Intracranial pressure (ICP) is a critical indicator of brain health, but its response to changes in volume, known as compensatory reserve, is difficult to assess in routine practice. A new study published on 15 September 2026 in Scientific Reports proposes a method for identifying hidden brain states by analysing the complexity of its pressure pulsations. This approach could help doctors better understand how well the brain can cope with elevated pressure.
Analysing the complexity of pressure pulsations
The scientists conducted a secondary analysis of data obtained from a pig model of reversible intracranial hypertension. They used three entropy metrics—normalised permutation entropy, wavelet entropy and sample entropy—to analyse ICP pulsations sampled at 200 hertz. These calculations were performed in non-overlapping windows of 0,5 seconds. Importantly, no absolute ICP values, volumes of infused fluid or other direct pressure and volume measurements were used.
A three-stage Gaussian hidden Markov model was used to analyse the entropy features. The resulting numerical states were provisionally labelled ‘Normal’, ‘Warning’ and ‘Alarm’, according to where they lay on the pressure–volume curve. The labels themselves did not affect state assignment. The study found that the local dP/dV measure, which is inversely related to compliance (the ability of brain tissue to stretch), increased from 0,53 to 3,84 and 7,96 mmHg per millilitre.
Study results and prospects
The method, which involved training on some animals and testing on others (leave-one-subject-out validation), showed that the ‘low–intermediate–high’ ordering of states was maintained in three of the four animals whose data had been excluded from model training. This indicates that entropy-derived states correlate with progressively steeper sections of the pressure–volume curve and depletion of the brain’s compensatory reserves under controlled loading.
The authors stress that this study is a proof of concept and requires independent validation. It does not establish a clinical alarm signal and is not a method for measuring compliance independently of phase and haemodynamics. Nevertheless, the results open up new possibilities for monitoring patients with intracranial hypertension.
