Rapid breathing blows off excess CO2. The breathing is an inherent response to chronic illness, not the other way around.
For example, people with emphysema/COPD/COAD/CAD all breathe rapidly in response to excessive build-up of CO2 in their blood due to inadequate expulsion of air. They can actually be seen to blow the air out. Excessive CO2 leads to acidosis in the blood and would be fatal if they did not respond with the rapid breathing/dyspnoea. The cause emanates from damaged lungs, not the rate of breathing. The breathing response acts as a buffer to the acidosis by blowing the excessive CO2 off.
On the other hand a healthy person who deliberately hyperventilates will end up 'on the floor' due to the excessive decrease of CO2 and resultant alkalosis of the blood.
Shortness of breath and resultant dyspnoea/rapid breathing also occurs when people suffer a fever due to increased oxygen requirements secondary to an increased metabolic rate.
Shortness of breath is also a common symptom of cardiac muscle damage owing to the heart's decreased ability to pump sufficient quantities of oxygenated blood. Acidosis is once again the end result and stimulates the person to breathe at an increased rate than is normal for a healthy individual.
All of the above is not to say that it is healthy that many people tend to breathe shallowly, using only their upper torso muscles, rather then diaphragmatically, which comes from the abdomen. Deeper, slower breathing is probably a better description of what is healthy, rather than the singularly descriptive rate of breathing.
