Numerical Simulation of the Effect of Sodium Profile on Cardiovascular Response to Hemodialysis

PURPOSE: We developed a numerical model that predicts cardiovascular system response to hemodialysis, focusing on the effect of sodium profile during treatment. MATERIALS and METHODS: The model consists of a 2-compartment solute kinetics model, 3-compartment body fluid model, and 12-lumped-parameter representation of the cardiovascular circulation model connected to set-point models of the arterial baroreflexes. The solute kinetics model includes the dynamics of solutes in the intracellular and extracellular pools and a fluid balance model for the intracellular, interstitial, and plasma volumes. Perturbation due to hemodialysis treatment induces a pressure change in the blood vessels and the arterial baroreceptors then trigger control mechanisms (autoregulation system). These in turn alter heart rate, systemic arterial resistance, and cardiac contractility. The model parameters are based largely on the reported values. RESULTS: We present the results obtained by numerical simulations of cardiovascular response during hemodialysis with 3 different dialysate sodium concentration profiles. In each case, dialysate sodium concentration profile was first calculated using an inverse algorithm according to plasma sodium concentration profiles, and then the percentage changes in each compartment pressure, heart rate, and systolic ventricular compliance and systemic arterial resistance during hemodialysis were determined. A plasma concentration with an upward convex curve profile produced a cardiovascular response more stable than linear or downward convex curves. CONCLUSION: By conducting numerical tests of dialysis/cardivascular models for various treatment profiles and creating a database from the results, it should be possible to estimate an optimal sodium profile for each patient.

Effects of an Extra-corporeal Life Support System Using a Dual Pulsatile Pump

PURPOSE: The purpose of this study was to observe and compare the changes in the patterns of hemodynamic and blood profiles on the circuit of Extra-corporeal life support system (ECLS) by using a dual pulsatile pump (T-PLS). METHODS: An acute heart failure model using partial pulmonary artery banding was constructed in 12 piglets (20 -25kg). The animals were divided into centrifugal (n=6) and dual pulsatile pump (n=6) group. Each animal was placed on an ECLS system with a membrane oxygenator bypassing the right atrium and the aorta for 2 hours under general anesthesia. The parameters mainly observed were intra-circuit pressure changes, arterial pulsatility (pulse pressure), plasma free hemoglobin, hemodynamic changes, and other blood profiles. The parameters obtained just prior to the bypass were compared with the corresponding parameters obtained two hours after the bypass. RESULTS: Before bypass, the parameters were statistically the same between the groups. Two hours after the bypass, no significant differences were observed between the groups in ABGA, VBGA, AST/ALT, BUN/Cr, and electrolytes; the plasma free hemoglobin was 14.8+/-4.7 g/dl in the dual pulsatile group and 19.1+/-9.1 g/dl in the centrifugal group (p=NS). The pulse pressure was higher in the dual pulsatile pump than in the centrifugal pump group (35+/-8 vs. 11+/-7 mmHg, p=0.0253 mmHg). The highest circuit pressure was generated at the inlet of the membrane oxygenator and was higher in the dual pulsatile group than in the centrifugal group (173+/-12 mmHg vs. 222+/-8 mmHg, p=0.0000). CONCLUSION: The results demonstrate that a dual pulsating mechanism lessens blood cell trauma while providing physiologic pulsatile blood flow. The ECLS system using a dual pulsatile pump (T-PLS) can be useed as an effective and safe driving motor for an ECLS.

MR Angiography of Stenosis and Aneurysm Models in the Pulsatile Flow: Variation with Imaging Parameters and Concentration of Contrast Media

PURPOSE: The image quality of magnetic resonance angiography (MRA) varies according to the imaging techniques applied and the parameters affected by blood flow patterns, as well as by the shape of the blood vessels. This study was designed to assess the influence on signal intensity and its distribution of the geometry of these vessels, the imaging parameters, and the concentration of contrast media in MRA of stenosis and aneurysm models. MATERIALS AND METHODS: MRA was performed in stenosis and aneurysm models made of glass tubes, using pulsatile flow with viscosity and flow profile similar to those of blood. Slice and maximum intensity projection (MIP) images were obtained using various imaging techniques and parameters ; there was variation in repetition time, flip angle, imaging planes, and concentrations of contrast media. On slice images of three-dimensional (3D) time-of-flight (TOF) techniques, flow signal intensity was measured at five locations in the models, and contrast ratio was calculated as the difference between flow signal intensity (SI) and background signal intensity (SIb) divided by background signal intensity or (SI-SIb)/SIb. MIP images obtained by various techniques and using various parameters were also analyzed, with emphasis in the stenosis model on demonstrated degree of stenosis, severity of signal void and image distortion, and in the aneurysm model, on degree of visualization, distortion of contour and distribution of signals. RESULTS: In 3D TOF, the shortest TR (36 msec) and the largest FA (50 degree) resulted in the highest contrast ratio, but larger flip angles did not effectively demonstrate the demonstration of the peripheral part of the aneurysm . Loss of signal was most prominent in images of the stenosis model obtained with parallel or oblique planes to the flow direction. The two-dimensional TOF technique also caused signal void in stenosis, but precisely demonstrated the aneurysm, with dense opacification of the peripheral part. The phase contrast technique showed some distortions in the imaging of stenosis, and partial opacification of ananeurysm. Contrast enhanced imaging offered no advantages in the imaging of the stenosis, but was excellent for demonstration of the aneurysm. CONCLUSION: This study demonstrates a spectrum of MRA images of stenosis and aneurysm model according to variation in imaging parameters and the concentration of contrast media.

