1. Initiation of exercise
During the start of exercise, the increase of respiratory rate is caused by neural changes and the excitatory impulses sent to the dorsal respiratory group. The stimulation of the limbic system due to the anticipation of the activity, sent sensory impulses and motor impulses are the changes involved.
2. Moderate exercise
During moderate exercise, the increase of respiratory rate is because of the increase in depth of breathing, where gradual chemical and physical changes in the bloodstream occur, such as an increase and decrease in the partial pressures of oxygen and CO2 due to the increases oxygen consumption and CO2 production, as well as an increase in temperature.
3. Abrupt ascent into high altitudes
High altitudes contain lower levels of oxygen which will cause an increase of respiratory rate as a response to obtain the needed supply of oxygen.
4. Paralysis of phrenic nerve
The phrenic nerve sends impulses that allows the contraction of the diaphragm to occur. The paralysis of the nerve will cause difficulties to perform respiration as the inability for the diaphragm to contract prevents inhalation.
5. Severe anemia
Iron deficiency causes a restriction in hemoglobin concentration which means that it inhibits the red blood cell's ability to utilize and carry oxygen, thus causing a lack of supply of oxygen in the bloodstream and consequentially causing shortness of breath or the increase of respiratory rate.
10. Advanced pregnancy
The diaphragm in the body during advanced pregnancy can be slightly compromised in the sense that it cannot perform complete contraction or descent due to the lack of space caused by the presence of the fetus, hence causing difficulties during respiration.