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At least 73 records · Page 4Linked to original sources
PubMed2002

Size separation of supermicrometer particles in asymmetrical flow field-flow fractionation. Flow conditions for rapid elution.

The performance of lift-hyperlayer asymmetrical flow field-flow fractionation using rapid elution conditions was tested through the separation of standard polystyrene latex particles of diameters from 2 to 20 microm. Optimization of flowrates was studied not only in order to obtain efficient and rapid separation, but also to work under conditions of various shape and steepness of the axial flow velocity gradient. Using extreme flow conditions, the five widely spaced particle sizes, 20.5-, 15.0-, 9.7-, 5.0-, and 2.0-microm diameter, could be resolved in 6 min, whereas for the narrower size range of 20.5-5.0 microm, 1 min was enough. The size selectivity in the size range 9.7-2.0 microm was studied as a function of flowrates and particle size and was found to be constant. A particle trapping device made it possible to separate particles of sizes > 10 microm, which has previously proven to be difficult in asymmetrical channels.

Chemical Fractionation↗
PubMed2005

Delineating the guide-wire flow obstruction effect in assessment of fractional flow reserve and coronary flow reserve measurements.

Hemodynamic analysis was conducted to determine uncertainty in clinical measurements of coronary flow reserve (CFR) and fractional flow reserve (FFR) over pathophysiological conditions in a patient group with coronary artery disease during angioplasty. The vasodilation-distal perfusion pressure (CFR-p(rh)) curve was obtained for 0.35- and 0.46-mm guide wires. Our hypothesis is that a guide wire spanning the lesions elevates the pressure gradient and reduces the flow during hyperemic measurements. Maximal CFR-p(rh) was uniquely determined by the intersection of measured CFR and calculated p(rh) of native and residual epicardial lesions in patients without microvascular disease, during angioplasty. Extrapolation of the linear curve gave a zero-coronary flow mean pressure (p(zf)) of approximately 20 mmHg and a corresponding p(rh) of 55 mmHg in the native lesions, which coincided with the level that causes ischemia in human hearts. On this linear curve, values of CFR and FFRmyo (pathophysiological condition) and CFRg and FFRmyog (in the presence of the guide wire) were obtained in native and residual lesions. A strong linear correlation was found between CFR and CFRg [CFR = CFRg x 0.689 + 1.271 (R2= 0.99) for 0.46 mm and CFR = CFRg x 0.757 + 1.004 (R2= 0.99) for 0.35 mm] and between FFRmyo and FFRmyog [FFRmyo = FFRmyog x 0.737 + 0.263 (R2= 0.99) for 0.46 mm and FFRmyo = FFRmyog x 0.790 + 0.210 (R2= 0.99) for 0.35 mm]. This study establishes a strong correlation between CFR and CFRg and between FFRmyo and FFRmyog, which could be used to obtain the true state of occlusion in the coronary artery during angioplasty.

Angioplasty, Balloon, Coronary↗
PubMed2000

Diastolic fractional flow reserve to assess the functional severity of moderate coronary artery stenoses: comparison with fractional flow reserve and coronary flow velocity reserve.

BACKGROUND: Coronary blood flow occurs mainly during the diastolic phase of each cardiac cycle and is mainly dependent on diastolic driving pressure, especially in the left anterior descending coronary artery (LAD). We hypothesized that calculation of the ratio of the diastolic driving pressure of a stenotic LAD to its normal value, namely diastolic FFR (d-FFR), might provide precise insight into the mechanism of FFR for assessment of the functional severity of the stenosis. We compared d-FFR with FFR, coronary flow reserve (CFR), and exercise myocardial thallium scintigraphy in an lesion of intermediate severity. METHODS AND RESULTS: The study population consisted of 46 consecutive patients with a moderate stenosis in the LAD in whom simultaneous measurements of aortic pressure, left ventricular pressure, and coronary pressure distal to the stenosis were obtained. Coronary flow velocity was successfully measured with a Doppler guidewire in 37 of the 46 patients. Values for FFR, d-FFR, and CFR in the noninvasive test-positive group were significantly lower than those in the negative group. With cutoff values of 0.75, 0.76, and 2.0 for FFR, d-FFR, and CFR, sensitivities were 83.3%, 95.8%, and 88.2% and specificities were 100%, 100%, and 95.0%, respectively. CONCLUSIONS: The close similarity of the sensitivity and specificity of FFR and d-FFR, around almost identical cutoff values (0.75 versus 0.76), confirms the physiological validity of FFR as a clinical standard. In clinical practice, FFR remains the index of choice for assessment of the functional severity of moderate coronary artery stenoses.

