Penn State Hershey Heart and Vascular Institute, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey, Pennsylvania.
J Appl Physiol (1985). 2014 Jan 15;116(2):216-21. doi: 10.1152/japplphysiol.01048.2013. Epub 2013 Dec 5.
Animal studies indicate alpha-adrenergic coronary vasoconstriction helps maintain left ventricular function during physiological stress. Whether this process occurs in humans is unknown. In the current study, we used transthoracic Doppler echocardiography to test the effect of lower body negative pressure (LBNP) on coronary blood flow velocity (CBV, left anterior descending coronary artery) and myocardial function in eight young healthy subjects before and after systemic infusion of phentolamine, a nonselective alpha blocker. Heart rate (HR) and blood pressure (BP) were monitored on a beat-by-beat basis. Peak diastolic CBV and myocardial systolic and diastolic tissue velocities (Sm and Em), were quantified at baseline, and at -5 mmHg, -10 mmHg, and -15 mmHg LBNP. Coronary vascular resistance index (CVRI) was calculated as the quotient of diastolic BP and CBV. Phentolamine reduced baseline diastolic BP and increased HR but did not affect the reflex adjustments to LBNP. The reduction in CBV due to LBNP was blunted by phentolamine at -10 mmHg and -15 mmHg. Importantly, the increase in CVRI (i.e., coronary vasoconstriction) was abolished by phentolamine at -5 mmHg (0.21 ± 0.06 vs. 0.83 ± 0.13), -10 mmHg (0.24 ± 0.03 vs. 1.68 ± 0.31), and -15 mmHg (0.27 ± 0.10 vs. 2.34 ± 0.43). These data indicate that alpha-adrenergic coronary vasoconstriction is present during low levels of LBNP. With alpha blockade, more coronary flow is needed to maintain cardiac function. Our data suggest that alpha-adrenergic tone enhances coronary flow efficiency, presumably by redistributing flow from the epicardium to the endocardium.
动物研究表明，α-肾上腺素能冠状血管收缩有助于在生理应激期间维持左心室功能。尚不清楚这一过程是否发生在人类中。在目前的研究中，我们使用经胸多普勒超声心动图在 8 名年轻健康受试者全身输注非选择性α阻滞剂酚妥拉明前后测试低体负压（LBNP）对冠状动脉血流速度（CBV，左前降支冠状动脉）和心肌功能的影响。心率（HR）和血压（BP）进行逐拍监测。在基线时以及在 LBNP 为-5mmHg、-10mmHg 和-15mmHg 时，量化峰值舒张期 CBV 和心肌收缩和舒张组织速度（Sm 和 Em）。冠状动脉阻力指数（CVRI）定义为舒张压与 CBV 的商。酚妥拉明降低了基础舒张血压并增加了 HR，但对 LBNP 的反射调节没有影响。酚妥拉明减弱了 LBNP 引起的 CBV 降低，在-10mmHg 和-15mmHg 时。重要的是，酚妥拉明消除了 CVRI（即冠状血管收缩）的增加，在-5mmHg（0.21±0.06 vs. 0.83±0.13）、-10mmHg（0.24±0.03 vs. 1.68±0.31）和-15mmHg（0.27±0.10 vs. 2.34±0.43）时。这些数据表明，在低水平的 LBNP 期间存在 α-肾上腺素能冠状血管收缩。用α阻断剂时，需要更多的冠状动脉流量来维持心脏功能。我们的数据表明，α-肾上腺素能张力增强了冠状动脉血流效率，可能是通过将血流从心外膜重新分配到心内膜。
