The lungs are an amazing pair of organs that are necessary for survival. There are two primary functions of the lungs, the first is to absorb oxygen from the atmosphere, and the second is to discard carbon dioxide from the body. Classical diseases of the lungs can be divided into either obstructive (difficulty exhaling) or restrictive (difficulty inhaling) pathologies. In addition, the lungs can be subject to a multitude of infections which can interfere with function. This brief review discusses the similarities and differences between these classical diseases of the lungs.
Obstructive Lung Disease
Diseases of exhalation are usually divided into asthma or chronic obstructive pulmonary disease. Under normal conditions, the lungs can exhale over 80 percent of the breath volume in one second. When the amount of air that can be exhaled in one second is less than that, there is considered to be an "obstruction" to airflow.
Asthma is defined as a chronic condition associated with two components: inflammation and reactivity. Inflammation refers to the growth of airway smooth muscle growth. Like skeletal muscle that gets thicker with exercise, the chronic inflammation of asthma causes these smooth muscles to get thicker, which makes it harder to breath. Reactivity refers to the acute constriction of the airways. Wheezing is the classical symptom that is described. This can be life threatening, and a quick acting medication needs to be available at all times for people with asthma.
Chronic obstructive pulmonary disease (COPD) is a broad term that refers to both chronic bronchitis or emphysema. This is usually associated with smoking, however it can be from other causes such as a genetic deficiency. People usually develop COPD later in life. These patient can have both the inflammation and the reactivity of asthma, in addition that also lose lung volume at twice the rate of the general population. Only two interventions have been shown to increase the life span of patients with COPD, quit smoking (for those people whose disease is related to cigarettes) and use of home oxygen.
Restrictive Lung disease
Diseases of inhalation are defined by loss of total lung volume. The most common restrictive lung disease is pulmonary fibrosis. People with this disease usually do not have wheezing, and the first symptoms they typically complain of is decreased tolerance for exercise. Multiple different things can cause this disease, such as sarcoidosis, or exposure to certain kinds of chemotherapy. Unfortunately the most common form of pulmonary fibrosis is idiopathic, in other words we don't fully understand the mechanism of the disease. Restrictive lung disease is very difficult to treat, and most patients will need a lung transplant at some point in their disease.
Pulmonary Infections
Most lung infections can be grouped in either viral or bacterial. There are of course some fungal diseases of the lungs, however these usually do not present major problems unless there is immunosuppression from drugs, chemotherapy, or genetic defect.
Pneumonia is the classical pulmonary infection. People that contract pneumonia usually have a high fever, chills and productive cough. When a chest X-ray is taken, pneumonia is diagnosed by a consolidation or infiltrate. This is just an increased lung density in a small area due to the infection. Most pneumonias can be treated with oral antibiotics, however if someone has underlying diseases, such as a heart or lung condition (COPD) more aggressive antibiotics are usually needed requiring hospitalization.
Bronchitis is an infection of the lungs by viruses or bacteria. However there is usually not an infiltrate or consolidation noted on chest X-ray. Bronchitis is usually accompanied by cough and fever as well, and is a more diffuse inflammation of the airways. Bronchitis is usually treated with antibiotics is the phlegm is dark colored or foul smelling, as these usually accompany bacterial infections.