Blood Flow Velocity↗
PubMed2001

Flow around cells adhered to a microvessel wall II: comparison to flow around adherent cells in channel flow.

The flow around adherent cells in a parallel-plate channel and that in a circular cylindrical tube are numerically analyzed, and their effects on the adherent cells are compared. The cells are modeled as rigid spherical particles and they are assumed to be attached to a wall of a 2D channel uniformly in a square array, or a wall of a circular tube regularly in a line along the tube axis. It is found that, when the size ratios of the particle-to-channel height and the particle-to-tube diameter are smaller than approximately 0.2, the distributions of the shear stress and the pressure exerted on the surface of an adherent particle as well as the drag force and torque acting on it compare favorably in the 2D channel flow and tube flow. As the size ratios increase from 0.2, the differences between the 2D channel and the tube increase drastically, especially when separation distances between neighboring particles are large.

Cell Adhesion↗
PubMed1993

Noninvasive estimation of regurgitant flow rate and volume in patients with mitral regurgitation by Doppler color mapping of accelerating flow field.

OBJECTIVES: This study was designed to examine the accuracy of proximal accelerating flow calculations in estimating regurgitant flow rate or volume in patients with different types of mitral valve disease. BACKGROUND: Flow acceleration proximal to a regurgitant orifice, observed with Doppler color flow mapping, is constituted by isovelocity surfaces centered at the orifice. By conservation of mass, the flow rate through each isovelocity surface equals the flow rate through the regurgitant orifice. METHODS: Forty-six adults with mitral regurgitation of angiographic grades I to IV were studied. The proximal accelerating flow rate (Q) was calculated by: Q = 2 pi r2.Vn, where pi r2 is the area of the hemisphere and Vn is the Nyquist velocity. Radius of the hemisphere (r) was measured from two-dimensional or M-mode Doppler color recording. From the M-mode color study, integration of accelerating flow rate throughout systole yielded stroke accelerating flow volume and mean flow rate. Mitral regurgitant flow rate and stroke regurgitant volume were measured by using a combination of pulsed wave Doppler and two-dimensional echocardiographic measurements of aortic forward flow and mitral inflow. RESULTS: The proximal accelerating flow region was observed in 42 of 46 patients. Maximal accelerating flow measured from either two-dimensional (372 +/- 389 ml/s) or M-mode (406 +/- 421 ml/s) Doppler color study tended to overestimate the mean regurgitant flow rate (306 +/- 253 ml/s, p < 0.05). Mean Doppler accelerating flow rate correlated well with mean regurgitant flow rate (r = 0.95, p < 0.001), although there was a tendency toward slight overestimation of mean regurgitant flow by mean accelerating flow in severe mitral regurgitation. However, there was no significant difference between the mean accelerating flow rate (318 +/- 304 ml/s) and the mean regurgitant flow rate (306 +/- 253 ml/s, p = NS) for all patients. A similar relation was found between accelerating flow stroke volume (78.27 +/- 62.72 ml) and regurgitant flow stroke volume (76.06 +/- 59.76 ml) (r = 0.95, p < 0.001). The etiology of mitral regurgitation did not appear to affect the relation between accelerating flow and regurgitant flow. CONCLUSIONS: Proximal accelerating flow rate calculated by the hemispheric model of the isovelocity surface was applicable and accurate in most patients with mitral regurgitation of a variety of causes. There was slight overestimation of regurgitant flow rate by accelerating flow rate when the regurgitant lesion was more severe.

