Experimental Studies On Changes Of Biomechanical Properties In Diaphragm Of Rats In Chronic Hypoxia And Emphysema

Objective: Diaphragm is one of the major respiratory muscles.There are many research on diaphragmatic structure,function and metabolism.In recent years,our research on diaphragma fatigue have great increased.But the biomechanical characteristics and molecular basis of diaphragm is not known very well up to now.The experiments have been employed to investigate the mechanical characteristics of diaphragmic strip and sigle cell , the relationship between biomechanical properties and titin and nebulin in rat diaphragm based upon the experimental models of hypoxia,emphysema and hypoxia-emphysema.Method: (1)Animal modal: Chronic hypoxia was induced by a intermission hypoxic enviroment.Emphysema was induced by a single intratracheal instillation of pancreatic porcine elastase.(2)The contractility and fatigue properties of isolated diaphragmic muscles were measured.(3)The passive elastic properties of isolated diaphragm muscles were analyzed by detecting stress and stain of muscle strips.(4)Using micropipette aspiration technique,We investigated the viscoelastic properties of rats diaphragma cells. (5)Immunocytochernistry procedures were used to analyze the distribution of two key elastec components of muscle, titin and nebuline. (6)The relation between biomechanical characteristics and expression of titin and nebulin of diaphragm was discussed.Result: (1)Animal modal : Compared with controls,oxygen pressure of hypoxic animals was lower, lung perfusion bulk left unchanged , and pathologyof lung.In emphysema animals, gentle decrease of oxygen pressure ,retention of carbon dioxide.In emphysema-hypoxia rats, changes appearing in emphysema animals sharpened, and oxygen pressure dropped. Ultrastructure of diaphragma cells was changed. In hypoxia rats, swollen mitochondria and thickened myocyte cell membrane. In emphysema rats, swollen mitochondria with critae loss and vacuolization, disorganized myofibrillae with some loss of myofilaments. (2)There were more significant increase in Pt and Po ,and more significant decrease in l/2Rt in emphysema and emphysema-hypoxia rats than that in hypoxic rats and controls. The force-frequency curve was right shifted in emphysema and emphysema-hypoxia rats. (3)Muscle stiffness constant was lower and muscle elastic modulus was higher in emphysema-hypoxia and emphysema rats than in controls. (4) Experimental results showed that the viscoelastic properties K1, K2 and of emphysema and emphysema-hypoxia cells are lower than that of hypoxia cells and controls .(5)Compared with controls, expression of titin and nebulin in diaphragmatic cell of emphysema and hypoxia-emphysema rats was significantly lower. There was no different in hypoxic rats. (6)The decrease of expression of diaphragmatic titin and nebulin was consistant with the decline of the stiffness constant of muscle and the increase of viscoelastic properties.Conclusion: (1)We replicate the experimental models of hypoxia, emphysema and hypoxia-emphysema successfully with a single intratracheal instillation of pancreatic porcine elastase and intermission hypoxia. (2)The contractility and fatigubility of diaphragma decrease in emphysema rats.Stress-strain of diaphragma and viscoelastic properties of diaphragmatic cells change in emphysema rats.(3) Expression level of titin and nebulin in diaphragmatic cells of emphysema rats decrease signicantly.