What is Emphysema?     Emphysema is a disease of lower respiratory tract that mainly affects the lungs, in particular the alveoli of the lungs. It is grouped under the major disease called chronic obstructive pulmonary disease or COPD.   It is characterized by coughing and shortness of breath. As the disease progresses,it can show other severe symptoms such as chest tightness,chest pain and altered blood oxygen levels,cyanosis,etc.   Smoking and middle age are the common known risk factors of emphysema.  See also : Asthma  What are alveoli? Let us understand it in simpler words.    Alveoli are the part of the lungs.  These are tiny air sacs with elastic walls.   Alveoli are the main site of gas-exchange in the lungs.   Oxygen from the air we inhale is transported to the blood via alveoli. these tiny air sacs expand or stretch when we inhale. As our lungs inhale the air, they expand. This fills up the alveo...