Pulmonary Function Testing Procedures
Spirometry performance
Know the acceptability criteria: free of artifact, no cough in the first second, no glottic closure or variable effort, and a satisfactory end of test, either a plateau of at least 1 second with less than 25 mL change or a forced expiratory time of at least 6 seconds, or the patient cannot continue. Back-extrapolated volume should be under 150 mL or 5 percent of FVC, whichever is greater. Obtain at least three acceptable maneuvers and meet repeatability: the two largest FEV1 values and the two largest FVC values within 150 mL. Report the largest FEV1 and the largest FVC, not necessarily from the same trial.
Other procedures
Slow vital capacity requires a stable tidal breath and a slow, complete exhalation to determine inspiratory capacity, expiratory reserve volume, and vital capacity. Plethysmographic lung volumes require quiet tidal breathing, shutter closure at end-expiration, and panting at about 1 Hz against the closed shutter, with thoracic gas volume derived from mouth pressure versus box volume. DLCO requires a rapid inhalation to near TLC from residual volume, an 8 to 10 second breath hold, a 0.75 to 1.5 L washout, and sample collection before dead space is exhaled. Methacholine challenge uses doubling doses and a fall in FEV1, usually 20 percent, to define a positive test.
Worked example
Three efforts give FEV1 of 2.00, 2.10, and 2.08 L. The two largest differ by 0.02 L, well inside 150 mL, so repeatability is met and the reported FEV1 is 2.10 L; the FVC and FEV1 need not come from the same trial.