A preliminary study on the application of electrical impedance tomography based on cerebral perfusion monitoring to intracranial pressure changes

Abstract

Background: In intracranial pathologic conditions of intracranial pressure (ICP) disturbance or hemodynamic instability, maintaining appropriate ICP may reduce the risk of ischemic brain injury. The change of ICP is often accompanied by the change of intracranial blood status. As a non-invasive functional imaging technique, the sensitivity of electrical impedance tomography (EIT) to cerebral hemodynamic changes has been preliminarily confirmed. However, no team has conducted a feasibility study on the dynamic detection of ICP by EIT technology from the perspective of non-invasive whole-brain blood perfusion monitoring. In this study, human brain EIT image sequence was obtained by in vivo measurement, from which a variety of indicators that can reflect the tidal changes of the whole brain impedance were extracted, in order to establish a new method for non-invasive monitoring of ICP changes from the level of cerebral blood perfusion monitoring.

Methods: Valsalva maneuver (VM) was used to temporarily change the cerebral blood perfusion status of volunteers. The electrical impedance information of the brain during this process was continuously monitored by EIT device and real-time imaging was performed, and the hemodynamic indexes of bilateral middle cerebral arteries were monitored by transcranial Doppler (TCD). The changes in monitoring information obtained by the two techniques were compared and observed.

Results: The EIT imaging results indicated that the image sequence showed obvious tidal changes with the heart beating. Perfusion indicators of vascular pulsation obtained from EIT images decreased significantly during the stabilization phase of the intervention (PAC: 242.94 ± 100.83, p < 0.01); perfusion index which reflects vascular resistance increased significantly in the stable stage of intervention (PDT: 79.72 ± 18.23, p < 0.001). After the intervention, the parameters gradually returned to the baseline level before compression. The changes of EIT indexes in the whole process are consistent with the changes of middle cerebral artery velocity related indexes shown in TCD results.

Conclusion: The EIT image combined with the blood perfusion index proposed in this paper can reflect the decrease of cerebral blood flow under the condition of increased ICP in real time and intuitively. With the advantages of high time resolution and high sensitivity, EIT provides a new idea for non-invasive bedside measurement of ICP.

Keywords: Valsalva maneuver; cerebral perfusion; electrical impedance tomography; hemodynamic; intracranial pressure.

Figure 1

Experimental environment of EIT cerebral blood perfusion monitoring under VM intervention. The leftmost image showed the expiratory pressure (about 40 mmHg, 5.33 kPa) required to maintain the VM. The objects in the middle figure showed a subject’s experimental environment (including EIT and TCD equipment and real-time expiratory pressure display). The rightmost image showed the wear of EIT brain electrode band. (EIT, electrical impedance tomography; VM, Valsalva maneuver).

Figure 2

(A) One-dimensional curve change of base impedance during VM intervention; (B) Reconstructed image of EIT base impedance (interval 2 s). (EIT, electrical impedance tomography; VM, Valsalva maneuver).

Figure 3

(A) EIT images of a single perfusion cycle during BP; (B) EIT images of a single perfusion cycle during IP; (C) A single perfusion cycle was selected every 2 s to obtain EIT images at the time of maximum cerebral blood flow perfusion. (EIT, electrical impedance tomography).

Figure 4

(A) Cerebral blood perfusion curves extracted from EIT reconstructed images were compared with PPG signals; (B) Results of statistical analysis of EIT cerebral blood perfusion monitoring indexes. (EIT, electrical impedance tomography; PPG, photoplethysmography). ** means p < 0.01. *** means p < 0.001.

Figure 5

Results of statistical analysis of blood flow parameters of bilateral MCAs monitored by TCD. (MCA, middle cerebral artery; TCD, transcranial Doppler). ** means p < 0.01. *** means p < 0.001.