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At least 163 records · Page 9Linked to original sources

PubMed2005

[Contribution of early systole to total antegrade flow volume in breath-hold phase-contrast flow measurements].

PURPOSE: To evaluate the contribution of early systole for the assessment of antegrade aortic flow volume by breath-hold velocity-encoded magnetic resonance (MR) flow measurements. MATERIALS AND METHODS: Expiratory breath-hold fast low-angle shot (FLASH) phase-contrast flow measurements (temporal resolution tRes 61 msec, shared phases) perpendicular to the proximal ascending aorta and short axis true fast imaging with steady-state precession (TrueFISP) cine MR ventriculometry (tRes 34.5 msec) were performed in ten healthy male volunteers on a 1.5 T MR system (Sonata, Siemens Medical Solutions). Antegrade aortic flow volume (AFV) and left ventricular stroke volume (LV-SV) were evaluated using Argus Ventricular Function and Argus Flow Software, version MR 2002B (Siemens Medical Solutions). A beta release of Argus Flow MR 2004A allowed interpolation of the flow up-slope during early systole to the preceding R-wave trigger. The respective intraindividual median differences between the AFV of each flow evaluation and LV-SV as well as between both AFV measurements were calculated and compared using the sign test for paired samples. RESULTS: Non-interpolated AFV significantly deviated from LV-SV (p = 0.006), underestimating the latter by 13.1 mL (13 %). Interpolating aortic flow during early systole significantly increased AFV by 10.8 mL (13 %) compared to the flow evaluation which did not take early systole into account (p = 0.006). AFV with interpolation of early systolic flow agreed well with LV-SV (median difference - 3.0 mL or - 3 %, respectively), and no significant difference between these measurements was found (p = 1.0). CONCLUSION: Flow during early systole contributes substantially to total forward flow volume in the ascending aorta. Interpolation of the early systolic up-slope is therefore recommended for the evaluation of breath-hold phase-contrast flow measurements.

Adult↗

PubMed1991

Increase in hepatic blood flow during early sepsis is due to increased portal blood flow.

Although hepatic blood flow increases significantly during early sepsis [as produced by cecal ligation and puncture (CLP)], it is not known whether this is due to the increase in portal or hepatic arterial blood flows. To study this, rats were subjected to CLP, after which they and sham-operated rats received either 3 or 6 ml normal saline/100 g body wt subcutaneously (i.e., all rats received crystalloid therapy). Blood flow in various organs was determined by using a radioactive microsphere technique at 5 and 20 h after CLP or sham operation. Portal blood flow was calculated as the sum of blood flows to the spleen, pancreas, gastrointestinal tract, and mesentery. Total hepatic blood flow was the sum of portal blood flow and hepatic arterial blood flow. A significant increase in portal blood flow and in total hepatic blood flow was observed at 5 h after CLP (i.e., early sepsis), and this was not altered by doubling the volume of crystalloid resuscitation after the induction of sepsis. In contrast, hepatic arterial blood flow during early sepsis was found to be similar to control; however, it was significantly reduced in late sepsis (i.e., 20 h after CLP). Cardiac output was significantly higher than the control in early sepsis. However, even in late sepsis, cardiac output and total hepatic blood flow were not significantly different from controls. These results indicate that the increased total hepatic blood flow during early hyperdynamic sepsis is solely due to the increased portal blood flow.

Animals↗

PubMed1999

Intraoperative flow rate measurements of T-grafts: calculating a flow reserve.

OBJECTIVE: To evaluate the inflow of the left internal thoracic artery (LITA) and the effect of adding a radial artery T-graft to distal LITA flow, and to calculate the LITA flow reserve. METHODS: Twenty-two patients underwent myocardial revascularization using the radial artery-LITA T-graft in which intraoperative flow measurements were recorded. An ultrasonic flowmeter was used to directly measure flow rates in the T-graft: 1) before completion of the distal anastomoses to measure maximum flow rates (free flow), and 2) after completion of distal anastomoses. RESULTS: The mean free flow rates of the LITA alone, radial artery graft alone, and T-graft (total flow) were 104 +/- 70, 151 +/- 89, and 230 +/- 102 ml/min, respectively. The mean flow rates on bypass of the distal LITA, radial artery graft, and T-graft after the distal anastomoses were completed were 24 +/- 16, 32 +/- 27, and 63 +/- 29 ml/min, respectively. The mean T-graft flow off bypass was 66 +/- 29 ml/min. The mean flow reserve was 70%. CONCLUSION: The LITA has a flow reserve by which proximal flow rates will increase to accommodate the addition of a radial artery T-graft without compromising LITA flow distal to the T anastomosis.

