Final answer:
Hypercapnia is a condition characterized by high blood levels of carbon dioxide, which can be caused by impaired respiratory functions or reduced breathing. On the other hand, hypocapnia is a condition characterized by low blood levels of carbon dioxide, which can be caused by hyperventilation.
Step-by-step explanation:
Hypercapnia, or abnormally elevated blood levels of CO2, occurs in any situation that impairs respiratory functions, including pneumonia and congestive heart failure. Reduced breathing (hypoventilation) due to drugs such as morphine, barbiturates, or ethanol (or even just holding one's breath) can also result in hypercapnia. Hypocapnia, or abnormally low blood levels of CO2, occurs with any cause of hyperventilation that drives off the CO2, such as salicylate toxicity, elevated room temperatures, fever, or hysteria.