Cerebrovascular time constant in patients suffering from hydrocephalus

Abstract

Objectives: We studied possible link between cerebrospinal fluid (CSF) compensation and indices describing pulsatile inflow of cerebral arterial blood.

Methods: A total of 50 infusion tests performed in patients with symptoms of normal pressure hydrocephalus (NPH) were examined retrospectively. Waveforms of CSF pressure, noninvasive arterial blood pressure (ABP), and transcranial Doppler (TCD) cerebral blood flow velocity (CBFV) were used to estimate relative changes in cerebral arterial compliance (C_a) and cerebrovascular resistance (CVR). Product of C_a and CVR, called cerebral arterial time constant (τ, unit: seconds), was calculated at the baseline and plateau phase of the test and compared with CSF compensatory parameters such as resistance to CSF outflow, elasticity, slope of amplitude–pressure line, and pulse amplitude of CSF pressure.

Results: Neither of CSF compensatory parameters correlated with hemodynamic indices. However, the change in cerebral perfusion pressure (CPP) provoked change in τ (R  =  0·33; P  =  0·017) secondary to a change in CVR (R  =  0·81; P < 0·0001). Changes in CVR and C_a had a reciprocal character (R  =  −0·64; P < 0·0001) with magnitude of variation in CVR (68%) prevailing over magnitude of changes in C_a (49%).

Discussion: Hemodynamics of pulsatile inflow of cerebral arterial blood assessed by cerebral arterial time constant is not directly linked to dynamics of CSF circulation and pressure–volume compensation but is sensitive to changes in CPP during infusion test.

Keywords:

• Hydrocephalus
• Cerebrospinal fluid
• Cerebral blood flow velocity
• Infusion test

Acknowledgements

Many thanks to Drs Christina Haubrich and Ruwan Weerakkody for assisting in collection of clinical data and all colleagues working for Hydrocephalus Clinic for their help, friendly advice, and clinical data collection. MK was supported by the Polish Ministry of Science and Higher Education.