Factors Determining the Circulatory Adjustments to Diving: I. Water immersion

A ndersen , H. T. Factors determining the circulatory adjustments to diving. I. Water immersion. Acta physiol. scand. 1963. 58. 173–185. — The importance of water immersion per se for the circulatory adjustments to diving has been studied in the domestic duck. The heart rate has been used as an index of the cardio‐vascular changes. The physiological reactions characteristic of diving were elicited upon submersion in ducks with free access to air through tracheal cannulas, just as well as in intact birds. Likewise, the adjustments to diving were maintained by emerging ducks after the nostrils were above the water surface, provided the rest of the beak was kept submerged. Also, when the lungs and air‐sacs were ventilated at the normal rate during descent and submersion, the diving bradycardia was nevertheless elicited. By studying the heart rate during slow submersions of the beak and the head, it was found that the most marked cardiac slowing resulted from immersion of the level of the nares, whereas the conspicuous post‐divc tachycardia was brought about during the first respiratory effort. It is concluded that the circulatory adjustments to diving are elicited by the actual water immersion, probably due to stimulation of peripheral receptors in the beak, especially in the region of the nostrils. The degree of distention of the lungs and the air‐sacs, as well as variations in the venous return may also be important factors for the elicitation and abolition of the diving characteristics.