Adult↗

PubMed2003

Visualization of intraaneurysmal flow patterns with transluminal flow images of 3D MR angiograms in conjunction with aneurysmal configurations.

BACKGROUND AND PURPOSE: How the complex flow phenomena generated within unruptured cerebral aneurysms relate to the corresponding aneurysmal geometry is unknown. To estimate the interaction between flow patterns and morphologic features of unruptured cerebral aneurysms, we developed a method to visualize intraanuerysmal flow patterns with transluminal flow imaging of 3D MR angiograms in conjunction with aneurysmal configurations. METHODS: Transluminal images of the vessel lumen were reconstructed with use of a parallel volume-rendering algorithm by selecting information on the margin of lumina from the volume data sets of 3D time-of-flight MR angiograms. Transluminal flow images were then created by superimposing flow-related intraluminal information onto transluminal images. Intraaneurysmal flow patterns were evaluated in three cases of unruptured cerebral aneurysms, based on the animated display of transluminal flow images with stepwise extracted intraluminal volume data of signal intensity, in conjunction with the corresponding aneurysmal configurations depicted on 3D MR angiograms. RESULTS: Transluminal flow images showed 3D visualization of flow-related signal intensity distribution obtained from volume data of MR angiograms, so that qualitative information regarding intraaneurysmal flow patterns could be estimated with respect to morphologic features of cerebral aneurysms. CONCLUSION: Transluminal flow images of 3D MR angiograms allowed feasible visualization of intraaneurysmal flow patterns that were studied. More work is required to validate the technique and clarify the significance of being able to visualize intraaneurysmal flow patterns.

Aged↗

PubMed2004

Impact of the new Beckman Coulter Cytomics FC 500 5-color flow cytometer on a regional flow cytometry clinical laboratory service.

Calgary Laboratory Services (CLS) in Alberta, Canada, is the regional reference laboratory providing flow cytometry services for southern Alberta and southeastern British Columbia. As a busy reference flow laboratory we provide flow cytometry immunophenotyping for investigation and diagnosis of acute and chronic leukemias, lymphomas, immunodeficiencies, neuroblastoma, platelet disorders, and interstitial lung disease (ILD). Because of increasing workload and the continual effort to improve the service to our health care providers, CLS invested in the new Beckman Coulter Cytomics FC 500 5-color flow cytometer. In addition to time and labor savings due to reduced maintenance and operating system design, this new flow cytometer automates many of the previous manual steps involved in quality control and flow cytometric analysis. It also incorporates 2 lasers and is capable of measuring 5-color antibody combinations in a single tube, enabling us to reduce the number of tubes and overall costs, giving us better gating options for minimal residual disease analysis. We present the first published evaluation, an assessment of the overall productivity and cost impact of the new state-of-the-art Cytomics FC 500 flow cytometer. Implementation of the Cytomics FC 500 has resulted in a 20% reduction in reagent costs and shorter turnaround time for analysis and diagnosis. This instrument has allowed us to reduce our acute leukemia panel from 17 to 13 tubes, our lymphoma panel from 13 to 7 tubes, and our ILD panel from 4 to 2 tubes. The availability of 2 lasers provides more flexibility in choosing antibodies and conjugates to customize immunophenotyping panels. It also allows us to use the DRAQ5 dye and simultaneously analyze the immunophenotype and DNA content of cells with very little compensation. Many of the arduous, time-consuming flow operator tasks often associated with previous generation flow cytometry instruments, such as color compensation, list mode analysis, sample repeats, and interpretations, have been substantially reduced with the Cytomics FC 500 5-color flow cytometer. In conclusion the Cytomics FC 500 5-color flow cytometer is a major advance in flow cytometry instrumentation and has reduced our overall reagent costs by 20%, provided better information and speedier turnaround time to our health care professionals. It is an ideal flow cytometer for any busy clinical or research flow cytometry service.

