Improved spirometric index to discriminate the severity of centrilobular emphysema

Abstract

Introduction/Aims: Obstructive Index (OI) is a spriometic index that reflects the shape of the maximal expiratory flow-volume (MEFV) curve. A previous study showed that OI reflects the concavity of the MEFV curve and the extent of emphysema (Mochizuki et al., Sci Rep 9, 13159, 2019). However, the association of OI with emphysema subtypes such as centrilobular emphysema (CLE) and paraseptal emphysema (PSE) has not yet been elucidated. This study aimed to investigate whether OI could reflect the severity of CLE and PSE.

Methods: This study retrospectively analyzed 917 subjects who underwent chest computed tomography (CT) and spirometry at three different facilities, namely, a medical checkup center (Tsukuba Medical Center, N=420), clinic (Terada Clinic, N=328), and university hospital (Kyoto University, N=169). The presence and severity of CLE and PSE on CT were assessed visually based on the Fleischner Society’s classification system. The OI was Box-Cox transformed for normalization and adjusted using least-squares mean regression. Tukey’s honest significant difference test was used for multiple comparisons.

Results: In subjects without PSE, OI increased with the severity grade of CLE (adjusted mean of Box-Cox transformed OI; absent: 2.08; trace: 2.14; mild: 2.22; moderate: 2.78; confluent: 2.90; advanced: 3.73). OI in subjects with moderate, confluent, and advanced CLE was significantly higher than that in those without CLE (all P <0.001). In contrast, OI did not differ among the different grades of PSE (absent, 2.07; mild, 2.09, and substantial, 2.06) in subjects without CLE.

Conclusions: OI could be useful as a biomarker to discriminate the severity of CLE.