1. Initiation of exercise
- At the initiation of exercise, 12 litres of air is increased at rest to 100 litres of air during exercise to meet the oxygen usage and carbon dioxide production. Then, the muscles receive oxygen at high circulation speed so they keep functioning.
2. Moderate exercise
- The activity is increased in the sympathetic division of the autonomic nervous system (ANS) and the epinephrine and norepinephrine hormones are released from the adrenal medulla which relaxes the smooth muscles in the bronchioles. As a result, it dilates the airways, improving lung ventilation as it makes the air reach alveoli quickly.
3. Abrupt ascent into high altitudes
- The partial pressure of oxygen (O2) and the overall air pressure both drop with altitude. Even though oxygen still makes up 20.9% of the total, altitude causes a drop in the oxygen partial pressure (PO2). In turn, O2 diffuses into the blood more slowly, and alveolar PO2 drops.
4. Paralysis of phrenic nerve
- The diaphragm is supplied with phrenic nerves for motor innervation that also works with secondary respiratory muscles for respiration. Thus, a paralyzed diaphragm impairs the exchange of gases in the lungs, resulting in shortness of breath when lying down.
5. Severe anemia
- The prevention of adequate oxygen reaching the brain is due to hemoglobin deficiency. Thus, the lungs are overcompensating to bring in more oxygen which causes respiratory difficulties.
10. Advanced pregnancy
- Excessive capillary permeability is induced by preeclampsia, one of the most common complications of advanced pregnancy. Due to this, the airway edema worsens, making intubation potentially exceedingly challenging.
References
Brichant, J. F., Brichant, G., Dewandre, P. Y., Foidart, J. M., Collége national des gynécologues et obstétriciens, Société française de médecine périnatale, Société française de néonatalogie, & Société française de anesthésie et de réanimation (2010). Manifestations hémodynamiques et respiratoires de la prééclampsie [Circulatory and respiratory problems in preeclampsia]. Annales francaises d'anesthesie et de reanimation, 29(4), e91–e95. https://doi.org/10.1016/j.annfar.2010.02.023
Oliver, K. A., & Ashurst, J. V. (2023). Anatomy, Thorax, Phrenic Nerves. In StatPearls. StatPearls Publishing.
Ouellette D. R. (2005). The impact of anemia in patients with respiratory failure. Chest, 128(5 Suppl 2), 576S–582S. https://doi.org/10.1378/chest.128.5_suppl_2.576S
Professional, C. C. M. (n.d.). Phrenic Nerve. Cleveland Clinic. https://my.clevelandclinic.org/health/body/22270-phrenic-nerve
Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy & physiology. Fifteenth edition; Wiley Loose-Leaf Print Companion. Hoboken, New Jersey, John Wiley & Sons, Inc.
Your lungs and exercise. (2016). Breathe (Sheffield, England), 12(1), 97–100. https://doi.org/10.1183/20734735.ELF121