Breathing is a complex process that brings oxygen into the body and removes carbon dioxide. Though breathing can be controlled voluntarily, it is a function that is usually automatically managed by the brain. The muscle that responsible for breathing, the diaphragm, is controlled by the brain. Changes in the levels of breathing happen when the levels of oxygen and carbon dioxide are altered. Important changes in the rate of breathing occur during exercise and when you travel to higher altitudes.
Carbon Dioxide
Your breathing rate is controlled by centers in the medulla and pons of the brain stem. Changes in levels of oxygen and carbon dioxide determine the rate of breathing. Of these, carbon dioxide levels are the most important factor. Carbon dioxide is a waste product produced as the body breaks down glucose. A rise in carbon dioxide acts on sensors within the brain and increases your rate of respiration. This allows the lungs to expel carbon dioxide and prevent it from accumulating in the body.
Oxygen
The importance of oxygen in controlling of breathing is greater than that of carbon dioxide. Oxygen must fall to low levels before it influences respiration. In addition, oxygen does not act directly on the brain itself but on sensors inside the major blood vessels. Normal oxygen levels are about 100 mm Hg, or millimeters of mercury. When levels fall to less than 60 mm Hg, they begin to stimulate respiration by acting on these sensors.
Breathing in Exercise
During exercise, your body's demand for oxygen increases as your muscles break down energy molecules. By the same token, your body produces more carbon dioxide. Because of the effect of carbon dioxide on the brain, your breathing rate increases to expel this waste gas. According to Costanzo's "Physiology," breathing rates may increase form a normal 7.5 liters of air per minute to 120 liters per minute, more than 15 times the resting level. In addition to the direct effect of carbon dioxide in increasing the rate of breathing, impulses from muscles and joints are also thought to act on the brain as well.
Breathing at High Altitude
As mountain climbers and travelers reach higher altitudes, the amount of oxygen in the air begins to fall. At 18,000 feet above sea level, the oxygen pressure in the atmosphere is decreased by 50 percent. Falling oxygen levels stimulate the receptors in the blood vessels, which in turn stimulate the brain to increase the rate of breathing. Increased breathing can lead to abnormally low levels of carbon dioxide, contributing to mountain sickness, a disease characterized by headache, fatigue and dizziness.
References
- "Physiology"; Linda Costanzo; 2009
- "Textbook of Medical Physiology"; John Hall; 2010
