ERS 2023: How Much Change in FEV1 is Associated with an Increased Risk of an Asthma Exacerbation?

In asthma management, spirometry, precisely the measurement of forced expiratory volume in one second (FEV1), is advocated by several guidelines. This practice is a foundation for treatment decisions, yet the precise clinical significance of changes in FEV1 remains uncertain. Data were extracted from five clinical trials wherein FEV1 measurements were conducted at three-month intervals over a year to shed light on this. Variations in FEV1 between these visits were quantified using different metrics, including %FEV1, FEV1 z score, and FEV1 change score (Zc). The Zc was a novel metric derived from stable measurements within this pediatric population, incorporating adjustments for age and the interval between measurements. Logistic regression analysis was employed to assess the relationship between changes in FEV1 between visits and asthma exacerbations within a three-month window. The dataset encompassed 8895 paired FEV1 measurements from 1264 children. Notably, a relative decline in %FEV1 between 14% and 20% was associated with an increased likelihood of experiencing an asthma exacerbation within the subsequent three months, with odds ratios (OR) ranging from 1.5 to 1.9.

Interestingly, absolute changes in zFEV1 were not associated with asthma exacerbations. However, a decline in the FEV1 change score within the 1.3 to 2.0 Zc range was linked to an increased risk of exacerbation, with ORs ranging from 1.3 to 1.6. Unexpectedly, rises in %FEV1 (14% to 20%), z score (1.3 to 1.6), and Zc (1.2 to 2.0) were also associated with elevated ORs for exacerbation, ranging from 1.3 to 1.7.

Additionally, it was observed that individuals with at least one Zc ≥±1.6 during follow-up exhibited a reduction of 0.4 in the mean initial FEV1 z score compared to those whose Zc remained <±1.6 throughout the study. In conclusion, this study suggests that both declines and increases in %FEV1 or change scores are linked to a modest elevation in the odds of experiencing future asthma exacerbations. These findings underscore the potential utility of considering both the "baseline" FEV1 and changes in FEV1 between visits as indicators for identifying children at risk of asthma exacerbations.