Introduction: Disturbance in cerebrospinal fluid (CSF) circulation may overlap with abnormality of cerebral blood flow (CBF) in hydrocephalus. Transcranial Doppler (TCD) ultrasonography is a non-invasive technique able to assess CBF velocity (CBFv) dynamics in response to a controlled rise in ICP during CSF infusion tests.
Research question: Which TCD-derived cerebral hemodynamic parameters change during controlled rise of ICP, and in which direction?
Material and methods: Infusion tests combined with TCD monitoring and non-invasive monitoring of arterial blood pressure (ABP) were conducted in 65 hydrocephalic patients. TCD-based hemodynamic variables: spectral pulsatility index (sPI), compliance of CSF space (Ci), cerebral autoregulation index (Mx), critical closing pressure (CrCP), cerebrovascular wall tension (WT) and diastolic closing margin (DCM-distance between diastolic ABP and CrCP) were calculated retrospectively.
Results: During the test ICP increased on average to 25 mm Hg (p < 0.0001), with a parallel decrease in cerebral perfusion pressure (CPP, p < 0.0003). The CBFv waveform changed, showing a rise in sPI (p < 0.0001). Ci decreased inversely proportional to a rise in ICP, and correlated well with changes of compliance calculated from the Marmarou model. CrCP increased in response to rising ICP (p < 0.001) while WT decreased (p < 0.002). DCM correlated with cerebrospinal elasticity (R = -0.31; p < 0.04). Cerebral autoregulation was worse in patients with normal CSF circulation, measured as resistance to CSF outflow (Rout): Pearson correlation between Mx and Rout was R = -0.41; p < 0.02.
Conclusion: A controlled rise in ICP affects cerebral hemodynamics in a moderate manner. Parameters like cerebral autoregulation index or DCM correlate with CSF dynamics and may be considered as supplementary variables for the diagnosis of hydrocephalus.
Keywords: Brain compliance; Cerebral autoregulation; Critical closing pressure; Pulsatility index; Transcranial Doppler.
© 2023 The Authors.