Chest
Clinical InvestigationsPartial and Maximal Expiratory Flow-Volume Curves in Normal and Asthmatic Subjects Before and After Inhalation of Metaproterenol
Section snippets
Materials and Methods
Twenty four non-smoking normal subjects (13 men, 11 women) with mean age 33.3±9.5 were studied; the asthmatic group consisted of 24 subjects (12 men, 12 women) with mean age 30.5±11.4 (p=NS). Four of the asthmatic subjects were light smokers (>ten pack-years); all of these subjects had asthma prior to the onset of cigarette smoking. All subjects gave informed consent to participate in the study. The asthmatic subjects all had a history of episodic dyspnea or bronchospasm but were selected by
Routine Pulmonary Function Tests (Table 1)
In the asthmatic group, abnormalities ranged from mild to severe. Compared to the normal subjects, FEV1, percent predicted FEV1, FVC, SGaw, max50, and RV were all significantly worse in the asthmatics. In addition, density-dependence of maximal expiratory flow (max50) was substantially lower in the asthmatic than in normal subjects (p<0.001). Total lung capacity and DLco did not differ significantly between the two groups.
In both groups, FEV1, percent predicted FEV1, FVC, percent predicted FVC,
Discussion
A total lung capacity (TLC) volume history could affect flow rates through several mechanisms. Using the equal pressure point model, =Pst/Rus, where Pst is lung elastic recoil pressure and Rus is upstream segment resistance.21 A deep inspiration is known to decrease Pst and thereby decrease the driving pressure for flow, as well as decrease external traction on the airways and airway diameter. Alternatively, a post inspiratory decrease in bronchomotor tone would decrease resistance. The net
ACKNOWLEDGMENTS
The authors thank R. Alfonso, Y. Franzen, and J. Lowe for technical assistance and R. Langenfeld and H. Buck for the typing of this manuscript.
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Manuscript received January 17; revision accepted May 8.
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Recipient of NHLBI Pulmonary Adacemic Award HL 00529.