One of the ways in which we diagnose and monitor our pulmonary disease patients is with pulmonary function studies. These studies measure several aspects of lung function. When a complete study is performed, we are measuring the flow of air in the airways and the response to medications called bronchodilators, there is a measurement of lung volumes and, lastly, a measurement called diffusing capacity which gives us an idea about the integrity of the capillaries of the lungs. Although all three of these measurements are important, the one that is often times most meaningful is the flow of air through the airways and the response to medication.
The response of the airways to bronchodilators allows us to see how much response a patient may have to these medications and help predict what the long term outlook may be for any given patient. The bronchodilator response or BDR unfortunately will have a natural day-to-day variation based on environment and other factors including whether or not the patient is a smoker. The smoking rate in the US has declined to 12.5% of the population but 38% of patients with COPD continue to smoke.
One unusual recent finding is that patients that smoke and have a measurable bronchodilator response tend to have the greatest declines in lung function over time when compared with patients with COPD who have less response but do not smoke. This observation may seem confusing but further supports the need for patients with or without COPD to stop smoking.