Non-invasive assessment of intracranial compliance using a new 2-D "transit time" vs "frequency centroid" map

The objective of this research was to develop a new static two dimensional graphic display indicating changes to intracranial compliance using non invasive ultrasonic Doppler measurements of the Middle Cerebral Artery (MCA) velocity and Arterial Blood Pressure (ABP). ABP and MCA velocity were measured in a volunteer patient study and the results for hypo-, normo- and hyper-capnia, conditions were recorded. Cross-correlation analysis between ABP and MCA velocity predicted a change in "transit time" between the two parameters and a Fourier Transform analysis of the MCA velocity data predicted a change in "frequency centroid" over the 0 to 10 Hz range indicating change with intracranial compliance. The results for the hyper-capnia condition were: "Transit Time"--0 ms, "Frequency Centroid"--1.9 Hz, for the normo-capnia condition: "Transit Time"--18 ms, "Frequency Centroid"--2.5 Hz, for the hypo-capnia condition: "Transit Time"--38 ms, "Frequency Centroid"--3.1 Hz. Plotting the results on a graph with "Frequency Centroid" as the vertical axis and "Transit Time" as the horizontal axis yields a locus possibly indicating a change to intracranial compliance.