Tobacco smoking is a well-established risk factor for a wide range of respiratory diseases, including chronic obstructive pulmonary disease (COPD), bronchitis, and lung cancer. According to the World Health Organization (WHO), tobacco use is responsible for over 8 million deaths annually, with a significant proportion attributable to smoking-related pulmonary complications (1). The lungs are among the primary organs affected by chronic smoking due to direct exposure to toxic chemicals and free radicals present in tobacco smoke, leading to airway inflammation, alveolar wall destruction, and structural remodeling (2).

Pulmonary Function Tests (PFTs) are essential non-invasive diagnostic tools used to assess lung performance and detect abnormalities in airflow and volume. Parameters such as Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV₁), and the FEV₁/FVC ratio provide critical insights into the presence and severity of obstructive or restrictive pulmonary patterns (3). In smokers, chronic exposure to tobacco smoke leads to small airway obstruction, mucus hypersecretion, and reduced elastic recoil, which are reflected as decreased values in spirometric indices (4).

Numerous studies have shown a significant decline in pulmonary function among chronic smokers compared to non-smokers, with the degree of impairment correlating with the duration and intensity of smoking (5). Early identification of declining lung function through spirometry may aid in timely intervention and reduction of long-term morbidity. Hence, the present study aims to evaluate the impact of chronic smoking on various pulmonary function parameters and compare them with those of healthy non-smokers.

A cross-sectional observational study was conducted over a period of six months in the Department of Physiology at a tertiary care medical institution.

A total of 100 male participants, aged between 25 and 60 years, were enrolled and divided into two groups: Group A (n = 50) consisted of chronic smokers, defined as individuals with a history of smoking more than 10 pack-years; Group B (n = 50) included age-matched healthy non-smokers with no prior exposure to active or passive smoking.

Participants with a history of respiratory diseases (e.g., asthma, tuberculosis), cardiovascular disorders, or current upper respiratory tract infections were excluded from the study. All participants underwent a detailed clinical history and general physical examination before pulmonary function testing.

Pulmonary function was assessed using a portable computerized spirometer (Model: RMS Helios 401, India), following the standard guidelines set by the American Thoracic Society/European Respiratory Society (ATS/ERS). The subjects were instructed to avoid smoking, eating heavy meals, or engaging in vigorous physical activity at least one hour before the test. All recordings were taken in a seated position, using a nose clip to prevent air leakage.

Key parameters recorded included:

• Forced Vital Capacity (FVC)
• Forced Expiratory Volume in 1 Second (FEV₁)
• FEV₁/FVC ratio
• Peak Expiratory Flow Rate (PEFR)

Each participant performed at least three acceptable maneuvers, and the best of the three consistent readings was selected for analysis. The data obtained were statistically analyzed using SPSS software version 25.0. An unpaired Student’s t-test was applied to compare means between groups, and a p-value of <0.05 was considered statistically significant.

The study evaluated the pulmonary function of 100 individuals, comprising 50 chronic smokers (Group A) and 50 non-smokers (Group B). The mean age of participants in Group A was 47.2 ± 6.5 years, while in Group B it was 45.9 ± 7.3 years, with no statistically significant difference between the two (p = 0.42).

Pulmonary Function Parameters

Table 1 presents a comparison of spirometric values between chronic smokers and non-smokers. The mean FVC in smokers was significantly lower (2.85 ± 0.56 L) compared to non-smokers (3.42 ± 0.48 L), with a p-value of <0.001. Similarly, FEV₁ was markedly reduced in Group A (1.91 ± 0.47 L) as compared to Group B (2.89 ± 0.44 L), which was statistically significant (p < 0.001).

The FEV₁/FVC ratio, an important marker of obstructive airway disease, was found to be significantly lower in smokers (66.9 ± 6.2%) versus non-smokers (82.3 ± 5.4%), indicating obstructive changes in lung function (p < 0.001). PEFR values also showed a substantial reduction in smokers (288.6 ± 42.5 L/min) in comparison to non-smokers (401.2 ± 50.7 L/min), with p < 0.001 (Table 1).

Table 1: Comparison of Pulmonary Function Parameters Between Smokers and Non-Smokers

The findings indicate that chronic smoking is associated with a significant reduction in all major spirometric parameters, suggesting a tendency toward obstructive ventilatory defects in long-term smokers (Table 1).

Table 2: Grading of Pulmonary Function Based on FEV₁ (%) Among Smokers and Non-Smokers

As shown in Table 2, a majority of non-smokers (88%) exhibited normal pulmonary function, while nearly 56% of smokers demonstrated moderate to severe airflow obstruction, based on FEV₁ percentage thresholds.

The present study demonstrates a statistically significant decline in pulmonary function among chronic smokers compared to non-smokers. Spirometric indices such as FVC, FEV₁, FEV₁/FVC ratio, and PEFR were markedly lower in individuals with a prolonged history of smoking, highlighting the detrimental impact of tobacco smoke on respiratory function.

The observed reduction in FEV₁ and FEV₁/FVC ratio among smokers is consistent with existing literature, which associates chronic tobacco exposure with airflow limitation and progressive obstruction of the small airways (1,2). Cigarette smoke contains thousands of harmful chemicals that trigger chronic inflammation, epithelial damage, and remodeling of the airway walls, eventually leading to irreversible airflow obstruction (3,4).

Previous epidemiological studies have shown that the decline in FEV₁ is directly proportional to the number of pack-years smoked and the duration of exposure (5,6). Our findings are in line with the results reported by Sherman et al., where smokers exhibited significant impairment in expiratory flow rates compared to age-matched non-smokers (7). Similarly, a study by Riyaz et al. also found lower PEFR and FVC values in smokers, indicative of compromised expiratory muscle function (8).

The reduced PEFR in smokers, as seen in our study, may be attributed to narrowed airway caliber, increased mucus secretion, and reduced elastic recoil of the lungs (9). Chronic exposure to tobacco also impairs mucociliary clearance, further predisposing individuals to recurrent infections and exacerbations of respiratory disease (10).

Several studies suggest that even asymptomatic smokers may show abnormal PFT values, underscoring the importance of early spirometric screening for timely intervention (11,12). While COPD is a well-known outcome of chronic smoking, the condition often remains undiagnosed until significant functional impairment has occurred (13). Spirometry serves as an effective tool to identify individuals at risk and initiate cessation strategies before irreversible damage sets in (14,15).

Our study reaffirms the role of spirometry in detecting early alterations in pulmonary function in smokers. It also emphasizes the need for public health measures targeting tobacco cessation, especially in high-risk populations.

Chronic smoking significantly impairs pulmonary function, as evidenced by reduced FEV₁, FVC, FEV₁/FVC ratio, and PEFR values. These findings highlight the importance of routine spirometric evaluation in smokers for early detection of obstructive airway changes and the need to strengthen tobacco cessation initiatives.

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