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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. ASAIO Journal 2013; 59:374–379.

The therapeutic effects of carbon dioxide (CO2) on cutaneous tissue blood flow in the human have long been well recognized. Although CO2 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 CO2 on in-vivo microvasculature and blood flow rate by using an intra-vital video-microscopic 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 CO2 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 CO2 application. The CO2 reduced the pH of subcutaneous tissue and inhibited vascular smooth muscle contraction, resulting in dilatation of the vasculature of the skin microcirculation.

Liposomes are phospholipid vesicles that can serve as carriers of biologically active agents in vitro and in vivo. Here, we describe the movement of liposomes suspended with blood flowing in capillaries. Liposomes were coated with a polymer to extend their lifespan in rat mesenteric blood vessels and detected by fluorescent staining. Liposome activity was observed by intravital microscopy using a high-speed camera system at 5 and 60 min after liposome administration. Liposome velocity was determined using two-dimensional cross-correlation, and blood flow was measured by high-resolution PIV (particle image velocimetry). The results showed that the motion of polymer-coated liposome followed the phase averaged velocity distribution of heartbeats while flowing with red blood cells in microvessels. Liposome particles tend to move toward the near blood vessel wall in the low velocity of blood flow.

Blood flow in microvessels, such as arterioles, capillaries and venules, whose diameter ranges from 5 to 50 μm, is responsible for the maintenance of tissue and organ functions. The measurement of microvascular blood flow velocity with high measurement accuracy is essential for basic and clinical studies in the assessment of flow shear stress at the vascular wall in relation to substance exchange between blood and tissue. This paper aimed to evaluate the velocity field of blood flow in microvessels with high spatial and temporal resolution. By using micro PIV system, the velocity distributions of red blood cells flowing in rat mesenteric arterioles, including near the wall in the axisymmetric plane, were obtained. Ensemble averaged time-series of velocity profiles in the cross-sections were calculated for comparison. It was shown that the arteriole velocity profile was blunt in the center region of the vessel cross-section while it was steep in the near wall region.

Since endothelial cells are subject to flow shear-stress, it is important to determine the fine velocity distribution in microvessels for studies of mechanical interactions between blood and endothelium. Recently, particle image velocimetry (PIV) is a quantitative method of measuring velocity fields instantaneously in experimental fluid mechanics. The authors have been developed a high-resolution PIV technique, which can improve the dynamic range, spatial resolution and measurement accuracy, and applied it to visualized images in a blood flow.In this paper, the proposed method is applied to visualized images in micro tube using an intravital-microscope and high-speed digital video system in order to assess measurement accuracy. The obtained velocity profile corresponds to a theoretical value. Then the micro PIV system is applied to a blood flow of straight tube in rat mesentery arterioles.

Particle image velocimetry (PIV) is a quantitative method of measuring velocity fields instantaneously in experimental fluid mechanics. In order to improve the dynamic range, resolution and accuracy, the authors has proposed a new high-resolution PIV technique based on iterative cross-correlation and gradient method. The proposed method has the error of the order of 0.01 pixels.In this paper, the proposed method is applied to visualized images of the arteriole in the rat mesentery using the intravital-microscope and the high-speed digital video system. Time-series of the velocity profiles of the arteriole was obtained. Averaged velocity profiles shows the blood flow volume were constant at five vessel cross-sections. The arteriole velocity profile was blunt at center region of the vessel cross-section and sharp profiles at near wall region, this suggests the shear stress on the vessel wall is higher than expected. The results show that the proposed method is very useful to measure the blood flow velocity profiles with high accurate, temporal and spatial resolution.

