Introduction: Silicosis is one of the oldest occupational lung diseases, occurring gradually over a period of 12-15 years in workers exposed to silica dust. However, there are very few studies identifying anthropometric variables associated with silicosis and their impact on disease progression. It would be of value to consider the physical characteristics of individuals as risk factors for developing occupational lung disease.
Aim: The objective of present study was to study the association between body surface area (BSA), pulmonary function indices and 6 minute-walk distance(6MWD) in patients of silicosis.
Materials and Methods: A cross-sectional study was conducted on 102 male patients diagnosed with silicosis. Height and weight were measured to calculate BSA. The subjects were divided into three groups on basis of BSA (square metre) – Group I with BSA< 1.6 sq. m., Group II with BSA =1.6- 1.9 sq. m. and Group III with BSA >1.9 sq. m. Each group was further subdivided into three subgroups according to years of exposure to silica dust, subgroups being Ia, IIa and IIIa (10-15 years of exposure), Ib, IIb and IIIb (15-20 years of exposure) and Ic, IIc and IIIc (>20 years of exposure). Spirometry and 6MWD were performed on all groups and subgroups. Data was expressed as mean and standard deviation. Statistical analysis was done using Epi info V7 software. The outcome variables were Forced expiratory volume in first second (FEV1), Forced vital capacity (FVC), FEV1/FVC ratio and Peak expiratory flow rate (PEFR). Student’s t test of significance (ANOVA) was applied to test the difference between means. Level of significance was set at 5%.
Results: Average age of subjects was 43.80±8.8 years. The average duration of exposure to silica dust was 21.25±6.35 years. 6MWD showed no significant changes with years of exposure and BSA. Except for FVC [2.80±0.76, 3.12± 0.51, 2.62 ± 0.69], the total mean of all other pulmonary function indices showed a statistically significant decrease as we move from subgroup ‘a’ (10-15 years of exposure) to subgroup ‘c’ (> 20 years of exposure) in each group [FEV1- 2.27±0.69, 2.44± 0.44, 1.91± 0.59 ; FEV1/FVC(%) – 80.14±5.84, 78.13 ± 5.15, 72.17± 10.45; PEFR(L/s) – 5.18±1.27, 6.15 ±1.29, 5.06 ± 1.88 respectively in each subgroup a, b, c].In group III, only FEV1 and FVC showed statistically significant decrease with increase in years of exposure [FEV1-3.05 ± 0.09(IIIa), 2.93 ± 0.66(IIIb), 2.23 ± 0.37(IIIc) (p<0.001) & FVC- 3.66 ± 0.31(IIIa), 3.5± 0.81(IIIb), 2.90 ± 0.20(IIIc)]. The spirometric indices were higher in group III compared to group I and group II. Statistically significant higher values of FEV1 [2.73 ± 0.37(p=0.03)] and FVC [3.35 ± 0.44 (p=0.01)] were observed in group III patients in all subcategories of exposure.
Conclusion: Patients of silicosis with BSA > 1.9 sq. m. had higher values of pulmonary function indices, irrespective of period of exposure to silica dust. Large body size may be of value in protection from developing occupational lung disease.