Automation↗

PubMed1999

The flow regimes and the pressure-flow relationship in the canine urethra.

Classical fluid dynamics predicts that the pressure difference Deltap between any two points along a fully developed, viscous flow stream is linearly proportional to the flow rate Q (the Poiseuille relation). However, the passive urethral resistance relationship (PURR) widely used in modern urodynamics describes the pressure difference Deltap between two points along the urethra as linearly proportional to the flow rate squared (Q(2)). It is our hypothesis that this functional dependence may have its origins in the developing flow field within the urethra. That is, rather than being fully developed hydrodynamically, urethral flow is more likely representative of flow within the entry length of a rigid conduit. In our study, we used a canine model of the lower urinary tract to investigate the possibility of entrance effects. Although the most rigorous model of urethral fluid mechanics would include the elastic properties of the urethra into its configuration, the solutions from such a model would be unnecessarily complex and not readily lend themselves to the analysis of clinical data. Therefore, we chose to model the canine urethra at each instant in time as a rigid tube, and characterized its instantaneous flow using viscous flow theory for a rigid tube. All urodynamic analyses were performed on a surgically exposed urinary tract. Solid state pressure transducers were used to measure the intravesical and distal urethral pressures, whereas an ultrasonic flowmeter was used to obtain a simultaneous measure of the urinary flow rate. Detrusor contractions were induced using bilateral electrical stimulation of the pelvic nerves. Varying degrees of outlet obstruction were created using an inflatable sphincter cuff secured around the bladder outlet. The experimental data were evaluated using the well-known laminar entry length model of Atkinson and Goldstein. The peak Reynolds numbers under nonobstructed R(p)(e non-obs) and obstructed R(p)(e obs) outlet conditions ranged between 500 < R(p)(e non-obs) < 1,500 and 300 < R(p)(e obs) < 1,700, respectively. Under non-obstructed outlet conditions, the urethral diameters D and total lengths l(T) ranged between 1.5 mm < D < 2.5 mm and 75 mm < l(T) < 95 mm, respectively, whereas the peak entrance lengths L(p)(e non-obs) ranged between 55 mm < L(p)(e non-obs) < 215 mm. These data suggest that flow in the canine urethra under both non-obstructed and obstructed outlet conditions is typically laminar. The data further support the hypothesis that non-obstructed flows are predominantly entry length in nature. Entry length flows are fluid dynamically described by a quadratic pressure-flow relationship, thus suggesting a physiological basis for Schäfer's quadratic pressure-flow relationship, and therefore, for the PURR. Neurourol. Urodynam. 18:521-541, 1999.

Animals↗

PubMed2005

Prediction of graft flow impairment by intraoperative transit time flow measurement in off-pump coronary artery bypass using arterial grafts.

BACKGROUND: We assessed the validity of intraoperative transit time flow measurement (TTFM) in predicting graft flow abnormalities. METHODS: Intraoperative graft flow measurement using TTFM and early postoperative coronary angiography was performed in 58 patients who underwent total arterial off-pump coronary artery bypass. Five variables (flow pattern, mean flow, pulsatility index, insufficiency ratio, and fast Fourier transformation ratio) were measured and compared between 103 normal and 14 abnormal (occluded or competitive) grafts. RESULTS: The grafts anastomosed to the right coronary territories showed significantly less diastolic dominant pattern, lower mean flow and fast Fourier transformation ratio, and higher pulsatility index than grafts to the left coronary artery territories (p < 0.05). None of the abnormal grafts showed a diastolic dominant flow pattern. The abnormal grafts demonstrated significantly lower mean flow and fast Fourier transformation ratio and higher pulsatility index and insufficiency ratio than normal grafts (p < 0.05). When our criteria for detection of abnormal graft flow, [(1) systolic dominant or balanced pattern of the flow curve in the left coronary territories, systolic dominant pattern of the flow curve in the right coronary territories; (2) mean flow < 15 mL/min; (3) pulsatility index > 3 in the left coronary territories and > 5 in the right coronary territories; and (4) insufficiency ratio > 2%] were applied, the sensitivity and specificity of TTFM to detect the graft flow abnormality were 96.2% and 76.9%, respectively. CONCLUSIONS: Our data suggest that TTFM is a reliable intraoperative tool to predict graft flow impairment.

