Question
How is reversible airflow obstruction determined in patients using bronchodilator studies?
Answer
Spirometry before and after bronchodilator is the preferred method for diagnosing asthma because it offers higher precision and can be calibrated. Additionally, using predicted values allows for a more accurate assessment. Analyzing the flow volume loops helps evaluate patient effort and bronchospasm reversibility, which is essential in determining the presence of airway obstruction. The ratio of Forced Expiratory Volume in one second (FEV1) to Forced Vital Capacity (FVC) is also examined during this test. Peak expiratory flow monitoring is another method used to assess airflow limitation. However, spirometry is generally considered more reliable due to its precision and ability to provide more comprehensive data. By utilizing these diagnostic methods, healthcare professionals can effectively evaluate and diagnose asthma, enabling the implementation of appropriate treatment plans to manage the condition and improve patients' respiratory health.
In adult patients, it is essential to differentiate pure asthma from asthma and COPD overlap, especially in chronic smokers. For non-smoking adults without a high suspicion of emphysema or chronic bronchitis, we can assess if their airway obstruction is reversible using a bronchodilator. To determine the need for bronchodilator studies, we examine the FEV1 to FVC percent ratio, which measures the amount of air a person can exhale in the first second (FEV1) compared to the total amount of air exhaled (FVC). A normal FEV1/FVC ratio is around 75 to 80%. If this ratio is less than predicted, it indicates possible airflow obstruction, which could result from inflammation, excess mucus, or bronchospasm. To confirm the presence of reversible airflow obstruction, we administer a bronchodilator, such as albuterol, and wait for 15 minutes, the peak onset of action for short-acting beta agonists like albuterol. Waiting for the peak effect ensures precise and valid measurement of lung function.
This Ask the Expert is an edited excerpt from the course, Objective Measures of Asthma, presented by Kevin Collins, PhD, RRT, RPFT, AE-C.
