A study in the relationship between the inspiratory capacity(IC) and exercise capacity in stable COPD

Objective To explore the relationship between the inspiratory capacity(IC) and exercise capacity in the stable COPD.Methods 30 patients with stable COPD were treated by inhaling 18 ug tiotropium a day,followed up 12 weeks.Respiratory difficulty was scored on day 1,43 and 85,6 minute-walk-distance(6MWD),FEV1,FEV1/FVC and IC were measured.The changes of these variables were statistically analyzed and the relationship were studied between the pulmonary function and 6MWD,after receiving tiotropium in 6 weeks and 12 weeks period.Results The FEV1 and FEV1/FVC were improved after receiving tiotropium,although there was no significant difference compared to before the treatment(P0.05 for all comparisons),and the improved level in FEV1 was greater than FEV1/FVC.Inspiratory capacity(IC) increased significantly after 6 weeks(t=4.596,P=0.000) and 12 week(t=5.405,P=0.000).The 6MWD significantly increased after receiving tiotropium 6 weeks(t=4.628,P=0.000) and 12 weeks(t=6.207,P=0.000).The level of respiratory difficulty significantly decreased after receiving tiotropium 6 weeks(z=4.433,P=0.000) and 12 weeks(z=4.026,P=0.0001).By linear regression analysis,a close relationship of the changes in 6MWD with those in IC was found in stable COPD(r=0.900,0.873,P0.01 for all comparisons),but the similar relationship was not found between FEV1,FEV1/FVC and 6MWD respectively.Conclusion IC maybe has a closer relationship with respiratory difficulty and exercise capacity.IC is more reliable than other targets in evaluating therapeutic effect and quality of life of the stable COPD.