Prevalence of a decreased FEV3/FEV6 ratio in symptomatic smokers with preserved lung function

Abstract

Background: The ratio of forced expiratory volume in 3 seconds to forced expiratory volume in 6 seconds (FEV3/FEV6) has been proposed as an index of peripheral airway disease, and could be decreased in patients at risk for COPD. However, the prevalence of FEV3/FEV6 decrease has never been assessed in patients attending a pneumology clinic. Here we set out to assess the prevalence of a decreased FEV3/FEV6 in smokers with symptoms of chronic bronchitis, and to test its predictive value for COPD diagnosis.

Methods: We performed a retrospective analysis of databased pulmonary function tests (PFTs) for smokers and ex-smokers aged >40 years old, with symptoms of chronic bronchitis and a normal FEV1/FVC ratio. Clinical data were retrieved from the hospital records. Patients presenting with clinical conditions liable to interfere with PFT results were excluded. For those included, we controlled for onset of an obstructive ventilatory defect 1 year later.

Results: The dataset included 67 patients (median age: 64 years [interquartile range: 53-72], 61% current smokers). FEV1/FVC was above lower limit of normal but lower than 0.7 in 18 patients (27%). FEV3/FEV6 was decreased below the lower limit of normal in 45 patients (67%). The latter did not differ from others patients in clinical data and PFTs except for a lower lung diffusion capacity (D_LCO). We found a weak correlation between FEV3/FEV6 and D_LCO (r=0.33, p=0.004). PFTs were repeated in 35 patients at 11 [7-12] months, and 20 (54%) presented with obstructive ventilatory defect defined by FEV1/FVC ratio <0.7. A reduction of FEV3/FEV6 was predictive of COPD onset one year later (p=0.04). These results may be biased by a discrepancy between the normality cut-offs used at inclusion and during follow-up (i.e. lower limit of normal and 0.7).

Conclusions: Decreased FEV3/FEV6 suggestive of peripheral airway disease is highly prevalent in smokers with symptoms of chronic bronchitis and preserved pulmonary function. Altered FEV3/FEV6 is predictive of reduced FEV1/FVC ratio in the mid-term. A larger prospective study is needed to determine whether decreased FEV3/FEV6 could be used to detect patients at risk for COPD.

Keywords: COPD; Diagnosis; Peripheral airway disease; Spirometry.