Oscillometry findings in altered spirometry patterns and relationship to respiratory symptoms.

Background: Preserved ratio impaired spirometry (PRISm) and restrictive spirometry pattern (RSP) are associated with increased morbidity and mortality, but the underlying mechanisms are unclear. Impulse oscillometry (IOS) measures small airway function more sensitively than spirometry. We aim to study the prevalence of abnormal IOS findings in relation to three spirometry patterns (obstructive, PRISm and RSP), and their associations with respiratory symptoms. Methods: In the Swedish CArdioPulmonary bioImage Study (SCAPIS), 10 360 participants aged 50-64 years underwent IOS and spirometry, and answered questionnaires on respiratory symptoms. Reference values were defined using healthy never-smoking participants. Abnormality was defined as <5th or >95th percentile, depending on the variable of interest. Results: Abnormal IOS indices were found in 31%, 38%, 28% and 40% of individuals with obstructive spirometry, only PRISm, only RSP and PRISm+RSP, respectively. Abnormal indices in individuals with obstructive spirometry (forced expiratory volume in 1 s/forced vital capacity <5th percentile) were associated with respiratory symptoms, particularly wheeze (adjusted (a)OR 2.84, 95% CI 2.02-3.99). In PRISm, abnormal indices were associated with dyspnoea (aOR 2.82, 95% CI 1.13-7.02), whereas in RSP, they were linked to wheeze (aOR 11.3, 95% CI 3.63-35.1) and any respiratory symptom (aOR 2.18, 95% CI 1.07-4.44). Abnormal indices were associated with increased sick leave due to respiratory problems in the obstructive group and the PRISm+RSP group, with highest risk in the latter (aOR 2.69, 95% CI 1.22-5.92). Conclusion: Abnormal IOS indices are common and can partially explain respiratory symptoms in individuals with altered spirometry patterns.