1. Initiation of exercise - Neural changes send impulses to the dorsal respiratory group of the medullary respiratory center in the medulla. This conditions the body to anticipate the exercise, and signal the limbic system, muscles and primary motor cortex.
2. Moderate exercise - Chemical and physical changes in the bloodstream causes the increase of breathing; Said changes are: increased temperature, decreased partial pressure of oxygen, and increased partial pressure of CO2.
3. Abrupt ascent into high altitudes - This increases ATP demand due to decrease of total atmospheric pressure and partial pressure of O2, leading to a slowed O2 diffusion in the body.
4. Paralysis of phrenic nerve - Impulses pass through the phrenic nerve in order to reach the diaphragm; paralysis of this nerve prevents the diaphragm to contract, therefore preventing inhalation.
5. Severe anemia - Lack of iron, certain amino acids, vitamin B12, and mainly, functioning hemoglobin decreases Oxygen delivery.
10. Advanced pregnancy - Advanced pregnancy causes incomplete descent of the diaphragm due to fetus inside the body; The person then experiences difficulty inhaling.
Reference:
Tortora, & Derrickson. (2017). Principles of anatomy and physiology (15th ed.).