A cross-sectional analytical study on the association of body mass index to dynamic lung volumes – assessed by digital spirometer in a tertiary care hospital in Chennai

Introduction: Obesity causes reduction of Lung compliance leading to decrease in lung volumes producing mostly a restrictive type of ventilatory defect. Compression of the thoracic cage by excessive fat and increased pooling of blood in pulmonary vasculature mainly contribute towards a reduction in respiratory compliance. Deposition of fat in diaphragm causes mechanical obstruction to the descent of diaphragm thereby causing increased work of breathing and metabolic demand thereby producing breathing difficulty. The aim of the study: To measure the association of body mass index (BMI) to lung volumes assessed by a digital spirometer. Materials and methods: Apparently healthy individuals above the age group of 15 years attending Master Health Check-up OP and attenders of in-patients of wards of general medicine department, Govt. Chengalpattu Medical College, Chengalpattu of either gender were recruited. Height and weight were measured and BMI was calculated as kg/m2. Subjects were categorized as normal (BMI=18.5 to 24.9 kg/m2); overweight (BMI=25 to 29.9 kg/m2); obese Class 1 (BMI=30 to 34.9 kg/m2) and obese class 2 (BMI=35 to 39.9) on the basis of BMI. Lung volumes were measured by digital spirometer and were reported as a percentage of predicted values for forced vital capacity (FVC%), forced expiratory volume in the first second (FEV1%) and the ratio of FEV1 to FVC (FEV1: FVC). Groups were compared using t-test and ANOVA, the correlation was assessed by Pearson's 'r'. Results: Significant differences in lung volumes were found in different BMI categories. Obese subjects had significantly lower FVC% and the significant difference calculated by using One Way ANOVA F = 11.9 with p = 0.0001. Similarly, obese participants have significantly lower values of FEV1% when compared to participants of normal BMI. The significant difference calculated by using One Way ANOVA F = 6.46 with p = 0.0001. Gender and age had no significant effect on mean values of PFTs. Conclusion: Obese individuals in this sample had a significant decline in lung volumes. The presence of nutritional abundance and a sedentary lifestyle, and importantly influenced by genetic endowment, this system increases adipose energy stores and obesity develops which produces adverse health consequences.