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Asthma

Understanding PFT Testing Results

03/18/2003

Question:

My seventeen year old son was diagnosed with asthma about 4 years ago. He receives PFT testing about every six months. I don`t understand how the PFT results are to be interpreted. He scores low on MEP, MIP, ERV(L), and FRC(N2(L). They always give him a nebulizer treatment and repeat the study. Many of his numbers get worse after the treatment. As an example, his FEF Max (L/sec) are 7.87 and after the nebulizer it drops 17% to 6.56. Shouldn`t all his numbers improve with treatments? His airways resistance drops by 42%.(sRaw and Raw. His pulmonologist has him on Serevent and MAxair as needed. Are there any statistics as to what his chances are for improving these numbers and being off medication all together? Thank you for your input.

Answer:

 Asthma is a lung disease that is associated with reversible obstruction of airflow. The PFT value most commonly followed for asthma is the FEV1 (the volume of air exhaled in the first second of a forced expiration). In asthma, FEV1 is decreased when obstruction to airflow is present, and increases when the obstruction is relieved. Although the indices you listed have utility in some settings, they are probably less useful in following asthma. With regards to the resistance measurement, a high value may indicate a higher degree of airflow obstruction. If the nebulized treatment, usually a bronchodilator such as a beta-agonist, relaxes the airway and relieves the obstruction to airflow, then resistance can be expected to decrease. Note that this is in contrast to the FEV1 response which increases when airflow obstruction is relieved. The clinical course of asthma can be highly variable, and PFT`s only provide information for a specific point in time. It would therefore be difficult to predict the long term course of asthma from a single set of PFT`s. However, following a trend over time may provide insight about disease progression and response to therapy. 

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Response by:

Dennis   McGraw, MD Dennis McGraw, MD
Assistant Professor
College of Medicine
University of Cincinnati