Assessment of Pain-Induced Changes in Cerebral Microcirculation by Imaging Photoplethysmography

Evaluation of the dynamics of cerebral blood flow during surgical treatment and during experiments with laboratory animals is an important component of assessment of physiological reactions of a body. None of the modern methods of hemodynamic assessment allows this to be done in the continuous registration mode. Here we propose to use green-light imaging photoplethysmography (IPPG) for assessment of cortical hemodynamics. The technique is capable for contactless assessment of dynamic parameters synchronized with the heart rate that reflect the state of cortical blood flow. To demonstrate feasibility of the technique, we carried out joint analysis of the dynamics of systemic arterial pressure and IPPG synchronized with electrocardiogram during visceral or somatic stimulation in an anesthetized rat. IPPG parameters were estimated from video recordings of the open rat brain without dissecting the dura mater. We found that both visceral and somatic painful stimulation results in short-term hypotension with simultaneous increase in the amplitude of blood pulsations (BPA) in the cerebral cortex. BPA changes were bigger in the primary somatosensory cortical area but they correlated with other areas of the cortex. Apparently, change of BPA is in the reciprocal relationship with variations of mean systemic and pulse pressure in femoral artery that is probably a consequence of cerebrovascular reflex regulating the cerebral blood flow. Therefore, BPA reflects dynamic properties of cortex microcirculation that are synchronized with systemic arterial pressure and depend from cortical area specialization.