Coronary Angiography↗

PubMed1994

Recirculation reassessed: the impact of blood flow rate and the low-flow method reevaluated.

The recognition that during hemodialysis the blood urea nitrogen level in a peripheral vein differs substantially from that in an artery has made invalid the conclusions of prior studies based on the standard (peripheral vein) means of calculating recirculation. The increase in recirculation associated with an increase in blood flow may be artifactual, as may the reported inaccuracy of the two-needle low blood flow technique for measuring recirculation. Using a stop-flow technique to measure recirculation, a study was performed to reassess these issues. Sixteen patients were each studied once within the first 30 minutes of a standard hemodialysis session (mean, 3.78 hour) at routine blood flow (mean, 419 mL/min) and at 200 mL/min. Dialyzer afferent and efferent blood line samples were obtained, as were afferent samples after sequential, rapid reductions in blood flow to 200, 50, and 0 mL/min. The final two samples were obtained within 30 seconds of reducing blood flow to less than 200 mL/min. Blood flow had a significant (P = 0.03) although clinically minor effect on recirculation (mean, 13.9% at 419 mL/min v 10.2% at 200 mL/min). The low blood flow technique yielded the same results as the stop flow technique (stop flow technique 13.9% v low blood flow technique 13.2% at 419 mL/min, P = 0.76). We conclude (1) that the increase in recirculation associated with increased blood flow is substantially less than has been reported previously and is minimal in a well-functioning access, and (2) that a modified low blood flow (50 mL/min) technique for measuring recirculation yields results equivalent to those obtained using the stop flow technique.

Adult↗

PubMed1991

Effect of antiischemic therapy on coronary flow reserve and the pressure-maximal coronary flow relationship in anesthetized swine.

The effect of nifedipine (0.5, 1.0, and 2.0 micrograms/kg/min), metoprolol (0.1, 0.5, and 1.0 mg/kg), the beta 1-selective adrenoceptor partial agonist epanolol (10, 50, and 200 micrograms/kg), or equivalent volumes of isotonic saline (n = 6, in each group), on coronary blood flow capacity were studied in anesthetized swine. Intracoronary bolus injections of adenosine (20 micrograms/kg/0.2 ml) were administered without and during three levels of coronary stenosis, prior to and following each dose of drug, to obtain maximal coronary blood flows at different perfusion pressures in the autoregulatory range. Coronary perfusion pressures were varied by partial inflation of a balloon around the left anterior descending coronary artery. Special care was taken that the stenoses not lead to myocardial ischemia. Three indices of coronary blood flow capacity were used: absolute coronary flow reserve (ACFR, the ratio of maximal to resting coronary blood flow), the slope and the extrapolated pressure at zero flow (Pzf) of the pressure-maximal coronary flow (PMCF) relationship, and relative coronary flow reserve (RCFR, the ratio of maximal coronary blood flow with a stenosis to maximal coronary blood flow without a stenosis) at two of the three levels of stenosis. Nifedipine decreased ACFR from 4.5 +/- 1.9 to 1.9 +/- 0.3 (mean +/- SD; p less than 0.05), reflecting in part the increase in resting coronary blood flow. The nifedipine-induced changes in maximal coronary blood flow were not only due to a drop in perfusion pressure, as the slope of the PMCF relationship decreased from 2.27 +/- 0.49 ml/(min.mm Hg) to 1.54 +/- 0.51 ml/(min.mm Hg) (p less than 0.05), and Pzf decreased from 30 +/- 4 mm Hg to 20 +/- 7 mm Hg (p less than 0.05). Consequently, calculated maximal coronary blood flow was attenuated from 114 +/- 31 ml/min to 93 +/- 37 ml/min at 80 mm Hg, but was enhanced from 23 +/- 13 to 37 +/- 24 ml/min at 40 mm Hg coronary perfusion pressure. In concert with the change in the PMCF relationship, RCFR at equivalent severe stenosis increased from 0.33 +/- 0.06 to 0.47 +/- 0.10 (p less than 0.05). No changes were observed with metoprolol, epanolol, or saline. The effect of nifedipine on the PMCF relationship not only provides a mechanism for the drug's antiischemic action, but should also be considered in the interpretation of coronary flow reserve measurements in patients on nifedipine treatment.

