Supramaximal flow in asthmatic patients

Abstract

In normal subjects supramaximal flows (SF) are known to be correlated with flow limitation. To further understand the mechanisms involved in SF this correlation and the influence of salbutamol and methacholine administration on SF have been investigated in asthmatic subjects. Protocol A involved obtaining basal maximal expiratory flow/volume curves and interrupted curves through a fast valve from 36 asthmatic patients. Maximal flow at 50% of forced vital capacity (V' max50) increase (ΔV' max50) was compared between basal curves and envelope curves passing through SF peaks obtained after each interruption. Protocol B involved the study of 33 asthmatic patients after salbutamol administration and 12 asthmatic patients after methacholine challenge. ΔV' max50 between basal versus interrupted curves were analysed (ΔV' max50B). Similar procedures were performed after salbutamol (ΔV' max50S) and after methacholine administration (ΔV' max50M). A significant negative correlation between forced expiratory volume in one second and ΔV' max50 was observed. SF decreased significantly after salbutamol administration and increased significantly after methacholine. The results of this study suggest that in asthmatic patients participation of "pendelluft" in SF increases as airflow limitation increases.