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The purpose of this study was to examine whether morphologic abnormalities in human respiratory muscles are related to increased airway obstruction. 43 patients who were undergoing thoracotomy for suspected neoplasm had biopsies taken from one or more of the following muscles: external intercostal (EXT), internal intercostal (INT), diaphragm (DIA), latissimus dorsi (LAT), and quadriceps femoris (LEG). Mean FEV1/FVC was 65% of predicted (range 43–90%). 21 of the 43 patients had a malignancy. Atrophy of type I fibers was found in 27% of respiratory and 11 % of nonrespiratory muscles. Type II fiber atrophy was more common, being found in 58% of all muscles studied. The degree of type II fiber atrophy correlated significantly with the amount of weight loss, but not with age or the presence of malignancy. A unique and significant relationship was found between type II fiber atrophy in the INT (an expiratory muscle) and all measured indices of airway obstruction. This relationship did not exist in the DIA, EXT, or LAT, ordinarily considered muscles of inspiration. The percentage of type I and type II fibers bore no relationship to indices of airway obstruction. Depletion of muscle metabolites was common to all muscles and could not be related to airway obstruction or fiber atrophy. These data suggest that fiber atrophy and metabolite depletion occur commonly in both respiratory and nonrespiratory muscles in patients with stable obstructive lung disease. These changes probably reflect a generalized disease process and may predispose to muscle fatigue. Whether or not airway obstruction produces fiber atrophy in expiratory muscles requires further investigation.
Hughes et al. (Thu,) studied this question.