Rheopheresis, but Not Phlebotomy, Improves Cerebral Vascular Response to Hypercapnia and Neuronal Activation

Background/Objectives: Several therapeutic approaches, including phlebotomy and rheopheresis, are used to improve hemorheological parameters. While the effects of phlebotomy on cerebral circulation have been described, the impact of rheopheresis on cerebral hemodynamics remains poorly understood. This study primarily aimed to evaluate the within-group effects of phlebotomy and rheopheresis on cerebral blood flow velocity changes evoked by neuronal activation and on cerebrovascular reactivity in patients with elevated hematocrit or hyperviscosity, respectively. Methods: In our present study, we used transcranial Doppler to examine the effects of phlebotomy (n = 11) and rheopheresis (n = 9) on cerebral hemodynamics in patients with elevated hematocrit and hyperviscosity, respectively. Measurements included resting flow velocity (FV) in the posterior cerebral artery (PCA) and middle cerebral artery (MCA), the visually evoked FV response in the PCA (neurovascular coupling) and the hypercapnia-induced FV response in the MCA (cerebral vasoreactivity). In addition to flow velocity data, visual evoked potential (VEP) parameters were also recorded to assess neuronal activation. Results: Phlebotomy significantly reduced hematocrit and hemoglobin levels, while rheopheresis led to a significant decrease in both blood and plasma viscosity. Although we observed no differences in resting FV values before and after either intervention, the FV increase in response to visual stimulation and hypercapnia was greater after rheopheresis than before, whereas no such difference was observed following phlebotomy. VEP parameters remained similar before and after both phlebotomy and rheopheresis. Conclusions: Our data indicate that rheopheresis reduces blood and plasma viscosity in patients with hyperviscosity and leads to a significant improvement in cerebral vasoreactivity and neurovascular coupling, without affecting VEP parameters. The improvement in cerebral vasoreactivity, but no changes in VEP parameters, suggests that the improved FV response to visual stimulation after rheopheresis is most likely caused by better vascular response rather than improved neuronal activation.