...
For each minute of average surrogate ICP waveform, two key parameters are estimated to derive relevant physiological information from relative and / or normalized measurements. The most relevant parameters meeting those conditions are estimated P2/P1 ratio and normalized time to peak and they are described as follows.
...
Invasive ICP’s percussion wave (A1) timing (T1) is almost the corresponding ABP’s waveform first peak
Invasive ICP’s notch (A3) timing (T3) is closely related to ABP’s dicrotic notch
Invasive ICP’s tidal wave (A2) timing (T2) is estimated to be midway between ABP’s T3 and T1
Based on this observation an algorithm was developed that estimates P1 and P2 amplitudes for the invasive ICP waveform, as well as the BcSs-PICNI-2000 (B4C Sensor) waveforms, based on the concurrent ABP pulse’s T1 and T2 normalized timings (Figure 07). This allowed for indirect (surrogate) P1 and P2 estimation when they are not visually identifiable in the invasive ICP.
The accuracy of this ABP based P2/P1 ratio estimation algorithm (ABP based algorithm) was validated resulting in a very high correlation was very high. (Figure 08).
...
Pearson correlation of 0.845 [0.797, 0.895], p-value 0.076 [0.000, 0.932]f, and normalized mutual information correlation of 0.772 [0.647, 0.923]
After verification of the ABP based algorithm (research algorithm), a mathematical model was developed to allow for P2/P1 ratio estimation without depending on having a concurrent ABP pulse waveform information being captured by the subject device since it is not the actual usage scenario. The mathematical model (Production algorithm) was developed using available pulses of invasive ICP (invasive device) and non-invasive BcSs-PICNI-2000 (B4C Sensor) sensors which had their P1 and P2 amplitudes calculated by the ABP based algorithm. The normalized timing of the amplitudes (moment during pulse duration where the peak happens) were defined from the duration from max slope (moment in time where pulse slope is steepest) to the P1 and P2 amplitudes and then normalized by the pulse total time. This then determined the most likely positions of P1 and P2 amplitudes.
A subsequent test was done to validate the production algorithm. All valid waveform data captured from the invasive ICP (invasive sensor) and non-invasive BcSs-PICNI-2000 (B4C Sensor device) had their minute by minute P2/P1 ratio calculated with the ABP based algorithm (research algorithm) and Production algorithm. When the P2/P1 ratio was calculated by both algorithms, one being the P2/P1 ratio estimated by using the concurrent APB waveform as defined in Figure 07, and the other being the estimation of the most probable position of P1 and P2, and then compared to each other, the correlation was extremely high for both ICP waveform (Figure 10) and non-invasive BcSs-PICNI-2000 (B4C Sensor waveform) (Figure 11).
...
ICP waveform with Pearson correlation of 0.916 [0.902, 0.930], p-value 0.000 [0.000, 0.000]
non-invasive B4C Sensor waveform with Pearson correlation of 0.867 [0.844, 0.887], p-value 0.000 [0.000, 0.000]
Normalized time to peak: normalized time to peak’s key hypothesis is that it is affected by compensatory reserve and intracranial compliance. The derived parameters required to identify time to peak are defined in Figure 11.Normalizedtime to peak is identified from point A, the max slope of the calculated average waveform (moment in time where pulse slope is steepest) to point B, normalized duration from the identified average pulse’s Max slope to highest pulse amplitude.
...