Characterizing the preserved ratio impaired spirometry phenotype in all severities of asthma

The preserved ratio impaired spirometry (PRISm) phenotype is characterized by a maintained FEV₁/FVC ratio ≥70 but an abnormal FEV₁<80 % predicted. Small airways dysfunction (SAD) is common amongst asthmatics and is associated with poorer clinical outcomes. SAD can be assessed using oscillometry as resistance between 5 and 20Hz (Rrs5-20), reactance at 5Hz (X5) and area under the reactance curve (AX). We aimed to investigate the prevalence of PRISm and its relationship with SAD in all severities of asthma with the primary outcome of annual exacerbation rate.

Data from the Oscillometry Asthma Registry comprising 937 adults with GINA-defined persistent asthma were retrospectively collected from two specialized asthma centres in UK and Italy. Multivariate analyses were performed using binary logistic regression to obtain adjusted odds ratios for the association between PRISm and exacerbation frequency and symptom control.

PRISm had a 19.6 % prevalence in moderate-to-severe asthma and was associated with a greater likelihood of ≥1 exacerbation [OR 95 %CI 3.00 (1.80,5.00) p < 0.001], ≥2 exacerbations [4.00 (1.86,8.59) p < 0.001] and uncontrolled symptoms [14.04 (4.87,40.50) p < 0.001] compared to patients with normal spirometry. Conversely, patients with PRISm were prescribed significantly lower ICS doses and had fewer exacerbations compared to those with airway obstruction.

The PRISm asthma phenotype is associated with greater exacerbation frequency, poorer symptom control and a higher SAD prevalence compared to patients with normal spirometry. Future research should focus on longitudinal follow-up to confirm the progression of PRISm to obstructive patterns and assess potential therapeutic interventions to modify this trajectory.