Clinical study
A reduction in maximum mid-expiratory flow rate: A spirographic manifestation of small airway disease

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Abstract

We studied the pulmonary function of fifty-three nonasthmatic patients who were heavy smokers and who complained of bouts of wheezing, cough and sputum production. The only findings on routine pulmonary function studies were a reduced maximum mid-expiratory flow rate (MMF) and an enlarged residual volume (RV). Airway resistance (Raw), specific conductance, one second forced expiratory volume (FEV1), maximum expiratory flow rate (MEFR) and total lung capacity (TLC) were all within predicted statistical norms. In twenty-five patients we measured static (Cstat) and dynamic compliance (Cdyn) and gas exchange both at rest and during exercise. Cstat was found to be normal in every case, but Cdyn was frequency dependent. Physiologic dead space to tidal volume ratios (VD:VT) and alveolar-arterial gradients for oxygen (A-aDO2) were found to be abnormally elevated both at rest and during exercise. After treatment with oral bronchodilators for one month the MMF improved in twenty-one patients. Cessation of smoking combined with the bronchodilators therapy completely reversed all the functional abnormalities in four subjects. We postulate that the low MMF represents significant airway obstruction in peripheral bronchioles and as such may represent an early manifestation of chronic bronchitis when the disease may be amenable to therapy.

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    Present address: Pulmonary Disease Division 5C, University of Texas Medical Branch, Galveston, Texas 77550.

    1

    From the Department of Medicine, William Beaumont General Hospital, El Paso, Texas 79920.

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