Figure 1

Illustration of the method of determining the RAP [correlation coefficient (R) between the intracranial pressure (ICP) wave amplitude (A) and the mean ICP level (P)] in patient 2. Following automatic identification of the cardiac induced single intracranial pressure (ICP) waves, the mean ICP and mean wave amplitude (MWA) are determined for every consecutive 6-sec time window. Trend plots of mean ICP and MWA determined during the same 6-sec time windows are shown for Signals 1 (a) and 2 (b) over subsequent 12 min periods (representing three 4-min periods, and 120 6-sec time windows). For Signal 1 (a) the average (± standard deviation) of mean ICP was 7.9 ± 1.2 mmHg and of MWA 4.6 ± 0.5 mmHg; while for Signal 2 (b) mean ICP -0.9 ± 1.9 mmHg and MWA 4.4 + 0.5 mmHg (mean difference of ICP -8.8 ± 2.2 mmHg; mean difference of MWA -0.2 ± 0.2 mmHg). In (c) one single 6-sec time window is shown, demonstrating the individual single ICP waves, each wave being characterized by the amplitude (dP), rise time (dT), and rise time coefficient (RT) (indicated for single wave 3). RAP is determined as the Pearson correlation coefficient between MWA and the mean ICP during subsequent 4 min periods (representing 40 6-sec time windows). In the patients included in this study, we compared the RAP values during identical 4-min periods for Signals 1 and 2 (referred to as method 1). This was performed for every consecutive 4-min period. For the three consecutive 4-min periods shown in (a) and (b), the corresponding scatter plots and RAP-values are presented in (d), (e), and (f), respectively. The differences in RAP were associated with marked differences in mean ICP between Signals 1 and 2 whereas the MWA was close to identical.