A number of neurohumoral factors participate in the regulation of renal hemodynamics. Several methods have been developed to study directly the regulation of renal microcirculation. Here, we introduce an in vivo method to visualize renal microcirculation by using hydronephrotic rat kidney, a unique method originally developed by Steinhausen et al. More than 10 weeks after unilateral ureteral ligation in rats, the renal parenchyme becomes thinner and suitable for transillumination. After anesthesia, the hydronephrotic kidney was split at the greater curvature with a thermal cautery and then fixed in a water chamber containing Kreb's solution. The renal tissue was transilluminated and microscopically visualized using water immersion objectives. Renal microvessels including arcuate and interlobular arteries, afferent and efferent arterioles and glomerular capillaries could be easily observed on a display monitor at a final magnification of 2, 700 times. Topical application of angiotensin II elicited constriction of the interlobular artery and afferent and efferent arterioles dose-dependently. Thus, this preparation is a unique model allowing visualization of the whole renal vascular tree in vivo.

We developed a new circulation-assist device that can generate pulsatile assist flow synchronized with the patient’s diastolic phase. The device is composed of a drainage tube, a centrifugal pump, an oxygenator, and a sending tube. A portable magnetic valve device composed of a pulse generator and a tamper, which produces intermittent mechanical compression, is attached to the pillow of the sending tube. Preliminary animal experiments were conducted. No changes in the animals’ hemodynamics or any device problems were observed during a preliminary 48-h test run. Significant diastolic augmentation was confirmed. This new device may be useful in treating patients with severe heart failure and could be more useful than using percutaneous cardiopulmonary support (PCPS) alone.

Carpronium chloride, a hair growth reagent, is known to have a vasodilatory action, but its direct effect on the microcirculation has been known very primitively. This study was aimed to examine its effects on the vascular smooth muscles and blood flow in rat mesenteric arterioles using intravital videomicroscopy. After topically applying carpronium chloride on the microvasculature, we measured changes of diameter and blood flow in the arterioles. During its topical application, arteriolar vasodilation and flow increase were observed, while no change occurred in the mean systemic blood pressure. Our in vivo studies indicated that carpronium chloride achieved dilatation of vascular smooth muscle in the microcirculation.

Red blood cells (RBC) become deformed while flowing through capillaries. We captured images of blood flow in capillaries and of RBC in the rat mesentery using a high-speed camera at 2000 frames/s and then directly measured and estimated the deformation and velocity of RBC in a non-uniform capillary. The distribution of the capillary diameter was determined by image processing. We applied a deformation index and simple modeling to observe RBC deformation in capillaries. The average capillary diameter was approximately 6.2 microm, and the average velocity of RBC was about 1.85 mm/s. The average deformation index of RBC in the capillary was about 1.55. The present results showed that RBC in capillaries generally assume a specific shape depending on external forces such as the velocity of the blood flow and capillary diameter in vivo.

A new technique using particle image velocimetry (PIV) has been developed to evaluate the detailed velocity profiles of red cells flowing in microvessels. The microcirculation in rat mesentery was directly observed using high-speed videomicroscopy, and the images of red cells flowing in the mesenteric arterioles were recorded simultaneously with the arterial blood pressure. Based on the high-speed videomicroscopic images obtained, velocity vectors in single or branched arterioles were evaluated to obtain velocity profiles across the cross-section of arterioles. It was shown that in single and straight arterioles the velocity profile was blunt with a pit at the central region, and its pit was marked in bifurcation. The present technique enables us to analyze red cell velocity profiles up to 0.8 microm in the spatial resolution and 1 msec in the time interval.

This review discusses the present knowledge on visualization and blood flow measuring of the organ micro-vascular network using intra-vital microscopy. There are demonstrable microscopic images of the mesentery, stomach, intestine, liver, kidney, ear lobe, skin, nail bed, conjunctiva, and hair follicle during the anesthesia or no anesthesia. Methods for measuring blood cell velocity in microvasculature are dual-slit method, dual video window method, laser-Doppler velocimetry and PIV(particle image velocimetry).

