What gas is primarily used during pulmonary ventilation studies involving FRC?

In pulmonary ventilation studies that assess Functional Residual Capacity (FRC), the primary gas used is oxygen. This is because oxygen is non-toxic at the concentrations typically used in these studies and effectively participates in gas exchange. When evaluating FRC, it is essential to determine the amount of air remaining in the lungs after a normal expiration, and oxygen is a reliable marker for tracking how well this process is taking place in the lungs.

Additionally, oxygen's role in ventilation studies allows for accurate measurement of the lung's ability to take in air and exchange gases, which is crucial in understanding various pulmonary functions. In contrast, the other gases listed, such as carbon dioxide, nitrous oxide, and hydrogen, have specific applications in medicine and research but are not primarily used for measuring FRC in standard pulmonary function tests. Carbon dioxide is often monitored for its levels in the blood during metabolic studies; nitrous oxide can be used for anesthesia and as a tracer gas due to its properties, and hydrogen is primarily used in single-breath tests to assess diffusion capacity in specific contexts.