[The clinical significance of inspiratory capacity measurement in patients with stable chronic obstructive pulmonary disease].

OBJECTIVE: To study the clinical significance of inspiratory capacity (IC) in the evaluation of airflow obstruction and chronic dyspnea in patients with stable chronic obstruction pulmonary disease (COPD). METHODS: Sixty-one moderate COPD patients underwent pulmonary function test. Borg Scales (BS) was used for the degree of exertional dyspnea. Measurements of pulmonary function and BS were also performed after salbutamol inhalation (400 microg) in 61 COPD patients and after 6-minute walk test (6MWT) in 36 COPD patients. RESULTS: After salbutamol administration, the patients showed a significant increase in IC [(1.6+/-0.5) L vs (1.4+/-0.5) L] and in FEV1 [(1.3+/-0.4) L vs (1.1+/-0.4) L]. The reversibility in IC was significantly higher than that in FEV1 [(20+/-16)% vs (11+/-4)%]. A reversibility greater or equal to 10% in IC was found in 75.4% (46/61) of the patients, but in FEV1 was found in 39.3% (24/61); the difference was significant (chi2=16.190, P<0.01). BS was significantly decreased after salbutamol administration (3.0+/-0.7 vs 3.9+/-0.8, P<0.01). After 6MWT, the 36 COPD patients showed a significant decrease in IC [(1.1+/-0.4) L vs (1.4+/-0.5) L] and in FEV1 [(1.0+/-0.4) L vs (1.1+/-0.4) L]. The decrease in IC was significantly greater than that in FEV1 [(26+/-8)% vs (14+/-6)%]. A decrease greater or equal to 10% in IC was found in 100% (36/36) of the patients and in FEV1 was found in 72.2% (26/36); the difference was significant (chi2=11.613, P<0.01). BS was significantly higher after 6MWT (5.6+/-1.0 vs 3.9+/-0.9, P<0.01). In the multiple regression analysis, the change of IC after and before therapy (DeltaICthe) with the change of BS after and before therapy (DeltaBSthe), and the change of IC after and before exercise (DeltaICexe) with the change of BS after and before exercise (DeltaBSexe), were significantly correlated (regression coefficient was 0.314 and 0.329, respectively, all P<0.05). In Pearson correlation analysis, IC with functional residual capacity (FRC), DeltaICthe with DeltaFRCthe and DeltaIC with DeltaFRC were negatively correlated (r=-0.416 and -0.826 and -0.778, respectively, all P<0.05 or P<0.01). CONCLUSION: IC may be more sensitive than FEV1 in evaluation of change of airflow obstruction and dyspnea in stable COPD patients.