Evaluation of a-adrenoceptor-mediated vasoconstriction to the subendocardial flow-coronary slosh phenomenon and intramyocardial arteriolar diameter change-

当心脏有肾上腺素能激活时，如心血管反射或运动时，就有α-肾上腺素受体介导的冠状血管收缩。本研究的目的是检验α-肾上腺素受体介导的血管收缩减少收缩期和舒张期冠状动脉树中发生的血流往复振荡的假设。用20 MHz脉冲多普勒测速仪测量麻醉开胸犬的冠状动脉间隔血流速度。微血管中的血流速度通过使用光学发光微球的高速系统可视化。与心外膜动脉血流模式不同，速度波形的特点是完全舒张期血流和两个峰值收缩期反向血流（早期和中期至晚期收缩期，晃动现象）。比较α受体阻滞前后去甲肾上腺素输注时的收缩期逆行血流速度和舒张期前向血流速度 ...更多信息 苯氧苄明。通过主动脉结扎术保持系统性主动脉压恒定;通过起搏以80、140和200次/min控制心率; α-阻滞剂保持最大左心室dP/dt不变。在每种起搏频率下，α-阻滞后收缩期逆行速度显著更大，表明α-血管收缩通过改变冠状动脉血管阻抗减少收缩期逆行血流。在相同的实验条件下，在第二组狗中用微球测量心室血流量，并且在250次/分钟的心率下通过α-肾上腺素受体阻断减少了流向左心室内层的血流量，证明了α-血管收缩的有益效果。总之，肾上腺素能α-肾上腺素受体介导的冠状血管收缩减少了去甲肾上腺素输注过程中的收缩期逆行冠状动脉血流。这减少了冠状动脉循环中的来回流动振荡，并且可能是α-血管收缩有助于在运动期间维持血液流向左心室内层的机制。少

There is alpha paradoxical a-adreno-ceptor-mediated coronary vasoconstriction whenever there is adrenergic activation of the heart, as during cardiovascular eflexes or exercise. The aim of the this study was to test the hypothesis that alpha-adrenoceptor-mediated vasoconstriction lessens the to-and-fro oscillation of blood flow that occurs in the coronary arterial tree during systole and diastole. Septal coronary artery blood velocity was measured in anesthetized open-chest dogs with a 20-MHz pulsed Doppler velocimeter. The blood flow velocity in the microvessels was visualized by the high-speed system using an optically shinning microspheres. Unlike epicardial arterial flow patterns, the velocity waveform was characterized by exclusively diastolic flow and by two peaked systolic reverse flow (early and mid-to-late systole, slosh phenomenon). Systolic retrograde velocity and diastolic forward velocity were compared during norepinephrine infusion before and after alpha-adrenoceptor bloc … More kade with phenoxybenzamine. Systo lic aortic pressure was held constant by aortic banding ; heart rate was controlled by pacing at 80, 140, and 200 beats/min ; and maximum left ventricular dP/dt was unchanged by alpha-blockade. At each pacing rate, systolic retro-grade velocity was significantly greater after alpha-blockade, indicating that alpha-vasoconstriction reduced systolic retrograde flow by changing coronary vascular impedance. Transmural blood flow was measured with microspheres in a second group of dogs during the same experimental conditions, and flow to the inner layer of the left ventricle was diminished by a-adrenoceptor blockade at a heart rate of 250 beats/min, demonstrating a beneficial effect of alpha-vasoconstriction. In conclusion, adrenergic alpha-adrenoceptor-mediated coronary vasoconstriction reduces systolic retrograde coronary flow during norepinephrine infusion. This lessens to-and-fro flow oscillation in the coronary circulation and probably is the mechanism whereby alpha-vasoconstriction helps maintain blood flow to the inner layer of the left ventricle during exercise. Less