Adrenergic beta-Antagonists↗

PubMed2006

A flow sensor suitable for use with split-flow ventilation--first preclinical data.

Volutrauma caused by artificial ventilation represents a major morbidity risk for premature infants. Our working group has recently developed an innovative "split-flow ventilation" system aiming at the reduction of tidal volumes (TVs). The main problem for the practical use of this system is the fact that conventional measurements of commercially available flow sensors are distorted by the split flow. In this study, we present the first preclinical data from testing an adapted flow sensor combination recognizing the split flow. A preterm infant test lung was conventionally ventilated, modified by insertion of a split-flow line. In addition to the customary flow sensor (FS-1), a second flow sensor (FS-2) was integrated into the split-flow line, and a third (FS-3) was placed at the exit of the test lung for reference measurements. The signals of all three flow sensors were read and processed by a computer. The program was set to graphically add up flow curves 1, 2, and 3 during one ventilation loop. After 10 runs, a mean curve of FS-1+2 was calculated and compared to the mean curve of FS-3. Furthermore, the mean TV of 10 runs measured by FS-1+2 was calculated and compared with the mean TV calculated by FS-3. The summation curve FS-1+2 proved identical to the reference curve FS-3. FS-1+2 yielded a TV of 6.6 +/- 0.01 mL (inspiratory) and 6.7 +/- 0.02 mL (expiratory). The corresponding values of FS-3 were 6.5 +/- 0.20 mL and 6.6 +/- 0.09 mL, respectively. According to our results, the presented flow sensor constellation allows exact flow measurements in the experimental setting and appears suitable for usage in a split-flow ventilation circuit under clinical conditions.

Equipment Design↗

PubMed1995

Flow structures at the proximal side-to-end anastomosis. Influence of geometry and flow division.

Flow structures were visualized in transparent polyurethane models of proximal side-to-end vascular anastomoses, using planar illumination of suspended tracer particles. Both the effects of geometry and flow division were determined under steady and pulsatile flow conditions, for anastomosis angles of 15, 30, and 45 degrees. The flow patterns were highly three-dimensional and were characterized by a series of vortices in the fully occluded distal artery and two helical vortices aligned with the axis of the graft. In steady flow, above a critical Reynolds number, the flow changed from a laminar regime to one displaying time-dependent behavior. In particular, significant fluctuating velocity components were observed in the distal artery and particles were shed periodically from the occluded artery into the graft. Pairs of asymmetric flow patterns were also observed in the graft, before the onset of the time-dependent flow regime. The critical Reynolds number ranged from 427 to 473 and appeared to be independent of anastomosis angle. The presence of a patent distal artery had a significant effect on the overall flow pattern and led to the formation of a large recirculation region at the toe of the anastomosis. The main structures observed in steady flow, such as vortices in the distal artery and helical flow in the graft, were also seen during the pulsatile cycle. However, the secondary flow components in the graft were more pronounced in pulsatile flow particularly during deceleration of the flow waveform. At higher mean Reynolds numbers, there was also a greater mixing between fluid in the occluded arterial section and that in the graft.

Arteries↗

PubMed1989

The diastolic hyperemic flow versus pressure relation. A new index of coronary stenosis severity and flow reserve.

