Smoking & Forced Expiratory Flow in COPD

Mainly the result of cigarette smoking, chronic obstructive pulmonary disease (COPD) is primarily characterized by persistent limitations in airflow that centralize in the small conducting airways.

Since airway obstruction is a harbinger of COPD and abnormalities in the small airways in smokers who may or may not have COPD, investigators from the Philippine Heart Center decided to investigate.

In the data presented at the 2018 CHEST Annual Meeting in San Antonio, TX, the team sought to analyze the early detection of small airway obstruction and determine the Correlation of Forced Expiratory Flow (FEF) (25%-75%) and pack-years.

In the prospective cross-sectional study, adult patients with at least 1 pack-year smoking history and with either normal or low FEV1/FVC were enrolled in the study. Age, sex, weight, height, body-mass index, smoking history, and the number of pack-years recorded were used to compose the clinical and demographic data.

A pulmonary function test (PFT) was performed in patients, and results concerning FEV1/FVC, FVC, FEV1, and FEF 25-75 were collected.

Stata version13 was used to perform the analysis. Quantitative variables included mean and standard deviation, and qualitative variables included frequency and percent. A scatter plot presented the correlation between FEF25-75 and pack years; person-product moment correlation was used for scatter plot analysis.

Based on its sensitivity and specificity, cut-off value of pack-years predictive of SAO was determined.

Of the 82 patients analyzed in the trial (who had a mean age of 56 years and a smoking history) 53 patients had FEV1/FVC equal to or greater than 70, while 29 patients had FEV1/FVC ratio lower than 70.

Compared to those in the normal ratio, those with lower FEV1/FVC ratio were notably older (64±11 years older versus 52±13 years of age respectively, p=.001) and taller (162.54±6.87 cm versus 165.93±5.95 cm, p=.028).

Among those with normal and low FEV1/FVC, a significant correlation between FEF 25-75 and smoking pack-year was observed.

Among patients with FEV1/FVC that gave low FEF25-75 (<65), the cut-off value of smoking packs-years was 16.5 pack-year.

From the data study, authors concluded that among those with normal and low FEV1/FVC, a significant correlation exists between FEF25-75 and smoking pack-year. Consequently, the authors suggested that FEF25-75 may be used as a parameter for early detection of beginning small airway obstruction in smokers with normal FEV1/FVC.

A noted clinical implication was that further deterioration of lung function, which can ultimately lead to COPD, can be prevented through physicians’ encouraging smokers to quit.

Estimating when small airway obstruction begins to occur may also be assisted with a cut-off value 16.5 pack-year smoking that gives low FEF 25-75.

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