Usefulness of laser speckle flowgraphy for the assessment of ocular blood flow in extracranial-intracranial bypass

Application of laser speckle flowgraphy to evaluate cerebral perfusion after carotid endarterectomy

Cerebral hyperperfusion syndrome (CHS) after carotid endarterectomy (CEA) is devastating, and postoperative monitoring of cerebral perfusion is essential to prevent CHS. We report two cases of successful measurement of ocular blood flow using laser speckle flowgraphy (LSFG) for bedside assessment of the changes in cerebral perfusion after CEA. An 18.7% (case 1) and 47.7% (case 2) increase in ocular blood flow were measured postoperatively using LSFG compared with the baseline. LSFG might be applicable to evaluate cerebral perfusion after CEA.

Assessment of ocular blood flow in continuous-flow ventricular assist device by laser speckle flowgraphy

Although the influence of continuous-flow left ventricular assist device (CF-LVAD) support on peripheral circulation has been widely discussed, its monitoring modalities are limited. The aim of this study was to assess the peripheral circulation using the laser speckle flowgraph (LSFG) which can quantitatively measure the ocular blood flow. We implanted a centrifugal CF-LVAD (EVAHEART^®; Sun Medical Technology Research Corporation, Nagano, Japan) in five adult goats (body weight 44.5 ± 2.9 kg) under general anesthesia. The waveform of the central retinal artery using the mean blur rate (MBR) for ocular blood velocity and fluctuations as a parameter of pulsatility were obtained before LVAD implantation and after LVAD full-bypass support. The MBR waveform and LSFG fluctuation data were compared with the waveform and pulsatility index of the external carotid artery using an ultrasonic flow meter to evaluate circulatory patterns at different levels. The MBR waveform pattern of the central retinal artery was pulsatile before LVAD implantation and less pulsatile under LVAD full bypass. The fluctuation was 14.7 ± 1.86 before LVAD implantation and 3.85 ± 0.61 under LVAD full bypass (p < 0.01), respectively. The fluctuations of LSFG showed a strong correlation with the pulsatility index of the external carotid artery meaning that similar changes in circulatory pattern were observed at two different levels. Measuring the ocular blood flow using LSFG has potential utility for the assessment of the status of the peripheral circulation and its pulsatility during CF-LVAD.

Longitudinal effects of common carotid artery stenosis on ocular hemodynamics assessed using laser speckle flowgraphy in a rabbit model

Real-time impairment of ocular blood flow (OBF) under common carotid artery stenosis (CCAS) has not been ascertained. We aimed to longitudinally assess the impact of CCAS on OBF using a rabbit model. About 75% stenosis was created by tying the common carotid artery with a plastic mandrel using a nylon suture. The plastic mandrel was gently removed, leaving a ligature. Neurological and behavioral assessments were recorded as the clinical indicator of stroke severity. With laser speckle flowgraphy, the pulse waveform parameters namely mean blur rate (MBR), blowout score (BOS), blowout time (BOT), rising rate, S1-area, falling rate (FR), S2-area, flow acceleration index (FAI), acceleration time index, resistive index (RI) and the difference between the maximum and minimum values of MBR (AC) were assessed in overall, vessel, and tissue regions of the optic nerve head (ONH). Longitudinally, BOS significantly increased until day 19 post-surgery, whereas FAI, RI, and AC significantly decreased. Beyond day 19, BOS, BOT, FR, FAI, RI, and AC significantly decreased. We defined two stages representing impaired vessel conditions, namely the vessel resistance phase, where BOS increases and FAI, RI, and AC decrease, and the vessel elasticity phase where BOS, BOT, FR, FAI, RI and AC decrease. These stages provide information about atherosclerosis, assessable non-invasively through the eye.

Ocular blood flow by laser speckle flowgraphy to detect cerebral ischemia during carotid endarterectomy

Laser speckle flowgraphy (LSFG) is a noninvasive technique that can measure relative blood flow velocity in the optic fundus contributed by the ophthalmic artery, the main first branch originating from the internal carotid artery (ICA). The aim of this study was to assess the feasibility of ocular blood flow measurement by LSFG to detect ischemic stress due to carotid clamping during carotid endarterectomy (CEA). Nineteen patients undergoing CEA with ocular blood flow measurement by LSFG and intraoperative monitoring (IOM) were prospectively enrolled between August 2016 and March 2019. The mean blur rate (MBR) of ocular blood flow by LSFG, representing relative blood flow of the branch of the retinal artery originating from the optic nerve head, was compared between before and after carotid clamping during CEA. The correlation between the reduction ratio of MBR and the regional saturation oxygen (rSO₂) index by near infrared spectroscopy was investigated. Ocular blood flow measurement by LSFG could not be performed in one patient with a severe cataract. In the other 18 patients, LSFG could be performed in all 106 sessions during surgery. The MBR reduction ratio between before and after carotid clamping ranged from - 12 to 100%. The MBR reduction ratio was positively correlated with the rSO₂ index (r = 0.694, 95% confidence interval: 0.336-0.877, p = 0.001). The MBR reduction ratio of ocular blood flow by LSFG after carotid clamping was significantly correlated with the rSO₂ index. The ocular blood flow by LSFG could be considered an adjunct modality for evaluating cerebral ischemic tolerance during CEA.

