Smoking remains a predominant preventable cause of morbidity and mortality globally, accounting for a significant burden of non-communicable diseases, especially those affecting the respiratory system (1). Cigarette smoke contains a wide array of toxic substances, including nicotine, carbon monoxide, and tar, which have deleterious effects on lung tissue, leading to inflammation, airway remodeling, and a decline in pulmonary function over time (2,3). Chronic exposure to tobacco smoke impairs mucociliary clearance, reduces alveolar elasticity, and contributes to airway obstruction, making smokers highly susceptible to chronic obstructive pulmonary disease (COPD), bronchitis, and emphysema (4).

Pulmonary function tests (PFTs), particularly spirometry, provide a quantitative evaluation of respiratory performance and are vital for detecting early abnormalities in lung function, even before clinical symptoms manifest (5). Parameters such as Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV₁), and FEV₁/FVC ratio are key indicators of ventilatory efficiency and are commonly used to differentiate between obstructive and restrictive lung disorders (6). Comparing these values in smokers and non-smokers helps assess the direct impact of smoking on respiratory health.

Several population-based studies have documented a significant reduction in FEV₁ and FEV₁/FVC ratio among smokers, indicating an obstructive pattern even in asymptomatic individuals (7,8). In contrast, non-smokers tend to maintain normal spirometric profiles across age groups, highlighting the damaging effects of tobacco inhalation. Early detection of subclinical respiratory impairment through PFTs can enable timely intervention, smoking cessation, and prevention of progressive lung disease (9).

The present study aims to evaluate and compare pulmonary function parameters among smokers and non-smokers using spirometry, thereby contributing to the growing body of evidence linking smoking with deteriorated lung function.

A total of 100 male participants aged between 20 and 50 years were enrolled after obtaining written informed consent. The study population was divided into two groups: Group A (smokers, n=50) and Group B (non-smokers, n=50). Smokers were defined as individuals with a history of smoking at least five cigarettes or bidis per day for a minimum duration of five years. Non-smokers had no history of tobacco use in any form.

Participants with a known history of chronic respiratory diseases (such as asthma, COPD, tuberculosis), cardiovascular illness, diabetes mellitus, recent respiratory tract infection, or occupational exposure to dust or fumes were excluded to minimize confounding factors.

Pulmonary function was assessed using a computerized spirometer (Model XYZ, Manufacturer). All tests were performed in accordance with the guidelines established by the American Thoracic Society and the European Respiratory Society (ATS/ERS 2005 standards). Each participant was instructed to avoid heavy meals, caffeine, and smoking (for smokers) for at least two hours before the test.

Key parameters measured included:

• Forced Vital Capacity (FVC)
• Forced Expiratory Volume in one second (FEV₁)
• FEV₁/FVC ratio
• Peak Expiratory Flow Rate (PEFR)

Each participant performed at least three acceptable spirometry maneuvers, and the best of the three readings was considered for analysis. The tests were conducted in a seated position using a nose clip to prevent air leakage.

All data were recorded in a structured proforma and analyzed using IBM SPSS version 25.0. Descriptive statistics such as mean and standard deviation were used. An independent sample t-test was applied to compare the mean values of PFT parameters between the two groups. A p-value < 0.05 was considered statistically significant.

A total of 100 male participants were included in the study, with 50 individuals in the smoker group and 50 in the non-smoker group. Both groups were age-matched to reduce bias. The comparison was made using pulmonary function parameters recorded via spirometry. The results have been presented under three main tables for demographic details, pulmonary function parameters, and categorization of airflow pattern.

Table 1: Demographic Characteristics of Study Participants

Table 1 shows no statistically significant difference in demographic parameters between the two groups, indicating proper matching.

Table 2: Comparison of Pulmonary Function Parameters Between Smokers and Non-Smokers

As seen in Table 2, all major pulmonary function parameters were significantly reduced in smokers compared to non-smokers, indicating the detrimental impact of tobacco use on respiratory function.

Table 3: Classification of Airflow Pattern Based on Spirometry Results

Table 3 illustrates the categorization of spirometric findings. A majority of non-smokers exhibited normal pulmonary function, whereas a significant number of smokers showed varying degrees of obstructive patterns.

Summary of Findings:

• Smokers showed significantly lower FVC, FEV₁, FEV₁/FVC ratio, and PEFR values compared to non-smokers (Table 2).
• Obstructive airflow patterns were more prevalent in smokers, including mild to moderate obstruction (Table 3).
• Baseline demographics between the groups were statistically comparable, ruling out confounding effects (Table 1).

The present study demonstrated a significant reduction in pulmonary function parameters—namely FVC, FEV₁, FEV₁/FVC ratio, and PEFR—in smokers as compared to non-smokers. These findings are in line with existing literature that consistently reports smoking as a major contributor to impaired lung function (1,2).

The reduced FEV₁ and FEV₁/FVC ratio observed in the smoker group suggest the development of an obstructive ventilatory defect, which may indicate early stages of chronic obstructive pulmonary disease (COPD) even in asymptomatic individuals (3,4). Smoking leads to chronic airway inflammation, structural changes in the airways, and parenchymal destruction, ultimately compromising airflow and gas exchange (5-7).

The deleterious effects of cigarette smoke are attributed to the generation of reactive oxygen species and inflammatory cytokines, which disrupt alveolar integrity and impair bronchial patency (8,9). Longitudinal studies have also shown accelerated decline in FEV₁ with the duration and intensity of smoking exposure (10).

Our results also indicated a statistically significant reduction in PEFR among smokers. PEFR reflects the effort-dependent component of expiratory airflow and is sensitive to large airway obstruction, commonly seen in habitual smokers (11). This decline further supports the hypothesis that smoking affects both central and peripheral airways (12).

Interestingly, some studies suggest that even passive smoking or exposure to environmental tobacco smoke can result in measurable declines in pulmonary function (13). Thus, early screening using spirometry is crucial for both smokers and those exposed to secondhand smoke.

The reversibility of these changes has been documented in individuals who quit smoking, with gradual improvement in spirometric indices over time, especially if cessation occurs before the onset of irreversible structural damage (14). These findings underline the significance of public health strategies focused on smoking cessation and preventive respiratory care.

One of the strengths of this study is the controlled exclusion of confounding variables such as occupational dust exposure and pre-existing respiratory disease, which strengthens the internal validity. However, the study is limited by its cross-sectional nature and reliance on self-reported smoking history, which may be subject to reporting bias. Additionally, female participants were not included, which restricts the generalizability of findings across genders.

Future studies should consider a longitudinal design with biomarker analysis to better understand the pathophysiological mechanisms underlying smoking-induced pulmonary impairment. Incorporating high-resolution imaging and diffusion capacity measurements could further enhance diagnostic precision (15).

The study clearly demonstrates that smokers exhibit significantly reduced pulmonary function compared to non-smokers, as evidenced by lower values of FVC, FEV₁, FEV₁/FVC ratio, and PEFR. These findings highlight the detrimental impact of smoking on respiratory health and underscore the importance of early screening and tobacco cessation to prevent long-term pulmonary complications.

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