Chest
Volume 96, Issue 5, November 1989, Pages 984-987
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Clinical Investigations
Cholinergic Bronchomotor Tone in COPD: Estimates of Its Amount in Comparison with That in Normal Subjects

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The use of anticholinergic bronchodilators in COPD is based on the reversal of cholinergic bronchomotor tone. There is little information about the magnitude of cholinergic tone in patients with COPD as compared with normal subjects. As an index of the amount of cholinergic tone we measured the maximum increase in FEV1 following administration of an optimal dose of the anticholinergic agent atropine methonitrate. The study included nine normal nonsmoking subjects, ten normal smokers and 22 subjects with mild to moderately severe COPD. We found that normal nonsmokers had smallest increases in FEV, following atropine methonitrate administration. Responses of subjects with airway disease were progressively greater. Greatest responses occurred in the group of subjects with prebronchodilator FEV, values less than 55 percent of predicted. The most plausible explanation for this is that cholinergic tone in COPD is increased in proportion to the severity of airway disease. Other explanations are possible.

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Subjects and Methods

All subjects were recruited from Hines VA Hospital. Those with COPD were outpatients who had chronic bronchitis and/or emphysema as defined by recently revised criteria of the American Thoracic Society.8 All had airflow limitation (FEV, less than 70 percent of the predicted value) and a history of cigarette smoking equivalent to at least one pack per day for ten years. Patients with any features of asthma, allergies, peripheral eosinophilia or elevated serum IgE levels were excluded. None was

Results

General features of the 41 subjects are present in Table 1. For simplicity they are divided into four groups based on their baseline FEV1 values. The normal subjects could be divided without overlap of baseline FEV, into smokers and nonsmokers, and the patients with COPD were divided into “mild” and “moderate” by virtue of a baseline FEV, of above or below 55 percent of predicted. Although none of the subjects in this study had baseline FEV, values below 31 percent of predicted, it should be

Discussion

The principal aim of this study was to estimate cholinergic tone in patients with COPD in comparison with normal subjects. We estimated cholinergic tone by measuring the increment in FEV, when cholinergic tone is abolished by an anticholinergic agent, atropine methonitrate. We consider first some factors which might confound the premise that the FEV, increment following anticholinergic administration can be equated with cholinergic tone.

First, performance of an FEV, requires an inspiration to

ACKNOWLEDGMENTS

We thank Donald P. Tashkin, M.D., UCLA School of Medicine, for helpful suggestions and David Smith, Ph.D., for valuable advice on statistical methods and analyses.

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Manuscript received November 21 1988; revision accepted March 15

Supported in part by Veterans Administration Research Service, Hines VA Hospital.

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