Interpreting response to bronchodilators

A response to bronchodilator drugs is regarded as unambiguous if the change in FEV1 >12% of the initial value and >200 mL. An isolated increase in (F)VC of >340 mL may be due either to better subject cooperation or a limited bronchodilator effect. In adults an increase in PEF larger than 60 L/s has been attributed to a bronchodilator response (ref. 1). A recent study suggests that, whilst PEF may be used to assess airways obstruction and exclude a response to bronchodilator drugs, it should not be used for assessing bronchodilator responsiveness in patients with chronic cough (ref. 2).

In keeping with the most recent ATS/ERS recommendation (ref. 12) the FEV1, FVC or another index is expressed as a percentage of the initial value. However, do consider the following:

1. Clinical data on effects of corticosteroids

   The change is not proportional to initial level. In patients with a ‘poor’ initial value the change in FEV1 due to a bronchodilator drug even has the tendency to be somewhat larger than in the case of a favorable initial value. Indeed the response to a bronchodilator drug may diminish if treatment with e.g. corticosteroids has been effective (view experimental data in the animation).
2. When measurements of FEV1 in adult patients with respiratory disease are repeated at short intervals, spontaneous variability is up to 200 mL (ref. 3). In a patient whose initial FEV1 is 700 mL this comes to 29% change due to spontaneous variability. Yet, if the initial value were 2 liter, the 200 mL spontaneous variability would come to only 10%.

In healthy subjects the change in FEV1 or VC due to a bronchodilator drug is maximally 9-11% (ref. 3) . The ATS and ERS (ref. 3-12) recommend to express changes in FEV1 post bronchodilator as a percentage of the initial value. Bronchodilator responsiveness is therefore categorized as follows:

The FEV1 is the best-studied index of lung function; hence the relationship of FEV1 and bronchodilator responsiveness with clinical condition or prognosis is well documented. One should keep in mind that a small increase in FEV1 due to a bronchodilator drug may be accompanied by a considerable fall in airway resistance during normal tidal breathing, and therefore in viscous work of breathing, which may be clinically relevant. Also, there may be symptomatic improvement without a significant increase in the FEV1 (ref. 4) .

See also:
Reference values for children, adolescents and adults

Ref. 1 - ECCS and ERS
In the revised 1993 version of the 1983 report ( Quanjer PhH (ed.) Standardized lung function testing. Bull Eur Physiopathol Respir 1983;
19 suppl. 5: 45-51) of the European Community for Coal and Steel (ECCS) predicted values of lung indices were unchanged. They are almost universally applied in Europe. The 1993 report was officially adopted by the European Respiratory Society (ERS).
The following chapter deals with spirometry, predicted values and bronchodilator responsiveness: Quanjer PhH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Eur Respir J 1993; 6 suppl. 16: 5-40. Erratum Eur Respir J 1995; 8: 1629.

Ref. 2 - Do not use PEF to assess airway obstruction
Thiadens HA, de Bock GH, van Houwelingen JC, Dekker FW, de Waal MWM, Springer MP, Postma DS. Can peak expiratory flow measurements reliably identify the presence of airway obstruction and bronchodilator response as assessed by FEV1 in primary care patients presenting with a persistent cough? Thorax 1999; 54: 1055-1060.