Pearson T C
Division of Haematology, United Medical School, Guy's Hospital, London, United Kingdom.
Semin Thromb Hemost. 1997;23(5):433-9. doi: 10.1055/s-2007-996120.
Polycythemia vera (PV) commonly presents with vascular occlusion. Untreated patients have a poor prognosis due to the occurrence of thromboses. Treatment outcomes in PV and thrombotic events in other forms of polycythemia and in primary thrombocythemia lead to the conclusion that both raised packed cell volume (PCV) values and quantitative/qualitative platelet changes play a role in the pathogenesis of these vascular occlusive events. In vitro blood viscosity values are predominantly affected by the PCV, particularly at low shear rates and are thus high in untreated PV. Generally, under physiologic conditions blood flow is not governed by blood viscosity due to a number of factors, such as prevailing high shear rates, red cell axial migration, and adaptive vessel diameter changes. Peripheral blood flow is low in untreated PV. Whereas some untreated patients maintain adequate oxygen transport to the tissues, this may not apply in those with cardiac or local vessel disease. There is evidence that low flow rates predispose to occlusive events. Under pathologic low blood flow or static conditions, the rheologic blood changes of untreated PV, demonstrated in vitro, play a role in producing a more deleterious outcome of an occlusive event. Under blood flow conditions, red cell axial migration occurs. This leaves a plasmatic zone at the vessel wall into which platelets are dispersed and where shearing forces are maximal. These forces lead to platelet activation. Increased PCV values reduce the width of the plasmatic zone and lead to an increased possibility of platelet activation, platelet-platelet contact and platelet-vessel wall interaction, particularly when the platelet count is raised as well. These effects increase the likelihood of the initiation of thrombus formation in PV.
真性红细胞增多症（PV）通常表现为血管阻塞。未经治疗的患者由于血栓形成而预后不良。PV的治疗结果以及其他形式的红细胞增多症和原发性血小板增多症中的血栓形成事件表明，升高的血细胞比容（PCV）值以及血小板数量/质量的变化在这些血管阻塞事件的发病机制中均起作用。体外血液粘度值主要受PCV影响，尤其是在低剪切速率下，因此未经治疗的PV患者血液粘度较高。一般来说，在生理条件下，由于多种因素，如普遍存在的高剪切速率、红细胞轴向迁移和适应性血管直径变化，血流不受血液粘度的控制。未经治疗的PV患者外周血流较低。虽然一些未经治疗的患者能够维持向组织的充足氧输送，但对于患有心脏或局部血管疾病的患者可能并非如此。有证据表明低流速易引发阻塞事件。在病理性低血流或静态条件下，体外显示的未经治疗的PV患者的血液流变学变化在产生更有害的阻塞事件结果中起作用。在血流条件下，会发生红细胞轴向迁移。这在血管壁处留下一个血浆区，血小板分散到该区域，且此处剪切力最大。这些力导致血小板活化。PCV值升高会减小血浆区的宽度，并增加血小板活化、血小板 - 血小板接触以及血小板 - 血管壁相互作用的可能性，特别是当血小板计数也升高时。这些效应增加了PV中血栓形成起始的可能性。