Blood Flow Velocity↗
PubMed1989

[Aortic flow patterns in normal neonates with patent ductus arteriosus: evaluation by Doppler color flow imaging].

Serial Doppler echocardiography was performed in 12 normal neonates (0.5-4.0 hrs after birth) to evaluate flow patterns through the ductus arteriosus, and in the aorta and brachiocephalic artery. At the initial examination, flow through the ductus arteriosus was bidirectional in eight of the 12 neonates and continuously left-to-right in the remaining four. The bidirectional ductal shunts became continuous left-to-right flows within 11-21 hrs after birth in seven of the eight neonates and resolved by 29-47 hrs after birth. In the remaining four neonates, the continuous left-to-right shunts disappeared 14-36 hrs after birth. Systolic ejection flow patterns in the aorta and brachiocephalic artery had a triangular shape with the peak velocity in early systole, followed by a minimal flow reversal in all sites examined. Diastolic flow patterns in each arterial site were as follows: 1. In the ascending aorta, there was slow and sustained diastolic forward flow, which did not change with increasing age. 2. In the brachiocephalic artery, there was a pan-diastolic flow reversal in the neonates with bidirectional ductal flow (7/8). This pattern changed to slow pan-diastolic forward flow when the ductal changed to continuous left-to-right flow or when the ductal closure was confirmed. Most (3/4) of the remaining four neonates with continuous left-to-right ductal flow exhibited pan-diastolic forward flow. Another showed a pan-diastolic flow reversal 2 hrs after birth, which changed to pan-diastolic forward flow in the second examination 6 hrs after birth. 3. In the distal aortic arch, there was a pan-diastolic forward flow in all the neonates, and the velocity decreased when a closure of the ductus was confirmed. 4. In the descending aorta, there was a pan-diastolic flow reversal in neonates with bidirectional ductal flow (7/8). This reversal changed to pan-diastolic forward flow, when the ductal flow changed to continuous left-to-right flow or when the ductal closure was confirmed. In the remaining four neonates with continuous left-to-right ductal flow, two showed a pan-diastolic flow reversal at the initial examinations 2 to 3 hrs after birth. This became a pan-diastolic forward flow at the second examinations 6 and 12 hrs after birth. In the other two, there was a pan-diastolic forward flow which did not change. This pan-diastolic flow reversal observed in the brachiocephalic artery and descending aorta was closely related to the bidirectional ductal flow.(ABSTRACT TRUNCATED AT 400 WORDS)

Aorta↗
PubMed2004

Influence of ionic strength, sample size, and flow conditions on the retention behavior of pullulan in flow field-flow fractionation.

Polymer molecular parameters such as hydrodynamic size are expected to be invariant regardless of the technique used to measure them, and to vary only, to some extent, with the solvent power and the polymer structure and properties as predicted from polymer chemistry. The hydrodynamic size of five pullulan standards derived from FlFFF in solutions of different ionic strength appears to correlate well to molecular mass as expected for neutral polymers for all fractions except that of lower mass. The correlation also holds for large amounts of injected sample even though with a slope which increases with rising polymer load. The evidence that the same result is obtained also for low sample amounts but with a higher cross-flow rate is interpreted as the manifestation of the presence of hydrodynamic interactions in concentrated polymer systems.

Fractionation, Field Flow↗
PubMed2006

Visual light spectroscopy reflects flow-related changes in brain oxygenation during regional low-flow perfusion and deep hypothermic circulatory arrest.

