Response in FEV1 and VC

An increase in FEV1 after administering a bronchodilator drug is usually accompanied by an increase in the VC. The correlation is not very strong: the VC may increase while the FEV1 diminishes, and vice versa. The data relate to about 4300 patients in whom spirometry was performed before and after bronchodilatation at Dijkzigt Ziekenhuis, Rotterdam.

Bronchodilator effectiveness has historically focused on improvement in the FEV1. However, the more severe the airway obstruction in COPD, the larger the improvement in the FVC in many patients with no or a small response in FEV1. Such a 'volume response' might be due to a more complete expiration, reflected by an increased forced expiratory time (FET), but occurs also when FET has not increased after bronchodilation. The 'volume response' is clinically relevant, as disclosed by decreased dyspnea and improved exercise performance.

'Volume response'

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