Abstract
PurposeThe retinal vasculature provides unique in vivo access to the microcirculation and presents the possibility of measuring small artery (retinal) stiffness using pulse wave velocity (PWV). This study investigates whether retinal artery PWV (rPWV) has a blood pressure (BP) dependency.MethodsFundus videos from eight Sprague-Dawley rats aged 12 weeks were captured (Zeiss fundus microscope with high-speed camera, 125 fps, Optronis, Germany) simultaneously with aortic BP. Retinal artery diameter waveforms at proximal and distal sites were extracted and transit time calculated from the phase delay between frequency components (4–6 Hz, typical heart rate of rats) of the waveforms. rPWV was measured across a physiological range of mean arterial pressure (MAP): baseline (90–110 mmHg); 130 mmHg to baseline following systemic phenylephrine (PE) infusion (30 µg/kg/min); 130 mmHg to baseline during PE infusion with simultaneous inferior vena cava occlusion (VO); 70 mmHg to baseline following systemic sodium nitroprusside infusion; and 70 mmHg to baseline following VO. The correlation between retinal artery rPWV and BP was quantified.ResultsThere was a significant positive correlation between retinal artery rPWV and MAP as expected (0.19 mm/s/mmHg, R2 = 0.59, p < 0.001). There was a positive correlation between retinal and aortic PWV (R2 = 0.09, p = 0.03).ConclusionThe pressure dependency of the measured rPWV indicates the measure has utility in in vivo quantification of the impact on microvessels of cardiovascular diseases. To elucidate the predictive value of screening rPWV in systemic cardiovascular abnormalities, the relation needs to be investigated in humans.
Highlights
Arterial stiffness increases through life due to changes in smooth muscle and endothelial function, and alteration of the extracellular matrix through elastin degeneration, collagen cross-linking, and calcification
Pulse wave velocity in macro-vessels as a measure of arterial stiffness is highly correlated with blood pressure (BP), this being a fundamental property of arterial biomechanics
This study does not tackle the issue of order of magnitude of the retinal artery PWV (rPWV) measure but attempts to validate the rPWV measure by demonstrating that it changes with BP – a fundamental property of arterial stiffness
Summary
Arterial stiffness increases through life due to changes in smooth muscle and endothelial function, and alteration of the extracellular matrix through elastin degeneration, collagen cross-linking, and calcification. These processes occur with age and are accelerated in certain diseases including hypertension, diabetes mellitus, and end-stage renal failure [1]. Arterial stiffness has been linked to vascular morbidity and mortality in cohorts with hypertension [6,7], end-stage renal disease [8], and type 2 diabetes mellitus [9]. The possibility that the microcirculatory impairment may occur early in the onset of increasing arterial stiffness underlines the importance of monitoring microcirculation for more effective preventive and therapeutic measures [13]
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