Abstract
Several studies have shown that the progression of communicating hydrocephalus is associated with diminished cerebral perfusion and microangiopathy. If communicating hydrocephalus similarly alters the cerebrospinal fluid circulation and cerebral blood flow, both may be related to intracranial mechanoelastic properties as, for instance, the volume pressure compliance. Twenty-three shunted patients with communicating hydrocephalus underwent intraventricular constant-flow infusion with Hartmann’s solution. The monitoring included transcranial Doppler (TCD) flow velocities (FV) in the middle (MCA) and posterior cerebral arteries (PCA), intracranial pressure (ICP), and systemic arterial blood pressure (ABP). The analysis covered cerebral perfusion pressure (CPP), the index of pressure-volume compensatory reserve (RAP), and phase shift angles between Mayer waves (3 to 9 cpm) in ABP and MCA-FV or PCA-FV. Due to intraventricular infusion, the pressure-volume reserve was exhausted (RAP) 0.84+/-0.1 and ICP was increased from baseline 11.5+/-5.6 to plateau levels of 20.7+/-6.4 mmHg. The ratio dRAP/dICP distinguished patients with large 0.1+/-0.01, medium 0.05+/-0.02, and small 0.02+/-0.01 intracranial volume compliances. Both M wave phase shift angles (r = 0.64; p<0.01) and CPP (r = 0.36; p<0.05) displayed a gradual decline with decreasing dRAP/dICP gradients. This study showed that in communicating hydrocephalus, CPP and dynamic cerebral autoregulation in particular, depend on the volume-pressure compliance. The results suggested that the alteration of mechanoelastic characteristics contributes to a reduced cerebral perfusion and a loss of autonomy of cerebral blood flow regulation. Results warrant a prospective TCD follow-up to verify whether the alteration of dynamic cerebral autoregulation may indicate a progression of communicating hydrocephalus.
Highlights
In communicating hydrocephalus, the disorders of cerebrospinal fluid- and cerebrovascular circulation can be found associated to one another [1]
Further hints for a direct interaction came from studies comparing clinical findings before and after shunting which revealed that in patients with normal pressure hydrocephalus cerebral blood flow improves after drainage of cerebrospinal fluid (CSF) [3]
Twenty-three data files depicting time courses of intracranial pressure (ICP), arterial blood pressure (ABP) and flow velocity (FV) (MCA and posterior cerebral arteries (PCA)) during 5 +/-3 min ICP baseline and during 5+/-3 min ICP plateau were included in the analysis
Summary
The disorders of cerebrospinal fluid- and cerebrovascular circulation can be found associated to one another [1]. Pena and colleagues have proposed that the chronic ventricular dilatation in communicating hydrocephalus results from a reversal of interstitial fluid flow into the parenchyma and a reduced tissue elasticity [2]. This may lead to a compression of local vessels and impaired cerebrovascular regulation. Further hints for a direct interaction came from studies comparing clinical findings before and after shunting which revealed that in patients with normal pressure hydrocephalus cerebral blood flow improves after drainage of cerebrospinal fluid (CSF) [3]. In order to test this hypothesis we have studied the relationship between peripheral arterial blood pressure and cerebral blood flow velocity before and during controlled ventricular volume load
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