1. Initiation of exercise
During initiation of exercise, an abrupt increase in respiratory rate occurs because of neural changes which send excitatory impulses to the dorsal respiratory group (DRG) located in the medulla, specifically in its medullary respiratory center. The changes involve stimulating the limbic system due to anticipation of the activity, proprioceptors’ sensory impulses in muscles, joints, and tendons, and lastly, motor impulses sent out from the primary motor cortex, otherwise known as precentral gyrus.
2. Moderate exercise
During moderate exercise, more gradual increase in respiratory rate occurs due to chemical and physical changes happening in the bloodstream which are as follows: (1) slight decrease in PO2 caused by increase in use of O2; (2) slight increase in PCO2 because of increase in production of CO2 by contracting muscle fibers; and (3) temperature increase caused by release of more heat while more O2 is exhausted.
3. Abrupt ascent into high altitudes
In the event of abrupt ascent into high altitudes which have low oxygen content, the lungs respond through hyperventilation in hopes of providing adequate supply of oxygen to the different tissues of the body.
4. Paralysis of phrenic nerve
Damage or paralysis of the phrenic nerve can cause diaphragm weakness or paralysis which affects the lungs’ ability to exchange air. In line with this, difficulty in breathing may occur together with shortness of breath.
5. Severe anemia
Severe anemia may cause respiratory distress and hyperventilation since the lungs overcompensate to bring in more oxygen. This is brought by low levels of hemoglobin which prevents enough oxygen from reaching the brain and insufficient red blood cells to transport oxygen in the different parts of the body.
6. Advanced pregnancy
As pregnancy advance, the following changes occurs in the respiratory system: (1) reduced lung capacity, (2) increase in oxygen use, (3) increase in the size of the chest, (4) stuffy nose, (5) difficulty for the lungs to expand due to size of womb or position of the baby. All of these result in difficulty in breathing and shortness of breath during advanced pregnancy.
References:
Cogo, A. (2011, February 28). The lung at high altitude. Multidisciplinary respiratory medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3463062/#:~:text=The%20lung%20response%20to%20acute,least%20up%20to%203500%20m.
The lungs in pregnancy. Nationwide Children’s Hospital. (n.d.). https://www.nationwidechildrens.org/family-resources-education/family-resources-library/the-lungs-in-pregnancy
Phrenic nerve: Anatomy & Function. Cleveland Clinic. (n.d.). https://my.clevelandclinic.org/health/body/22270-phrenic-nerve
Rojas, Y. (2020, July 23). 10 symptoms of anemia you shouldn’t ignore. Texas Medical Institute. https://www.texasmedicalinstitute.com/10-symptoms-of-anemia-you-shouldnt-ignore/#:~:text=With%20anemia%2C%20the%20lungs%20overcompensate,%2C%20neurological%20issues%2C%20and%20vertigo.
Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy and physiology. Wiley Custom Learning Solutions.