A. ACTIVITY
1. Initiation of exercise
The occurrence of an increase in respiratory rate and depth of breathing during the initiation of exercise happens when: 1) the sensory receptors, called proprioceptors, receive stimuli during joint and muscle movement and then send this information to the brain, allowing the release of nerve impulses that stimulate the dorsal respiratory group or the inspiratory area of the medulla; and 2) at the same time, the axon branches of the upper motor neurons originating from the primary motor cortex (also called the precentral gyrus) send excitatory impulses, indicating a need for inspiration, resulting in stimulation of the diaphragm and contraction of the intercostal muscles (Tortora & Derrickson, 2017).
2. Moderate exercise
During exercise, there is increased activity in the sympathetic division of the autonomic nervous system, increasing the release of hormones in the adrenal medulla, which causes dilation of the airways by relaxing the smooth muscle in the bronchioles. Since the air reaches the alveoli more quickly, lung ventilation and respiratory rate increase (Tortora & Derrickson, 2017).
3. Abrupt ascent into high altitudes
An abrupt ascent into high altitudes may cause an increase in respiratory rate as higher altitudes generate faster pulse rates, characterised by increased pumping of the heart. However, it may also develop into respiratory difficulty because, according to Boyle's law, higher volume results in lower pressure; hence, abruptly ascending to higher altitudes results in the slowing down of oxygen diffusion into the blood due to the decreasing partial pressure of oxygen in the inhaled air, which in turn results in a decrease in alveolar pressure of oxygen (Human Biological Adaptability: Adapting to High Altitude, n.d. ; Tortora & Derrickson, 2017).
4.Paralysis of phrenic nerve
The phrenic nerve provides complete motor supply to the diaphragm, which is the main muscle for respiration. However, in cases where these nerves become paralysed, they can result in unilateral diaphragmatic paralysis (paralysis to either the left or right side of the diaphragm) or bilateral diaphragmatic paralysis (the entire diaphragm is paralysed), which can lead to respiratory difficulties as the diaphragm loses the ability to contract, disallowing proper inspiration (Mandoorah, 2023).
5. Severe anemia
Anemia is a blood disorder that develops when the blood produces below the normal amount of healthy red blood cells which are protein molecules called hemoglobin that primarily aid in the transportation of oxygen through heme attachment. Therefore, when a person has severe anemia, they experience respiratory distress as the lungs have to overcompensate with the inadequate level of hemoglobin which in turn decreases the amount of oxygen-rich blood, and they may experience difficulty breathing or shortness of breath (Rhodes et al., 2022).
10. Advanced pregnancy
Pregnancy causes several anatomical and physiologic changes in mothers, such as increased lung resistance and diaphragmatic excursion, which result in an increase in tidal volume and an increase in respiratory rate due to hormonal changes. On the other hand, studies show that preterm infants born to mothers with advanced maternal age (over 35 years old) have a higher rate of acquiring respiratory distress syndrome, which may cause the infant to have difficulty breathing due to hypoxemia or a decrease in the partial pressure of oxygen in the blood (Ceran et al., n.d.).
References:
Ceran, B., Çakır, U., Yıldız, D., Tuğcu, A. U., Sınacı, S., & Tayman, C. (n.d.). Risk of morbidity and mortality in preterm infants born to advanced maternal age pregnancies. Archives of Current Medical Research (ACMR), 3(3), 208–213. https://doi.org/10.47482/acmr.1134592
Human biological adaptability: adapting to high altitude. (n.d.). https://www.palomar.edu/anthro/adapt/adapt_3.htm
Mandoorah, S. (2023, August 8). Phrenic nerve injury. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK482227/
Rhodes, C. E., Denault, D., & Varacallo, M. (2022, November). Physiology, Oxygen Transport. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK538336/
Tortora, G. J., & Derrickson, B. (2017). Principles of ANATOMY & PHYSIOLOGY (15th ed.).