Effects of digital image processing on the detection of simulated lesion in chest radiographs: an experimental study

The receiver operating characteristic (ROC) curve analysis was done to evaluate the effects of digital image processing techniques on the detectability of simulated pulmonary nodules and cysts in chest radiographs. Image processing techniques used were the contrast inversion, unsharp masking, and filtered equalization method. Simulated pulmonary nodules and cysts were generated by the computed program using Turbo-C language for personal computer. Each processed and unprocessed image sets of sixty images with pulmonary nodules and cysts and one hundred and twenty normal images were analyzed by three board-certified radiologists and four senior residents training in diagnostic radiology by five rating category. Area under the ROC curve was calculated using the trapezoidal rule. Mean area under the ROC curve of seven radiologists of the unprocessed image was 0.6360±0.0583, contrast inversion was 0.5660±0.0478, unsharp masking was 0.7534±0.0355 and filtered equalization was 0.6915±0.0472. Unsharp masking(p<0.01) and filtered equalization image(p<0.05) was statistically significant than unprocessed image. Digital chest radiographs processed by the unsharp masking method significantly increased the detectability of simulated pulmonary nodules and cysts overlapped with mediastinum and pulmonary cysts in free lung fields.

An Experimental Study on the Effect of Reperfusion on Changes of rCBF in Focal Cerebral Ischemia

Reperfusion into focal ischemia using a transorbital snare ligature was studied in 20 unanesthetized cats following middle cerebral artery(MCA) occlusion of 1 to 6 hours duration. Changes of a regional cerebral flow(rCBF) were investigated upon with a hydrogen clearance method in the center and periphery of the MCA territory, which were correlated with the size of infarct delineated by a 2% triphenyl tetrazolium chloride solution and with the occurrence of severe brain edema or hemorrhagic infarct. The results were as followings: 1) Post-ischemic hyperperfusion was usually found after 1 hour occlusion of MCA followed by 2 hours recirculation. Final rCBF, however, reached pre-occlusion value and little or no infarct was found. 2) In the 2 hours occlusion-reperfusion group, hypoperfusion after reopening of MCA was regularly found in both the center and the periphery of ischemia, which was well contrasted with hyperperfusion in the 1 hour occlusion group and was accompained by evident but mild infarcts. 3) After 4 and 6 hours occlusion, there was usually evident post-ischemic hyperperfusion soon followed by development of severe hypoperfusion and a higher grade of infarct and hemispheric swelling was found. 4) Final hypoperfusion after transient MCA occlusion was observed only after ischemic periods lasting 2 hours or more irrespective of preceding post-ischemic hyperperfusion and was only related to the duration of the occlusion and not to the degree of blood flow disturbance. 5) Spontaneous hyperemia during occlusion was found in 3 of the 5 cats used in each of the 4 and 6 hours occlusion groups, in which there was marked hyperperfusion after reopening of MCA followed by severe hypoperfusion and transtentorial herniation associated with resulting extensive hemorrhagic infarct and marked hemispheric swelling. 6) Hemorrhagic infarcts were found in one cat of the 4 hour-occlusing group and two of the 6 hour-occlusion group, all of whom showed early hyperemia before reperfusion predictable of such a detrimental result. 7) These data indicate that potential hazard for surgical early revascularization in the acute stage of ischemic stroke should be considered in case profound ischemia had already progressed for 4 hours or more and especially when hyperemia during the initial stage of severe ischemia is observed at the center and the periphery of the ischemic area expected.

A Study of Regional Myocardial Function by Biplane Coronary Cineangiogram

The analysis of regional myocardial function is important for the evaluation of myocardial performance. We evaluated whether the motion images of the coronary bifurcation points can be used for computation of the regional deformation and the regional wall stress. In 5 mongrel dogs, 4 to 7 lead markers were implanted adjacent to the bifurcarion points of coronary artery. Left ventricular pressure curve was obtained, and left ventriculography was performed to measure the major and minor axes of the left ventricle. Afterthen, biplane coronary arteriography was performed. The motion images of the lead markers and the corresponding coronary bifurcation points were used as landmarkers for the kinetic analysis of the regional wall deformation and wall stress. The results of the analysis using two kinds of landmarkers were well correlated(P<0.001). Analysis of the diagnosis biplane coronary cineangiograms of each patient group demonstrated that quite difference wave forms between the normally perfused segment and the underperfused segments. In group I there was no coronary arterial narrowings and no regional wall motion abnormalities. Their mean and peak wall thicking were 10.10+/-9.28% and 47.99+/-20.70%. And their peak and mean values of circumferential and longitudinal wall stresses are as follows; 2.70+/-0.74x10(5)dyn/cm2, 2.34+/-0.71x10(5)dyn/cm2, 0.84+/-0.21x10(5)dyn/cm2, 2.34+/-0.71x10(5)dyn/cm2, 0.84+/-0.21x10(5)dyn/cm2 and 0.64+/-0.13x10(5)dyn/cm2. Of 5 male patients having coronary arterial disease with regional wall motion abnotmalities(Group III), 2patients have single vessel disease, 2 paitents have 2 vessel disease. In subgroup b of group III, there was a significant decrease of regional wall thickening(mean and peak value; 0.54+/-9.91%.14.87+/-12.055; P<0.001 vs. group I), and increasing tendency of regional wall stresses. Using biplane coronary cineangiogram, which is routine diagnostic procedure in coronary artery disease, this method can valuate regional myocardial function. And this method can evaluate regional myocardial function. And this method will be especially useful, when serial coronary cineangiograms are needed for serial evaluation of patients, such as before and after percutaneous transluminal coronary angioplasty, coronary arterial bypass graft surgery, etc.