Difference in Respiratory Function Between GOLD Stage 1 and Preserved Ratio Impaired Spirometry as Assessed by...

Preserved ratio impaired spirometry (PRISm) is heterogeneous, and its physiological relationship to early COPD remains unclear. We compared respiratory-mechanical patterns between non-restrictive PRISm (NrP) and GOLD stage 1 COPD (GOLD 1) using impulse oscillometry (IOS) and spirometry and explored longitudinal changes in a trackable subset.

We retrospectively analyzed 1,139 adults who underwent post-bronchodilator spirometry in 2013; IOS was available for a subset. PRISm was defined by FEV₁/FVC ≥ LLN with %FEV₁ <80%. GOLD 1 was defined per GOLD criteria (FEV₁/FVC <0.70; %FEV₁ ≥80%). Longitudinal analyses were restricted to individuals with >10 pack-years, IgE <170 U/L, eosinophils <300/µL, and ≥2 examinations to minimize Th2-high asthma confounding.

Among PRISm cases, 18 met NrP criteria, and 127 met GOLD 1 criteria; IOS was available for all 18 NrP and for 39 GOLD 1 participants cross-sectionally. IOS indicated greater peripheral airway dysfunction in NrP than in GOLD 1, with higher R5-R20 and Fres and more negative X5, despite relatively preserved spirometric indices. In the longitudinal subset (39 GOLD 1; 8 NrP), annual changes in spirometry and IOS exhibited wide variability and did not differ meaningfully between groups. These analyses were limited by small NrP sample size and incomplete IOS availability.

PRISm and GOLD 1 demonstrated distinct respiratory-mechanical patterns despite partially overlapping spirometric profiles. IOS identified peripheral airway abnormalities in PRISm that were not evident on spirometry, suggesting potential value for characterizing early or atypical airway dysfunction. However, sample-size limitations and major confounding factors-including age, smoking status, and bronchodilator exposure-preclude causal inference. Findings should be considered descriptive and hypothesis-generating. Larger prospective studies with balanced treatment exposure and comprehensive imaging and lung-volume assessment are needed to clarify the clinical relevance of IOS patterns in PRISm.