Assessment of cerebral blood flow during infusion test in the diagnosis of normal pressure hydrocephalus.

Background: Many studies indicate that the increase in intracranial pressure (ICP) leads to cerebral blood flow velocity (CBFV) changes. This relationship was accurately determined in patients with traumatic brain injury,

Objectives: The aim of this study was to determine how the changes in intracranial pressure induced during an infusion test influence cerebral blood flow.

Material And Methods: 40 patients with enlarged ventricular systems (Evan's ratio > 30%) who underwent a diagnostic lumbar infusion test (LIT) were included. Tests were performed at the Department of Neurosurgery, Wroclaw Medical University. CBFV in the middle cerebral artery was measured using transcranial Doppler (TCD) simultaneously during the standard lumbar infusion test. TCD measurements were continued with simultaneous recording of CSF pressure with a frequency of 100Hz. A total number of 5800 measurements (10-second periods) performed during the three phases of the infusion test (stable, infusion and decrease) was obtained.

Results: In the stable phase of LIT, a weak positive correlation between ICP and mean CBFV (R = 0.193, p < 0.01) was observed. There was no statistically significant correlation between ICP and the pulsatility index (PI, Gosling Index). During the increased-ICP phase of LIT (infusion, decrease), we observed significant changes in CBFV expressed by a decrease of diastolic velocity and an increase of systolic velocity. A simultaneous increase of pulsation correlated with an increase in ICP (R = 0.371, p < 0.01). There were no significant changes in mean CBFV.

Conclusions: In patients with ventriculomegaly, the mean cerebral blood flow is maintained despite a significant increase in ICP, within the limits of the infusion test. It is noted the relative increase of the pulsatility indices of CBF may indicate preserved cerebrovascular reactivity.