Iqbal, Z., Z. Ullah, A. Basit, M. Y. Khan, and A. Javaid. “CHANGES IN ARTERIAL BLOOD GASES AND RESPIRATORY RATE BEFORE AND AFTER NON INVASIVE POSITIVE PRESSURE VENTILATION IN ACUTE EXACERBATION OF COPD”. Pakistan Journal of Chest Medicine, vol. 14, no. 3, June 2015, https://pjcm.net/index.php/pjcm/article/view/178.