REGIONAL LUNG CLEARANCE DURING COUGH AND FORCED EXPIRATION TECHNIQUE (FET) - EFFECTS OF FLOW AND VISCOELASTICITY

Background - In vitro studies have suggested that both the viscoelasti c properties of lung secretions and the peak flow attained during simu lated cough influence clearance. This study examines the possible asso ciation of the viscoelastic properties of sputum and maximum expirator y flow with measured effectiveness of mucus clearance induced by instr ucted cough and by forced expiration technique (FET) in patients with airways obstruction. Methods - Nineteen patients (11 men and eight wom en) of mean (SE) age, % predicted FEV(1), and daily sputum wet weight of 64 (2) years, 52 (6)%, and 37.5 (7.9)g respectively participated in the study. Mucus movement from proximal and peripheral lung regions w as measured by an objective non-invasive radioaerosol technique. Each patient underwent three assessments: control, cough, and FET. During c ough and FET, maximum expiratory flow was measured at the mouth level. Apparent viscosity and elasticity of the expectorated sputum samples were measured with a viscometer, Results - Compared with the control r un (mean (SE) clearance: 16 (3)%) there was an increase in clearance f rom the whole lung during cough (44 (5)%) and FET (42 (5)%), and also an enhanced clearance of inhaled, deposited radioaerosol from the trac hea, inner and intermediate regions of the lungs, but not from the out er region. There were, however, no differences in regional clearance b etween cough and FET. Neither regional nor total clearance correlated with maximum expiratory flow, apparent viscosity, elasticity, or daily sputum wet weight.Conclusions - These results confirm that cough and FET both promote effective clearance but suggest that, unlike in vitro studies, sputum production and viscoelasticity, as well as maximum ex piratory flow, provide no guide to clearance efficacy in humans.