Patterns of response to inhaled bronchodilators in asthmatics

In response to inhaled bronchodilators, asthmatic subjects may show a predominant increase in expiratory flow rate (flow responders) or forced vital capacity (volume responders). The pattern of response could relate to the site of expiratory flow limitation and/or the site of action of the inhaled bronchodilator. We studied 15 asthmatic subjects, and measured lung volumes and maximal expiratory flow-volume curves while they breathed room air and 80% He-20% O2 (He-O2) before and after inhalation of fenoterol 400 micrograms (Berotec), and ipratropium bromide 40 micrograms (SCH 1000). Subjects were categorized as flow responders (FR) or as volume responders (VR) by the ratio delta FEV1/delta FVC (ratio less than 1 predominant VR, ratio greater than 1 = predominant FR). The site of expiratory air-flow limitation was assessed by the percent increase in maximal expiratory flow breathing He-O2 at an absolute lung volume (delta Vmax), and the change in He response from control was calculated (delta delta Vmax). The ratio delta FEV1/delta FVC varied between 0 and 10 and did not correlate with initial density dependence. There was no difference in the pattern or apparent site of response to Berotec or SCH 1000. There was a positive relationship between control FEV1 and FVC percent predicted and delta FEV1/delta FVC. The subjects with worse pulmonary function showed a decrease in He-O2 response postbronchodilator and a predominant volume response suggesting recruitment of peripheral diseased airways.