CARDIAC OUTPUT DURING DIVING IN AN UNRESTRAINED SEA LION.

AQUATIC mammals and birds experience abrupt and profound cardiovascular changes during water immersion. In seals, for example, a diving bradycardia of one-tenth the normal rate without change in pressure has commonly been observed1,2. The evidence suggests that this is accompanied by a reduction in cardiac output and widespread vasoconstriction in skeletal muscle1,3, skin1 and kidneys4. Even in man, a relatively poor diver, the flow of blood in the limbs has been shown to decrease during breath-holding dives5. A single determination of cardiac output has been made in a seal during non-diving asphyxia6, but direct blood flow measurements are lacking.