Haemodynamic evaluation of carotid artery disease

Effect of bilateral carotid occlusion on cerebral hemodynamics and perivascular innervation: An experimental rat model

We aimed to investigate the effect of chronic cerebral hypoperfusion on cerebral hemodynamics and perivascular nerve density in a rat model. Bilateral common carotid artery (CCA) ligation (n = 24) or sham‐operation (n = 24) was performed with a 1‐week interval. A subgroup (ligated n = 6; sham‐operated n = 3) underwent magnetic resonance imaging (MRI) before the procedures and 2 and 4 weeks after the second procedure. After termination, carotids were harvested for assessment of complete ligation and nerve density in cerebral arteries that were stained for the general neural marker PGP 9.5 and sympathetic marker TH by computerized image analysis. Five rats were excluded because of incomplete ligation. MRI‐based tortuosity of the posterior communicating artery (Pcom), first part of the posterior cerebral artery (P1) and basilar artery was observed in the ligated group, as well as an increased volume (p = 0.05) and relative signal intensity in the basilar artery (p = 0.04; sham‐group unchanged). Immunohistochemical analysis revealed that compared to sham‐operated rats, ligated rats had increased diameters of all intracircular segments and the extracircular part of the internal carotid artery (p < 0.05). Ligated rats showed a higher general nerve density compared to controls in P1 (10%, IQR:8.7–10.5 vs. 6.6%, IQR:5.5–7.4, p = 0.003) and Pcom segments (6.4%, IQR:5.8–6.5 vs. 3.2%, IQR:2.4–4.3, p = 0.003) and higher sympathetic nerve density in Pcom segments (3.7%, IQR:2.8–4.8 vs. 1.7%, IQR:1.3–2.2, p = 0.02). Bilateral CCA occlusion resulted in redistribution of blood flow to posteriorly located cerebral arteries with remarkable changes in morphology and perivascular nerve density, suggesting a functional role for perivascular nerves in cerebral autoregulation.

In vivo hemodynamic evaluation based on transverse Doppler measurements of blood velocities and vessel diameter

We have developed a method for simultaneously measuring the blood flow velocity distributions along a line perpendicular to the vessel wall and the instantaneous diameter of the common carotid artery. Thus, the wall shear rates and shear rate distribution across the arterial lumen could be computed accurately. In this method, transverse Doppler technique is combined with ultrasonic A echo-mode, using only one single crystal transducer. In order to satisfy the requirements of high spatial and velocity resolutions, especially extending to a very low velocity range in the case of low signal-to-noise ratio, a combination scheme of 10-MHz operating frequency, sample volume tracking, 12-bit A/D, 512-point fast Fourier transform with 5-kHz sample rate, spectrum average, variable threshold for bandwidth estimation, smoothing of velocity curves, and hardware was carefully designed. The velocity distribution measurements based on transverse Doppler spectrums were also validated under the steady flow conditions using a flow loop system. Results from this study show this ultrasonic system to be capable of measuring the shear rates at wall accurately and shear rate distributions across the common carotid arterial lumen.