Final answer:
The measurement of blood PCO₂ is typically done through calculations of blood pH and total CO₂ concentration. This process takes into account the various methods by which CO₂ is transported in the blood, primarily as bicarbonate ions.
Step-by-step explanation:
The question addresses the measurement of blood PCO₂, or partial pressure of carbon dioxide, which is an important indicator of respiratory function and metabolic rate. The correct answer is b. Calculations of blood pH and total CO₂ concentration. By measuring the blood pH and knowing the total concentration of CO₂, one can calculate the partial pressure of CO₂ in the blood. This involves understanding how CO₂ is transported in the bloodstream—mainly as bicarbonate ions, but also dissolved in plasma or bound to hemoglobin (carbaminohemoglobin). Relevant lab tests can determine if there is an acid-base imbalance, such as acidosis or alkalosis, and whether the issue is metabolic or respiratory in nature.
Carbon dioxide dissolves in blood, but only about 5 to 7 percent of it is transported this way. A small percentage of CO₂ binds to hemoglobin to form carbaminohemoglobin, but the majority is converted to bicarbonate ions with the help of the enzyme carbonic anhydrase. This bicarbonate buffer system is crucial for maintaining the body's pH balance and facilitating CO₂ transport.