Investigation of the hypercapnial effect on cerebral blood flow using imaging photoplethysmography
Maxim A. Volynsky, 1,2
Oleg V. Mamontov, 1,3
Anastasiia V. Osipchuk, 4
Valery V. Zaytsev, 1,3
Alexey Y. Sokolov, 4,5
Alexei A. Kamshilin 1,3
1 Institute of Automation and Control Processes of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia;
2 ITMO University, Saint Petersburg, Russia;
3 Almazov National Medical Research Centre, Saint Petersburg, Russia;
4 Valdman Institute of Pharmacology, Pavlov First Saint Petersburg State Medical University, Saint Petersburg, Russia;
5 Pavlov Institute of Physiology of the Russian Academy of Sciences, Saint Petersburg, Russia
Abstract
Evaluation of the functional reserve of cerebral blood flow during surgery is necessary to determine the degree of hemodynamic significance of intracranial artery stenosis, as well as to monitor the effectiveness of surgical treatment. Today in clinical practice, PET and MRI methods are used applying functional tests with vasodilators, but these methods require expensive equipment and are not available in most clinics. We were the first to propose a method for assessing the functional reserve of cerebral blood flow using imaging photoplethysmography (iPPG), which is cheap, technically simple, reliable, and claims to be widely translated into clinical practice.
Adult male Wistar rats were used in our study. The number of animals under study (n = 21) was minimized for humanistic reasons, but sufficient for the statistical significance of the obtained results.
Special attention in the study was paid to investigation the influence of the state of the brain surroundings on the cerebrovascular response to hypercapnia. Changes in cerebral blood flow measured through intact skull were compared to that through open cranial window in two cases: with intact dura mater and after its removal. As a result, we have shown for the first time that changes in cerebral blood circulation with an open and closed brain in response to a hypercapnic test are bidirectional: there is an increase in vascular tone with a closed brain and a decrease with an open brain. Moreover, the effect of CO2 inhalation duration on hemodynamic parameters was studied. Based on our studies, we proposed a new objective quantitative parameter of regional peripheral vascular resistance, which, regardless of the direction of changes in local and systemic hemodynamics, as well as the state of the brain surroundings, reflects only the vasodilation effect of CO2 inhalation thus assessing the functional reserve of cerebral blood flow.
In conclusion, we have shown feasibility of using optical iPPG system for intraoperative assessment of the functional reserve of the brain and demonstrated the influence of the brain surroundings and hypercapnia duration on the hemodynamic response.
The work was financially supported by the Russian Science Foundation (Grant No. 21-15-00265) in part of development of high-speed iPPG system and the computer software for experimental data processing and by the Ministry of Education and Science of the Russian Federation (Grant No. 075-15-2020-800) in the part of carrying out the experimental study and theoretical analysis of the obtained results.
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Speaker
Maxim A. Volynsky
Institute of Automation and Control Processes, FEB RAS; ITMO University
Russia
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