THE REGULATION OF ARTERIAL BLOOD PRESSURE IN THE SEAL DURING DIVING

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Abstract
The blood pressure in the femoral artery of a seal remains at the resting level during a dive in spite of the fact that the heart slows to about 10% of its frequency at rest. Normal pressure is thus available for the circulation of a small part of the tissues. In a toe artery in the hind flipper about 1 mm in bore, the pressure fell to the venous level during a dive, showing the occurrence of active arterial constriction as a factor in the elective restriction of blood flow. The arterial constriction was sudden, and practically completely abolished the difference between arterial and venous pressures. In the "mesenterial region" the size of the vessels diminished during diving and the tissues became cyanotic. The reduction of pressure in the toe artery in the flipper may be caused to occur by pinching, sound and visual stimuli, which often do not affect the femoral blood pressure or heart rate in a noticeable way. Evidently the control of the smaller arteries of the seal is reflex in nature, and it resembles and often coincides with the type of vasomotor control which is exerted upon the arterioles.

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