Initiation of exercise
Exercising makes our muscles work harder, using up more oxygen and creating carbon dioxide faster. To make up for the need for more oxygen, our breathing or respiratory rate will start increasing from 15 times per minute (12L of air) in preparation for moderate exercise.
Moderate exercise
The more exercising we do and the longer we do it, the more oxygen is required and the more carbon dioxide is released. Eventually our respiratory rate will increase to 40 to 60 times a minute (100L of air) in order to cope with the increased demand.
Asthma attack
One’s airway muscles, which should be thin and clear for the passage of air, abruptly expand or swell causing a great difficulty in breathing. This can be caused by a variety of triggers such as allergies, exercise, weather, smoke, strong emotions, viruses, and other irritants.
Abrupt ascent into high altitudes
At high altitudes, the air contains significantly less oxygen molecules than our bodies are used to. We react to this by hyperventilating, increasing our respiratory rate, in an attempt to compensate for the decreased amount of oxygen entering our lungs and transported throughout our body.
Pneumonia
This is the inflammation of the lungs caused by bacteria, viruses, or fungi that inflame the alveoli and fill it with fluids (or pus) that make it difficult for oxygen to get into one’s bloodstream.
Paralysis of phrenic nerve
The phrenic nerve is what allows our diaphragm to contract, allowing us to take in oxygen and release carbon dioxide. As a result, the paralysis of this nerve will inevitably lead to difficulty, if not complete inability, to breathe and the diaphragm will need to be mechanically ventilated.
Severe tuberculosis resulting lung scar tissue
Severe tuberculosis and the resulting the scar tissue in the lungs can cause inflammation and the shrinking of one’s airways. This makes breathing difficult and is known to leave this lasting effect on the patient throughout their life.
Severe anemia
Severe anemia, characterized by the decreased amount of red blood cells available to transport oxygen, decreases the respiratory rate simply being there isn’t enough RBC to transport oxygen and carbon dioxide.
Advanced pregnancy
Shortness of breath or difficulty in breathing during advanced pregnancy is normal as this is simply a hormonal response to the growing fetus by increasing progesterone.