Acute exacerbations of chronic obstructive disease (AECOPD) are characterised by worsening dyspnoea that is variably prolonged. In this study, physiological changes during moderate AECOPD were examined and the factors associated with dyspnoea resolution over time were determined. In total, 20 patients experiencing an AECOPD were evaluated within 72 h of initial worsening of symptoms (day 0) with pulmonary function testing, metabolic testing and symptom assessment using the dyspnoea domain of the Chronic Respiratory Disease Questionnaire (CRQ). Treatment was optimised and testing was repeated after 7, 14, 30 and 60 days. At day 0, patients were very short of breath (CRQ-dyspnoea mean+/-SEM 2.4+/-0.3) and showed significant airflow obstruction (forced expiratory volume in one second (FEV1) 41+/-3% predicted) and lung hyperinflation (forced residual capacity (FRC) 164+/-7% pred). By day 60 CRQ-dyspnoea improved to 4.6+/-0.5 (some shortness of breath); FRC and residual volume decreased by 5 and 11%, respectively; inspiratory capacity (IC) and slow vital capacity increased by 18 and 17%, respectively; and FEV1 increased by 18% with no change in FEV1/FVC. Total lung capacity did not change during AECOPD, and thus, changes in IC reliably reflected changes in end-expiratory lung volume. In conclusion, moderate acute exacerbation of chronic obstructive pulmonary disease is characterised by worsening airflow obstruction and lung hyperinflation. Improvement of dyspnoea following acute exacerbations of chronic obstructive pulmonary disease was associated with reduction in lung hyperinflation and consequent increase in expiratory flow rates.