Cerebrovascular pressure transmission analysis as a guide to the pathophysiology of raised intracranial pressure.

1. Raised intracranial pressure (ICP) is a major factor associated with morbidity and mortality in patients with severe head injury. Identifying the mechanisms responsible for raised ICP may be difficult and, as a result, treatment prescribed may be non-specific and often ineffective. 2. Research aimed at obtaining more information from measurement of ICP was initially focused on measurements of compliance. This was achieved by introducing fluid volume into the craniospinal compartment and measuring the response. Although shown to be clinically useful, associated technical problems have precluded the routine use of these measurements. 3. Cerebrovascular pressure transmission (CVPT) analysis has been suggested as an alternative method of deriving more information from the ICP wave-form. Pressure transmission across the cerebrovascular bed is assessed by a systems analysis approach whereby blood pressure and ICP wave-form pairs are resolved by fast Fourier transform analysis into component harmonic frequencies, each with a specific amplitude and phase. These are expressed as a ratio or 'transfer function' for each harmonic peak. 4. Laboratory models have identified specific CVPT patterns associated with various causes of raised ICP. These studies have been extended to clinical practice and have been used to define patterns of CVPT in head-injured patients, which may be used to identify mechanisms responsible for raised ICP, thus assisting in directing treatment strategy. Clinical usefulness of this technique in patient management is currently under investigation.