A region of the brain stem called the medulla contains the respiratory center, which controls the body's respiratory rate. This respiratory center stimulates the phrenic nerves that innervate the diaphragm and the intercostal nerves that innervate the chest wall muscles. Increased carbon dioxide levels in the blood stimulate the respiratory center, sending a signal to breathe. As the respiratory rate increases, the bloodstream absorbs more oxygen from the lungs, while carbon dioxide passes into the atmosphere through exhalation. Any one of a number of factors can affect this process.
Oxygen Deficiency
The brain requires oxygen and is extremely sensitive to any reduction in the oxygen supply, even for a few minutes. Anything that interferes with the brain's blood supply or prevents oxygen from entering the blood can quickly cause brain damage and severely impair respiration. As the brain receives signals that the level of carbon dioxide is rising, it signals the body to breathe more. If the heart has ceased functioning and oxygenated blood is no longer going to the brain, cell death occurs.
Impaired Oxygen and Carbon Dioxide Exchange
Any condition that disrupts the normal exchange of oxygen and carbon dioxide in the lungs can result in respiratory failure. The thin walls of the alveoli or air sacs in the lungs lie very close to the thin walls of the capillaries within the lungs. At the cellular level, the air in the alveoli and the blood in the capillaries are separated only be a structure called the respiratory membrane. In a healthy lung this close proximity allows oxygen and carbon dioxide to pass freely between the air in the alveoli and the blood in the capillaries. According to the Cleveland Clinic, diseases such as chronic bronchitis, emphysema, pneumonia, pulmonary edema or severe asthma can adversely affect respiration by clogging the alveoli with mucus, which impairs the oxygen carbon dioxide exchange.
Respiratory and Cardiac Response
The respiratory center sends signals to increase breathing and stimulates the cardiac centers to increase heart rate simultaneously. According to the Mayo Clinic, because control of breathing and heart rate are closely linked and the control centers for each of these functions lie close to each other, any impairment of the heart or circulation can affect respiration. A faster or slower than normal heart rate can reduce the efficiency of the oxygen carbon-dioxide exchange by diminishing the flow of oxygenated blood to the alveoli in the lungs. As signals are sent to the brain that the body is oxygen deprived, both the respiratory and cardiac centers respond by increasing the respiratory and heart rate.
Reduced Compliance and Resistance
Two factors that play a role in respiration are compliance and resistance. Compliance is how elastic or stretchy the lungs are, which relates to how the lungs expand during inhalation and relax during exhalation. Resistance relates to how easily air flows in and out of the lungs. When the lungs have reduced compliance and resistance, it becomes more difficult for respiration to take place. As a result, the blood and body tissue becomes oxygen starved.
