Preserved ratio impaired spirometry, dysanapsis and airflow obstruction with low forced expiratory volume in 1 s in childhood asthma.

Background: Airway obstruction is a characteristic spirometric finding in asthma but the clinical significance of other abnormal spirometric patterns is less well described. We aimed to explore pre- and post-bronchodilator (BD) prevalences and clinical characteristics of preserved ratio impaired spirometry (PRISm), dysanapsis and airflow obstruction with low forced expiratory volume in 1 s (FEV₁) in children diagnosed with asthma.

Methods: We extracted specialist care data (clinical and spirometry) from the Swedish National Airway Register (n=3301, age 5-17 years). Normal spirometry was defined as FEV₁≥ lower limit of normal (LLN) and FEV₁/forced vital capacity (FVC)≥LLN. PRISm was defined as forced FEV₁< LLN and FEV₁/FVC≥LLN, dysanapsis as FEV₁/FVC1≥LLN, and airflow obstruction with reduced FEV₁ as FEV₁/FVC110% were considered positive (BDRpos). Groups were compared using parametric tests and associations were explored using logistic regression analysis.

Results: Pre-/post-BD PRISm, dysanapsis and obstruction with low FEV₁ were identified in 9%/7%, 10%/4% and 8%/2%, respectively. Compared with normal spirometry, all three groups were associated with older age and BDRpos in pre-BD analyses. Furthermore, dysanapsis was associated with overweight/obesity and obstruction with low FEV₁ with uncontrolled asthma and more treatment.

Interpretation: In this paediatric asthma cohort, PRISm and dysanapsis were associated with BDRpos and they were at least as common as airflow obstruction with reduced FEV₁. These spirometric phenotypes should be addressed in the management of childhood asthma and testing of BDR should be considered also in children with PRISm and dysanapsis.