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Thursday, June 10, 2010

Types of airflow obstruction

This venn diagram is used in many respiratory books and articles to show the relationship between chronic bronchitis, emphysema and asthma. As you can see there is some overlapping.

The patients that fall within the rectangle have some degree of airflow limitation or obstruction. I actually would put all of asthma inside this rectangle.

(1) The asthmatics that fall outside the shaded blue area consist of a majority of asthmatics who have completely reversible asthma, or pure asthma. They have episodes of asthma while exposed to their asthma triggers, but live most of their lives symptoms free. If they have an attack, asthma treatment will at least eventually reverse the process.

Those asthmatics who fall inside the shaded blue area have more than just your typical asthma. In many cases you may classify these asthmatics as your severe asthmatics. They, to some extent, have some permanent damage to their airways causing some degree of constant airflow obstruction. In some cases this may involve airway changes or scarring caused by uncontrolled asthma, or perhaps loss of tissue caused by smoking (emphysema). When an asthmatic smokes, he may end up chronic bronchitis at a young age.

Asthmatics who fall into the shaded blue area have asthma with either a (2) chronic cough or (3) emphysema. Likewise, some asthmatics may have (4) COPD/asthma, or both chronic bronchitis and emphysema. Chances are that the majority of patients we RTs see in the hospital fall into this category 7 as I describe below.

Some believe that COPD may result in hyperactivity in some patients. I believe that it is more
likely the patient had asthma all along, and never had trouble breathing until the diagnosis of COPD was made (probably after years of smoking). These patients, perhaps, have the most
grim outlook, and may have a shortened lifespan.

Those patients with (5) pure chronic bronchitis (they do not fall into the asthma or emphysema circles but are in the rectangle) have a chronic productive cough and chronic airflow obstruction. They do not have emphysema and do not have asthma, and they may always have some degree of mild shortness of breath. The dyspnea may be so mild they may not even notice it.

Those patients with (6) pure emphysema (they do not fall into the asthma or chronic bronchitis circles but are in the rectangle) have loss of lung tissue and chronic airflow obstruction as a result. Of all the diseases listed here, emphysema is the easiest to diagnose as the x-ray will always show an increased airway diameter.

(7) Severe COPD would consist of those patients who fall inside the shaded blue area, inside the rectangle, and have both emphysema and COPD, but not asthma. Along with your COPD/asthmatics. Patients who fall within this area, along with your COPD/asthmatics, are the patients we see most often in hospitals.

(8) Simple chronic bronchitis are those patients that have chronic bronchitis but fall outside the shaded blue area. They do not have airflow obstruction. Their FEV1 will show up as normal on their pulmonary function test, yet their x-ray may show signs of chronic bronchitis.

(9) Simple emphysema are those patients that have emphysema but fall outside the shaded blue area. They do not have airflow obstruction. Their FEV1 will show up as normal on their pulmonary function test, yet their x-ray will show signs of emphysema.

Of all the above listed emphysema is the easiest to diagnose. Asthma can be tricky to diagnose, although not altogether impossible, although when a patient has both asthma and one or both bronchitis and emphysema diagnosis can be tricky, although a good history can be helpful.

While asthma, chronic bronchitis and emphysema are all typically diseases of airway obstruction, pure asthma is usually not defined as COPD. Thus, 2 through 8 as defined above ARE all classified as COPD.

It is not possible to know what percentages fall within each of the above. I would imagine that 90% of asthmatics have pure asthma. I have seen many COPD patients who have also been diagnosed with asthma, and these are usually your more difficult patients to care for and treat. These are the one's who continue to return to the hospital, and become our regulars.

I have taken care of many COPD patients with simple bronchitis or emphysema. So, it is difficult to truly put a percentage inside any of these COPD types.

It's important to note here that any of the above conditions can be controlled with proper medication and management.

Likewise, any one of the above conditions that fall outside the rectangle (pure asthma, pure COPD, and pure emphysema) can progress to the more severe types inside the rectangle without proper management.

This is why it is important to get proper diagnosis and treatment as soon as possible, and for you and your doctor to take your disease seriously regardless of severity.

(Source: Robert L. Wilkins, James R. Dexter, "Respiratory Disease: Principles of Respiratory Care," 1993, page 30.)

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