Obstructive lung disease
Depiction of a person withbronchiectasis, a type of obstructive lung disease
Specialty	Pulmonology

Obstructive lung disease is a category ofrespiratory disease characterized byairway obstruction. Many obstructive diseases of thelung result from narrowing (obstruction) of the smaller bronchi and larger bronchioles, often because of excessive contraction of the smooth muscle itself. It is generally characterized by inflamed and easily collapsible airways, obstruction to airflow, problems exhaling, and frequent medical clinic visits and hospitalizations. Types of obstructive lung disease includeasthma,bronchiectasis,bronchitis andchronic obstructive pulmonary disease (COPD). Although COPD shares similar characteristics with all other obstructive lung diseases, such as the signs ofcoughing andwheezing, they are distinct conditions in terms of disease onset, frequency of symptoms, and reversibility of airway obstruction.^[1]Cystic fibrosis is also sometimes included in obstructive pulmonary disease.^[2]

Asthma is an obstructive lung disease where thebronchial tubes (airways) are extra sensitive (hyperresponsive). The airways become inflamed and produce excess mucus and the muscles around the airways tighten making the airways narrower. Asthma is usually triggered by breathing in things in the air such as dust or pollen that produce an allergic reaction. It may be triggered by other things such as anupper respiratory tract infection, cold air, exercise, or smoke. Asthma is a common condition and affects over 300 million people around the world.^[3]Asthma causes recurring episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or in the early morning.^[4]

• Exercise-induced asthma is common in asthmatics, especially after participation in outdoor activities in cold weather.
• Occupational asthma – an estimated 2% to 5% of all asthma episodes may be caused by exposure to a specific sensitizing agent in the workplace.
• Nocturnal asthma is a characteristic problem in poorly controlled asthma and is reported by more than two-thirds of sub-optimally treated patients.

Apeak flow meter can record variations in the severity of asthma over time.Spirometry, a measurement of lung function, can provide an assessment of the severity, reversibility, and variability of airflow limitation, and help confirm the diagnosis of asthma.^[3]

Bronchiectasis refers to the abnormal, irreversible dilatation of the bronchi caused by destructive and inflammatory changes in the airway walls. Bronchiectasis has three major anatomical patterns: cylindrical bronchiectasis, varicose bronchiectasis and cystic bronchiectasis.^[5]

Chronic obstructive pulmonary disease (COPD), previously known as chronic obstructive airways disease (COAD) or chronic airflow limitation (CAL), is a group of illnesses characterised by airflow limitation that is not fully reversible. The flow of air into and out of the lungs is impaired.^[6] This can be measured with breathing devices such as apeak flow meter or byspirometry. Most people with COPD have characteristics ofemphysema andchronic bronchitis to varying degrees.Asthma being a reversible obstruction of airways is often considered separately, but many COPD patients also have some degree of reversibility in their airways.^[7]

In COPD, there is an increase inairway resistance, shown by a decrease in the forced expiratory volume in 1 second (FEV1) measured byspirometry. COPD is defined as a forced expiratory volume in 1 second divided by the forced vital capacity (FEV1/FVC) that is less than 0.7 (or 70%).^[8] The residual volume, the volume of air left in the lungs following full expiration, is often increased in COPD, as is the total lung capacity, while the vital capacity remains relatively normal. The increased total lung capacity (hyperinflation) can result in the clinical feature of abarrel chest – a chest with a large front-to-back diameter that occurs in some individuals withemphysematous COPD. Hyperinflation can also be seen on achest X-ray as a flattening of thediaphragm.^{[citation needed]}

The most common cause of COPD is cigarettesmoking. COPD is a gradually progressive condition and usually only develops after about 20pack-years of smoking. COPD may also be caused by breathing in other particles and gases.^{[citation needed]}

The diagnosis of COPD is established throughspirometry although other pulmonary function tests can be helpful. A chest X-ray is often ordered to look for hyperinflation and rule out other lung conditions but the lung damage of COPD is not always visible on a chest x-ray. Emphysema, for example, can only be seen onCT scan.

The main form of long term management involves the use ofinhaled bronchodilators (specificallybeta agonists andanticholinergics) and inhaledcorticosteroids. Many patients eventually requireoxygen supplementation at home. In severe cases that are difficult to control, chronic treatment with oralcorticosteroids may be necessary, although this is fraught with significant side effects.

COPD is generally irreversible although lung function can partially recover if the patient stops smoking. Smoking cessation is an essential aspect of treatment.^[9] Pulmonary rehabilitation programmes involve intensive exercise training combined with education and are effective in improving shortness of breath. Severe emphysema has been treated withlung volume reduction surgery, with in carefully chosen cases.Lung transplantation is also performed for severe COPD in carefully chosen cases.^[10]

Alpha 1-antitrypsin deficiency is a fairly rare genetic condition that results in COPD (particularly emphysema) due to a lack of the antitrypsin protein which protects the fragile alveolar walls from protease enzymes released byinflammatory processes.^{[citation needed]}

Diagnosis of obstructive disease requires several factors depending on the exact disease being diagnosed. However one commonality between them is anFEV1/FVC ratio less than 0.7, i.e. the inability to exhale 70% of their breath within one second.^[11]

Following is an overview of the main obstructive lung diseases. Chronic obstructive pulmonary disease is mainly a combination of chronic bronchitis and emphysema, but may be more or less overlapping with all conditions.^[12]

• Restrictive lung disease

• Lung disorders
• Respiratory therapy

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