Study On Cardiac Function Of Rats With Chronic Plateau Hypoxia By 7.0T Cardiac Magnetic Resonance And Tissue Tracking Technique

Objectives: To evaluate the changes of left and right ventricular function and myocardial stress in rats with chronic hypoxia at high altitude by cardiac magnetic resonance tissue tracking(CMR-TT).Methods: Six-week-old male SD rats were divided into two groups: plateau group(n=22,Yushu,Qinghai,altitude 3700m),and plain group(n=10,Chengdu,Sichuan,altitude 500m).Both groups were scanned with 7.0T cardiac MRI cine,and used professional cardiac software to analyze the left and right ventricular(LV,RV)function and stress of the two groups,which including ejection fraction(EF),end diastolic volume(EDV),end systolic volume(ESV),stroke volume(SV),the overall contraction peak longitudinal stress(GLS),circumferential stress(GCS)and radial stress(GRS).The blood related indexes of the two groups were collected before CMR scanning,and then we took the myocardial tissue and stained with HE,analyze the pathological changes of myocardial tissue.Results:1.After comparing the general basic data of rats,we found that the heart rate and respiration values of the plateau group were slightly lower than those of the plain group,but there was no difference.However,there was no difference in body weight index between the two groups(P>0.05).It was also found that the red blood cell(RBC),hemoglobin(HGB)and hematocrit(HCT)values of the plain group were significantly lower than those of the plateau group,with differences(P < 0.01).2.Comparison of normal cardiac function and stress parameters.(1)Plateau group RVEDV,RVESV and RVSV parameter values were greater than the plain group,there was difference(P<0.01).Plateau RVEF value than plain group decreased slightly,but there was no statistical difference(P>0.05).(2)In addition,we compared the values of cardiac function parameters,such as LVEF,LVEDV,LVESV and LVSV,and found no statistical difference between the two groups(P>0.05).(3)The stress parameters,RVGLS,RVGCS,RVGRS,LVGRS and LVGLS parameters of plateau group were lower than those of plain group(P<0.05).The stress parameters,LVGCS of plateau group were lower than those of plain group,but there was no significant difference.3.We found under an optical microscope that the morphology and structure of myocardial cells in the plain group had no obvious abnormal changes.We also found that the right ventricular myocardial space of rats in the plateau group was slightly widened,vascular congestion and a small amount of vacuolar degeneration were seen,the cells became turbid and swollen and accompanied by a small amount of inflammatory cells.Conclusions:1.After 12 weeks of adaptation to the natural environment of 3700 m hypoxia in SD rats,the function and pathology of right ventricle were changed,the whole stress was damaged,and the whole stress of left ventricle was partially damaged.2.After 12 weeks of continuous exposure to high altitude hypoxia in rats,the overall contractile stress of the right ventricle is impaired,but the cardiac ejection can still be maintained at a relatively normal level.It is speculated that myocardial stress can detect cardiac function earlier and more sensitively than EF damaged.