Abstract
Pulse wave attenuation characteristics reflect compliance and resistance properties of the vessel wall as well as initial pulse generation factors. Recently, it has become possible to measure and map the retinal vessel wall pulse wave amplitudes. Predictable pulse wave amplitude distribution may allow inferences to be made concerning vascular compliance and resistance. Twenty-eight eyes from sixteen subjects (8 male and 8 female) were examined using modified retinal photoplethysmography with simultaneous ophthalmodynamometry. This allowed the assessment of vessel wall pulsation amplitudes under a dynamic range of intraocular pressures. Pulse amplitudes were calculated using harmonic regression analysis. The pulse wave attenuation was measured under different ranges of ophthalmodynamometric force (ODF) as a function of distance along the vessel (VDist), which in turn was calculated in disc diameters (DD) from the center of the optic disc. A linear mixed-effects model with randomized slopes and intercepts was used to estimate the correlations between the logarithmically transformed harmonic regression wave amplitude (HRWa) and the Fourier trigonometric coefficients with the predictors (VDist and ODF). The retinal venous harmonic regression wave attenuation (coefficient value±standard error) -0.40±0.065/DD, (p-value < 0.00001, 95% confidence interval (CI) -0.53 to -0.27), which was approximately twice that of the arterial -0.17±0.048/DD, (p-value < 0.0004, 95% CI = -0.27 to -0.08). There was a positive correlation between attenuation of the harmonic regression wave and ophthalmodynamometric force in both vascular systems. The attenuation of all but the sine coefficient of the second Fourier harmonic (bn2) achieved statistical significance in the correlation with VDist. The cosine coefficient of the first Fourier harmonic an1 was the only coefficient to achieve statistical significance in the correlation with the predictors VDist and ODF in both vascular systems. The an1 coefficient value in the correlation with VDist was -3.79±0.78 and -1.269±0.37 (p < 0.0006), while this coefficient value in the correlation with ODF was 0.026±0.0099 and 0.009±0.04 (p < 0.01) in both the retinal veins and arteries respectively. The predictable attenuation characteristics in normal subjects suggest that this technique may allow the non-invasive quantification of retinal vascular compliance and other hemodynamic parameters.
Highlights
The vascular pulse wave is a mechanical pressure wave propagating in the wall of the blood vessel at a velocity different to that of blood flow but physiologically coupled to flow through the radially directed transmural pressure and a shear stress force, which is oriented in a parallel direction to the blood vessel wall [1, 2]
Due to the non-normal distribution of the harmonic regression wave amplitude (HRWa) in the venous and arterial systems, logarithmic transformation was performed, normal quantile-quantile plots (q-q plots) in Fig 5 demonstrated a favorable approximation of the residuals to a normal distribution
The mean logarithmically transformed ±standard error of the mean (SEM) HRWa was greater in the venous system 0.84±0.034 (95% confidence interval (CI) = 0.77–0.92), than the arterial system 0.65±0.025
Summary
The vascular pulse wave is a mechanical pressure wave propagating in the wall of the blood vessel at a velocity different to that of blood flow but physiologically coupled to flow through the radially directed transmural pressure and a shear stress force, which is oriented in a parallel direction to the blood vessel wall [1, 2]. The physiologic mechanisms of the retinal venous pulse are poorly understood; being generated by the heart and transmitted via the cerebrospinal fluid space, it propagates in the wall of the central retinal vein in a retrograde direction to blood flow, entering the eye through the optic cup, where it attenuates (decays in amplitude) rapidly [13, 15].
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