Real Blood Flow Research Articles

Blood Flow, Negative Pressure, and Hemolysis During Hemodialysis.

Blood flow, measured by an ultrasound flowmeter, and the extent of hemolysis were assessed during a single, routine dialysis in 100 patients. Before and after the hemodialysis session, blood was drawn for measurements of haptoglobin (HPT), hemoglobin (HGB), albumin (ALB), and lactate dehydrogenase (LDH). The average values were as follows: pump speed 510 mL/ min, real blood flow 422 mL/min, arterial chamber pressure -350 mm Hg, and venous chamber pressure 279 mm Hg. Haptoglobin concentrations were higher in patients with central vein catheters compared to patients with arteriovenous access. The meaning of this finding is unclear. Mean HPT concentrations increased significantly less during hemodialysis (2.37%) than concentrations of ALB (11.3%), HGB (9.17%), and LDH (18.2%), indicating that some hemolysis is present in all dialyses. In dialyses with arterial chamber pressures more negative than -350 the median concentration of ALB (8.70%) increased significantly more than the median concentration of HGB (7.99%). This indicates significantly more hemolysis in dialyses with more negative pressures compared to those with less negative arterial chamber pressures. Median LDH increased more in dialyses with more negative prepump chamber pressures (16.19% vs 13.78%), but not significantly; however, LDH increases were significantly higher than either HGB or ALB, thus indicating significantly more hemolysis in dialyses with more negative pressures compared to those with less negative arterial chamber pressures. Erythropoietin dose was not significantly different in patients dialyzed with more or less negative arterial chamber pressures (17 645 ± 1226 U/week vs 16 308 ± 1506 U/week). We conclude that dialyses with negative arterial chamber pressures greater than -350 mm Hg cause slightly higher hemolysis than dialyses with less negative arterial chamber pressures, but this increased hemolysis is not associated with an increased requirement of erythropoietin dose. Whether this increased hemolysis is of clinical significance is uncertain.

Proposition of a technique to assess the vasoactive effects of hemoglobin-based oxygen carrying solutions in vivo: preliminary results in the rabbit aorta.

Most of hemoglobin-based oxygen carriers (HBOCs) increase the blood pressure after injection in the blood stream by a mechanism involving one or more factors that contribute to the regulation of the vascular tone. Many techniques make it possible to study the vascular effects of HBOCs both in vivo and in vitro. The in vivo methods assess the blood pressure and some estimated regional blood flows (use of radioactive or colored microspheres). Measurements of the real vessel diameter and blood flow would be useful to understand hemoglobin-mediated vasoconstriction mechanism. Our purpose was to elaborate an experimental model in anesthetized rabbits to monitor the diameter and the blood flow velocity in the same vessel in order to calculate the absolute blood flow. The blood flow velocity (in cm/s) was assessed by pulsed Doppler velocimetry and the diameter (in mm) was assessed by a technique of Wall Tracking. The first results indicate that the method is well adapted to study the effects of resuscitative fluids (plasma and blood substitutes) on the aorta vascular tone after hemodilution or resuscitation from severe hemorrhage.

Real time blood flow imaging by spiral scan phase velocity mapping.

The work describes the development of a novel sequence that uses rapid spiral k-space sampling, combined with phase velocity mapping, for real time flow velocity imaging. The performance of the technique is assessed on phantoms for both through-plane and in-plane flows. The flow measurements compared well with those measured using a bucket and stopwatch. One advantage of the technique is that flow related signal loss is minimal due to the early acquisition of the center of k-space data. Flow artifacts were observed for in-plane flow and these were understood with the aid of computer simulations. In vivo studies involved cine velocity mapping in normal volunteers; aortic blood flow waveforms acquired by spiral scanning in two cardiac cycles compared well with data from a conventional gradient-echo sequence. Potential applications of the method are demonstrated by studying the response of aortic flow to physical exercise and the real time monitoring of aortic flow during a valsalver maneuver.

Current perspectives in the treatment of thrombotic disorders.