Successful retinal blood flow augmentation after extracranial-intracranial bypass

A 61-year-old woman visited us with recent onset right-side weakness. Magnetic resonance imaging showed ischemic changes at the left internal border zone due to occlusive disease affecting the left proximal internal carotid artery. Prompt oral dual antiplatelet therapy and intravenous fluid were administered with subsequent induced hypertension and without reperfusion therapy. Although the hemiparesis was improved, she complained of a new-onset transient left-side monocular visual loss. Fluorescein angiography confirmed delayed perfusion in the left eye. We performed extracranial-intracranial bypass for flow augmentation. After bypass, the amaurosis fugax resolved. Follow-up retinal fluorescein angiography also showed improved retinal perfusion.

Association Between Optic Nerve Head Blood Flow Measured Using Laser Speckle Flowgraphy and Radial Arterial Pressure During Aortic Arch Surgery

OBJECTIVE

This study was designed to investigate the association between ocular blood flow measured using laser speckle flowgraphy (LSFG) and radial arterial pressure during aortic arch surgery.

DESIGN

A prospective study.

SETTING

A single university hospital.

PARTICIPANTS

This study included 24 patients undergoing aortic arch surgery with cardiopulmonary bypass (CPB) using antegrade selective cerebral perfusion (SCP).

INTERVENTIONS

Measurement of optic nerve head blood flow using LSFG and radial arterial pressure via a catheter in the radial artery METHODS AND MAIN RESULTS: Antegrade SCP was managed with 24℃ and 40-to-60 mmHg at the right radial artery, which usually corresponds to a flow rate of 10 mL/kg/min. Optic nerve head blood flow using LSFG and radial arterial blood pressure were evaluated simultaneously at the right side and recorded at the following 4 points: after the induction of anesthesia (phase 1), after the beginning of CPB (phase 2), after the beginning of antegrade SCP (phase 3), and after cessation of CPB (phase 4). A moderate positive correlation between %change of mean blur rate in the optic nerve head measured using LSFG and %change of radial mean arterial pressure was identified (r = 0.604, p < 0.001). Bland-Altman analysis showed that the bias (mean difference) was -1.2% (95% limits of agreement -47.4% to 45.0%), indicating good agreement between %changes of the values recorded using the 2 measurements.

CONCLUSIONS

Intraoperative monitoring of optic nerve head blood flow using LSFG can be used as an additional cerebral perfusion parameter during aortic arch surgery with CPB using antegrade SCP.

Ocular Blood Flow Measured Using Laser Speckle Flowgraphy During Aortic Arch Surgery With Antegrade Selective Cerebral Perfusion

OBJECTIVE

The objective of this study was to evaluate the validity of ocular blood flow measured using laser speckle flowgraphy (LSFG) for the assessment of cerebral perfusion during aortic arch surgery.

DESIGN

A prospective study.

SETTING

A single university hospital.

PARTICIPANTS

The study included 17 patients undergoing aortic arch surgery with cardiopulmonary bypass (CPB) using antegrade selective cerebral perfusion (ASCP).

INTERVENTIONS

Measurement of ocular blood flow using LSFG.

MEASUREMENTS AND MAIN RESULTS

Measurement of ocular perfusion that is supplied mainly from the ophthalmic artery might be useful as an indicator of cerebral blood flow because the ophthalmic artery is the first branch of the internal carotid artery. Recently, LSFG has been developed for noncontact estimation of ocular perfusion using the laser speckle phenomenon. In this study, the LSFG system was used to measure blood flow in the optic nerve head during aortic arch surgery with CPB using ASCP. The blood flow in the optic nerve head during ASCP was statistically significantly reduced by 40.6% compared with the baseline value after anesthetic induction.

CONCLUSIONS

Ocular blood flow measured using LSFG showed favorable validity for assessment of cerebral perfusion during aortic arch surgery with ASCP.