A vasomotion activity in the mesentery of anesthetized rabbits were studied by simultaneous measurements of inside diameters at multiple sites in arterioles, precapillaries and their bifurcations. A frame-by-frame diameter determination technique was used with a microcomputer-assisted laser video disk recorder and video-image analysis system. Simultaneous intensity profiles across microvessels were continuously obtained. Applying an automatic wall surface tracer and a graphic editor to construct temporal sequences of intensity profiles, we obtained digitized data of inside diameters of microvessels, and implemented cross-correlation analysis between data sets to calculate phase differences of vasomotion at separated sites. The present analysis of the propagation of vasomotion showed that the vasomotion originated from the orifice of precapillaries at the bifurcations, spreading downstream in the precapillary. The vasomotion wave spreads both upstream and downstream along single arterioles from various origins of the vasomotion activity. The propagation velocity of vasomotion was 0.17 +/- 0.03 mm/sec (n = 19), and it became significantly slower through the branching points than along the arterioles. It is suggested that the vasomotion in terminal arterioles and precapillaries may spread through some mechanical transmission factors.

The total blood flow and microvessel blood flow in the mesentery and the intestine anesthetized rabbits were measured while systemic hemodynamics were altered by baroreceptor stimulation and by noradrenaline injection. The percent change of the total peripheral resistance (Rt) was greater than the change in resistance in the intestinal vascular bed (Ri) during baroreceptor stimulation. The capillary blood flow in the intestinal muscle layer (Qs) and villus (Qv) increased slightly while the intestinal arterial flow (Qa) and the arteriolar flow in the mesentery (Qm) decreased. These data indicated that Qs and Qv were not controlled by the sympathetic vasoconstrictor system. The percent change of Ri was greater than that of Rt during noradrenaline injection. Noradrenaline decreased Qa, but Qs and Qv were decreased while Qm was increased. These results show that noradrenaline stimulates alpha-adrenoceptors on small arteries and arterioles in the intestine. The observed Qm changed was in response to the systemic hemodynamic change caused either by the baroreceptor input or by noradrenaline.

Many different methods have been developed for the measurement of blood vessel dimensions, such as diameter and wall thickness. Especially for microvessels, optical and electronic techniques have been widely used [1–4]. With such techniques, the vessel must be observed under a transparent light source during the invasive operation. In contrast, for noninvasive evaluation of living tissue dimensions, ultrasonic echography is commonly used [5]. The diameter and wall thickness of the artery are visually observed from an echo signal chart [6] or by the ultrasonic echo-tracking method with a phased locked loop [7]. However, the conventional pulse-echo method has only a limited range of resolution, inversely proportional to the frequency bandwidth of the measurement system.

Arterioles in various vascular beds have been often observed to have nonuniform diameters along the vessel axis. The effect of nonuniformity of arteriolar diameter on vascular resistance was investigated using a theoretical model of blood flow in arterioles. Viscous flow of a Newtonian fluid in tubes with periodically changing diameters along the tube axis was analyzed by a finite element method based on the Stokes equations. Vascular resistance for the nonuniform tube was computed over a spatial period of the variation in diameter and was compared to resistance for a uniform tube with a constant diameter equal to the mean diameter of the nonuniform tube. In all cases, resistance for a tube with a nonuniform diameter was larger than resistance for a uniform tube with a diameter equal to the mean diameter of the nonuniform tube. Increases in the amplitude of the variation in diameter resulted in a rapid increase in resistance when the period of the variation remained constant. On the other hand, as the period of the diameter variation increased when amplitude remained constant, resistance decreased and approached the values obtained under the assumption of a Poiseuille flow at each cross section of the tube in the limit of an infinite period. Our theoretical model was applied to our previous in vivo studies of vessel diameter nonuniformity for rabbit mesentery arterioles in a contracted state. It was shown that vascular resistance calculated by our model was 2 to 11% higher than resistance obtained for a uniform tube with a diameter equal to the mean diameter of the arteriole.

An exact solution of the Navier-Stokes equation is given for a steady axisymmetrical stagnation-point flow of a viscous fiuid impinging obliquely on a plane wall. The flow structure around the point of stagnation is examined.