An investigation of systemic haemodynamic correlates of intracranial pressure

Monitoring intracranial pressure (ICP) is vital to decide the appropriate clinical treatment of patients with conditions potentially causing high ICP (e.g. brain injury, cerebral tumor, and hydrocephalus). On the path for finding an alternative means to invasive ICP measurement, the only means to date for accurate ICP monitoring, this study investigates the relationship of ICP with systemic cardiovascular signals ─heart rate (HR), aortic blood pressure (aBP), and carotid blood flow (cBF)─ via rat experiments and signal analysis techniques. Whilst induced changes in aBP and cBF resulted in evident alterations of ICP magnitude, increases of mean ICP up to 49 mmHg showed minimal effect on HR, aBP, or cBF signals. Thus, a stepwise mixed-model regression proved that the cardiovascular parameters here studied have minimal but significant predictive value of ICP magnitude. Changes in HR were found to modify the waveforms observed in ICP, aBP, and cBF signals, without altering the magnitude or phase of transfer function models. The transfer function models were constructed as a function of mean ICP, mean aBP, and aBP or cBF waveforms, and they showed potential to reproduce the ICP waveform (Root Mean Square Error (RMSE)≤4 mmHg), being more accurate for mean aBP above 100 mmHg and mean ICP below 20 mmHg (RMSE≤0.5 mmHg). Likewise, estimation of pulse ICP showed a small error (<1±1.0 mmHg) for mean ICP below 20 mmHg across a range of mean aBP (70-130 mmHg), proving considerable accuracy improvement in relation to previous studies.