Flow-over-volume elevation (FOVE) on Spirometry Allows for Early Recognition of Usual Interstitial Pneumonia

While most patients with usual interstitial pneumonia (UIP) have reduced DLCO at the time of diagnosis, many have normal FEV1, FVC, and FEV1/FVC. Other PFT parameters representing increased lung stiffness and elastic recoil may allow earlier identification of UIP.

This retrospective cohort study evaluated the relationships among spirometry, including novel parameters, lung volume, and DLCO in patients with UIP. Findings were evaluated by first versus last study, smoking history, and whether “normal spirometry” by ATS/ERS criteria.

At first testing, 56.7% of 194 UIP patients had FOVE (flow-over-volume elevation) with PEF/FVC, FEF25-75/FVC, or FEF75/FVC above the ULN, and 68.6% were near FOVE. 53.1% had “normal spirometry,” and of those, 47.6% were FOVE and 63.1% near FOVE. At first DLCO testing, 21.2% had normal spirometry, lung volume, and KCO, and of those, 48.3% were FOVE, 58.6% near FOVE, and 37.9% low DACO (predicted DLCO adjusted for lung volume). Heavy smokers had higher FVC (p<.001) and TLC (p=.004) and lower flows/FVC, DLCO, DACO, and DLCO and DACO relative to FVC or TLC (p<.001). There were significant changes from first to final testing. DACO better measured diffusion than KCO.

Existing standards for PFT interpretation do not consider novel spirometry parameters. This study shows that patients with UIP often have FOVE with elevated flows/FVC. Recommendations are provided for race-neutral PFT reference equations and for improving PFT reporting and interpretation.

FOVE is common in UIP patients with otherwise normal spirometry. PFT reporting and interpretation should include PEF/FVC and DACO. Identifying FOVE improves spirometry interpretation and may lead to earlier identification of UIP.