Contactless Assessment of Cerebral Autoregulation by Photoplethysmographic Imaging at Green Illumination

Abstract

Accurate and practical assessment of the brain circulation is needed to adequately estimate the viability of cerebral blood flow regulatory mechanisms in various physiological conditions. The objective of our study was to examine feasibility of the contactless green-light imaging photoplethysmography (PPG) for assessing cerebral autoregulation by revealing the dynamic relationships between cortical microcirculation assessed by PPG and changes in systemic blood pressure caused by visceral and somatic peripheral stimuli. In anesthetized male Wistar rats, the PPG video images of the open parietal cortex (either with unimpaired or dissected dura mater), electrocardiogram, and systemic arterial blood pressure (ABP) in the femoral artery were continuously recorded before, during and after visceral (colorectal distension) or somatic (tail squeezing) stimulation. In the vast majority of experiments with intact and removed dura mater, both spontaneous and peripheral stimulation-evoked changes in ABP negatively correlated with the accompanying alterations in the amplitude of pulsatile PPG component (APC), i.e., an increase of ABP resulted in a decrease of APC and vice versa. The most pronounced ABP and APC alterations were induced by noxious stimuli. Visceral painful stimulation in all cases caused short-term hypotension with simultaneous increase in cortical APC, whereas somatic noxious stimuli in 8 of 21 trials produced hypertensive effect with decreased APC. Animals with pressure 50-70 mmHg possessed higher negative cerebrovascular response rate of ABP-APC gradients than rats with either lower or higher pressure. Severe hypotension reversed the negative ratio to positive one, which was especially evident under visceral pain stimulation. Amplitude of the pulsatile PPG component probably reflects the regulation of vascular tone of cerebral cortex in response to systemic blood pressure fluctuations. When combined with different kinds of peripheral stimuli, the technique is capable for evaluation of normal and elucidation of impaired cerebrovascular system reactivity to particular physiological events, for example pain. The reported contactless PPG monitoring of cortical circulatory dynamics during neurosurgical interventions in combination with recordings of changes in other physiological parameters, such as systemic blood pressure and ECG, has the appealing potential to monitor viability of the cortex vessels and determine the state of patient’s cerebrovascular autoregulation.

Intraoperative Imaging of Cortical Blood Flow by Camera-Based Photoplethysmography at Green Light

“…We hypothesize that the observed decrease in APC after anastomosis is caused by an increase in the volumetric blood-flow velocity, which, through the autoregulation mechanism, increases the vascular tone, ensuring the constancy of cerebral perfusion. A similar decrease in APC in the cerebral cortex of animals was recently observed in response to an increase in systemic arterial pressure [20].…”

“…Effective use of the cbPPG technique for quantitative evaluation of changes in cortical blood perfusion of rats caused by painful stimuli was recently demonstrated by our group [20]. It was shown in these experiments that the amplitude of the PPG waveform is a measure of the cerebral arterial tone.…”

Imaging photoplethysmography as an easy-to-use tool for monitoring changes in tissue blood perfusion during abdominal surgery

“…The details of calculating the APC parameter are described below in the “ Methods and patients ” section. It was shown that this parameter is a measure of tissue perfusion 19 – 21 , and can be referred to as the perfusion index. Medical diagnoses, types of surgery, and estimated perfusion indices are listed in Table 1 for all 14 patients.…”

Advantages of imaging photoplethysmography for migraine modeling: new optical markers of trigemino‐vascular activation in rats

“…Imaging photoplethysmography (PPG) is a relatively simple, informative, and inexpensive method for assessing the parameters of tissue blood flow. This technique was demonstrated to be very effective in both identifying microcirculation features in migraine patients [ 30 ] and studying intracranial vascular reactions in laboratory animals in various experimental conditions [ 31 , 32 ]. Therefore, the aim of our study was to evaluate imaging PPG as a method of assessing intracranial blood flow in rats and its changes in response to electrical stimulation of dural trigeminal afferents.…”