Department of Pulmonary Medicine,
Zakaria Research Center, Medical School of Mashhad Islamic Azad University,
Zakaria Research Center, Medical School of Mashhad Islamic Azad University
Department of Physiology, Mashhad University of Medical Sciences, MASHHAD-IRAN.
Background: The most sensitive parameter for evaluation of airway hyper-responsiveness is PC35 (35% decrease in specific airway conductance). But assessment of this parameter requires expensive equipments. This study aimed to evaluate mid expiratory flow and dysanapsis parameters in standard spirometry for possible substitution of PC35. Materials and Methods: Thirty-seven subjects with clinical findings suggestive of asthma who had normal standard spirogram were entered in this case-control prospective study. Thirty- seven healthy volunteers were also included in this study as controls. Airway responsiveness was examined by methacholine challenge test and measurement of PC20 and PC35. In addition, concentration of methacholine needed for 20% reduction in FEF25-75%, MEF50%, and FEF25-75%/FVC was determined and compared with PC35 as the gold standard. FEF25-75%/FVC ratio was used for evaluation of dysanapsis. Results: PC35 was more sensitive than PC20 and was obtained in 93% (68/73) of patients in both groups. Although PC35 and new parameters could be positive in both groups, the concentrations in two groups were significantly different. Regression model showed that in asthmatic patients all the conventional and new parameters had good and comparable correlations with PC35. But in the control group alone and in both asthmatic and control groups, PC 20 of FEF25-75%/FVC showed a significant correlation with PC35. PC20 of FEF25-75/FVC was also significantly correlated with PC20 of FEV1 in asthmatic and control groups. PC20 of FEF25-75/FVC and MEF50% revealed the best accuracy. An equation was determined for calculation of PC35 according to PC20 of FEF25-75 /FVC and MEF50% when PC35 was unavailable. Conclusion: PC20 of FEF25-75/FVC ratio and MEF50% are sensitive parameters for diagnosis of airway responsiveness. PC20 of FEF25-75/FVC is the best substitution for PC35. (Tanaffos 2009; 8(2): 24-30)