Gupta, R., and S. Mann. “Correlation Between COPD And Echocardiographic Features With Severity Of Disease: Correlation Between COPD And Echocardiographic Features With Severity Of Disease”. National Journal of Integrated Research in Medicine, vol. 7, no. 1, Jan. 2018, pp. 26-30, http://nicpd.ac.in/ojs-/index.php/njirm/article/view/1038.