Abstract Background Chronic obstructive pulmonary disease (COPD) is a common. preventable. and treatable disease that is characterized by persistent respiratory symptoms and airflow limitation that is due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles or gasses. An acute exacerbation of COPD refers to a flare up or episode where a p... https://www.roneverhart.com/2-1-2-x-1-4-x-36-Smooth-Saddle-Threshold-NGP-410-36/