Analysis of relative changes in pulse shapes of intracranial pressure and cerebral blood flow velocity during infusion test

Objective: Analysis of relative changes in the shapes of pulse waveform of intracranial pressure (ICP) and transcranial Doppler cerebral blood flow velocity (CBFV) may provide information on intracranial compliance. We tested this hypothesis, introducing an index named the Ratio of Pulse Slopes (RPS) that is based on inclinations of the ascending parts of ICP and CBFV pulse waveforms. It has hypothetically a simple interpretation: 1 – good compliance, the less than 1, reduced compliance. Here, we investigated the usefulness of RPS for intracranial compliance assessment. Approach: ICP and CBFV signals recorded simultaneously in 30 normal pressure hydrocephalus patients during infusion test were retrospectively analysed. CBFV was measured in the middle cerebral artery. Changes in RPS during the test were compared to changes in the height ratio of the first and second peak of ICP pulse (P1/P2) and the shape of ICP pulse classified from normal (1) to pathological (4). Values are medians (lower, upper quartiles). Main results: There was a significant correlation between baseline RPS and brain elasticity (R = -0.55, p=0.0018). During infusion test, both RPS and P1/P2 decreased with rising ICP (RPS: 0.80 (0.56, 0.92) vs. 0.63 (0.44, 0.80), p = 0.00015; P1/P2: 0.58 (0.50, 0.91) vs. 0.52 (0.36, 071), p=0.00009) while the ICP pulses became more pathological in shape (class: 3 (2, 3) vs. 3 (3, 4), p=0.04). The magnitude of decrease in RPS during infusion was inversely correlated with baseline P1/P2 (R= -0.40, p<0.03). Significance: During infusion, the slopes of ascending parts of ICP and CBFV pulses become increasingly divergent with a shift in opposite directions. RPS seems a promising methodological tool to monitor brain compliance with no additional volumetric manipulation required.