Evaluate The Effects Of High Intensity Exercise On The Myocardial Function Of Rats By Two-dimensional Speckle Tracking Imaging

Background and ObjectiveExercise has a bidirectional effect on the heart.As an adaptive change after running,cardiac hypertrophy can be physiological or pathological.But the pump function of the heart usually does not change in the early stage of pathological changes.Strain can not only reflect the global function of the heart,but also be used to analyze the intrinsic contractile characteristics of local myocardium,so as to detect myocardial injury early.In this study,we use two-dimensional speckle tracking imaging to evaluate the dynamic effects of treadmill running at different intensities and times on left ventricular function in rats,and to explore the value of strain in early detection of local myocardial function impairment.MethodsA total of 72 adult SD rats were randomly divided into Sedentary group(SED),Low-intensity running group(LIR),Medium-intensity running group(MIR)and High-intensity running group(HIR)with 18 rats in each group,and further divided into three subgroups(6 rats in each group)base on differnent running duration.SED were housed in cages,while the running groups were carried out treadmill running according to their respective exercise plan.All animals received heart ultrasound exam at 1week,4 weeks,and 8 weeks as for measurements,including left atrial diameter(LAD)and LV diameter(LVIDd),LV wall thickness,and LVEF;2D strain included LV longitudinal,radial and circumferen tial strain(SL,SR and SC respectively).Histological parameters included myocyte area,CVF and PVCA.Results1.left ventricular index:SHR LVIDd and LVEF of each exercise intensity group showed no significant changes between different exercise weeks.2.2DSE index:In exercise duration of 1 week and 4 weeks,there was no significant change in the strain indexes among all groups.However,at the end of 8weeks,SL in the HIR group was significantly lower than that in the control group[HIR8:(8.72±1.79)%vs SED8:(10.93±1.35)%,p<0.05]and the MIR group[HIR8:(8.72±1.79)%vs MIR8:(12.05±0.86)%,p<0.05].SL and SC was also significantly lower than that in the one-week exercise:SL[HIR8:(8.72±1.79)%vs HIR1:(11.38±2.90)%,p<0.05];SC[HIR8:(15.27±2.90)%vs HIR1:(19.64±0.99)%,p<0.05].There was no statistically significant difference in the strain indexes between the exercise duration of the LIR and MIR groups.3.Histologic findings:HE staining showed myocardial cell swelling,ill-defined cell boundaries,and disordered arrangement of myocardial fibers in local area of HIR group after 8 weeks’exercise.The area of myocardial cells in the HIR group increased at 1 week of exercise[HIR1:(4423±1454)μm~2vs SED1:(3096±734)μm~2,p<0.05],and in the MIR group increased at 4 weeks of exercise[MIR4:(4799±1479)μm~2vs SED4:(3233±657)μm~2,p<0.05],and even more at 8weeks of exercise[HIR8:(6670±2981)μm~2vs SED8:(4584±1341)μm~2,p<0.05][MIR8:(5772±1640)μm~2vs SED8:(4584±1341)μm~2,p<0.05].PVCA increased at the end of 4 weeks in the HIR group[HIR4:(2.00±0.73)%vs SED4:(1.20±0.28)%,P<0.05],CVF increased at the end of 8 weeks[HIR8:(1.76±0.91)%vs SED8:(1.00±0.27)%,P<0.05].4.Linear correlation:SL was negatively correlated with CVF and PVCA(r=-0.415,-0.400;p=0.023,0.029).SR also was negatively correlated with CVF and PVCA(r=-0.384,-0.415;p=0.030,0.018).SC was negatively correlated with CVF(r=-0.364;p=0.032).ConclusionCardiac remodeling induced by long-term low-and medium-intensity endurance exercise are physiologically adaptive,while high-intensity exercise may lead to pathological injury.Speckle tracking imaging can detect impaired myocardial systolic function in rats before LVEF abnormalities appear.