Background: Small airway disease continuous to be an important component of patients with chronic obstructive pulmonary disease (COPD). Spirometric measurements for assessing small airway pathology are simple to obtain, low-cost, readily available and show acceptable repeatability. We wanted to determine the accuracy of forced expiratory volume in six seconds of exhalation (FEV6) in detecting small airwar disease using forced expiratory flow 25%-75% of FVC (FEF25%-75%) as a reference standard.
Methods: This is a cross-sectional study done at Pulmonary Laboratory, Division of Pulmonary and Critical Care Medicine of the Philippine Heart Center. All adult patients who underwent spirometric studies from October 2013 to September 2014 were included. Baseline demographic data, smoking history and spirometric results were evaluated. The highest post-bronchodilator FEF 25-75% and FEV6 from test of acceptable quality were used for analysis. We used FEF 25% -75% as the reference standard for detecting small airway disease. Each subject was categorized as having "small airway disease" if the post bronchodilator value of FEF 25% -75% is <65% of the predicted as the lower limit of normality. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of FEV6 in detecting small airway disease as defined by FEF 25- 75% were calculated.
Results: Of the 386 spirometric test analyzed, 245 were males and 141 were females. 61% of the subjects had smoking history and 33% had significant airflow obstruction. FEV6 has a 35.40 % sensitivity and has 35.63% specificity in detecting small airway disease. With a positive and negative predictive values of 43.52% and 28.08% respectively. Subgroup analysis among subjects with airflow obstruction showed 62.20% diagnostic accuracy and 73.04 % diagnostic accuracy among those with smoking history.
Conclusion: Forced expiratory volume at 6 seconds (FEV6) has a limited value in detecting small airway disease among adult patients. However, its value can be represented by patients with significant airway obstruction and smoking history.