Since long time ago, COPD has been considered an obstructive disease (its name says it clearly). Of course, there is obstruction in the lung airways as a result of persistent bronchospasm. However, an effect of the obstruction has been studied recently and has been associated to the symptoms more than the obstructive component itself.
More than obstruction: air trapping
The obstruction of lung airways leads to air trapping in the distant units. These units, called alveoli, are the areas where gas exchange occurs as well as the pulmonary blood circulation has place. When the air gets trapped inside them both processes occur slower than expected and symptoms appear.
Dyspnea, the most bothering symptom for patients, has been associated to the levels of air trapped more than obstruction. Airflow obstruction has been found to represent the severity of the disease but air trapping is a consequence that leads to increased local pressure and physiological changes reflected in exercise intolerance.
A recent article
In his recent “ Update in the Management of COPD ” ( Chest 2008;133:1451-1462 ), Dr. Bartolome R. Celli points out the relevance of air trapping in the manifestations of symptoms independent of airflow obstruction. The fact that COPD is a multicomponent disease help us understand that management should be addressed to relieve all the manifestations possible and the management of dyspnea should be kept in mind when considering decisions.
Although Dr. Celli says that lung excess inflation is key in the genesis of symptoms in advanced disease, the importance of this physiologic hallmark has not been assessed in early stages. Two main factor may be defining this issue: the lungs’ elasticity and the symptoms minimization by patients.
Air trapping during physical activities
The concept of air trapping in COPD is more impacting during exercise or any other physical activity. When oxygen demand increase, the exhalation can not happen smoothly and air gets trapped in lungs. Unless the patient stop the activity, the excess inflation will limit normal breathing (particularly gas exchange and blood circulation in the lungs).
Not under the microscopy
Severe patients with emphysema may have their symptoms more severe due to those facts. These patients have the trend to develop considerable bubbles called bullae that take out space from the functional lung. This may be the macroscopical evidence of air trapping relevance, but it’s not necessary to wait until there.
How to find out if there’s air trapping
The true of the matter is asking for breathlessness to patients when they are smokers, when they already have cough and sputum production, when they say “ I have smoker’s cough only “, is paramount to help them and take decisions. How much the activity is limited because of some “Tiredness” or “Fatigue” needs to be carefully assessed to find the results of air trapping in the elastic lungs. Masking symptoms is not good, in any case. Let’s assume the importance of the underlying air trapping (and lung excess inflation or hyperinflation).