title: Short-term influences of lung volume reduction surgery on the diaphragm in emphysematous hamsters.
abstract: With emphysema, diaphragm length adaptation results in shortened fibers. We hypothesize that passive diaphragm stretch occurring acutely after lung volume reduction surgery (LVRS) results in fiber injury. Bilateral LVRS was performed in emphysematous hamsters. Studies were performed 1 (D1) and 4 (D4) days after LVRS, and compared with sham-treated groups. Sarcolemmal rupture was evident in 10.9% of fibers in LVRS-D1 and reduced to 1.6% in LVRS-D4. Ultrastructural analysis revealed focal abnormalities in both LVRS-D1 and LVRS-D4 animals in over one-third of fibers. Myofibrillar disruption was not observed in sham-treated animals. Diaphragm insulin-like growth factor-I (IGF-I) was increased in LVRS-D4 compared with other emphysematous groups. Increased IGF-I immunoreactivity was localized to types IIA and I fibers. The abundance of the splice variant of IGF-I mRNA sensitive to muscle stretch (IGF-IEb) increased 3.2-fold in LVRS D-4 diaphragms, compared with emphysema-sham animals. The main form of IGF-I mRNA was unchanged. Marked force deficit was observed in the LVRS-D1 diaphragm, compared with emphysema-sham and emphysema (no surgery) animals. These data highlight a markedly compromised ventilatory pump acutely after LVRS. Acute fiber stretch predisposes to muscle fiber injury and may also be a necessary mechanotransductive stimulus for fiber remodeling as the diaphragm adapts to reduced lung volume.
authors.affiliation: Division of Pulmonary/Critical Care Medicine, Cedars-Sinai Medical Center, David Geffen School of Medicine at University of California, Los Angeles, CA 90048, USA. lewism@cshs.org
authors.forename: Michael I
authors.initials: MI
authors.lastname: Lewis
authors.forename: Mario
authors.initials: M
authors.lastname: Fournier
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Da
authors.forename: Hongmei
authors.initials: H
authors.lastname: Li
authors.forename: Zab
authors.initials: Z
authors.lastname: Mosenifar
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McKenna
authors.forename: Arthur H
authors.initials: AH
authors.lastname: Cohen
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D015984:Causality; D006224:Cricetinae; D003964:Diaphragm / Q000737:chemistry / Q000293:injuries* / Q000503:physiopathology / Q000648:ultrastructure; D004195:Disease Models, Animal; D004548:Elasticity; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics / Q000276:immunology; D008297:Male; D008854:Microscopy, Electron; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000648:ultrastructure; D009210:Myofibrils / Q000648:ultrastructure; D011013:Pneumonectomy / Q000009:adverse effects*; D011656:Pulmonary Emphysema / Q000601:surgery*; D012333:RNA, Messenger / Q000032:analysis; D012038:Regeneration; D015656:Respiratory Mechanics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012421:Rupture; D012508:Sarcolemma / Q000648:ultrastructure; D013997:Time Factors; D016896:Treatment Outcome; D015854:Up-Regulation
chemical_list: D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I