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 (FEV) 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 FEV≥ lower limit of normal (LLN) and FEV/forced vital capacity (FVC)≥LLN. PRISm was defined as forced FEV< LLN and FEV/FVC≥LLN, dysanapsis as FEV/FVC<LLN and FEV≥LLN, and airflow obstruction with reduced FEV as FEV/FVC<LLN and FEV<LLN. The BD response (BDR) was calculated as ((post-BD(L)-pre-BD(L))/predicted (L))×100. Values >10% 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 FEV 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 FEV 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 FEV. 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.