What happens to the human circulatory system when breathing is shut off?
Dr. Per Frederik Scholander wanted to know, because the information might help to save lives threatened by suffocation. The answer, he learned, is that the body takes heroic measures to protect its inner fortress — the brain, lungs and heart itself. In accomplishing this, the rest of the body is starved of blood, a process that may have unwanted and dangerous side effects.
More remarkable than Dr. Scholander's interest in the subject and the answer he found was his experimental approach. He took seals to his laboratory at the University of Oslo, strapped them to boards and dunked them in a bathtub, to simulate diving. Now at the Scripps Institution of Oceanography at La Jolla, Calif., he works with Dr. Robert W. Eisner, a physiologist who trains seals to simulate diving by voluntarily holding their own noses under a few inches of water.
The researchers were well aware that any land animal, including man, suffers irreparable brain damage if his supply of circulating oxygen is cut off for more than four or five minutes, and drowns in a few minutes more. But they also knew that any one of several diving birds (loons, grebes, cormorants and "sea ducks") can endure immersion for more than ten minutes. The warmblooded seal can endure under water for more than 20 minutes, and the equally warm-blooded whale can last for an hour, perhaps even two. Scholander's odd experiments were carefully designed to discover how the aquatic animals survive.
Not More, but Less. The idea that these birds and mammals store up extra oxygen for their endurance dives was exploded long ago. Somehow they manage to survive on less oxygen rather than more. But how? Dr. Scholander soon found out that on submergence in a bathtub the seal's heartbeat is slowed to about one-tenth of its normal rate. This happens so fast that the trigger for the circulatory defense mechanism seems to be psychological rather than physical. Scholander's experiments proved this. A loud, sharp noise produces the same heart-slowing effect on a seal at the edge of a tank; a seal swimming free, close to the surface, aware that it can raise its head to take a breath any time it chooses, does not slow down its heart at all.
What happens in man, Dr. Scholander told the American Philosophical Society last month, is much the same as what happens in the seal, though less pronounced. The human volunteer who holds his breath while his mouth is under water reacts in much the same way as a seal trained to perform a symbolic dive by keeping its snout submerged in a tub. In both, the heartbeat is slowed. More significant, the flow of blood through flippers or feet is sharply reduced. So is the flow of blood through intestines and kidneys—everywhere except in the brain, lungs and heart. Even in active swimming, the extremities can get along for a while on stored oxygen, then switch over to using the muscles' store of glycogen, a fuel form of starch that the body can "burn" without oxygen. The brain-lungs-heart assembly gets all the available blood.