Assessing Pulmonary Function

FEV and FVC Pulmonary Function Testing Graph, Small

Of the parameters outlined by the ATS/ERS/JRS/ALAT guidelines, pulmonary function testing provides the most objective and standardized measure for quantifying progression of disease. In particular, FVC and DLCO are recommended during routine monitoring of patients with IPF.1

Forced Vital Capacity

Forced vital capacity (FVC) is widely recognized as a valid and reliable clinical measure of pulmonary function that is useful not only for assessing IPF disease progression, but also for predicting risk of mortality in IPF.1112 Two clinical trials demonstrated that FVC is reliable, valid, and responsive as a measurement of clinical status. In these trials, there was a nearly 5-fold increase in the risk of death for patients with absolute declines in percent predicted FVC of ≥10% and a more than 2-fold increase in risk of death for patients with absolute declines in percent predicted FVC between 5% and 10%,11 though even marginal decreases in FVC are associated with worse IPF prognosis.12

While FVC has been correlated with survival in multiple large patient cohorts, it is not fully accepted as a surrogate for all-cause or disease-specific mortality in IPF.7

Referral to a pulmonary transplant center is suggested if a patient with IPF has an FVC decrease of 10% or more and has no contraindications.13

Diffusing Capacity for Carbon Monoxide

A decline in absolute DLCO also may reflect progressive disease; as such, it is a measurement recommended during routine monitoring of patients with IPF.1 However, caution should be taken when measuring absolute DLCO, because declines observed also may be affected by the presence of pulmonary hypertension, anemia, active smoking causing elevated carboxyhemoglobin levels, and concomitant emphysema.1

A decrease in DLCO has been correlated with increased risk of mortality,13513 though this finding is not universally found and thought to be reflective of the underlying variability in the test.420

Pulmonary function tests are critical in the assessment of patients with IPF–a relationship with mortality and disease progression has been established. More specifically, analysis of various clinical cohorts has shown that a ≥10% absolute change in FVC or a ≥15% absolute change in DLCO are markers for increased risk of mortality and disease progression over the subsequent year.23456 Measuring FVC and DLCO in 3-6 month intervals is recommended by ATS/ERS/JRS/ALAT.1

Content contributed by:
Ryan Hadley, MD
University of Michigan