Forced Vital Capacity and Low Frequency Reactance Area Measurements Are Associated with Asthma Control and Exacerbations

Introduction: Forced vital capacity (FVC) is often preserved in severe asthma unless there is evidence of either airway remodelling or air trapping. Area under the reactance curve (AX) can be used to assess small airways dysfunction related lung stiffness and is related to disease control in severe asthma. Methods: We explore if there may be a potential synergistic interaction between FVC and AX in terms of impaired asthma control as ACQ and exacerbations requiring oral corticosteroids (OCS). We pragmatically defined < 100% and ≥ 1.0 kPa/L/s as impaired FVC or AX, respectively. Results: Patients with combined impairment of FVC and AX had significantly worse asthma control as higher ACQ, more severe exacerbations requiring OCS and worse spirometry (FEV ₁ and FEF _25–75) than those with impaired FVC but preserved AX. Conclusion: This in turn supports using both spirometry and oscillometry to characterise airway physiology more comprehensively in patients with more severe asthma.