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.[1]References
- Patterns of response to inhaled bronchodilators in asthmatics. Paré, P.D., Lawson, L.M., Brooks, L.A. Am. Rev. Respir. Dis. (1983) [Pubmed]
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