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Initiation of exercise: At the onset of exercise, there is an abrupt increase in respiratory rate, attributed to the neural changes that transmit stimulating signals to the dorsal respiratory group (DRG) within the medullary respiratory center located in the medulla (Tortora, 2017).
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Moderate exercise: The gradual increase in respiration rate observed during moderate physical activity is a result of chemical and physical changes in the blood composition, including (1) a slightly reduced PO2 due to heightened oxygen consumption, (2) a slightly increased PCO2 due to increased CO2 production of contracting muscle, and (3) an increase in temperature stemming from the release of more heat as more oxygen is utilized (Tortora, 2017).
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Abrupt ascent into high altitudes: At higher altitudes, the overall atmospheric pressure is lower compared to sea level, resulting in a decreased oxygen partial pressure gradient, which leads to reduced oxygen intake with each breath. In response, the body compensates by increasing the respiratory rate, ensuring an adequate supply of oxygen reaches the lungs (Seeley et al., 2016).
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Paralysis of phrenic nerve: The phrenic nerves innervate the diaphragm and damage to these may cause the paralysis of the latter (Tortora, 2017 ), affecting the normal mechanism of the body to inhale and exhale air. Thus, in response to this, the body experiences an increase in respiratory rate.
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Severe anemia: In cases of severe anemia, there oxygen-carrying capacity of the blood is reduced due to decreased numbers of hemoglobin (Seeley et al., 2016 ). The increase in respiratory rate is likely to be a response to compensate for this.
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Advanced pregnancy: Advanced pregnancy can prevent the complete descent of the diaphragm, which is responsible for about 75% of the air that enters the lungs during quiet breathing (Tortora, 2017). The increase in respiratory rate is also likely to be a response to compensate for this.
References:
Seeley, R., VanPutte, C., Russo, A., & Regan, J. (2016). Seeley’s Anatomy & Physiology. McGraw-Hill Education.
Tortora, G. J. (2017). Tortora’s Principles of Anatomy and Physiology. In John Wiley & Sons, Inc. eBooks. https://ci.nii.ac.jp/ncid/BB23861293.