Evaluation of bronchodilator responsiveness
In assessing bronchodilator responsiveness attention is paid to two test results: the increase in FEV1, and the maximum level of FEV1 obtained.
Increase in FEV1
In adults an increase in FEV1 by 12% of the initial value is regarded as a significant bronchodilator response. An increase by 9%-12% of the initial value, or >200 mL, is regarded as mild bronchodilatation. In children the 200 mL criterion does not apply. Do keep in mind that bronchodilator responsiveness depends on:
- The initial value of FEV1
If the FEV1 is within the normal range there is limited room for improvement. Also in the case of an appreciably diminished value an inflammatory component which limits bronchodilator responsiveness may play a role. In the latter case treatment with corticosteroids is usually in place.
- Bronchomotor tone
If airway smooth muscle is not stimulated and not in a contracted state, the bronchodilator effect is limited. This may change rapidly when the patient is exposed to bronchoconstricting stimuli from the environment. Bronchodilator responsiveness, therefore, only provides a picture at a certain moment in time.
of FEV1 obtained
Apart from the increase in FEV1 it is important to take into account the maximum level obtained. For example: is there residual airflow limitation in spite of an appreciable increase in FEV1? Or was airway obstruction relieved even though the increase in FEV1 was rather small? The maximum level of FEV1 depends less on initial value, bronchomotor tone or previously used bronchodilators. It is very important, in considering therapy with oral or inhaled corticosteroids, to look in the patient file for the maximum achievable level of FEV1.
Treat the patient, not the numbers
Bronchodilator responsiveness: children, adolescents and adults
Bronchodilator responsiveness: clinical population
Corticosteroids (and list of references)