Freon12 and SF6 was introduced into the peritoneal cavity. ⋯ Further, VD,phys/VT was larger than VD,Fowler/VT for SF6 and acetone. However, for gases with intermediate solubility in blood VD,phys/VT tended to be smaller than VD,Fowler/VT. We conclude that the respiratory dead spaces are affected by the breathing pattern and by the physical properties of gases, i.e. their diffusivity in alveolar gas and their solubility in blood or lung tissue.
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Effects of changes in blood volume on changes in pulmonary blood flow and pulmonary blood volume during the ventilatory cycle during mechanical ventilation with a positive end-expiratory pressure of 2 cm H2O were determined in six pentobarbital anaesthetized, curarized pigs weighing about 10 kg. Haemodynamic variables were analysed for each cardiac cycle in eight ventilatory cycles in four consecutive series under hyper-, normo- and hypovolaemic conditions. Cardiac output was highest in hypervolaemia. ⋯ The difference between right ventricular-output (electromagnetic flow measurement) and left ventricular-output (pulse contour) indicated changes in pulmonary blood volume. In hypervolaemia less blood shifted from the pulmonary circulation into the systemic system during inflation than in normo- and hypovolaemia. This difference can be explained by two mechanisms namely, the smaller fall in input into the pulmonary vascular beds and a smaller pulmonary vascular volume decrease as a result of transmural pressure fall at a steeper part of the pressure-volume curve.
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V1-antagonist, [Mca1, D-Phe2, Sar7] arginine vasopressin, at a concentration 0.5 nM to 5 nM increased hydroosmotic effect of 5 nM arginine vasopressin in frog urinary bladder. 1 nM V1-antagonist [Mca1, O-Me-Tyr2] arginine vasopressin does not changed hydroosmotic effect of 0.1 nM dibutyryl cAMP. We suggest that-both V1- and V2-receptors are present on epithelial cells of frog urinary bladder and that V1-receptors are involved in the modulation of the hydroosmotic effect of arginine vasopressin-mediated by V2-receptors. by V2-receptors.
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We have investigated the role of the sympathetic innervation of the vasculature of the head in the control of selective brain cooling of sheep, during exposure to high and low ambient temperatures and during endotoxin-induced fever. Bilateral removal of the superior cervical ganglia resulted in a significant reduction of hypothalamic temperature during all procedures. ⋯ Rectal temperature changes after sympathectomy were dependent on the experimental conditions, and the rectal - hypothalamic temperature difference was enhanced during heat exposure and fever. Our results support the contention that sympathetically mediated changes in nasal blood flow and in venous return from the nasal cavity, via the angularis oculi and facial veins, may be involved in the control of selective brain cooling in sheep.
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This study examined the effect of local heating on the blood flow of the finger or forearm in male subjects in an environment of 35 degrees C--40% (r.h.). One hand or forearm was immersed in a water bath the temperature of which (Tw) was raised by 1 degrees C every 10th min from 35 degrees to 43 degrees C, while the other hand or forearm was kept at a constant Tw of 35 degrees C. Blood-flow (BF) was measured by venous occlusion plethysmography, using temperature-compensated mercury-in-Silastic strain gauges. ⋯ At TwS of 42 degrees -43 degrees C, finger BF in the heated hand greatly increased after an initial transitory fall. In the forearm skin, however, no such vasoconstriction in response to local heating was observed. All this suggests that a rise in skin temperature to above the core temperature produces paradoxical vasoconstriction in the finger, which may be a mechanism to reduce heat gain through the hand heated locally at higher temperatures.