Investigating the Relationship Between Intracranial Pressure and Cerebral Blood Flow Using Near-infrared Diffuse Correlation Spectroscopy

Cerebral Autoregulation (CA) is the complex process whereby the body maintains constant blood flow to the brain (cerebral blood flow, CBF) over a wide range of mean arterial pressures (MAP) in order to provide constant oxygenation and nutrition supply to cerebral tissue. By balancing blood and cerebrospinal fluid (CSF) pressures, CA dynamically stabilises cerebral perfusion pressure (CPP) and hence blood flow. Disordered CA may result in reduced oxygen and nutrient delivery to the brain tissue leading to hypoxic and ischaemic damage resulting in significant morbidity and mortality.

High intracranial pressure (ICP) is frequently associated with failing CA. Hence ICP is routinely monitored in patients suffering from traumatic brain injury (TBI) and other conditions which may result in CA failure. Raised ICP contributes to the majority of mortalities following severe TBI. All currently available ICP monitoring systems require insertion of an electrical or pneumatic transducer into the cranial cavity, usually sited within the brain parenchyma but occasionally into the subdural space (between the brain and the skull) or into the ventricles. This is currently only performed by neurosurgeons and carries a small but significant risk of haemorrhage or infection.

Non-invasive ICP and hence CA monitoring would eliminate the risk of complications, could be used by all healthcare professionals, would extend the use to outside a hospital settings and may extend the range of conditions to benefit from ICP monitoring.

This project pilots an approach to expand our understanding of the basic physiological interplay between intracranial pressure, arterial blood pressure, and cerebral blood flow in adult in-patients.

A recently-developed form of near-infrared (NIR) optical sensing known as Diffuse Correlation Spectroscopy (DCS) offers an opportunity to investigate cerebral blood flow at the bed-side continuously. DCS measures blood flow in the microvasculature of the brain by determining a blood flow index (BFi).