Blood flow velocity profile in microvessels is essential for in vivo studies of substance exchange between blood and tissue. This paper was aimed to investigate the temporal and spatial variations in the velocity profile of red blood cell (RBC) flow in arterioles with both bifurcation and confluence in the rat mesentery, using a particle image velocimetry (PIV). The microcirculation in rat mesentery was observed under a microscopic system with a high-speed digital camera. The images of RBCs flow in microvessels were recorded simultaneously with the arterial blood pressure. Based on the high-speed video images, instantaneous velocity vectors of RBCs in arterioles with bifurcation and confluence were evaluated using a high spatial-resolution PIV algorithm. Then, the time-averaged and ensemble-averaged velocity profiles over the cross-section were calculated from the proximal through the bifurcation to the distal to the confluence. The velocity profile of RBCs showed two peaks at bifurcation and confluence, respectively. The double peaks were most marked at the apex of bifurcation, but not so much marked at the confluence. The variation of centerline velocity showed that the length of vessel under the influence of bifurcation or confluence, was approximately 1.5 times the diameter at the proximal to the apex of bifurcation, but its length was reduced significantly at the distal of confluence.
The therapeutic effects of carbon dioxide (CO 2 ) on cutaneous tissue blood flow in the human have long been well recognized. Although CO 2 has vasodilator action, in-vivo evidence of its action on the microcirculation of the skin, and of its mechanism, has rarely been reported. We studied the direct effects of CO 2 on in-vivo microvasculature and blood flow rate by using an intra-vital videomicroscopic system. Brown Norway rats were anesthetized by intraperitoneal administration of alpha-chloralose and urethane. In order to measure inner diameter and red blood cell velocity (Vrbc) for a microvessel, the dorsal skin window was draped on an observation box placed inside a bath. Vrbc was derived from the cross-correlation function of paired segments of dual-window intensity in the video of microvascular images of the subcutaneous tissue. We measured pH in subcutaneous tissue by making a dorsal skin tube. After topical application of CO 2 dissolved in water via the skin of the rat, we observed both vasodilatation and an increase in blood flow of the micro vessels. The pH of subcutaneous tissue also decreased after CO 2 application. The CO 2 reduced the pH of subcutaneous tissue and inhibited vascular smooth muscle contraction, resulting in dilatation of the vasculature of the skin microcirculation.
Currently, nonpulsatile selective cerebral perfusion for cerebroprotection against thoracic aortic aneurysm is used in clinical settings. We performed synchrotron radiation microangiography to determine the effects on selective cerebral perfusion modulation by pulsatile flow. We established cerebral perfusion at normothermia and severe hypothermia in anesthetized rats, during which cerebral angiography was performed. NG-nitro-L-arginine-methyl ester hydrochloride (L-NAME) was administered to determine the effect of pulsatile flow with nitric oxide synthesis. In comparison with nonpulsatile flow, the relative diameters of small internal carotid artery were 132.11 ± 5.49% and 114.96 ± 4.60% during pulsatile flow at normothermia and severe hypothermia (p < 0.05). The angiographic scores, an indicator of vessel count, for nonpulsatile and pulsatile flow at normothermia were 0.198 ± 0.013 vs. 0.258 ± 0.010 (p < 0.001) and those at severe hypothermia were 0.158 ± 0.017 vs. 0.214 ± 0.015 (p < 0.01), respectively. In comparison with nonpulsatile flow, the relative internal carotid artery diameters during pulsatile flow with and without L-NAME were 98.50 ± 1.7% vs. 114.96 ± 4.6%, respectively, during severe hypothermia. These results show that pulsatile flow is effective in increasing blood vessel diameter, number of vessels, and perfusion distribution range in the rat model and that it was more effective at normothermia during nitric oxide production.
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