Frequency dependent hemodynamic response to intracranial pressure changes

Guiding treatment in traumatic brain injury based on managing and optimizing cerebral perfusion pressure, which is the difference between mean arterial blood pressure and intracranial pressure (ICP), has been demonstrated to improve patient outcome. However, this requires ICP to be measured, which currently is only possible by placing pressure probes inside the brain. The feasibility of optical systems to measure ICP non-invasively has shown preliminary promising evidence of feasibility. To pursue the goal of non-invasive ICP acquisition further, an understanding of the influence of different pressure changes on the brain and their hemodynamic response is necessary. To investigate the frequency content of hemodynamic reactions to pressure changes in both ICP as well as arterial blood pressure (ABP), we induced changes of both pressures in non-human primates. We then demonstrate that ABP and ICP changes both influence cerebral blood flow and hemoglobin concentrations, measured with diffuse correlation spectroscopy (DCS) and near-infrared spectroscopy (NIRS), respectively. We found that the magnitude of induced oscillations is dependent on the frequency of the oscillation. Our data suggests, changes in ABP and ICP influence the hemodynamics differently, which we can use as a basis for non-invasive ICP measurements.