Chest
Clinical InvestigationsThe Significance of Volume-Adjusting the Maximal Midexpiratory Flow in Assessing the Response to a Bronchodilator Drug
Section snippets
MATERIALS AND METHODS
Twenty-five patients with reversible obstruction of the airways were selected from the outpatient population of our clinic. The purpose of the study was explained, and informed consents were obtained. Each patient demonstrated greater than 25 percent improvement in their FEV1.0 after inhaling 2 ml of a 1:800 solution of isoproterenol nebulized over a five-minute period by a modified nebulizer (Deutraband D-31). The mean age of the patients was 49 years, with a range of 20 to 73 years.
RESULTS
The mean baseline values for the population under study, expressed as the percentage of predicted values (±1 SE), are as follows: TLC, 136 ± 4 percent; FVC, 70 ± 4 percent; FEV1.0, 49 ± 4 percent; and FEF25-75%, 26 ± 4 percent. There was less than a 5 percent difference between mean baseline values on the days of study.
Figure 2 is a plot of FVC (percent of change from baseline) against time after ingestion of ephedrine and placebo. Compared with placebo, ingestion of ephedrine produced
DISCUSSION
It seemed paradoxical to us that while we were studying a relatively weak bronchodilator drug, the FVC and FEV1.0 should change significantly while the FEF25-75% changed little. At different lung volumes, values for elastic recoil pressure (and thus airway driving pressure) are different, and this difference may obscure or enhance a true change in resistance to flow. In all subjects, there were no significant differences in measured TLC before and 30 minutes after ingestion of ephedrine. In the
ACKNOWLEDGMENTS
Statistical assistance was provided by Mr. Emmanual Lerner, Eastern Research Support Center, Veterans Administration, West Haven, Conn. We wish to thank Mr. John O. Ponder for his technical assistance and Gordon L. Snider, M.D., F.C.C.P., for his help with the manuscript.
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Manuscript received March 15; revision accepted August 3.