Background: Cerebrospinal fluid movement (CSF) through the pathways within the central nervous system is of high significance for maintaining normal brain health and function. Low frequency hemodynamics and respiration have both been shown to independently drive CSF in humans. Here, we hypothesize that CSF movement may be driven simultaneously (and in synchrony) by both mechanisms and we study their independent and interactive effects on CSF movement using novel neck fMRI scans.
Methods: Caudad CSF movement at the fourth ventricle and hemodynamics of the major neck blood vessels (internal carotid arteries and internal jugular veins) were captured from 11 young healthy volunteers using novel neck fMRI scans with simultaneous measurement of respiration. Two distinct models of CSF movement (1. Low-frequency hemodynamics and 2. Respiration) were independently investigated in corresponding frequency ranges. Possible interactions between these mechanisms were also studied using cross-frequency coupling.
Results: The results from this study validated that the caudad CSF movement may be driven by both low frequency hemodynamics (0.01 Hz – 0.1 Hz) and respiration (0.2 Hz - 0.4 Hz), through different mechanisms. We show that the dynamics of brain fluids can be assessed from the neck, by studying the interrelationships between major neck blood vessels and the CSF movement at the fourth ventricle. We also demonstrate that there exists a cross-frequency interaction between two separable mechanisms.
Conclusions: The human CSF system is capable of responding to multiple interacting physiological forces at the same time. This information may help inform the pathological mechanisms behind CSF movement-related disorders and facilitate new approaches to therapeutic interventions.