Restrictive pulmonary function pattern and its impact on asthma severity

Abstract

Introduction: The restrictive pattern with low forced vital capacity (FVC) and normal forced expiratory volume (FEV1 )/FVC ratio has been described in many patients with bronchial asthma. In most cases, this finding is due to extrapulmonary causes such as obesity or chest wall abnormalities. Objectives: To identify the association between true restrictive pulmonary function pattern and asthma severity, determined by FEV1 value, and rate of asthma-related emergency room (ER) visits, compared with pure obstructive changes among asthmatic patients. Materials and methods: A retrospective chart review of all adult patients who were referred for full pulmonary function tests with a diagnosis of asthma from 2010 to 2014 at King Abdulaziz Medical City, Riyadh. We defined true restriction as a total lung capacity <80% predicted with normal chest radiograph. Patients with restrictive lung disease, chest wall abnormalities and pseudorestriction were excluded. Comparative analysis was performed using chi-squared and t -test. For comparison between the incidence of ER visits, we measured the incidence rate ratio using Poisson regression analysis. Factors that could potentially confound the association between restriction and ER visits were adjusted for using multiple regression analysis. Results: A total of 141 patients were enrolled for analysis. True restrictive pattern was documented in 75 patients (53.19%) while 66 patients (46.80%) had pure obstruction. Moderate to severe obstruction was found more frequently in the restrictive group (56% vs. 25.8%; P -value <0.0001). The incidence rate of ER visits was five times higher among asthmatics with restriction than in asthmatics with pure obstruction, a finding that was statistically significant. The incidence rate ratio is 4.9 (95% confidence interval 3.1 to 8.0; P -value <0.001). Conclusions: Moderate to severe obstruction was more common in patients with true restrictive pattern with no apparent air trapping. Moreover, these patients have a higher incidence of ER-related visits than patients with pure obstruction.