Consistent changes in intracranial pressure waveform morphology induced by acute hypercapnic cerebral vasodilatation

Abstract

Background: Intracranial pressure (ICP) remains a pivotal physiological signal for managing brain injury and subarachnoid hemorrhage (SAH) patients in neurocritical care units. Given the vascular origin of the ICP, changes in ICP waveform morphology could be used to infer cerebrovascular changes. Clinical validation of this association in the setting of brain trauma, and SAH is challenging due to the multi-factorial influences on, and uncertainty of, the state of the cerebral vasculature.

Methods: To gain a more controlled setting, in this articel, we study ICP signals recorded in four uninjured patients undergoing a CO2 inhalation challenge in which hypercapnia induced acute cerebral vasodilatation. We apply our morphological clustering and analysis of intracranial pressure (MOCAIP) algorithm to identify six landmarks on individual ICP pulses (based on the three established ICP sub-peaks; P1, P2, and P3) and extract 128 ICP morphological metrics. Then by comparing baseline, test, and post-test data, we assess the consistency and rate of change for each individual metric.

Results: Acute vasodilatation causes consistent changes in a total of 72 ICP pulse morphological metrics and the P2 sub-region responds to cerebral vascular changes in the most consistent way with the greatest change as compared to P1 and P3 sub-regions.

Conclusions: Since the dilation/constriction of the cerebral vasculature resulted in detectable consistent changes in ICP MOCIAP metrics, by an extended monitoring practice of ICP that includes characterizing ICP pulse morphology, one can potentially detect cerebrovascular changes, continuously, for patients under neurocritical care.

Fig. 1

Illustration of the six landmarks detected by the morphological clustering and analysis of ICP (MOCAIP) algorithm

Fig. 2

Mean ICP during baseline, CO₂ challenge test and post-test normal breathing for a headache patient. The dashed lines are the robustly fitted lines to the rising and falling edge of ICP employed to define the direction of the mean ICP change

Fig. 3

a The rising segment of the ICP signal, b the extracted pulse latency and the robustly fitted line to define the hourly rate of change, c the normalized ICP pulses from the first and last beat of the segment, obtained during CO₂ inhalation of the subject of Fig. 2

Fig. 4

The histogram of the three bit binary words based on the contribution of the three sub-peak regions to the 128 MOCAIP metrics

Fig. 5

The relative hourly rate of change during hypercapnia and normal breathing post-test for the 10 metrics with the highest relative rate of change from a the “+” group, b the “−” group. The 10 metrics from “+” group in the ascending order of index (1,…,10) are (‘RCurvp2Curvp3’, ‘diasP’, ‘Curvp2’, ‘mICP’, ‘k2’, ‘RCurvp2Curvv3’, ‘dV3’, ‘RC3’, ‘dP3’, ‘dP2’). The 10 metrics from “−” group in the ascending order of index are (‘RCurvp3Curvv2’, ‘RCurvp1Curvv2’, ‘RCurvv1Curvp2’, ‘RLv3p3Lp1p2’, ‘Lv3p3’, ‘RP1V3’, ‘RV1V3’, ‘RLv1p3Lv2p2’, ‘RV2V3’, ‘RLv3p3Lp1p3’)