| Stiffness is one of the mechanical characteristics of heart,including myocardium stiffness and chamber stiffness. Evaluation of myocardium stiffness is based on detecting of stress-strain relationship, and chamber stiffness is always evaluated by stiffness constant k. Stiffness can indicate pathological changes and heart functions. Thus evaluating stiffness accurately can help us diagnose and therapy heart disease. Ascensus and sustain stiffness in systolic phase can conduce to heart ejection, while descensus in diastolic phase can conduce to better engorge. thus myocardium stiffness systole-diastole constantα(end-systole stiffness / end-diastole stiffness) can indicate heart blood-pumping function directly. With regard to myocardium stiffness in vivo, there is no unified detecting standard. With improvement of intervention and ultrasound techniques, chamber pressure together with ultrasound can possibly evaluate mechanical characteristics of heart in vivo.1.Evaluation of myocardium stiffnessMyocardial infarction group and sham group each has 15 rabbits. Myocardial infarction model is set up though ligating left anterior descending branch (LAD) for 14 days, and no ligating in sham group. After 14 days, with pressure catheter inlaied to left ventricle and 2D ultrasound, we quote equation of heart ellipse model to evaluate myocardium stiffness. Result: Compared to Sham group, end–systolic stiffness of MI group has decreased 43.31% (MI group 4.73±1.43 kpa vs. Sham group 7.55±1.22,P<0.05), while end-diastolic stiffness has increased 80.19%(MI group 2.43±0.35 kpa vs. Sham group 1.35±0.21 kpa). Stiffness systole-diastole constantαhas decreased 65.1%(MI group 1.95±0.47 vs. Sham group 5.59±1.30,P<0.05). Conclusion: Stiffness in end-diastole has decreased In MI group while end-diastolic stiffness has increased. Thus stiffness systole-diastole constantαhas decreased. Heart compliance has decreased.2.Evaluation of LV chamber stiffnessMyocardial infarction group and sham group each has 15 rabbits. Myocardial infarction model is set up though ligating left anterior descending branch (LAD) for 14 days, and no ligating in sham group. After 14 days, with pressure catheter inlaied to left ventricle and 2D ultrasound, we quote Simpson methord to estimate bulk of left ventricle and draw the Pressure-Volume curve circle, then get the end-systolic stiffness constant k. Result: Compared to Sham group,ESPVR curve of MI group has shifted to the right. End-systolic stiffness constant k2 in MI group has decreased (k2 0.91±0.12 vs. k1 1.81±0.16,P<0.05)compared to k1 in Sham group. Conclusion: In MI group, ESPVR curve has shifted to the right and end-systolic stiffness constant k has decreased. It indicated that in MI group, LV end-systolic chamber stiffness has decreased, myocardium is debility in systolic phase.3. Study on pathomechanism of myocardium stiffness increasing in MI groupThe myocardium samples mentioned above were respectively detected by the following methods: hydroxyproline concentration determination evaluating collagen contents,and ELISA determination evaluating I type collagen contents. Result: Collagen contents in MI group has obviously increased (about 4 times compared to Sham group),and mainly is I type collagen. Conclusion: 14 days after myocardium infarction, collagen contents increased in infarcted myocardium,mainly is I type collagen, thus myocardium passive stiffness has increased, the compliance has decreased.
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