The measurement of coronary flow reserve, traditionally calculated as the ratio of maximal hyperemic blood flow divided by basal flow, is difficult to interpret in serial studies because fluctuating hemodynamic parameters may affect either basal or hyperemic flow measurements. To determine the magnitude of this problem and to develop alternative approaches for measuring vascular reserve, 10 anesthetized dogs were instrumented with aortic and inferior vena cava occluders, electromagnetic coronary flow probes, and high-fidelity micromanometers in the left ventricle and aortic root. Coronary flow was measured in the basal state and during maximal hyperemia induced by a steady-state adenosine infusion. Observations were made in the absence of a stenosis and in the presence of two incremental degrees of subcritical stenosis produced by a rigid, external screw occluder. Several parameters of vascular reserve were determined: 1) coronary flow reserve (defined above), 2) mean hyperemic flow divided by mean aortic pressure, 3) mean hyperemic flow divided by the difference between mean aortic pressure and left ventricular end-diastolic pressure, and 4) the slope of the instantaneous relation between diastolic hyperemic flow versus pressure. Each parameter was measured during five steady-state pressure levels achieved by partial occlusion of either the inferior vena cava or the aorta and the levels ranged from 82 +/- 8 mm Hg (mean +/- SD) to 127 +/- 9 mm Hg during hyperemia. All measures of vascular reserve were found to be dependent on hemodynamic parameters such as heart rate and mean aortic pressure. The slope of the instantaneous relation between diastolic hyperemic flow and pressure, however, showed only minimal dependence on heart rate and, in contrast to coronary flow reserve measurements, distinguished between the normal and the two stenotic states. Further, this optimal performance of the hyperemic flow versus pressure slope index was shown in a model in which coronary flow and myocardial work were not independently controlled. This index provides a sensitive and reliable indication of subcritical stenosis severity that may have clinical applications.

Animals↗

PubMed1995

Effect of short-term cardiovascular conditioning and low-fat diet on myocardial blood flow and flow reserve.

BACKGROUND: Cardiovascular conditioning reduces resting myocardial oxygen demand by lowering systolic blood pressure and heart rate. Lower myocardial oxygen demand at rest would be expected to be associated with a decrease in resting myocardial blood flow and, consequently, an increase in myocardial flow reserve as the ratio of hyperemic to resting blood flow. However, the effect of controlled exercise together with a low-lipid diet on myocardial blood flow and flow reserve has not been examined in humans. METHODS AND RESULTS: Myocardial blood flow at rest and after dipyridamole-induced hyperemia (0.56 mg/kg i.v.) was quantified with [13N]ammonia and positron emission tomography in 13 volunteers before and upon completion of a 6-week program of cardiovascular conditioning and a low-fat diet. Exercise capacity and serum lipid profiles were also assessed at the start and finish of the program. Eight normal volunteers of similar age not participating in the conditioning program served as a control group. Cardiovascular conditioning lowered the resting rate-pressure product (8859 +/- 2128 versus 7450 +/- 1496, P < .001), serum cholesterol (217 +/- 36 versus 181 +/- 26 mg/dL), LDL cholesterol (140 +/- 32 versus 114 +/- 24 mg/dL), and triglycerides (145 +/- 53 versus 116 +/- 33 mg/dL, all P < .05). Exercise tolerance (metabolic equivalent of the task, METs) improved significantly from 10.0 +/- 3.0 to 14.4 +/- 3.6 (P < .01). Resting blood flow decreased (0.78 +/- 0.18 versus 0.69 +/- 0.14 mL.g-1.min-1, P < .05), whereas hyperemic blood flow increased (2.06 +/- 0.35 versus 2.25 +/- 0.40 mL.g-1.min-1, P < .05), resulting in an improved myocardial flow reserve (2.82 +/- 1.07 versus 3.39 +/- 0.91, P < .05). Overall, the myocardial flow reserve was significantly related to exercise performance (METs). In the control group, no changes in resting rate-pressure product, serum cholesterol levels, exercise performance, resting or hyperemic myocardial blood flow, or flow reserve were observed. CONCLUSIONS: Short-term cardiovascular conditioning together with a low-fat diet results in an improved myocardial flow reserve by lowering resting blood flow and increasing coronary vasodilatory capacity. These changes are associated with an improved exercise capacity and may offer a protective effect in patients with coronary artery disease.

