Adaptation of the diaphragm and the vastus lateralis in mild-to-moderate COPD

Abstract

The chronology of diaphragm and vastus lateralis adaptation in chronic obstructive pulmonary disease (COPD) has not been studied. The hypothesis of this study was that muscle changes would occur earlier in the diaphragm than in the vastus lateralis in COPD, a finding that would suggest that local factors would be more important than systemic factors in determining the muscle phenotypic expression, at least in mild-to-moderate disease.The adaptation of the vastus lateralis and diaphragm muscles was evaluated in patients with mild-to-moderate COPD and in subjects with normal pulmonary function.In both groups, the oxidative potential and the number of lipofuscin inclusions were higher in the diaphragm than in the vastus lateralis. Compared to control, the diaphragm in COPD had a higher oxidative capacity and a higher proportion of type I fibres, with a reciprocal decrease in type IIA fibres, while there was no difference in diaphragmatic cross sectional areas, capillarisation and lipofuscin inclusions. No significant differences were found in the vastus lateralis from both groups.In conclusion, these data indicate that the diaphragm in controls and in chronic obstructive pulmonary disease has a higher oxidative potential than the vastus lateralis, and that muscle adaptation occurs earlier in the diaphragm than in the vastus lateralis in mild-to-moderate chronic obstructive pulmonary disease. Eur Respir J 2004; 24: 971-979.

Respiratory muscle fiber remodeling in chronic hyperinflation: dysfunction or adaptation?

“…Figure 2, A and B, illustrates the contrasting differences in fiber populations in control vs. severe emphysema patients. There is also reported a reduction in the percentage of IIA (18,38) and IIX (38) fibers. These results are complimented by analysis of MHC expression (Table 2).…”

“…Multiple studies from several laboratories have shown statistically significant increases in the relative proportions of type I fibers in the costal diaphragm (18,37,38,40,84), with two of the laboratories demonstrating a strong correlative relationship of the proportion of type I oxidative fibers with deterioration of lung function (40,84). Figure 2, A and B, illustrates the contrasting differences in fiber populations in control vs. severe emphysema patients.…”

“…Costal diaphragms from hamsters have about 23-27% type I, 33-47% IIA, and 28 -44% IIX/IIB fibers (31,49,52). Humans have a greater predominance of slow fibers, 45-50% type I, 35-40% type IIa, and 15-20% type IIx (18,38). These differences and differences in contractile patterns could be responsible for different adaptive strategies.…”

“…Scott et al (79) showed overall reductions in median fiber area of all muscle cells in the diaphragm (ϳ14%), but did not evaluate individual categories of fiber. Doucet et al (18) found only small changes in fiber size in COPD patients, and Ottenheijm et al (64) found a small but insignificant increases in type I fiber CSA in mild COPD patients. Therefore, human type I fibers may undergo selective atrophy in patients with COPD, but it is not a universal finding and is probably more likely to be present in patients with severe disease (40).…”

“…One study has addressed this in human diaphragm, but found no significant increase in the number of capillary contacts per fiber, although COPD patients trended toward having more contacts compared with controls (18). In the hamster model of elastaseinduced emphysema, the number of capillaries per muscle fiber is increased, with no change in capillary density per fiber, due to a simultaneous fiber hypertrophy in this model (44).…”