How does the increased respiratory rate at a high altitude indirectly recalibrates the sensitivity of central chemoreceptors to a lower PaCO2?
How does the increased respiratory rate at a high altitude indirectly recalibrates the sensitivity of central chemoreceptors to a lower PaCO2?
Respiratory rate is the rate at which breathing occurs. While the respiratory rate may be an important physiological quantity, it is often overlooked during routine clinical examinations despite its ease of measurement. The normal human respiratory rate is about 12-20 breaths per minute, with age being a major factor in establishing this standard range.
The respiratory rate up-regulates itself to a much higher level in response to the decreased partial pressure of oxygen (PaO2). However, this can indirectly lead to an increase in sensitivity of central chemoreceptors which respond when the PaCO2 is lower. This increased overall respiratory drive causes inhalation and exhalation planes which overlap so that the individual both inhales and exhales on the same respiratory cycle. This means that they are breathing back in CO2 which they just breathed out, so the PCO2 is higher than it was before they started to climb. At sea level, this would lead to significant hyperventilation with respiratory alkalosis, whereas at high altitudes it leads to respiratory compensation of the decreased PaO2. The increase in the rate of breathing allows the individual to get rid of CO2 more efficiently, so he/she can maintain their blood pH around 7.4 at all times despite the increased PCO2 which is due to the lower O2 available for respiration.
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