Effect of combination inhaled therapy on ventilation distribution measured by SPECT/CT imaging in uncontrolled asthma

Asthma is characterized by heterogeneous ventilation as measured by three-dimensional ventilation imaging. Combination inhaled corticosteroid/long-acting β₂-agonist (ICS/LABA) treatment response is variable in asthma, and effects on regional ventilation are unknown. Our aims were to determine whether regional ventilation defects decrease after ICS/LABA treatment and whether small airways dysfunction predicts response in uncontrolled asthma. Twenty-two symptomatic participants with asthma underwent single-photon emission computed tomography (SPECT)/CT imaging with Technegas, before and after 8-wk fluticasone/formoterol (1,000/40 µg/day) treatment. Lung regions that were nonventilated, low ventilated, or well ventilated were calculated using an adaptive threshold method and were expressed as a percentage of total lung volume. Multiple-breath nitrogen washout (MBNW) was used to measure diffusion-dependent and convection-dependent small airways function (Sacin and Scond, respectively). Forced oscillation technique (FOT) was used to measure respiratory system resistance and reactance. At baseline and posttreatment, Scond z-score was related to percentage of nonventilated lung, whereas Sacin z-score was related to percentage of low-ventilated lung. Although symptoms, spirometry, FOT, and MBNW improved following treatment, there was no mean change in ventilation measured by SPECT. There was, however, a wide range of changes in SPECT ventilation such that greater percentage of nonventilated lung, older age, and higher Scond predicted a reduction in nonventilated lung after treatment. SPECT ventilation defects are overall unresponsive to ICS/LABA, but the response is variable, with improvement occurring when small airways dysfunction and ventilation defects are more severe. Persistent ventilation defects that correlate with Scond suggest that mechanisms such as non-ICS responsive inflammation or remodeling underlie these defects.NEW & NOTEWORTHY This study provides insights into the mechanisms of high-dose ICS treatment in uncontrolled asthma. Ventilation defects as measured by SPECT/CT imaging respond heterogeneously to increased ICS/LABA treatment, with improvement occurring when ventilation defects and impairment of convection-dependent small airways function are more severe. Persistent correlations between ventilation defects and measures of small airways function suggest the potential presence of ICS nonresponsive inflammation and/or remodeling.