Background: Little is known regarding annual changes of respiratory functions among patients with asthma after asthma symptoms enter remission.
Objective: Annual changes of respiratory function and influence of patient characteristics and treatment variables on these changes were assessed in patients with adult asthma.
Methods: Respiratory function (pre- and postbronchodilator forced expiratory volume in one second [FEV₁] and reversibility by short-acting β₂-agonist) and their changes were retrospectively investigated and relationships between these changes, after symptomatic remission, and patient characteristics and treatments were analyzed in adult outpatients with asthma who had undergone spirometry (including a reversibility test) ≥5 times in >5 years.
Results: In patients ≥40 years old, or with disease duration ≥10 years or receiving treatment for severe asthma (steps 4-5, high-dose inhaled glucocorticosteroids, or addition of other medications), both pre- and postbronchodilator FEV₁ values were significantly lower (p < .05). Mean annual change of prebronchodilator FEV₁ (Δpre-FEV₁), annual change of postbronchodilator FEV₁ (Δpost-FEV₁), and annual change of reversibility (Δ reversibility) were -13.8 ± 59.7 ml/year, -25.9 ± 51.0 ml/year, and -0.56% ± 1.89%/year, respectively. Multivariate analysis after stepwise selection for variables in patient characteristics or treatments showed that disease duration ≥10 years contributed to annual improvement of respiratory functions (Δpre-FEV₁: odds ratio [OR] 1.57, 95% confidence interval [CI] 1.01-2.46; Δpost-FEV₁: OR 2.13, 95% CI 1.25-3.66), treatment with long-acting β₂-agonists (LABAs) contributed to annual improvement of respiratory function (Δpre-FEV₁: OR 2.05, 95% CI 1.23-3.16; Δpost-FEV₁: OR 1.78, 95% CI 1.11-2.87), and poor compliance contributed to annual worsening of respiratory functions (Δpre-FEV₁: OR 0.43, 95% CI 0.24-0.76; Δpost-FEV₁: OR 0.39, 95% CI 0.22-0.70). In addition, duration of disease ≥10 years and severe treatment (steps 4-5) from the beginning contributed to decreasing Δreversibility (OR 0.55, 95% CI 0.34-0.87 and OR 0.50, 95% CI 0.29-0.83, respectively).
Conclusions: Long-term treatments for asthma are expected to normalize respiratory dysfunction, which cannot be repaired in the short term. Treatment with LABAs and patient compliance may be the most important factors associated with annual improvement of respiratory functions.