1. Initiation of exercise - There is an abrupt increase in breathing by neural changes that send excitatory impulses to the dorsal respiratory group (DRG) of the medullary respiratory center in medulla.
2. Moderate exercise - A gradual rise in breathing caused by chemical and physical changes in the bloodstream.
3. Abrupt ascent into high altitudes - At high altitudes, a drop in a drop in air pressure and oxygen level result in breathing difficulty. This is due to the external air pressure being lower than that within the lungs, thereby making it difficult to pull in the thinner air and for veins to pump oxygen throughout the body.
4. Paralysis of phrenic nerve - Phrenic nerve allows diaphragm to contract and expand, thus giving the lungs the ability to inhale and exhale air. Paralysis of phrenic nerve would paralyzed diaphragm, therefore, resulting to respiratory difficulties like shortness of breath.
5. Severe anemia - Too little functioning hemoglobin is present in the blood, which reduces oxygen transport to tissue cells. As a result, the body needs to work harder to compensate for this causing increase in respiratory rate or respiratory distress.
6. Advanced pregnancy - As the uterus expands and pushes upward into the abdomen, it compresses the lungs, limiting their capacity for oxygen exchange which results to respiratory difficulties. Additionally, elevated hormone levels, especially progesterone, cause shortness of breath.
References:
Byju’s. (2022, July 4). Why do human beings face difficulty in breathing at high elevations-. https://byjus.com/question-answer/why-do-human-beings-face-difficulty-in-breathing-at-high-elevations/
Professional, C. C. M. (n.d.). Phrenic nerve. Cleveland Clinic. https://my.clevelandclinic.org/health/body/22270-phrenic-nerve
Harvard Health. (n.d.). Shortness of Breath In Pregnancy. https://www.health.harvard.edu/decision_guide/shortness-of-breath-in-pregnancy#:~:text=One%20reason%20is%20that%20the,hormone%20that%20increases%20during%20pregnancy.