The relationship between respiratory system impedance and lung function in asthmatics: A prospective observational study

Sixty-four patients were completed this study. The median follow-up period was 55 months. At enrollment, although resistance showed no relationship with forced expiratory volume in one second (%FEV1), the reactance was moderately correlated with X5 (r = 0.524, r2 = 0.275, <0.001), Fres (r = −0.498, r2 = 0.248, <0.001) and ALX (r = −0.416, r2 = 0.173, p = < 0.001). By contrast, the annual resistance change at 5 Hz (R5) was highly and significantly associated with%FEV1 change (r = −0.564, r2 = 0.318, p < 0.001). Longitudinal changes in airway resistance and reactance measured by FOT might be useful for the assessment of lung function in patients with asthma.