Background and aims: Asthma is a chronic disease characterized by airway inflammation; it is sometimes difficult to diagnose. For clinical diagnosis, forced oscillation technique (FOT) measures airway reactance and resistance. By FOT, we investigated respiratory resistance and ventilation perfusion ratio inequality in adults with mild asthma.
Methods: We examined 58 adult patients with mild asthma having no inhaled corticosteroid treatment, and 10 adult patients with post-infectious prolonged cough. Using a MostGraph-01 FOT instrument, we evaluated these patients before and after bronchial hyperresponsiveness to acetylcholine (ACh) or histamine (Hist). We measured the following conditions: change of resistance at 5Hz (R5) and 20Hz (R20), R5-R20, reactance at 5Hz, frequency of resonance (Fres), low-frequency reactance area (ALX), and forced expiratory volume in 1 second (FEV1).
Results: There were significant changes of R5, R20, R5-R20, X5, Fres, ALX after provocations for ACh or Hist in all patients with asthma, but not in patients with post-infectious prolonged cough. We calculated the percent decrease in FEV1 after provocation with ACh or Hist. For Ach, this decrease in FEV1 correlated with changes in R20 and Fres for all patients. For Hist, the percent decrease in FEV1 correlated with changes in R5, R20, Fres, and ALX for all patients. Furthermore, we investigated these correlations in patients with normalized bronchial hyperresponsiveness to ACh or Hist. For Ach, the percent decrease in FEV1 correlated with changes in Fres or R5-R20. For Hist, this decrease in FEV1 correlated with changes in R5, R20, and Fres. ROC analysis was used to evaluate the diagnostic value of the ratio of change of Fres in BHR to Hist. The area under the curve was 0.7808 (95% CI=0.657-0.904). A reasonably high specificity (100.0%) and a high sensitivity (53.8%) with a cut-off point of 1.5 in the ratio before and after of Fres were obtained.
Conclusion: The changes in FOT parameters (before and after bronchial airway responses) may detect airway resistance and ventilation perfusion ratio inequality even in adult patients with asthma having normalized bronchial hyperresponsiveness to ACh or Hist. That results may be useful for an early diagnosis of asthma.