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Respiration and circulation in Amphiuma Tridactylum Toews, Daniel Peter


Respiratory and circulatory changes which accompany submergence were studied in Amphiuma tridactylum, an aquatic urodele. All experimentation was performed at 15° C with the exception of oxygen consumption recording taken at 25° C. The lungs, systemic arches, pulmonary arteries, pulmonary veins, post caval vein and dorsal aorta were cannulated. Serial sampling procedures enabled PO₂ and PCO₂ measurements to be made through several breathing cycles on all animals. Oxygen consumption in Amphiuma at 15° C was the lowest recorded for any amphibian at a comparable temperature. It was found that the lungs were the primary respiratory exchange surface for oxygen consumption and were used very little for carbon dioxide elimination. Oxygen tensions in the major vessels showed large fluctuations which were related to the breathing cycle of the animal. Amphiuma breathed about once every hour at 15° C and it was just after a breath that oxygen tensions in the lungs and major vessels were the highest. There was a definite gradient between the pulmonary artery and systemic arch which persisted throughout the breathing cycle. Termination of inspiration in Amphiuma was shown to be controlled by a volume detection mechanism. It was found that low oxygen tensions in the blood brought about a breathing response whereas there was no relationship between the carbon dioxide levels in the body and the breathing response. The pulmonary artery had a lower diastolic blood pressure than did the systemic arch. There was a slight pulse lag in the systemic arch when compared to the pressure rise in the pulmonary artery such that a pressure rise was not recorded in the systemic arch until the blood pressure in the two circuits became equal. It was suggested that the pulse lag could account for deoxy genated blood being primarily shunted to the pulmonary circuit, and oxygenated blood being shunted to the systemic circuit.

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