Emphysema Severity Index: a new spirometric parameter in epidemiology

The Emphysema Severity Index (ESI) is a recently developed parameter describing the curvilinear shape of the expiratory flow/volume curve to evaluate the emphysema contribution to airflow obstruction (AO), as observed in COPD patients and geriatric populations. The aim of the present study was to assess ESI usefulness in respiratory epidemiology studies where spirometry is typically the only available objective tool.

An adult population sample of Pisa (Central Italy) (n=685, 47.3% male, mean age 53.3 years) participated in an epidemiological survey through standardised questionnaire and spirometry (2009-2011); information on hospital admissions was available up to 2017. The input variables for the ESI computing algorithm are peak expiratory flow, forced vital capacity (FVC) and the forced expiratory flows at 25%, 50% and 75% of FVC. ESI is a numerical value ranging from 0 (no emphysema) to 10 (very severe emphysema). Statistics included descriptive analyses, Kruskas-Wallis nonparametric test and logistic regression models.

The ESI mean±sd value was: 1.16±0.78; median (IQR) 0.98 (0.39). The ESI was significantly higher in males, ex-smokers, the elderly, subjects with asthma/COPD, and in those with limited daily activities, higher number of doctor visits and hospital admission for respiratory disease. For each increment of an ESI IQR, higher odds of respiratory outcomes, daily activity limitations and use of health services emerged in the total sample, but also in subjects without AO.

ESI represents a potentially valuable indicator in epidemiological surveys on the general population and allows early changes in lung function to be identified also in subjects without AO, which is valuable for secondary prevention.