Factors for the Variability of Three Acceptable Maximal Expiratory Flow–Volume Curves in Chronic Obstructive Pulmonary Disease

BACKGROUND: Generally, the maximal expiratory flow–volume (MEFV) curve must be measured for the diagnosis and staging of chronic obstructive pulmonary disease (COPD). As this test is effort dependent, international guidelines recommend that three acceptable trials are required for each test. However, no study has examined the magnitude and factors for the variability in parameters among three acceptable trials. METHODS: We evaluated the intra-individual variations in several parameters among three acceptable MEFV curves obtained at one-time point in patients with COPD (n = 28, stage 1; n = 36, stage 2; n = 21, stages 3–4). Next, the factors for such variations were examined using forced expiratory volume in 1 second (FEV(1)) and forced vital capacity (FVC). RESULTS: The averages of coefficient of variation (CV) for FEV(1) and FVC were 2.0% (range: 1.0–3.0%) and 1.6% (0.9–2.2%), respectively. Both parameters were significantly better than peak expiratory flow rate, forced expiratory flow at 50% of expired FVC, and forced expiratory flow at 75% of expired FVC (CVs: 5.0–6.9%). A higher spirometric stage was significantly associated with higher CVs for FVC and FEV(1,) and older age was significantly correlated with a higher variation in FEV(1) alone. Furthermore, a significantly inverse association was observed between emphysema severity, and the CVs for FEV(1), but not that for FVC, regardless of spirometric stage. CONCLUSION: Both FVC and FEV(1) are highly reproducible; nevertheless, older age, lower FEV(1) at baseline, and non-emphysema phenotype are factors for a higher variability in FEV(1) in patients with COPD.