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Updated: Aug 5, 2026
Assessing Cerebral Autoregulation via Oscillatory Lower Body Negative Pressure and Projection Pursuit Regression
Published on: December 10, 2014
Waveform-Derived Metrics of Intracranial Compliance: Validation and Pulsatile Dynamics
Ihsane Olakorede1, Stefan Yu Bögli2,3, Marek Czosnyka2,4
1Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK. imo25@cam.ac.uk.
Objective:
Visual interpretation of intracranial pressure (ICP) waveforms is widely used to assess intracranial compliance but lacks rigorous validation. We evaluated the pulse shape index (PSI) against the tidal wave (P2)/percussion wave (P1) ratio and examined the contributions of pulse amplitude, compensatory reserve [pressure-volume compensatory reserve index (RAP)] and transcranial Doppler (TCD)-derived indices.
Methods:
A total of 4388 non-overlapping 5-min segments from 96 high-resolution recordings of simultaneous ICP and TCD blood velocity were analysed. PSI and P2/P1 were derived from normalised ICP pulses. ICP pulse amplitude (AMP), RAP and TCD-derived arterial and intracranial compliance indices [arterial compliance (CA), intracranial compliance (CI)] were calculated per segment. Associations were assessed at segment, recording, and patient levels using correlation and mixed-effects models. Discriminatory performance for impaired (P2/P1 > 1.1) and preserved (P2/P1 < 0.9) compliance was evaluated using receiver operating characteristic (ROC) and precision-recall analyses. Concordance between PSI and P2/P1 classifications was assessed using Chi-squared threshold mapping.
Results:
PSI demonstrated a strong association with P2/P1 (r ≈ 0.74-0.76 across analysis levels) and high discrimination for impaired compliance [area under the curve (AUC) ≈ 0.93]. RAP and CI showed weak and inconsistent population-level associations with P2/P1, with substantial inter-individual variability. A distinct phenotype of low AMP (< 1.5 mm Hg) despite impaired waveform-derived compliance was associated with lower RAP. CA and CI provided limited incremental explanatory value, whereas inclusion of AMP improved model fit and classification performance beyond morphology-based metrics alone.
Conclusions:
PSI closely reflects P2/P1 and supports automated waveform-based compliance assessment. However, morphology alone is insufficient; amplitude and reserve indices provide complementary information, supporting a multiparametric approach to intracranial monitoring.
