Differences in total lung capacity among Indians and Europeans

Abstract

Background: Total lung capacity (TLC) is the volume of air in the lungs at the end of a maximal inhalation. TLC mainly depends on various factors/predictors such as height, age, gender, and ethnicity, and therefore, population-specific reference equations should be used. Currently, in India, we use the (European committee for coal and steel [ECCS], published in the year 1993) reference equation with no correction factor for TLC. It is recommended that the reference equation should be tested on a sample of local healthy participants, differences between the measured values and the predicted values are determined to see if the reference equation is a suitable/good fit for the population. Aim: The aim of this study was to compare the actual values of TLC from the healthy male and female volunteers from Pune city with the reference values obtained from the ECCS equations in these participants and determine the correction factor/percent differences between the mean values for different age and height groups. Design and Setting: A prospective, cross-sectional study of lung function measurements (TLC) by body plethysmography was carried out in a research center. Methodology: TLC was measured by Jaeger's Body Plethysmograph (model: Master scope) according to the recommendation of the American Thoracic Society's/European Respiratory Society's standards 2005 in a sample of 241 healthy nonsmoking volunteers (150 men and 82 women) aged 20–70 years, living in Pune city of Maharashtra, India. Statistical Analysis: The mean of actual TLC and the reference TLC were plotted against the different age groups and height groups and percentage difference was determined. Multiple linear regression was carried out to find the predictive equations for TLC parameter measured by the body plethysmography. Age, height, and weight were used as the predictors (independent variables) in the multiple regression analysis. Since sex is also a predictor of TLC, separate models were run for men and women. Results: There were statistically significant differences between the measured TLC and the reference TLC obtained from the ECCS equation in both males (5.05 L ± 0.69 vs. 6.3 L ± 0.50) and females (3.69 L ± 0.54 vs. 4.39 L ± 0.36), respectively. Males have higher TLC as compared to females of the same age and height. The mean of actual TLC and the reference TLC was plotted against different age groups and height groups, and percentage difference was determined. The percentage differences ranged from 17% to 21% in males and 13%–17% in females. Conclusion: The ECCS equation is not suitable for Pune population and may lead to misinterpretation of restrictive lung diseases and hyperinflation. A correction factor of 18.5% in males and 15% in females may be used for the ECCS equation for TLC in Pune population.

Keywords

• body plethysmography
• correction factor
• european committee for coal and steel
• lung function tests
• reference equation
• restrictive lung disease
• total lung capacity