Passive Properties of Cerebral Arteries

The superior cerebellar artery was used to determine the passive properties of cerebral arteries. The most proximal segment of the right superior cerebellar artery was mounted onto glass cannulas in a pressure myograph setup. Both ends were secured on the cannulas by nylon sutures. Segments were straightened by adjusting the position of the cannulas at an intraluminal pressure of 100 mmHg. Artery segments were then equilibrated to 37 °C for 15 min in Ca²⁺-free MOPS-buffered PSS containing 1 · 10^–4 mol/L papaverine (Sigma-Aldrich). A charge-coupled device (CCD) camera connected to an inverted microscope (Nikon) was used to visualise the vessel. Inner and outer diameters were recorded using an in-house written program in MATLAB. The diameter of the superior cerebellar artery was assessed by determining the diameters at an increasing pressure from 1 to 150 mmHg and subsequent decreasing pressure from 150 to 1 mmHg using steps of 25 mmHg of 2 min each. Diameters were subsequently averaged over the two measurements. Distensibility was calculated as (1/ΔP) × (Δd/d) = fractional change in lumen diameter (Δd/d) per change in intraluminal pressure (ΔP). The wall cross-sectional area (CSA) was then calculated at an intraluminal pressure of 1 mmHg as: $$\text{Wall CSA}=0.5\mathrm{\pi }({{\mathrm{d}}_{\mathrm{Outer}}}^2-{{\mathrm{d}}_{\mathrm{Inner}}}^2)$$ where d_Outer is the outer diameter and d_Inner is the inner diameter of the vessel. Wall-to-lumen ratio was calculated at an intraluminal pressure of 150 mmHg as: $$\text{Wall-to-lumen ratio}=\frac{\text{(}{\mathrm{d}}_{\mathrm{Outer}}-{\mathrm{d}}_{\mathrm{Inner}})/2}{{\mathrm{d}}_{\mathrm{Inner}}}$$