On the diagnosis of smallairway dysfunction in mild asthma

Aim . To assess the functional status of the small airways by bodyplethysmography and to determine the degree of small-airway dysfunction (SAD) in patients with mild asthma. Materials and methods . We examined 191 patients with mild asthma. The control group consisted of 36 healthy volunteers. Using bodyplethysmography, we evaluated functional residual capacity (FRC), residual volume (RV), total lung capacity (TLC) and the RV/TLC ratio. SAD was defined as RV > 140% predicted, RV/TLC > 125% predicted or FRC > 130% predicted. The severity of SAD was graded by percentage deviation from predicted values and z-scores. Results . SAD was detected in 44 asthma patients. Cluster analysis based on RV, RV/TLC and FRC divided these patients into three clusters. Statistically significant differences between clusters were found for RV, RV/TLC and their z-scores. Cluster 1 was characterised by elevated RV and RV/TLC. In Cluster 2, compared with Cluster 1, high RV and RV/TLC were accompanied by an FRC increase in 50% of cases. Cluster 3 showed high RV, RV/TLC and FRC, along with a TLC increase in 55% of cases. Spirometry demonstrated a progressive decline in airway patency, reflected by reduced FEV1 and maximum expiratory flow rates (MEF); worsening obstruction resulted in reduced VC in Clusters 2 and 3. SAD was consistently accompanied by elevated RV and RV/TLC, indicating marked air-trapping. Conclusion . SAD occurred in 23% of patients with mild asthma and was accompanied by a pronounced decrease in indices characteristic of bronchial-obstructive syndrome, including distal airways. RV, RV/TLC and their z-scores constitute the primary criteria for grading SAD in this patient population.