Briefly explain the main cause or mechanism of increase in respiratory rate or depth and/or respiratory difficulties in the following cases:
Initiation of exercise
The main cause for the increase in respiratory rate or depth is due to excitatory impulses sent by neural changes to the dorsal respiratory group (DRG) of the medullary respiratory center in the medulla. These neural changes include (1) anticipation of the activity, which stimulates the limbic system; (2) sensory impulses from proprioceptors in muscles, tendons, and joints; and (3) motor impulses from the primary motor cortex (precentral gyrus).
Moderate exercise
With moderate exercise, there is first an abrupt increase in breathing followed by a more gradual increase. The gradual increase in respiratory rate is due to chemical and physical changes in the bloodstream, including (1) slightly decreased PO2, due to increased O2 consumption; (2) slightly increased PCO2, due to increased CO2 production by muscle contracting muscle fibers; and (3) increased temperature, due to liberation of more heat as O2 is utilized.
Abrupt ascent into high altitudes
Acute exposure high altitudes results into low blood and tissue levels of oxygen which triggers a hyperventilating response to supply for the lack of oxygen. This is mainly caused by a low partial pressure of oxygen in the air because the atmospheric pressure at high altitudes is lower than the atmospheric pressure at sea level.
Paralysis of phrenic nerve
As the phrenic nerve provides motor innervation to the diaphragm, it is detrimental to the function of the respiratory system if dysfunction or paralysis of the diaphragm is caused by paralysis of phrenic nerve.
Severe anemia
An increase in respiratory rate will be observed when there is a very low level of hemoglobin due to the need of oxygen throughout the body. As hemoglobin is the primary carrier of oxygen in humans, the body will respond to this severe anemia through increasing respiratory rate.
Advanced pregnancy
Increased respiratory rate and depth will be experienced by the mother due to the growing fetus inside the mother's body. As the fetus grows inside the mother's womb, the diaphragm of the mother is compressed which inevitably decreases lung capacity, thus results in rapid breathing from the mother.