Pulmonary function tests (PFTs) sort out the ability of the lungs to ventilate and oxygenate. Perhaps the most useful PFT measures arterial blood gas (ABG). Once we've established that the ABG is normal, it doesn't much matter whether pulmonary function is provided by a machine or is natural, nor do specific respiratory parameters (eg, tidal volume, respiratory rate, flow rate) matter as much as the end result of pulmonary function—the ABGs. The next type of PFT is spirometry, is the measurement of inhaled and exhaled lung gas. The next PFT is the flow-volume loop. Before looking at how the loop changes with pathologic conditions, you should be familiar with the axes of the graph. Note that the horizontal axis is inverted, with high volumes closer to the origin and low volumes further from the origin. Finally, the test measuring diffusing capacity of the lung for carbon monoxide (DLCO) rounds out the list of commonly used PFTs.