Correlation among functional respiratory parameters and disease control in asthma.

Asthma is a complex inflammatory disease involving large and small airways with different degrees of inflammation and remodeling which are responsible for disease symptoms. We evaluated clinical and functional data in a group of 26 patients (18 women, age range 18-75 years) with mild-to-severe asthma in order to correlate functional markers of airways dysfunction and ventilation inequality with clinical data. Global spirometry, single-breath nitrogen washout (SBN2W), body pletysmograph and impulse oscillometry (IOS) were performed, both at baseline and after bronchodilator test with salbutamol 400 mcg. Asthma severity was assessed according to GINA guidelines and disease control was evaluated using the Asthma Control Test (ACT). All IOS parameters (resistance of the respiratory system at 5Hz [R5], and 20Hz [R20], difference of R5 and R20 [Di5-20], reactance area [AX], resonant frequency [FRes]) and airway resistance (Raw) were negatively correlated (p<0,01) with forced expiratory volume in 1 sec (FEV1), forced mid-expiratory flow (FEF25-75) and peak of expiratory flow (PEF) but not with disease severity. None of the IOS parameters directly correlated with the ACT score, but Di5-20 was at limit of the statistical significance (p=0,054). We found a significant negative correlation between the ACT score and the change in N2 concentration in phase 3 (DeltaN2) of the SBN2W test (p<0,05). In a multiple regression model, Di5-20 but not R20 significantly contributed to determination of DeltaN2 (p<0,05). Our results suggest that in asthmatic patients the inequality of ventilation is associated with poor disease control, but is not related to the severity of disease.