Uneven distribution of air trapping and its impact on physical activity in patients with asthma.

Background: The underlying pathophysiology of varying physical activity levels in patients with asthma remains unclear. In this study, we investigated the association between physical activity and air trapping, identified via chest computed tomography, in patients with asthma.

Methods: The following computed tomography analyses were used to evaluate air trapping in two cohorts (Cohort 1: 27 patients with asthma, 12 healthy individuals; Cohort 2: 90 patients with asthma, 43 healthy individuals): density analysis, focusing on air trapping characteristics during expiration, and parametric response mapping (PRM), which integrates inspiratory and expiratory computed tomography scans to categorize air trapping into small airway disease (PRM^SAD) and low-attenuation areas. Mucus plug scores were also measured.

Results: Patients with asthma exhibited significantly reduced activity levels compared with healthy participants at intensities of ≥2, ≥3, and ≥4 metabolic equivalents (METs) in both cohorts. Among patients with asthma, air trapping was significantly associated with decreased physical activity of ≥4 METs, corresponding to moderate-to-vigorous exercise intensity. Among the air-trapping components, increased PRM^SAD significantly contributed to reduced physical activity at ≥4 METs. Regarding the relationship between PRM^SAD and physical activity for each lung lobe, elevated PRM^SAD in the left upper lobe played a significant role in decreasing physical activity. The presence of mucus plugs was associated with elevated PRM^SAD.

Conclusions: The uneven distribution of air trapping in the lungs of patients with asthma, particularly in the upper lobe, was linked to reduced moderate-to-vigorous-intensity physical activity and was partially attributable to small airway obstruction caused by mucus plugs.