Emphysema overview

# Overview
Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. It is included in a group of diseases called chronic obstructive pulmonary disease or COPD (pulmonary refers to the lungs). Emphysema is called an obstructive lung disease because the destruction of lung tissue around smaller sacs, called alveoli, makes these air sacs unable to hold their functional shape upon exhalation. Emphysema is most often caused by tobacco smoking and long-term exposure to air pollution.
The term emphysema means "swelling" and derives from the Greek  emphysan meaning "inflate" - itself composed of  en, meaning "in", and  physan, meaning "breath, blast".

# Historical perspective
The terms chronic bronchitis and emphysema were formally defined at the CIBA guest symposium of physicians in 1959. COPD has probably always existed but has been called by different names in the past. Bonet described a condition of  voluminous lungs in 1679. Matthew Baillie illustrated an emphysematous lung in 1789 and described the destructive character of the condition.  The term COPD was first used by William Briscoe in 1965 and has gradually overtaken other terms to become established today as the preferred name for this disease.

# Pathophysiology
Emphysema is caused by loss of elasticity of the lung tissue, from  destruction of structures supporting the alveoli, and destruction of capillaries feeding the alveoli. The result is that the  small airways collapse during exhalation, leading to an obstructive form of lung disease (airflow is impeded and air is generally "trapped" in the lungs in obstructive lung diseases). When toxins such as smoke are breathed into the lungs, the particles are trapped and cause a localized inflammatory response. Chemicals released during the inflammatory response (e.g., elastase) can break down the walls of alveoli (alveolar septum). This leads to fewer but larger alveoli, with a decreased surface area and a decreased ability to absorb oxygen and exude carbon dioxide by diffusion. The activity of another molecule called alpha 1-antitrypsin normally neutralizes the destructive action of one of these damaging molecules.

# Risk Factors
Chronic obstructive pulmonary disease is a group of diseases characterized by the pathological limitation of airflow in the airway that is not fully reversible. A full comprehensive diagnosis is needed to eliminate related conditions and isolate the influence of lifestyle and behavior risk factors on condition outcome. Some common risk factors are cigarette smoking, occupational pollutants, air pollution and genetics. Other risk factors are increasing age, male gender, allergy, repeated airway infection.

# Differential Diagnosis
In clinical practice, COPD is defined by its characteristically low airflow on lung function tests. In contrast to asthma, this limitation is poorly reversible and usually gets progressively worse over time. It should be differentiated from certain conditions that have similar presentation for instance congestive heart failure, chronic asthma, bronchiectasis, and bronchiolitis obliterans.