# Imaging photoplethysmography reveals differences in the reactions of cerebral and systemic hemodynamics to infusion of vasoactive drugs

## TL;DR

This study uses imaging photoplethysmography to show that cerebral and systemic blood flow react differently to vasoactive drugs.

## Contribution

It is the first to detect opposite reaction vectors of intracranial and systemic hemodynamics in response to vasodilators and vasoconstrictors.

## Key findings

- APC changes in response to vasoactive drugs are multiphasic and do not correlate with blood pressure changes.
- Cerebral and systemic hemodynamics show opposite reaction vectors when exposed to vasodilators or vasoconstrictors.
- APC can serve as a quantitative marker for local vasomotor reactions independent of systemic hemodynamics.

## Abstract

According to the recent data, imaging photoplethysmography has extensive capabilities in clinical and experimental biomedical research. However, relationship between local vasomotor reactions, estimated as fluctuations of the amplitude of pulsatile component (APC) of a photoplethysmographic waveform, and changes in systemic hemodynamic parameters remains unclear. The study aims to assess APC changes concurrently with changes in basic physiological parameters in response to administration of either vasodilating adenosine triphosphate or vasoconstrictor norepinephrine.

In anesthetized, artificially ventilated rats (n=10), a video recording of the cerebral cortex was performed through thinned parietal bones synchronously with an electrocardiogram. Simultaneously, systemic blood pressure and end-tidal CO2 were monitored.

Cerebrovascular effects of vasoactive agents are expressed in transient, pronounced and stereotypical changes in APC for all animals. For both substances, these changes are multiphasic, with at least two episodes of rise and fall in APC that do not correlate with changes in blood pressure. For the first time, opposite reaction vectors of intracranial and systemic hemodynamics were detected with the administration of either vasodilators and vasoconstrictors.

Our study demonstrates that APC can be considered as a quantitative marker of local vasodilation/vasoconstriction, which does not necessarily coincide with systemic hemodynamics, thus enabling an experimental investigation of autoregulation processes. The results obtained make it possible to link systemic and intracranial hemodynamic shifts caused by drugs into a single picture and clarify how adenosine triphosphate or norepinephrine affect the cardiovascular system and blood supply to the brain, which is very important due to the widespread use of these drugs in practical medicine.