Physiological characteristics and temporal transitions of preserved ratio impaired spirometry

The pattern of preserved ratio impaired spirometry (PRISm) has gained increased attention in the last few years. While PRISm has been linked to increased morbidity and mortality, the underlying physiological causes remain unclear and the stability of PRISm over time remains uncertain.

We investigated 6571 individuals (≥25 years, 51.4% female) from the Austrian population-based, longitudinal LEAD (Lung, hEart, sociAl, boDy) study who underwent post-bronchodilator spirometry and body plethysmography twice within a 4-year interval. Individuals were classified into normal spirometry (forced expiratory volume in 1 s (FEV₁)/forced vital capacity (FVC)≥0.7 and FEV₁≥80% predicted Global Lung Function Initiative (GLI)); airflow limitation (AFL) (FEV₁/FVC<0.7); and PRISm (FEV₁/FVC≥0.7 and FEV₁<80% predicted GLI). Body composition was assessed by bone density scanning.

PRISm was present in 2.6% of individuals (n=171) at baseline. Different subgroups of PRISm were identified: after 4 years, 45.6% had persistent PRISm, 37.4% PRISm-to-normal and 17.0% had PRISm-to-AFL. Persistent PRISm individuals were characterised by significantly lower total lung capacity (TLC), with two-thirds meeting TLC criteria for restriction. PRISm-to-AFL had a higher TLC and lower airway conductance as well as a higher FEV₁ decline. Participants with new PRISm after 4 years (n=71) had the highest decline of vital capacity and TLC. Smoking status was not associated with PRISm progression or resolution as never- and ever-smokers with PRISm showed no difference in frequency of transitions after 4 years.

PRISm is primarily defined by low lung volumes and is characterised by a dynamic course, with more than two-thirds demonstrating stable or improving lung function. Lung volume assessment in PRISm is mandatory for precise evaluation of pulmonary function. Similar transition patterns in smokers and never-smokers challenge the assumption of PRISm as an early smoking-related obstructive state and emphasise the importance of repeated lung function testing over time.