| Part one : The effects of dexmedetomidine on atrial-ventricular and interventricular synchronization in patients undergoing coronary artery bypass graftingObjective To evaluate the effects of dexmedetomidine on artrial-ventricular and interbentricular synchronization in patients with coronary artery bypass grafting under cardiopulmonary bypass.Methods Twenty four patients(ASA II or III, NYHA II or III), aged 43 to 75 yr, with body surface area 1.53 to 2.00 m2, undergoing coronary artery bypass grafting were randomized into 2 groups(n=12 each): control group(group C) and dexmedetomidine group(group D). Total intravenous anesthesia was used in both groups. In group D, a 0.5μg·kg-1 bolus dose of dexmedetomidine was administered within 10 minutes after aortic cross-clamp removing, followed by a 0.5μg·kg-1·h-1 intravenous injection until the end of operation, while in the group C the same amount of saline was used instead of dexmedetomidine. Hemodynamic, left and right ventricular systolic function parameters, and cardiac synchronization parameters were recorded before sternotomy(T1), at 30 min(T2), and 60min(T3) after CPB.Results HR and CI were significantly higher at T2 and T3 than T1 in both groups(P<0.01). Compared with group C, PR at T2 and T3 were significantly longer in group D(P<0.05).Conclusion Dexmedetomidin with a 0.5μg·kg-1 bolus followed by 0.5μg·kg-1·h-1 infusion after aortic cross-clamp removing in patients undergoing coronary artery bypass grafting can prolong PR interval but have no influences on interventricular electro-mechanical synchrony. Part two: Effects of dexmedetomidine on systolic and diastolic function of the left and right ventricles in patients with mitral valve replacementObjective To evaluate effects of dexmedetomidine on systolic and diastolic function of the left and right ventricles in patients with mitral valve replacement(MVR) under cardiopulmonary bypass(CPB).Methods Thirty two patients(ASA II or III, NYHA II or III, LVEF≥45%) aged 42 to 70 yr, with body surface area 1.43 to 2.04 m2, with MVR under CPB were randomized into control group(group C) and dexmedetomidine group(group D). Total intravenous anesthesia was used in both groups. In group D, a 1μg·kg-1 bolus dose of dexmedetomidine was administered within 10 minutes after surgical incision, followed by a 0.5μg·kg-1·h-1 intravenous injection until the end of operation, while the same amount of saline was used instead of dexmedetomidine in group C. Left ventricle parameters including Sm1, Sm2, E-MV, Ea-MV and right ventricle parameters containing St1, St2, E-TV, Ea-TV were measured by transesophageal echocardiography(TEE) and tissue doppler imaging(TDI). HR, MAP, CVP, cardiac index(CI),LVEF, left and right ventricle myocardial mechanics parameters were recorded after anesthesia induction(T1), at 30min(T2) and 60min(T3) after CPB.Results HR, CVP, CI increased significantly at T2 and T3 compared with T1 in both groups, while MAP decreased. Compared with T1, E/Ea-TV increased significantly at T2, T3 in group C and at T3 in group D.Conclusion Preoperative left ventricular diastolic and right ventricular systolic function were impaired in patients with MVR, but CPB did not aggravate this injury. Dexmedetomidine may delay the right ventricular impaired relaxation after CPB and have a protection of myocardial. Part three: Effects of dexmedetomidine on myocardial ischemia-reperfusion injury and myocardial cellular CX43 protein in patients with mitral valve replacementObjective To evaluate the effects of dexmedetomidine on myocardial ischemia-reperfusion injury and myocardial connexin 43(CX43) protein in patients with mitral valve replacement(MVR) under cardiopulmonary bypass(CPB) and explore the myocardial protection mechanism of dexmedetomidine.Methods Twenty patients(ASA II or III, NYHA II or III, LVEF≥45%) aged 42 to 70 yr, with body surface area 1.43 to 1.92 m2, with MVR under CPB were randomized into control group(group C) and dexmedetomidine group(group D), ten people was involved in each group. Total intravenous anesthesia was used in both groups. In group D, a 1μg·kg-1 bolus dose of dexmedetomidine was administered within 10 minutes after surgical incision, followed by a 0.5μg·kg-1·h-1 intravenous injection until the end of operation, while the same amount of saline was used instead of dexmedetomidine in group C. c Tn I was tested before anesthesia induction(T1) and six hours after aortic cross-clamp removing. The time of aortic cross-clamping, CPB, operation, mechanical ventilation, ICU stay, and hospitalization were recorded in all patients. The level of CX43 expression was detected by Immunohistochemistry and western blot.Results The level of plasma c Tn I increased at T2 in both group compared with T1. The plasma c Tn I in group D was significantly less than group C at T2(P<0.01). The expression of CX43 were stongly positive before CPB and in group D after CPB, however it was weakly positive in group C after CPB. The expression of CX43 in group C decreased significantly after CPB. The expression of CX43 decreased significantly in group C after CPB compared with group D after CPB(P<0.01).Conclusion Dexmedetomidine can protect against myocardial ischemia reperfusion injury in patients with MVR under CPB. It probably because that dexmedetomidine may inhibit the degradation of myocardial cellular CX43.
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