Influence of the lung function abnormalities fixed obstruction ( forced expiratory volume in 1s ( FEV1 ) / forced vital capacity ( FVC ) ratio < 0.7 ) and bronchodilator responsiveness ( FEV1 increase of 12 % or 200ml after 400g salbutamol ) on symptom severity , duration and worsening were evaluated using uni - and multivariable regression models .