Final answer:
Capnometry specifically measures the partial pressure of carbon dioxide in expired air, indicating the effectiveness of a person's ventilation and respiratory functions.
Step-by-step explanation:
Capnometry measures the partial pressure of CO2 (carbon dioxide) in C) expired air. This process is key for assessing the effectiveness of ventilation and the body's metabolism and respiratory function. During external respiration, the partial pressure of carbon dioxide in arterial blood is about 40 mm Hg, and upon reaching the alveoli in the lungs, it gets exhaled.
In contrast, the partial pressure of CO2 in the capillary blood is about 45 mm Hg before reaching the lungs. Due to the solubility of carbon dioxide in alveolar fluids and plasma, the relative concentrations that diffuse across the respiratory membrane are similar, maintaining the vital exchange during the respiratory process.