Lucy is traveling to the top of Pike's Peak. The elevation is 14,000 feet. At the base, her respiration rate is 12 breaths per minute. At the top of Pike's Peak, her respiration rate increases to 20 breaths per minute. Why does Lucy's respiration rate most likely increase at the higher elevation

Lucy's respiration rate increases because of the decrease in the atmospheric pressure and the partial pressure of O₂.

Explanation:

As Lucy ascends, the atmospheric pressure decreases. The decrease in this pressure decreases the partial pressure of inspired O₂, which causes less oxygen saturation in the blood. As oxygen is essential for the vital functions of the body, the respiratory rate increases to valance the loss of oxygen. In other words, the oxygen that the body had in one inspiration, now it has to obtain with multiple breaths. The same happens with the CO₂ that Lucy expels from her body.