Objective To evaluate if the difference between slow vital capacity ( VC) and forced vital capacity ( FVC) could be used to predict severity of airflow limitation in patients with stable chronic obstructive pulmonary disease ( COPD) . Methods VC and FVC were measured in 200 patients with COPD [ 159 males;mean FEV1 , ( 49.31 ±15.75) % of predicted] and 114 healthy controls [ 64 males; mean FEV1 , ( 99.67 ±13.62) % of predicted] . Results The difference between VC and FVC ( VC - FVC) , which showed a negative correlation with FEV1 of predicted ( r=- 0.412, Plt;0.001) , was significantly larger in the COPD patients than that in the controls [ ( 145.40 ±157.50) mL vs. ( 21. 10 ±61. 30) mL, Plt; 0. 001] . The FVC/VC ratio was significantly lower in the COPD patients than that in the controls [ ( 93. 61 ± 7. 10) % vs. ( 99.27 ±2.24) % , P lt; 0.001] , and was positively correlated with FEV1 of predicted in the COPD patients ( r =0.517, P lt;0.001) . There was significant difference in VC - FVC in the COPD patients with FEV1≥50% of predicted ( 5 patients in GOLD level 1 and 74 patients in GOLD level 2) and those patients with FEV1 lt;50% of predicted ( 106 patients in GOLD level 3 and 15 patients in GOLD level 4) [ ( 78.23 ±108.26) mL vs. ( 189.26 ±169.21) mL, P =0.003] . Conclusion The difference between VC and FVC and the FVC/VC ratio, which are more easily obtained from spirometric test, are able to detect severity of airflow limitation in patients with stable COPD.
Objective To determine the efficacy of forced expiratory volume in six seconds( FEV6 ) as an alternative for forced vital capacity( FVC) in the diagnosis for mild-moderate chronic obstructive pulmonary disease( COPD) .Methods A total of 402 mild-moderate COPD and 217 non-COPD patients’ spirometric examinations were retrospectively analyzed. The correlation between FEV6 and FVC, FEV1 /FVC and FEV1 /FEV6 was evaluated by the Spearman test. Considering FEV1 /FVC lt;70% as being the ‘golden standard’ for airway obstruction, a ROC curve was used to determine the best cut-off point for the FEV1 /FEV6 ratio in the diagnosis for COPD. Results The Spearman correlation test revealed the FEV1 and FEV6 , FEV1 /FEV6 and FEV1 /FVC ratios were highly correlated ( r = 0. 992, 0. 980, respectively, P = 0. 000) . Using FEV1 /FEV6 lt; 70% as the diagnosis standard, 12. 69% of the 402 patients could not be diagnosed as COPD. The FEV1 /FVC ratio of these patients was very close to 70% . The best cut-off point for the FEV1 /FEV6 ratio in the diagnosis of mild-moderate COPD was 72% while the sensitivity and specificity were 94. 7% and 92. 2% , respectively. Conclusions There is a b correlation between FEV1 /FVC and FEV1 /FEV6 . The FEV6 can be a valid alternative for FVC in the diagnosis for mild-moderate COPD, although it may result in false negative. The best cut-off point for the FEV1 /FEV6 ratio is 72% .