We investigated the possible relationship between vascular reactivity and the resistance to CSF outflow in a group of shunted and non-shunted NPH patients.

Sixty eight patients (47 non-shunted and 21 shunted) with NPH have been examined. During the examination ICP was measured in the ventricles (using a needle inserted into a pre-implanted Ommaya reservoir) at baseline and in response to a constant rate infusion (1.5 ml/min) of normal saline. Resistance to CSF outflow (Rcsf) was measured as an increase of ICP divided by the infusion rate. During the test, arterial pressure was monitored continuously using a Finapress finger cuff. Cerebrovascular pressure-reactivity was assessed as a moving correlation coefficient between coherent 'slow waves' of ICP and spontaneous fluctuations of arterial blood pressure (PRx index). This variable has been demonstrated previously to correlate with autoregulation of CBF 1. Positive value of PRx reveals impaired cerebrovascular pressure-reactivity, whereas negative values indicate normal reactivity.

In non-shunted patients impaired pressure reactivity was associated with lower resistance to CSF outflow: (PRx versus Rcsf: R = -0.5; P < 0.0005). This relationship was inverted in shunted patients: PRx was positively correlated with Rcsf (R = 0.51; P < 0.03).

Cerebrovascular pressure-reactivity is disturbed in patients with normal resistance to CSF outflow, suggesting underlying cerebrovascular disease. After shunting the pressure-reactivity strongly depends on shunt function and may deteriorate when the shunt malfunctions.