New trends in antithrombotic therapy should reside in a better adaptation, both in potency and in target to the involved thrombogenic mechanism. Thrombogenesis as hemostasis is the result of cooperation between plasma coagulation factors and platelet functions, and these two systems are themselves in equilibrated antagonism with the vessel wall, mainly endothelial cells. These triangular relations between coagulation factors, platelet functions, and endothelial cell reactivity are quantitatively regulated by flow conditions. The relative importance of each of these protagonists in the genesis of vascular thrombosis varies along the vascular tree, mainly due to changes in flow characteristics, and explain the usual separation between venous and arterial thrombosis: venous thrombosis involves mainly coagulation factors and the vascular fibrinolytic response whereas arterial thrombosis involves the thromboresistant characteristics of the endothelial cell membrane and platelet functions. The real blood flow characteristics may be altered by local disease and influences the relative involvement of coagulation and fibrinolytic factors, platelet functions, and endothelial cells. Prevention of thrombosis must take into account all these phenomena and must be targeted to the predominant factor or factors. Depending on the local conditions, the therapeutical goal can be: (1) limitation of platelet functions or coagulation factors; (2) stimulation of thromboresistant properties of the endothelium (mainly its profibrinolytic characteristics); and (3) modification of the flow conditions. Several targets can be associated: the level of inhibition or stimulation of a function depends on the dysequilibrium, and efficient prevention does not always require complete inhibition of a function. Once a thrombus has developed, antithrombotic treatment will prevent its extension, and thrombolytic therapy will try to restore vascular patency. Once patency has been restored antithrombotic therapy is still needed to prevent recurrence of the thrombus. Even if the main targeting is on platelets, the choice in the molecule to be clinically used must be defined by the function of the platelet involved: thrombogenesis or vasospasm, and even by the metabolic pathway predominantly activated. In coagulation strategy, differences must be drawn between antithrombotic therapy directed against thrombin formation, complexes of coagulation, free enzymes or activation phases. In thrombolytic therapy all procedural uses of extrinsic thrombolytic agents (natural, modified, or artificial), increase of susceptibility to endogenous thrombolytic systems, and stimulation of endogenous thrombolytic activity do not bear the same efficiency. As a consequence, the responsibility for clinical use of new molecules with more specific activity can allow more efficient antithrombotic therapy directed at the condition of an indication targeted at the exact mechanisms involved.(ABSTRACT TRUNCATED AT 400 WORDS)

Doppler echocardiographic flow characteristics of isolated patent ductus arteriosus: Better delineation by Doppler color flow mapping

Eighteen infants and children with isolated ductus arteriosus and various hemodynamic states were examined with the Doppler color flow mapping technique to study the flow patterns of the patent ductus and its adjacent structures. Direct visualization of the ductus was achieved in all patients. All ductal flow was shunting left to right from the descending aorta to the pulmonary artery even in the presence of significant elevation of pulmonary artery pressure. However, transient bidirectional shunting was observed in two patients on serial studies. Disturbed systolic and diastolic flows were demonstrated within the ductus in each case.The blood flows in the main pulmonary artery consisted of three distinguishable areas: 1) a characteristic high velocity turbulent retrograde ductal jet throughout the entire cardiac cycle, located in the anterolateral aspect of the main pulmonary artery; 2) nonspecific low velocity retrograde late systolic and early diastolic flow, located in the posteromedial aspect of the mata pulmonary artery; and 3) low velocity forward systolic and diastolic flow, occupying the remaining area of the pulmonary artery. The blood flows in the descending aorta pear the ductal orifice consisted of disturbed systolic and diastolic flows in a reversed direction.By providing detailed real time blood flow information with simultaneous imaging of the ductus, Doppler color flow mapping greatly facilitates the detection of a small ductal shunt. This technique also allows detection of a bidirectional or right to left ductal shunt.

Measurement of optic nerve blood flow with iodoantipyrine: Limitations caused by diffusion from the choroid

Radioactively labelled iodoantipyrine has been used to measure optic nerve blood flow in experimental animals. The reliability of blood flow measurements with this technique may be limited by diffusion of tracer from the nearby choroid. The activity of tracer in the peripapillary choroid and anterior optic nerve was measured in a series of in vivo optic nerve blood flow experiments in cats. The diffusion of iodoantipyrine into cat optic nerve segments was also measured in vitro, and a model for diffusion of tracer from the peripapillary choroid into the anterior optic nerve was developed. The activity profiles established by simple diffusion experiments were similar to the activity profiles in the anterior optic nerve established by blood flow experiments. Apparent blood flow measurements in the anterior optic nerve made with iodoantipyrine may be largely influenced by tracer diffusion from the nearby choroid. For measurements of tracer activity which are statistically similar between control and experimental optic nerve samples, and with a total diffusion time of 60 sec (a well-done experiment), real blood flow in the experimental sample may differ by as much as 60% from the control at a point 50 μm from the choroid. At 300 μm from the choroid, the maximum undetectable difference because of diffusion declines to approx. 12%. These estimates assume an autoradiographic technique which can reliably detect tissue tracer activity differences of ± 10%. Measurements of optic nerve blood flow made with diffusible tracers are affected by diffusion from the choroid and should be reported with estimated limits of reliability.

Localized real time blood flow measurements

A novel method for real time, localized, flow measurements is applied to blood flow in human fingers. Results for arterial and venous flow in normal subjects and patients with abnormal blood circulation are presented. Effects of blood flow regulation by the autonomic nervous system have been observed. Stricture of the digital arteries could be clearly demonstrated in a patient with Raynaud's phenomenon. Experimental signals due to pulsatile flow in a model system can be simulated in a quantitative way. The calibration, however, depends on the actual spin-spin relaxation time and the shape of the pulsatile flow vs. time curve. Due to these limitations, the volume flow rate can be measured with a relative error of approximately +/- 25%.