Histological and biomechanical properties of systemic arteries in young and old Warmblood horses

Figures

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  Fig 1. Schematic overview of the locations at which samples were collected. *: samples of 14 old and 6 young horses were collected for histology. °: samples of 14 old and 6 young horses were collected for histology and biomechanical testing.

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  Fig 2. Schematic overview of the custom-made pressurisation system for the inflation-extension test under ultrasound monitoring. 1: pressure reservoir containing 0.9% NaCl at 37°C; 2: inflation balloon to adjust pressure; 3: water bath containing 0.9% NaCl at 37°C; 4: pressurised arterial sample; 5: silicone window in the water tank, through which ultrasound images were obtained; 6: bath thermometer; 7: fluid filled pressure transducer; 8: acquisition station; 9: visualisation of actual pressure in the arterial segment on screen.

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  Fig 3. Example of the proximal aorta, mounted in the pressurisation system but out of the water bath, and derived ultrasound images at 30 (left) and 300 (right) mmHg. Double-sided arrows indicate diameter measurements performed from inner edge to inner edge.

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  Fig 4. Immunostaining for elastin and smooth muscle actin of the caudal common carotid artery, showing two clearly distinguishable layers: Layer 1 (1) consisting mainly of smooth muscle cells and layer 2 (2) consisting predominantly of elastin fibres.

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  Fig 5. Overview of the overall mean intima media thickness, area % of elastin, area % of smooth muscle cells, area % of collagen type I and area % of collagen type III in young (blue) and old (red) horses, grouped by location. For each variable, the median and spread is indicated by a boxplot with the line in the box marking the median value, the box span indicating half of the observations and the whiskers indicating the range. Outliers (open circles) and extreme outliers (asterisks) are plotted individually at the end of the whiskers. A significant effect of age was found for the overall mean intima media thickness (p = 0.001) and the overall area % of smooth muscle actin (p = 0.027), independent from arterial location. Different characters above the boxplots indicate a significant difference between locations, independent of age. CaCCA: caudal common carotid artery; CrCCA: cranial common carotid artery; ProxAo: proximal aorta; DistAo: distal aorta; MA: median artery; EIA: external iliac artery; FA: femoral artery.

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  Fig 6. Immunohistochemistry for elastin and collagen type III (brown) of longitudinal sections through the vessel wall. The proximal aorta contains a higher area % of elastin and a lower area % of collagen type III compared to peripheral arteries. Magnification x400; bar = 250μm. Black arrows indicate nuclei of myocytes.

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  Fig 7. Typical cross-sectional rupture of the proximal aorta, close to the mounting side, which occurred predominantly in older horses (> 15 years) at high pressures (250–300 mmHg).

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  Fig 8. Pressure-area, pressure-compliance and pressure-distensibility curves of the proximal aorta, distal aorta, common carotid artery and external iliac artery in young (blue) and old horses (red). Dots and triangles represent individual values of young and old horses, respectively; full lines and dotted lines represent the fitted regression curves of young and old horses, respectively. Asterisks indicate a significant difference between old and young horses for the pressure-area, pressure-compliance or pressure-distensibility curves.