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.

The shape of the pulse waveforms of intracranial pressure (ICP) and cerebral blood flow velocity (CBFV) typically contains three characteristic peaks. It was reported that alterations in cerebral hemodynamics may influence the shape of the pulse waveforms by changing peaks’ configuration. However, the changes in peak appearance time (PAT) in ICP and CBFV pulses are only described superficially. We analyzed retrospectively ICP and CBFV signals recorded in traumatic brain injury patients during decrease in ICP induced by hypocapnia (n = 11) and rise in ICP during episodes of ICP plateau waves (n = 8). All three peaks were manually annotated in over 48 thousand individual pulses. The changes in PAT were compared between periods of vasoconstriction (expected during hypocapnia) and vasodilation (expected during ICP plateau waves) and their corresponding baselines. Correlation coefficient (rS) analysis between mean ICP and mean PATs was performed in each individual recording. Vasodilation prolonged PAT of the first peaks of ICP and CBFV pulses and the third peak of CBFV pulse. It also accelerated PAT of the third peak of ICP pulse. In contrast, vasoconstriction shortened appearance time of the first peaks of ICP and CBFV pulses and the second peak of ICP pulses. Analysis of individual recordings demonstrated positive association between changes in PAT of all three peaks in the CBFV pulse and mean ICP (rS range: 0.32–0.79 for significant correlations). Further study is needed to test whether PAT of the CBFV pulse may serve as an indicator of changes in ICP–this may open a perspective for non-invasive monitoring of alterations in mean ICP.

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