Obstructive Airway Disease (OAD) is a common respiratory disease that includes many other lung conditions such as asthma, chronic bronchitis or emphysema, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. Most of the patients affected with obstructive airway disease present with chronic breathlessness, wheeze and cough which may or may not be productive.



The pathophysiology of OAD is due to an abnormal airway structure or due to secretions or deposits that results in obstruction to airflow. In emphysema, obstruction is due to the pulmonary parenchyma cells that have lost normal elastic tension. Cigarette smoke is the most important cause of emphysema. Other injurious agents such as smoke, fumes or particulate matter bring about proteolysis in the lung, resulting in the distress or obstruction. As with emphysema or chronic bronchitis, other OADs are also due to the narrowing of the airways. This brings about reduction in the rate of airflow from and to the alveoli, therefore limiting the efficiency of the lungs.



In COPD, there is an increased reduction in airflow during expiration, due to which the pressure within the chest causes compression rather than expansion of airways, known as expiratory flow limitation. Dynamic hyperinflation is yet another common process in COPD, due to low rates of airflow. Dynamic hyperinflation is due to patients experiencing the tendency to inhale even before complete expiration especially during exertion and exercise. Dynamic hyperinflation is related to shortness of breath or dysnea which causes significant distress. Flow limitation or hyperinflation makes the breathing difficult. Shortness of breath is also due to loss of surface area, which affects the ability and efficiency in exchange of respiratory gases, oxygen and carbon dioxide. This leads to low oxygen and high carbon dioxide levels in the body causing a person with obstructive airway disease to breathe faster and more deeply to compensate.

No single sign or symptom helps in diagnosing OAD, however, anyone with dysnea and chronic cough productive or otherwise can be evaluated for the condition. History of smoking or exposure to cigarette smoke is also a risk factor. Spirometry, the best test, is used to measure the forced expiratory volume (FEV1) per sec and the forced vital capacity (FVC) of the lungs. Spirometry also helps in determining the severity of the condition especially in COPD. X-rays are useful in identifying hyperinflated lungs and thus excluding other lung conditions. Differentiation between the various OAD conditions such as COPD and emphysema is by pulmonary function tests that measure lung volumes and gas transfer. High-resolution chest CT scans are useful in determining the distribution of emphysema in the lungs. Arterial blood gas levels show hypoxemia or low oxygen levels. A venous sample reveals high blood counts or reactive polycythemia, which is due long-term hypoxemia.

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