FEV3/FVC ratio in early detection of airway obstruction

Introduction: An obstructive ventilatory pattern is defined by the FEV1/VC ratio. Since obstruction begins at the small airways, this ratio may not be adequate to detect this early event. Objective: Determine the relationship between a diminished FEV3/FVC and other functional parameters in subjects with a normal FEV1/VC. Methods: A cross-sectional study was performed selecting lung function tests (LFT).Lower limit of normal (LLN) was obtained using the NHANES III reference equations. Results: 221 LFT were included, with a female predominance. 65.3% were non-smokers and 21.3% were former smokers. Mean age was 56±16 years. Sample was divided into four groups according to the table. Comparing groups 1 and 2, subjects with isolated FEV3/FVC decrease had greater ITGV (3.28±0.06L vs 4.27±0.4L, p 0.011), greater TLC (5.91±1.2L vs 7.03±1.44L, p 0.028) and lower maximum mid-expiratory flow (MMEF 75-25: 2.25±1.14L/s vs 1.24±0.3L/s, p p 0.022), lower inspiratory capacity (2.76±0.8L vs 1.99±0.58L, p 0.034), greater airway resistance (0.22±0.1cmH2O/L*s vs 0.52±0.18cmH2O/L*s, p 0.02) and lower conductance (1.07±0.29cmH2O*s vs 0.55±0.19cmH2O*s, p Conclusion: This study demonstrates that subjects with decreased FEV3/FVC have higher ITGV and TLC values. In this context, these changes can represent an early phase of pulmonary inflation by small airways involvement.