Blood velocity

It is also possible to calculate the pressure gradients across heart valves using the Doppler principle to measure the blood velocity and entering the result into the Bernoulli equation. 

Penile erection occurs by relaxation of the smooth muscle of the corpus cavernosum, increasing blood flow into the penis and producing erection and rigidity. In a parallel fashion, vaginal pressure stimulation increases blood velocity and flow into clitoral arteries (Lavoisier et al. 1995). Cavernosal vasodilation is accomplished by neurotransmitters released from the cavernosal nerve and endothelial cells. One of the most important transmitters in this cascade is nitric oxide (NO), which induces synthesis of cyclic GMP from guanylate cyclase (Rajfer et al. 1992). Thus, ginkgo s vascular mechanisms could be responsible for some of the putative sexual effects. 

Equation 8.7 [6] was obtained to correlate the experimental data on membrane plasmapheresis, which is the MF of blood to separate the blood cells from the plasma. The filtrate flux is affected by the blood velocity along the membrane. Since, in plasmapheresis, all of the protein molecules and other solutes will pass into the filtrate, the concentration polarization of protein molecules is inconceivable. In fact, the hydraulic pressure difference in plasmapheresis is smaller than that in the UF of plasma. Thus, the concentration polarization of red blood cells was assumed in deriving Equation 8.7. The shape of the red blood cell is approximately discoid, with a concave area at the central portion, the cells being approximately 1-2.5 pm thick and 7-8.5 pm in diameter. Thus, a value of r (= 0.000257 cm), the radius of the sphere with a volume equal to that of a red blood cell, was used in Equation 8.7. 

The flow rate of blood through the heart is approximately 4-5lmin for adults. The typical mean blood velocity through the aorta (which is the largest artery with a diameter of 2-3 cm), when pumped from the left heart, is approximately 25 cm s"i (mean) the maximum velocity is approximately 60 cm s h The Reynolds number for the maximum velocity is about 3000. In general, the blood flow through arteries and veins is laminar in nature. In capillaries, the typical blood velocity is 0.5-1 mm s , and the Reynolds number is on the order of 0.001. 

Average blood velocity through the follow fiber v = 5.06 cm s Oxygen concentration difference in moll ... 

Brain perfusion refers to the microcirculation of the brain (see Chap. 6). Microcirculation comprises the blood circulation in capillary networks and the exchange of oxygen and nutrients between the blood and the brain tissue. The effectiveness of brain perfusion depends on blood pressure, blood velocity, characteristics of the capillary network, capillary wall permeability, and diffusion rates of oxygen and nutrients. In the healthy brain, perfusion is symmetrical, and is substantially higher in the CM than in the WM. It has been approximated that the CBF is about 80 ml/100 g/min in the CM, and 20 ml/100 g/ min in the WM. Brain perfusion is usually quantified in terms of ml/100 g (cerebral blood volume,... 

Since this model does not account for chemical transformation or diffusion in the axial direction, the rate of change of mass of solute at any location along the capillary is driven by advection alone. If the blood velocity were zero, then the total mass density at any location z would remain constant. 

Tafluprost significantly increases retinal blood flow and blood velocity in animal models. The improvement of ocular blood flow is thought to be relevant in glaucoma therapy, especially for normal-tension glaucoma patients since it is assumed that optic nerve damage is involved not only in mechanical compression caused by IOPbut also in impairment of ocular blood flow. 

The effects of tafluprost on IOP and retinal blood flow (RBF) were studied in adult cats [41]. A single drop of tafluprost was placed in one eye and IOP, vessel diameter, blood velocity, and RBF were measured simultaneously by laser Doppler velocimetry. Measurements carried out at 30 and 60min after dosing showed 16.1% and 21.0% IOP reduction, respectively, as well as 1% and 2.4% reduction in mean vessel diameter, respectively. The mean blood velocity increases were 17.4% and 13.7%, respectively, and the mean RBF increases were 20.7% and 18.8%, respectively, 30 and 60min after dosing. 

Khoobehi B, Aly OM, Schuele KM, Stradtmann MO, Peyman G. Determination of retinal blood velocity with respect to the cardiac cycle using laser-triggered release of liposome-encapsulated dye. Lasers Surg Med 2000 10 469-475. 

Sonkin PL, Sinclair SH, Hatchell D. The effect of pentoxyfylline on retinal capillary blood flow velocity and whole blood velocity. Am J Ophthalmol 1993 115 775-780. 

The bio-heat transfer equation with both of these assumptions has been solved for various tissue geometries and initial and boundary conditions (Shitzer and Eberhart, 1985). Because of scalar treatment of the convective heat transport by blood, the use of the bio-heat transfer equation has been questioned repeatedly (Charny, 1992). Considering tissue as porous media, Wulff (1974, 1980) introduced the blood velocity vector ub, in the bio-heat transfer equation. Unfortunately, the complex nature of the system defies any attempt to specify the circulation vector at the microscopic level. As non-invasive technologies (e.g., MRI) provide improved spatial resolution, it may be possible to incorporate such data numerically (Dutton et al., 1992). 

Since the consumption of oxygen by the fetus is not considered in this study, a maternal blood velocity change to a zero velocity would result in a fetal end capillary oxygen concentration that is equal to the... 

Unsteady-State Analysis Including Axial Dispersion. As in the previous unsteady-state analysis, the effects of placental barrier tissue oxygen consumption are neglected in this study. For the unsteady-state analysis of the model in which axial dispersion was included, one study was conducted. This study involved placing a step change on the maternal blood velocity to a new maternal blood velocity of 0.125 times the normal in an attempt to determine the effects of axial dispersion on the system at low maternal blood velocities. The discussion of this study is divided into the following two parts first, the effect of axial dispersion on the response of the fetal blood end capillary oxygen concentration, and second, the effect on the transient axial profiles. 

Figure 24 shows the axial oxygen concentration profiles for the fetal channel for the same transient conditions that were just discussed but for the case which neglected axial dispersion. These may be compared directly with the profiles in Figure 23 which represent the case which includes axial dispersion. As in the previous discussion, comparison of these figures shows that at this reduced maternal blood velocity the results are essentially the same, and the effects of axial diffusion are negligible. 

In our analysis the influence of blood flow differences in the different capillaries of the branched network were considered. A model structure was chosen which includes differences in capillary blood velocities in a ratio of 27 1. 

Imaging of flows of water and other hydrogen-containing liquids through pipes, orifices, and porous media is of considerable interest. In medicine, the distribution of blood velocity in the aorta can be charted in a noninvasive manner. An example relevant to chemical engineering is illustrated in Fig. 27 [192]. 

Structure Diameter (cm) Blood velocity (cm/s) Tube Reynolds number ... 

Structure Diameter (cm) Total cross-sectional Number area (cm ) Length (cm) Total volume (cm ) Blood velocity (cm/s) Tube Reynolds number ... 

Ultrasound is used chiefly to measure blood velocity, but recently research is based on the use of microbubbles to serve as an intravascular contrast agent to image blood flow at the level of the microcirculation, e.g in the myocardium. 

Va is the aortic blood velocity, m/s is the cross-sectional area of aorta, m ... 

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