It is important to predict the exercise capacity and dyspnea, as measurements of lung volume, in patients with COPD. However, lung volume changes in response to an improvement in airflow limitation have not been explored in detail. In the present study, it is hypothesized that lung volume responses might not be accurately predicted by flow responses in patients with moderate to severe airflow limitations.

To evaluate lung volume responses, baseline and follow up, flow and lung volumes were measured in moderate to severe COPD patients. The flow response was defined by an improvement in the FEV₁ of more than 12.3%; lung volume changes were analyzed in 17 patients for the flow response.

The mean age of the subjects was 66 years; 76% were men. The mean baseline FEV₁, FEV₁/FVC and RV were 0.98L (44.2% predicted), 47.5% and 4.65 L (241.5%), respectively. The mean follow up duration was 80 days. The mean differences in the FEV₁, FVC, TLC and RV were 0.27 L, 0.39 L, -0.69 L and -1.04 L, respectively, during the follow up periods. There was no correlation between the delta FEV₁ and delta RV values(r=0.072, p=0.738).

To appropriately evaluate the lung function in patients with moderate to severe airflow limitations; serial lung volume measurements would be helpful.