Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
Anat Rec (Hoboken). 2022 Nov;305(11):3199-3211. doi: 10.1002/ar.24951. Epub 2022 May 25.
The assumption that the coronary capillary blood flow is exclusively regulated by precapillary vessels is not supported by recent data. Rather, the complex coronary capillary bed has unique structural and geometric characteristics that invalidate many assumptions regarding red blood cell (RBC) transport, for example, data based on a single capillary or that increases in flow are the result of capillary recruitment. It is now recognized that all coronary capillaries are open and that their variations in flow are due to structural differences, local O demand and delivery, and variations in hematocrit. Recent data reveal that local mechanisms within the capillary bed regulate flow via signaling mechanisms involving RBC signaling and endothelial-associated pericytes that contract and relax in response to humoral and neural signaling. The discovery that pericytes respond to vasoactive signals (e.g., nitric oxide, phenylephrine, and adenosine) underscores the role of these cells in regulating capillary diameter and consequently RBC flux and oxygen delivery. RBCs also affect blood flow by sensing and releasing nitric oxide to facilitate relaxation of pericytes and a consequential capillary dilation. New data indicate that these signaling mechanisms allow control of blood flow in specific coronary capillaries according to their oxygen requirements. In conclusion, mechanisms in the coronary capillary bed facilitate RBC density and transit time, hematocrit, blood flow and O delivery, factors that decrease capillary heterogeneity. These findings have important clinical implications for myocardial ischemia and infarction, as well as other vascular diseases.
认为冠状动脉毛细血管血流仅受前毛细血管血管调节的假设，并不被最近的数据所支持。相反，复杂的冠状动脉毛细血管床具有独特的结构和几何特征，这使得许多关于红细胞（RBC）运输的假设变得无效，例如基于单个毛细血管的数据，或者流动的增加是毛细血管募集的结果。现在人们认识到，所有的冠状动脉毛细血管都是开放的，它们的流量变化是由于结构差异、局部 O 需求和输送、以及红细胞压积的变化。最近的数据表明，毛细血管床内的局部机制通过涉及 RBC 信号和内皮相关周细胞的信号转导机制来调节血流，这些周细胞根据体液和神经信号收缩和舒张。发现周细胞对血管活性信号（如一氧化氮、苯肾上腺素和腺苷）有反应，强调了这些细胞在调节毛细血管直径以及红细胞通量和氧输送中的作用。红细胞还通过感知来影响血流，释放一氧化氮，以促进周细胞的松弛和随之而来的毛细血管扩张。新数据表明，这些信号转导机制允许根据特定冠状动脉毛细血管的氧气需求来控制血流。总之，冠状动脉毛细血管床中的机制促进了 RBC 密度和通过时间、红细胞压积、血流和 O 输送，这些因素降低了毛细血管的异质性。这些发现对心肌缺血和梗死以及其他血管疾病具有重要的临床意义。
