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PREVALENCE OF HYPERINFLATION IN COPD AND CORRELATION WITH FLOW-VOLUME INDICES

UMCU, Utrecht, Netherlands

PURPOSE: Identification of hyperinflation in COPD is important, because it causes dyspnea and limitation of exercise, and it is a predictor of mortality. Detection of hyperinflation in primary care, however, is difficult because only hand-held spirometers are used.

METHODS: 441 patients, classified as COPD by their general practitioner, visited our out-patient clinic for further pulmonary investigations. Diagnosis of COPD was based on the GOLD criteria (postbronchodilator FEV1/FVC <0.70). The RV/TLC ratio was used to chart hyperinflation, and a value 1.64 SD from the predicted value was used to indicate hyperinflation. Prevalence of hyperinflation, and correlation with pre-bronchodilator spirometry indices were calculated. The latter was done to assess whether spirometry indices could be used as surrogate marker of hyperinflation.

RESULTS: In COPD patients with GOLD stage 0, 13% of the subjects showed hyperinflation. 22.4% of the patients in GOLD stage 1 were hyperinflated, in GOLD stage 2 55.1%, and patients in GOLD stage 3 87.2%. Non-parametric correlation showed that of the spirometry indices, FEV1 (as percent of predicted) correlated best with RV/TLC ratio (r= -0.682; p<0.001). Second and third best were the MEF75 and PEF with r = -0.656, and r= -0.649 (both p<0.001). The FEV1-reversibility had a low correlation (r= 0.217; p<0.001).Linear regression showed that with each percent of FEV1 lost, the RV/TLC ratio increased by 0.044 SD points. The optimal cut off value for the baseline FEV1 ap-peared to be 70% of the predicted value (<70% indicates hyperinflation). Receiver Op-erating Characteristics (ROC) curve analysis showed that a high FEV1 correctly diag-nosed an absence of hyperinflation in 85.6% of all cases. The sensitivity/specificity of excluding hyperinflation at this 70% cut off level was 78.0% and 76.7%.

CONCLUSION: Hyperinflation is often present in COPD and when FEV1 <70% of predicted hyperinflation is very probable.

CLINICAL IMPLICATIONS: FEV1 may be used as a surrogate marker for detect hyperinflation when helium dilution and/or bodyplethysmography are unavailable.

DISCLOSURE: Pieter Zanen, None.