A new method of intraoperative assessment of the dynamics of cortical blood flow using imaging photoplethysmography

Background . Intraoperative assessment of changes in cerebral blood flow is an important component of objective quality control of surgical treatment of cerebral artery aneurysms. Various techniques have been tried to solve this task, but they all have their drawbacks, which forces us to look for new ways of blood flow monitoring. We propose to use the technology of imaging photoplethysmography (IPPG) – a technically simple, contactless, safe and cheap optical method for assessing the perfusion of biological tissues. Aim . To demonstrate the possibility of using IPPG to assess the dynamics of cerebral blood flow parameters during aneurysm clipping surgery, as well as to identify early changes in blood supply to the cerebral cortex. Materials and methods . The study was carried out during six surgeries of clipping aneurysms of the anterior part of the Willis’s circle, both in the acute stage of rupture (n = 1) and in a planned manner (n = 5). The IPPG system, which is an LED illuminator in a single unit with a digital video camera, was located on a tripod 25 cm from the intervention zone. During each operation, two one-minute recordings of the illuminated surface of the cerebral cortex were performed: after dissection of the dura mater and before its suturing at the end of the main stage of the intervention. To improve the measurement accuracy, video frames of the studied area were recorded synchronously with the registration of an electrocardiogram. After recording, two IPPG parameters were calculated and compared: the amplitude of the pulsatile component and the pulse wave transit time. Thereafter, the obtained data were compared with the results of computed tomography. Statistical analysis was performed using pairwise comparison tests in the GraphPad Prism software package. Results . Clipping of cerebral vessel aneurysms are accompanied by significant changes in the parameters of cerebral blood flow. Analysis of the data for all patients revealed significant differences in IPPG parameters before and after surgery, namely, statistically significant increase in amplitude of the pulsatile component (n = 3) and decrease in pulse wave transit time (n = 5). The absence of significant changes in both parameters was found only in one patient who had mechanical damage in the cortex in the region of video recording. Conclusion . The IPPG system is capable to quantify changes in blood supply to the cortex during surgical treatment of cerebral artery aneurysms and to identify areas with either increased or decreased blood supply. In-depth studies are required to obtain additional markers of the postoperative state of cerebral blood flow.