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Collagen content of the human diaphragm Scott, Alexander


INTRODUCTION: In limb muscle, the amount of endomysial, perimysial, and basal lamina collagen can increase as an adaptive response to endurance training or in response to exertion-induced injury. In the costal diaphragm, there is evidence for both adaptation and injury in people with chronic obstructive pulmonary disease (COPD). The present study had four objectives: (1) to quantify the proportional cross-sectional area of collagen (CSA[sub coll]) and the percentage of myofibres with abnormal or injured morphology (P[sub abn]) in the post-mortem COPD diaphragm, and to compare this in individuals with no significant respiratory diagnosis (NSRD); (2) to determine the CSA[sub coll] and P[sub abn] in different regions of the human diaphragm (midcostal, costal insertion, central tendon region, crural); (3) to compare the CSA[sub coll] and P[sub abn] in the diaphragm and a non-respiratory muscle (psoas major); (4) to determine the relationship between CSA[sub coll] and fibre cross-sectional area and P[sub abn]. METHODS: Mid-costal diaphragm biopsies were obtained and formalin-fixed from 6 COPD and 6 age- and gender-matched NSRD subjects. For the regional studies, whole diaphragms were obtained and formalin-fixed from 18 subjects. CSA[sub coll] was determined by computer-assisted point-counting of a 1.3 mm² area on 6 μm-thick cross-sections. P[sub abn] was calculated by categorizing all muscle fibres within an area of 1.7 mm² as normal or abnormal based on morphological criteria with an inter-rater reliability of 0.957. Fibre areas were calculated from the means of at least 200 fibres per biopsy using computerized image analysis software. RESULTS: The COPD diaphragm displayed a greater CS[sub coll], than NSRD (mean ± SE: 24.2 ± 1.0% vs 18.6 ±1.1%, p< 0.001) and a greater P[sub abn] (28.4 ± 7.2% vs. 12.0 ±1.3%, p< 0.05). Abnormal areas of accumulated endomysial and perimysial collagen (i.e. fibrosis) were observed more frequently in the COPD diaphragm, often in association with small, abnormally shaped muscle fibres. The COPD diaphragm displayed features of acute and chronic injury including inflammation and necrosis. The CSA[sub coll] and P[sub abn] of the crural diaphragm were smaller than the mid-costal values (18.0 ± 0.6% vs. 20.9 ± 0.6%, p < 0.01 and 11.9 ± 2.5% vs. 14.6 ± 2.6%, p<0.01 respectively). The psoas major displayed a lower P[sub abn] (8.3 ± 2.2%) and CSA[sub coll] (12.3 ± 0.5%) than the mid-costal (p < 0.01) and crural diaphragm (p < 0.001). CONCLUSION: The increased injury and collagen in the post-mortem COPD diaphragm is extensive.

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