Association of demographic variables and smoking habits with the severity of lung function in adult smokers

BACKGROUND: This study aims to evaluate the association between demographic and smoking variables with the severity of lung function loss (Stage I to IV) and spirometry data in smokers. MATERIALS AND METHODS: Three hundred and fifty smoker men over the age of 20 who had visited in AL-Zahra hospital were involved. Spirometry tests were performed for measuring forced vital capacity (FVC), FEV1, and FEV1%FVC. COPD was categorized into four stages by the (Global Initiative for Chronic Obstructive Lung Disease) criteria of postbronchodilator FEV1/FVC <0.70. FEV1/FVC <70%, in combination with FEV1 ≥80% (Stage I), or 50%≤FEV1 <80% (Stage II), or 30%≤FEV1 <50% (Stage III), or FEV1 ≤30% (Stage IV). Independent t-test, Spearman correlation analysis was used for data analysis. To determine the predicting factors for pulmonary function multiple regressions analysis was performed. RESULTS: 43 (19.5%) of men were defined as Chronic Obstructive Lung Disease (COPD) which 7% of them were Stage I, 23.3% were Stage II, 39.5% were III and 30.2% were stage IV. In 60 (27.1%) of men, the index of Fev1/FVC was <80%. The criteria of PRIS in 74 (33.5%) of the patients and BDR in 59 (26.7%) of participation was positive. There were significant differences in the mean of FEV1 with respect to history of lung disease in relatives (P = 0.035), lung disease hospitalization (P < 0.001) and previous diagnosis of asthma variables (P < 0.001). The mean of FVC was significantly different in patients categorized based on lung disease hospitalization (P < 0.001) and previous diagnosis of asthma (P = 0.018). Furthermore, there was a significant difference in the mean of FEV1/FVC for variables as follows: Time to start smoking after waking up (P = 0.007), lung disease hospitalization (P < 0.001) and previous diagnosis of asthma (P < 0.001). There was a significant association between stages of lung function loss and age of onset of smoking (β-0.355 P = 0.019) and pack per year (β = 0.354 P = 0.02). A linear regression model showed that lung disease hospitalization and age were the influential variables on FEV1 with (B = −21.79 confidence interval [CI]: −28.7, −14.87, P < 0.001and B = −0.418 CI: −0.63, −0.21, P < 0.001), respectively. The only significant influential variable on FVC was lung disease hospitalization (B = −15.89 CI: −21.49, −10.296, P < 0.001). Body mass index, lung disease hospitalization, time to start smoking after waking up in the morning and age had significant relationship on FEV1/FVC with (B = 0.71CI: 0.32, 1.11, P < 0.001, B = −14.29, CI: −19.61,-8.97, P < 0.001, B = 6.54, CI: 2.26, 10.82, P = 0.003 and B = −0.44, CI: −0.59, −0.28, P < 0.001), respectively. CONCLUSION: The age of onset of smoking and pack-year appears to be associated with the severity of COPD. Hospitalization history due to lung disease, age, the time between waking up in the morning and first cigarette use, BMI, lung disease history in relatives, previous diagnosis of asthma have a negative relationship with lung function.