Occupational exposure to airborne dusts, fumes and chemicals is a major and largely preventable cause of chronic respiratory morbidity worldwide, and construction and agriculture are among the largest and most hazardous employment sectors, particularly in low- and middle-income countries such as India [1,2]. Both sectors are characterised by informal employment, limited health surveillance and inconsistent use of respiratory protection, so that workers commonly inhale harmful agents over working lifetimes measured in decades without baseline or periodic medical evaluation [2].

Construction activity generates respirable dust during cutting, grinding, drilling and demolition, and during the handling of cement, concrete, stone and sand. The most important single hazard is respirable crystalline silica, which is engulfed by alveolar macrophages and initiates a self-perpetuating cycle of inflammation and interstitial fibrosis culminating in silicosis, an irreversible and incurable pneumoconiosis [3,4]. Cement, marble and quarry dusts produce comparable impairment, and several studies have shown that the magnitude of lung-function loss increases with the duration of exposure [4,5,6]. Silicosis continues to be reported widely across the Indian stone-crushing, quarrying and mining sectors, where regulation is often weak [7,8,9].

Agricultural exposures are more biologically and chemically complex. Organic dust is a heterogeneous mixture of plant material, fungal spores, bacterial endotoxin and animal proteins, and in enclosed livestock units it is accompanied by irritant gases such as ammonia and hydrogen sulfide [10,11]. These exposures cause hypersensitivity pneumonitis, organic dust toxic syndrome, chronic bronchitis and an asthma-like syndrome, and frequently produce an acute within-shift fall in FEV1 [10,12,13]. Pesticides add a further mechanism of injury, with reviews reporting associations with cough, wheeze, asthma and impaired spirometry suggestive of obstructive or restrictive defects depending on the chemical class involved [14,15]. Comparative studies consistently find lower mean FVC, FEV1 and flow rates in farmers than in controls, declining further with longer exposure [16,17].

Spirometry is well suited to detecting and monitoring this impairment because it is non-invasive, inexpensive, portable, reproducible when performed to standard, and sensitive to both airflow obstruction and volume restriction [18,19]. Despite this, directly comparative data on construction versus agricultural workers within a single population are scarce, and the relative contribution of restrictive and obstructive defects in each group is not well characterised in many regional settings. The present study was therefore undertaken to compare spirometric indices and the prevalence of ventilatory patterns among construction workers, agricultural workers and unexposed controls, and to examine the relationship between duration of occupational exposure and pulmonary function.

Study design and setting. This was a comparative, observational, cross-sectional study conducted in the Department of Physiology, [Institution], [City], over a period of [12 months] from [month/year] to [month/year]. The study was approved by the Institutional Ethics Committee ([approval number]), and written informed consent was obtained from every participant before enrolment. Participants. Three groups were studied: construction workers, agricultural workers and unexposed controls (office or clerical staff of comparable socioeconomic status). Inclusion criteria were male sex, age [20-50] years, and a minimum of [two] years in the current occupation for the exposed groups. Exclusion criteria were a prior diagnosis of asthma, tuberculosis, chronic bronchitis or other chronic respiratory or cardiac disease; recent respiratory infection (within four weeks); thoracic or spinal deformity; recent thoraco-abdominal surgery; and inability to perform acceptable spirometry. Participants were recruited by [convenience / systematic random] sampling from [sites]. Sample size. The sample size was calculated to detect a clinically meaningful difference of [X]% in mean FEV1 (% predicted) between groups, assuming a standard deviation of [X]%, 80% power and a 5% level of significance, giving a minimum of [80] participants per group ([240] total). [State the formula/software used, e.g., G*Power.] Data collection and anthropometry. A structured proforma recorded demographic details, occupational history including duration of exposure and use of protective equipment, smoking history, and respiratory symptoms using a validated questionnaire (British Medical Research Council / American Thoracic Society) [16]. Height was measured to the nearest 0.1 cm with a stadiometer and weight to 0.1 kg; body mass index was calculated as weight divided by height squared. Spirometry. Spirometry was performed with a calibrated [make/model] spirometer by a single trained operator, following the American Thoracic Society/European Respiratory Society 2019 standardisation criteria for acceptability and repeatability [18]. Testing was done in the sitting position with a nose clip, after demonstration; at least three acceptable manoeuvres were obtained and the best values of FVC and FEV1 retained. FVC, FEV1, FEV1/FVC ratio, peak expiratory flow rate (PEFR) and forced expiratory flow at 25-75% of FVC (FEF25-75) were recorded and expressed as percent of predicted using [reference equation, e.g., Hankinson/region-specific] values [19]. Interpretation. Patterns were classified as normal (FEV1, FVC and FEV1/FVC within normal limits), obstructive (reduced FEV1/FVC with reduced FEV1), restrictive (reduced FVC with preserved or raised FEV1/FVC) or mixed, in accordance with standard guidelines [18]. Statistical analysis. Data were analysed using [SPSS v.XX / R]. Continuous variables are presented as mean +/- standard deviation and categorical variables as frequencies and percentages. Between-group differences in spirometric indices were tested by one-way analysis of variance (ANOVA) with post-hoc [Tukey] correction; the distribution of ventilatory patterns was compared by the chi-square test; and the association between duration of exposure and spirometric indices was assessed by Pearson correlation. A two-sided p-value <0.05 was considered statistically significant.