Ammonia↗

PubMedDate not supplied

Effect of nitrogen flow on recovery of vision after excimer laser photorefractive keratectomy without nitrogen flow.

BACKGROUND: Excimer laser (VISX) photorefractive keratectomy was performed using nitrogen flowing through the ocular fixation ring. It was felt that eliminating nitrogen flow may provide faster early visual rehabilitation. METHODS: Two groups of 50 consecutive eyes underwent photorefractive keratectomy with (N2 flow) and without (no N2 flow) nitrogen flow, and were evaluated at 1 month postoperatively. RESULTS: There were more under- or overcorrections exceeding 1.00 diopter (D) in the N2 flow than in the no N2 flow groups. Eighteen eyes in the N2 flow and 11 in no N2 flow groups saw 20/50 or less, without correction. Fourteen eyes in the N2 flow and nine eyes in the no N2 flow groups lost two or more lines of best spectacle-corrected visual acuity. Four eyes in the N2 flow and none in the no N2 flow groups increased more than 1.00 D of astigmatism. CONCLUSION: The elimination of nitrogen flow in photorefractive keratectomy performed with the VISX laser appears to improve visual results in the early postoperative period.

Adult↗

PubMed1993

The effects of curvature on fluid flow fields in pulmonary artery models: flow visualization studies.

In vitro pulsatile flow visualization studies were conducted to assess the effects of varying radii of curvature of the right ventricular outflow tract (RVOT) and main pulmonary artery (MPA) on the flow fields in the main, right, and left pulmonary arteries of a one month lamb pulmonary artery model. Three glass flow-through models were studied; one with no curvature, one with the correct anatomic curvature, and one with an overaccentuated curvature on the RVOT and MPA. All other geometric parameters were held constant. Pulsatile flow visualization studies were conducted at nine flow conditions; heart rates of 70, 100, and 140 bpm, and cardiac outputs of 1.5, 2.5 and 3.5 l/min with corresponding mean pulmonary pressures of 10, 20, and 30 mmHg. Changes were observed in the pulmonary flow fields as the curvature of the outflow tract, heart rate and mean pulmonary pressure were varied. An increase in vessel curvature led to an increase in the overall radial nature of the flow field as well as flow separation regions which formed faster, originated further downstream, and occupied more of the vessel area. At higher heart rates, the maximum size of the separation regions decreased, while flow separation regions appeared earlier in the cardiac cycle and grew more quickly. Heart rate also affected the initiation of flow reversal; flow reversal occurred later in the cardiac cycle at lower heart rates. Both heart rate and mean pulmonary pressure influenced the stability of the pulmonary flow field and the appearance of coherent structures. In addition, an increase in mean pulmonary pressure increased the magnitude of reverse flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1976

[The value of the thermocouple in the measurement of the gastric mucosal blood-flow. The influence of the occlusion of the celiac artery and prostaglandin E1 on the gastric mucosal blood flow. An experimental study in animals (author's transl)].

The study has been carried out to ensure the positive evidence of the measurement of the gastric mucosal blood-flow with the aid of the thermocouple (heat-clearance technique). The experiments have shown that the suction pressure of 600 mm mercury column which was used to fix the Thermocouple to the mucosa was indispensable in order to assess the blood-flow in the entire depth of the mucosa. Changes in the mucosal blood-flow are measuured at the same rate in all quadrants of the gastric corpus. The measuring of the blood-flow of a well circumscribed area of the mucosa is therefore representative for the entire corpus. Vasopressin led to a significant reduction of the gastric mucosal blood-flow measured with heat-clearance as well aminopyrine-clearance. There was a linear correlation between the results of both methods. Vasopressin selectively reduces the blood-flow of the gastric mucosa but not of the submucosa, the muscular layer and the serosa. Therefore it seems to be probable that changes in mucosal blood-flow selectively can be measured with the aid of the thermocouple. After previous stimulation with pentagastrin neither mucosal blood-flow nor acid secretion of the stomach were influenced by the occlusion of the celiac artery by 25 %. The occlusion of the celiac artery by 50 % reduced significantly the pentagastrin-stimulated gastric mucosal blood-flow whereas the acid secretion was not influenced. Prostaglandin E1 at a dose rate of 2 mug/kg-h increased significantly arterial and mucosal blood-flow as well as acid secretion of the stomach. In comparison PGE1 administered at a dose rate of 4 mug/kg-h reduced significantly gastric mucosal blood-flow and gastric secretion. PGE1 at a dose rate of 8 mug/kg-h did not produce any significant changes in blood-flow and secretion. The results suggested that the changes of gastric secretion observed with PGE1 were the consequence of primary changes in the gastric mucosal blood-flow.

