D1.122 - Inspiratory and expiratory airway resistance and expiratory flow limitation in patients with asthma and in response to biological treatment in asthma

Airway resistance in asthma can be measured with respiratory oscillometry. Inspiratory and expiratory resistance can be assessed separately, allowing estimation of expiratory flow limitation (EFL). The aim of this study was to investigate airway resistance and EFL in patients with asthma, and to examine its association with asthma severity, bronchodilator response, and biological treatment. 

A total of 75 participants were included in this study (58 patients with asthma and 17 healthy controls). All subjects underwent spirometry and impulse oscillometry, and symptoms were assessed using the Asthma Control Test (ACT) and the Asthma Control Questionnaire (ACQ). Patients initiating biological treatment were followed up after 4 weeks and 4 months.

Patients with asthma patients exhibited higher inspiratory and expiratory resistance, as well as higher EFL, compared to healthy controls. The differences were most pronounced in the peripheral airways, reflected by R5 and R5-R20 (p<0.001). After bronchodilation, most airway resistance parameters improved; however, they remained impaired compared to the healthy controls (including R5 and R5-R20, p<0.001). EFL after bronchodilation remained significantly different in the peripheral airways (R5-R20, p<0.001).

No significant correlation was found between EFL and asthma symptom scores (ACT and ACQ). Patients receiving biological treatment showed significant clinical improvement within 4 months, with reduced symptom scores (p=0.017 and p<0.001) and a modest increase in forced expiratory volume in 1 second (FEV1; p=0.011). Inspiratory resistance decreased significantly after 4 months of biological treatment (R5; p=0.011, R20; p=0.028 and R5-R20; p=0.004), whereas expiratory resistance did not a corresponding reduction.  Changes in symptom scores were not correlated with changes in airway resistance.

Both Inspiratory and expiratory airway resistance were increased in patients with asthma compared to healthy controls, particularly in the peripheral airways. Bronchodilation mainly improved resistance in the peripheral airways. Biological treatment reduced asthma symptoms and primarily improved inspiratory resistance. No association was found between symptom burden and airway resistance. Separate assessment of inspiratory and expiratory may provide additional value in characterizing asthma and understanding disease patterns.