Quantification of Retinal Vessel Myogenic Constriction in Response to Blood Pressure Peaks: Implications for Flicker Light-Induced Dilatation

Abstract

Background/AimsFlicker-light induced retinal vessel dilatation (FID), a marker of microvascular endothelial function, has been shown to be blunted in sedentary cardiovascular risk patients (SR) as well as healthy physically active individuals (HA). This study aimed to quantify the retinal myogenic response to blood pressure (BP) peaks and its effects on consecutive FID for differentiation of microvascular health.MethodsTen HA and eleven SR with a previously established restriction of arteriolar FID (aFID) (<2.2%) were invited in order to assess BP-induced myogenic constriction following a standardized handgrip task and a consecutive FID. BP was measured beat-to-beat.ResultsThe complete dataset of nine HA (3 female, mean age 65 years) and nine SR (5 female, mean age 61 years) individuals was analyzed. The central retinal arteriolar diameter equivalent (CRAE) was 183 ± 11 μm for HA and 176 ± 20 μm for SR. Initial baseline aFID was 1.6 ± 0.4% in HA and 1.6 ± 0.7% in SR. Systolic (p = 0.334) and diastolic (p = 0.245) BP increase following the handgrip task was in the range of 20–30% and comparable in both groups. BP increase was followed by a significantly higher arteriolar (−2.9 ± 1.3% vs. −1.3 ± 0.6%, p < 0.01) myogenic constriction in HA compared to SR. Moreover, in the consecutive assessment of FID directly after the BP-induced vessel constriction, aFID (4.1 ± 2.0% vs. 1.6 ± 0.9%, p < 0.01) was higher in HA compared to SR.ConclusionInitial baseline aFID was blunted in HA and SR. Retinal myogenic constriction was impaired in SR compared to HA. The consecutive aFID after BP-induced myogenic constriction recovered in HA but remained blunted in SR. Additional assessment of retinal myogenic constriction needs to be considered to improve CV risk stratification and reduce false-positive findings of endothelial dysfunction in otherwise healthy active individuals.Clinical Trial RegistrationClinicalTrials.gov: NCT03986892 (https://clinicaltrials.gov/ct2/show/NCT03986892).

Normative data and standard operating procedures for static and dynamic retinal vessel analysis as biomarker for cardiovascular risk

“…5 E,F). In a previous study, we showed that BP-induced narrowing of arteriolar diameters at rest resulted in an increase in aFID 34 . This was likely explained by an increase in dilatation reserve after BP-induced constriction.…”

“…We previously showed that wider arteriolar baseline diameters resulted in a blunted FID, best explained by a reduced dilatation reserve in predilated arterioles. Potentially this may lead to a false diagnosis of microvascular endothelial dysfunction 30 , 34 . Based on these principles we would like to speculate that wider arteriolar vessel diameters at younger age may be associated with a reduced dilatation reserve and, subsequently, with a relatively low aFID in young and healthy individuals.…”

Hypertension and retinal microvascular dysfunction (HyperVasc): protocol of a randomised controlled exercise trial in patients with hypertension

“… 32 By inducing an acute standardised BP rise using a defined hand-grip exercise, we are able to assess the retinal myogenic constriction in addition to and as a counter regulatory mechanism of FID. 33 …”

“…The setup has been described in detail previously. 33 The second protocol starts with a 50 s rest phase. This rest phase is used to calculate the baseline diameter.…”

“…We have recently established normative data and recommendations for standard operating procedures for SVA and DVA 6. In addition, we developed two new methods to improve non-invasive phenotyping in the retinal microcirculation, which have not yet been applied in patients with hypertension 32 33. The first new approach allows for the investigation of the wall-to-lumen ratio in retinal arterioles and venules 32.…”