Animals↗

PubMed2000

Flow velocity and flow volume measurements in the extracranial carotid and vertebral arteries in healthy adults: reference data and the effects of age.

To establish reference data and to investigate the development of haemodynamics in the extracranial carotid and vertebral arteries, we performed a prospective study in 78 age- and gender-matched healthy adults from 20 to 85 y old. Angle-corrected flow velocities and luminal diameters were measured and waveform parameters and flow volumes calculated in all the arteries. Side-to-side differences and the influence of age on these parameters were also investigated. In the common carotid arteries, the internal carotid arteries and the vertebral arteries (CCA, ICA and VA, respectively) all flow velocities decreased significantly during ageing. The luminal diameter remained constant in all the carotid arteries, but increased slightly with age in the VA. An age-related decline of intravascular flow volume was observed in the ICA. Due to a pronounced decrease in end-diastolic flow velocity, the resistance index decreased in ICA and VA during ageing. There were no significant side-to-side differences in flow velocities and flow volumes in any of the extracranial arteries. The luminal diameters of the CCA, ICA and ECA were significantly smaller in women than in men. No relevant gender-related differences in flow velocities or waveform parameters were found in the extracranial arteries. There was no gender-linked difference in the flow volumes of the brain-feeding arteries and, in the ECA, flow volumes were significantly higher in men. Reference data on all flow velocities and waveform parameters, luminal diameters and flow volumes were established for different age groups between 20 and 85 y old. These data allow us to outline the development of cerebral haemodynamics during "benign ageing" and to utilise flow volume measurements in clinical practice, especially in patients with cerebrovascular diseases.

Adult↗

PubMedDate not supplied

Quantification of mitral flow by Doppler color flow mapping.

This study was performed to develop and validate Doppler color flow methods for quantifying forward transmitral flow rates and volumes with isovelocity aliasing contours. We undertook computer modeling of flows and studied an animal model with strictly controlled mitral flows. Finite element analysis was first used to establish the isovelocity surface contours reconstructed from the magnitudes and directions of the velocity vectors proximal to the normal mitral orifice. We modeled finite element-simulated Doppler color flow isovelocity surfaces and computed non-angle-dependent simulated isovelocities to compare them. Then 24 pharmacologically induced hemodynamic states in six sheep in which mitral regurgitation had been previously created surgically were studied. Three methods were used for peak flow (PF) computation: (1) the classic hemispheric methods: PF = 2 pi r2.aliasing velocity; (2) a modified hemispheric method: PF = 2 pi r2.aliasing velocity Vo/Vo-aliasing velocity; and (3) a new segment of sphere method: PF = pi p2.aliasing velocity, where p is the chord from the zenith of the first aliasing contour to the circumference at its base. Mean volume flow was also calculated in combination with phasic flow information from continuous-wave Doppler echocardiography: mean volume flow = PF.VTI/Vmax.heart rate, where VTI and Vmax are the velocity-time integral and maximal velocity of mitral inflow by continuous-wave Doppler echocardiography. Compared with the flow rates obtained by electromagnetic flowmeters, different correlations and agreements were achieved for these methods. Correlation (r = 0.86) and agreement were best for the segment of sphere method for computation of forward mean volume flows in our model. Color flow Doppler quantitation with a segment of sphere or modified hemispheric method appears applicable for quantification of forward transmitral valve flow rates and volumes with reasonable accuracy.

Animals↗