Steve Cain, age 12, of Mableton, Georgia, for his question:
Why does the breathing rate increase with exercise?
When resting, the body breathes in and out at a steady rate of about 17 times per minute. During a brisk run of two minutes, this rate may double. With more strenuous exercise, it may increase to 75 times per minute. Meantime, the heart also beats faster and the blood swooshes faster through the body. These automatic responses to exercise are related to the normal balances of two gases present in the blood.
During exercise, the body needs extra oxygen for increased cellular activity. At the same time, it strives to get rid of the surplus waste carbon dioxide created by this extra work performed by the cells. This exchange of gases involves the lungs, the heart, the bloodstream and especially the miraculous hemoglobin in the red blood cells. Changes in the breathing rate are adjusted to maintain a normal balance of oxygen and carbon dioxide gases in the blood.
When the body . inactive, it requires the use of about one pint of air per minute. This supplies the right amount of oxygen to fuel the various chemical activities of the living cells. Exercise comes in a variety of forms all of which require the movement of muscles. This muscular activity is effort and the energy for this is produced by a speed up of metabolism. For this, the cells need more oxygen fuel and more carbon dioxide is produced as a waste product of metabolism.
The body solves these problems by speeding up its respiration and heart beat. With each pulse, the heart sends a swoosh of used blood through the lungs. There the blood gives up its waste carbon dioxide and the hemoglobin in the red cells takes on a fresh quota of oxygen. Each heart beat also sends a swoosh of this recharged blood pulsing through the body. When exercise creates more work'for the cellular tissues, breathing becomes faster and deeper to adjust the extra oxygen and carbon dioxide. The heart beats faster to match the increased pace of these gaseous exchanges.
This teamwork is governed by centers in the brain, connected to a network of nerves through the chest region and nerves to other parts of the body. Respiration and circulation are automatic operations, geared to meet the needs of the body. During sleep, the breathing and pulse slow down because less oxygen is needed and less waste carbon is produced for disposal. But during strenuous exercise, the body may require four times more oxygen than usual and at the same time produce four times more waste carbon dioxide. The normal breathing rate of 17 times per minute increases to 70 or maybe higher.
The breathing rate may be changed by other things besides exercise. During emotional excitement, certain glands secret substances that trigger increased rates in the breathing and pulse. Sicknesses that cause high fevers also speed up respiration. On the other hand, certain drugs cause the breathing and pulse rate to decrease. An overdose of a harmful drug may slow down the breathing and pulse to a permanent standstill.