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Original Article
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Volume 337:1799-1806 December 18, 1997 Number 25
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Cellular Adaptations in the Diaphragm in Chronic Obstructive Pulmonary Disease
Sanford Levine, M.D., Larry Kaiser, M.D., John Leferovich, M.S., and Boris Tikunov, Ph.D.

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ABSTRACT

Background In patients with severe chronic obstructive pulmonary disease, the diaphragm undergoes physiologic adaptations characterized by an increase in energy expenditure and relative resistance to fatigue. We hypothesized that these physiologic characteristics would be associated with structural adaptations consisting of an increased proportion of less-fatigable slow-twitch muscle fibers and slow isoforms of myofibrillar proteins.

Methods We obtained biopsy specimens of the diaphragm from 6 patients with severe chronic obstructive pulmonary disease (mean [±SE] forced expiratory volume in one second, 33±4 percent of the predicted value; residual volume, 259±25 percent of the predicted value) and 10 control subjects. The proportions of the various isoforms of myosin heavy chains, myosin light chains, troponin, and tropomyosin were determined by sodium dodecyl sulfate–polyacrylamide-gel electrophoresis. We also used immunocytochemical techniques to determine the proportions of the various types of muscle fibers.

Results The diaphragm-biopsy specimens from the patients had higher percentages of slow myosin heavy chain I (64±3 vs. 45±2 percent, P<0.001), and lower percentages of fast myosin heavy chains IIa (29 ± 3 vs. 39 ± 2 percent, P = 0.01) and IIb (8±1 vs. 17±1 percent, P<0.001) than the diaphragms of the controls. Similar differences were noted when immunohistochemical techniques were used to compare the percentages of these fiber types in the two groups. In addition, the patients had higher percentages of the slow isoforms of myosin light chains, troponins, and tropomyosin, whereas the controls had higher percentages of the fast isoforms of these proteins.

Conclusions Severe chronic obstructive pulmonary disease increases the slow-twitch characteristics of the muscle fibers in the diaphragm, an adaptation that increases resistance to fatigue.


Source Information

From the Pulmonary and Critical Care Divisions, Philadelphia Veterans Affairs Medical Center, Allegheny University of the Health Sciences, and the University of Pennsylvania (S.L.); and the Division of Thoracic Surgery (L.K.) and the Pennsylvania Muscle Institute (S.L., J.L., B.T.), University of Pennsylvania — all in Philadelphia.

Address reprint requests to Dr. Levine at the Pulmonary and Critical Care Division (111P), Veterans Affairs Medical Center, University and Woodland Aves., Philadelphia, PA 19104.

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