Development of a custom imaging system for simultaneous monitoring of retinal and cortical physiology

Abstract

Purpose : Retinal blood flow (RBF) may offer insights into systemic health, providing physiological markers for disease and recovery. Researchers may benefit from the ability to simultaneously monitor RBF and other functional data such as systemic blood pressure (BP), electrocardiogram (ECG) and electroencephalogram (EEG) readings, and cerebral blood flow (CBF). The purpose of this study was to develop novel instrumentation for multi-parameter functional data and demonstrate feasibility by characterizing changes that accompany cardiac arrest, resuscitation and recovery.

Methods : A modular imaging platform—VasoVUE Research System^TM—was designed to produce vessel-specific blood flow in the rat retina and cortex using laser speckle contrast imaging and high-speed photography. Image acquisition was synchronized with ECG, EEG, and BP recordings. An adult male Wistar rat (350g) was prepared by implanting EEG electrodes (right hemisphere) and exposing a thinned-skull cortical imaging window of 5mm diameter (left hemisphere). BP was measured by cannulating the left femoral artery. The rat was laid supine and the VasoVUE was oriented such that retinal and cortical vasculature was visualized clearly (Fig. 1). The rat was anesthetized with 2% isoflurane for 20 min. to establish baseline, after which a 5-min washout period (no isoflurane) was recorded. Asphyxia was induced by stopping mechanical ventilation for 6 min. Subsequently, cardiopulmonary resuscitation (CPR) was performed by ventilation, external chest compression, epinephrine and NaHCO₃ until return of spontaneous circulation (ROSC, mean BP >50 mmHg). Recovery was monitored for 25 min.

Results : The VasoVUE simultaneously measured RBF and CBF with a mean coefficient of variation of 9.0% and 8.1%, respectively, and synchronously with EEG, ECG, and BP over the course of the procedure (Fig. 2). Trends in RBF and CBF were strongly correlated at baseline and during asphyxia (R² = 0.998, p < 0.01). Trends were only weakly correlated during CPR and ROSC (R² = 0.008, p > 0.80), requiring further investigation. A short yet temporally correlated period of elevated BP and hyperperfusion in both RBF and CBF was observed 3-4 minutes post-ROSC.

Conclusions : This study shows the feasibility of capturing RBF and CBF using the VasoVUE and utilizing these data in conjunction with multi-parameter brain and cardiovascular data for research.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.