A total of [240] participants ([80] construction workers, [80] agricultural workers and [80] controls) completed the study. The three groups were comparable in age, height, weight, body mass index and smoking prevalence (p>0.05 for all), so that observed differences in lung function were unlikely to be explained by these factors. The mean duration of occupational exposure was [12.6 +/- 6.8] years in construction workers and [15.3 +/- 8.1] years in agricultural workers (Table 1).

Table 1. Demographic and baseline characteristics by group (illustrative data - replace with your own).

Spirometric indices differed significantly across the three groups (Table 2). In this illustrative dataset, mean FVC and FEV1 (% predicted) were lowest in construction workers ([78.2] and [75.6]), intermediate in agricultural workers ([81.5] and [79.0]) and highest in controls ([92.6] and [91.8]), with p<0.001 on ANOVA. The FEV1/FVC ratio was comparatively preserved in construction workers but lower in agricultural workers, consistent with a greater obstructive component in the latter, while PEFR and the small-airway index FEF25-75 were reduced in both exposed groups relative to controls.

Table 2. Spirometric indices (% predicted), mean +/- SD (illustrative data - replace with your own).

The distribution of ventilatory patterns also differed significantly between groups (Table 3; chi-square p<0.001). Abnormal spirometry was far more common in the exposed groups than in controls. A restrictive pattern predominated among construction workers ([35%]), in keeping with the fibrotic effect of mineral dust, whereas obstructive defects were relatively more frequent among agricultural workers ([22.5%]), consistent with airway-centred responses to organic dust and chemicals.

Table 3. Distribution of ventilatory patterns, n (%) (illustrative data - replace with your own).

Duration of occupational exposure correlated negatively with all major spirometric indices in both exposed groups (Table 4), indicating that lung function declined as cumulative exposure increased. The strongest associations in this illustrative dataset were with FEV1 and FVC.

Table 4. Correlation (Pearson r) between duration of exposure and spirometric indices (illustrative data - replace with your own).

This study compared pulmonary function across construction workers, agricultural workers and unexposed controls. The principal (illustrative) findings were a significant reduction in FVC, FEV1, PEFR and FEF25-75 in both exposed groups relative to controls, a predominance of restrictive defects in construction workers and a relatively greater obstructive component in agricultural workers, and a consistent decline in lung function with increasing duration of exposure. These patterns are concordant with the published literature and are biologically plausible. The restrictive picture in construction workers reflects the fibrotic action of respirable crystalline silica and related mineral dusts, which are phagocytosed by alveolar macrophages and drive progressive interstitial fibrosis [3,4]. Comparable reductions in FVC and FEV1, with a high prevalence of restrictive impairment, have been reported among construction, marble, cement and stone-quarry workers, and several studies emphasise that the deficit worsens with the duration of exposure [4,5,6,7]. The continuing burden of silicosis in Indian stone-crushing and quarrying populations underscores the public-health relevance of these findings [8,9]. The greater obstructive component among agricultural workers is consistent with the airway-centred inflammatory and hypersensitivity responses provoked by organic dust, endotoxin and animal-confinement gases, and by pesticide exposure [10,11,12]. A substantial minority of grain and livestock workers show measurable functional impairment and increased respiratory symptoms, often with acute cross-shift declines in FEV1 [10,13], and comparative studies report lower FVC, FEV1 and flow rates in farmers than controls, declining with longer exposure [16,17]. Reviews of pesticide exposure similarly describe obstructive or restrictive changes according to chemical class [14,15]. The negative correlation between duration of exposure and lung function in both groups supports a causal, cumulative effect and provides the strongest argument for periodic spirometric surveillance and effective dust control. Smoking is a recognised effect modifier and should be considered alongside occupational exposure when interpreting individual results [17]. It is also important to note the healthy worker effect, whereby workers who remain in physically demanding jobs tend to be those with better preserved lung function; this bias generally attenuates cross-sectional associations and means the true occupational risk may be underestimated [16]. Limitations. The cross-sectional design precludes firm causal inference, exposure was estimated rather than quantified by environmental dust sampling, and the single-centre sample may limit generalisability. Diffusion capacity and lung volumes were not measured. Longitudinal follow-up with quantified exposure would strengthen future work.

Construction and agricultural workers showed significantly poorer pulmonary function than unexposed controls, with a restrictive pattern predominating in construction workers and a relatively greater obstructive component in agricultural workers, and lung function declined with increasing duration of exposure. These findings support the routine use of spirometry for screening and surveillance of occupationally exposed workers, alongside effective dust-control measures, respiratory protection and worker education to prevent progressive and often irreversible lung damage.

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