OBJECTIVES: Regional low-flow perfusion has been used to minimize ischemic brain injury during complex heart surgery in children. However, optimal regional low-flow perfusion remains undetermined. Visible light spectroscopy is a reliable method for continuous determination of capillary oxygen saturation (SgvO2). We used visible light spectroscopy to follow deep and superficial brain SgvO2 during cardiopulmonary bypass, regional low-flow perfusion, and deep hypothermic circulatory arrest. METHODS: Visible light spectroscopy probes were inserted into the superficial and deep brain of neonatal (3.9-4.5 kg) piglets, targeting the caudate and thalamic nuclei. The piglets were subjected to cardiopulmonary bypass and cooled to a rectal temperature of 18 degrees C using pH stat. Regional low-flow perfusion was initiated through the innominate artery at 18 degrees C, and pump flows were adjusted to 40, 30, 20, and 10 mL/kg/min for 10-minute intervals followed by 30 minutes of deep hypothermic circulatory arrest. Regional low-flow perfusion was reestablished, and flows were increased in a stepwise manner from 10 to 40 mL/kg/min. SgvO2 was continuously monitored. Carotid flow was measured using a flow probe, and cerebral blood flow (milliliters per kilogram body weight per minute) was calculated. RESULTS: There were no significant differences between the deep and superficial brain tissue oxygenation during regional low flow brain perfusion before deep hypothermic circulatory arrest. However, after deep hypothermic circulatory arrest, the superficial brain SgvO2 was lower than the deep brain SgvO2 (24 +/- 12 vs 55.3 +/- 8, P = .05, at flows of 30 mL/kg/min, and 34.2 +/- 17 vs 62.5 + 8, P = .06, at a flow rate of 40 mL/kg/min). During regional low-flow perfusion, SgvO2 was maintained at flows of 30 to 40 mL/kg/min (cerebral blood flows of 15 to 21 mL/kg/min and 19 to 24 mL/kg/min, respectively), but was significantly lower at pump flows of 20 mL/kg/min (cerebral blood flow of 10 to 14 mL/kg/min) and 10 mL/kg/min (cerebral blood flow of 5 to 9 mL/kg/min) compared with the values obtained just before regional low-flow perfusion (pre-deep hypothermic circulatory arrest, 37 +/- 6 vs 65.5 +/- 4.4, P < .05, and 21.6 +/- 3.7 vs 65.5 +/- 4.4, P < .01, respectively; and post-deep hypothermic circulatory arrest, 32 +/- 4.5 vs 65.5 +/- 4.4, P < .05, and 16.6 +/- 4.7 vs 65.5 +/- 4.4, P < .01, respectively). CONCLUSIONS: Regional low-flow perfusion at pump flows of 30 to 40 mL/kg/min with resulting cerebral blood flows of 14 to 24 mL/kg/min was adequate in maintaining both deep and superficial brain oxygenation. However, lower pump flows of 20 and 10 mL/kg/min, associated with cerebral blood flow of 9 to 14 mL/kg/min, resulted in significantly reduced SgvO2 values.

Animals↗
PubMed2005

Phasic coronary blood flow pattern during a continuous flow left ventricular assist support.

OBJECTIVE: Continuous flow left ventricular assist devices (LVADs) have been introduced and tested as a bridge to heart transplantation, bridge to recovery, and destination therapy, and several studies have been conducted to assess the physiologic effects of continuous flow LVADs. However, the effect of reduced pulsatility on the phasic coronary blood flow pattern is unknown. The aim of this study was to investigate the phasic coronary blood flow patterns during continuous flow LVAD support. METHODS: Phasic coronary blood flow patterns and hemodynamic data were analyzed using three flow probes placed around the left anterior descending coronary artery (LAD), left circumflex coronary artery (LCX), and the right coronary artery (RCA) in 16 pigs before and after initiating the LVAD support with or without creating LAD stenosis. RESULTS: The total coronary blood flow (TCBF, 112.8+/-31.4 mL/min) gradually decreased when the continuous flow LVAD support increased to 2.0 L/min (110.7+/-29.0 mL/min, P = 0.571), 2.5 L/min (103.7+/-26.1 mL/min, P = 0.079), and 3.0 L/min (101.5+/-27.2 mL/min, P = 0.027) because of decreases in LAD flow and LCX flow. LVAD support caused decrease in systolic and peak systolic LAD flow, LCX flow, and RCA flow, whereas diastolic RCA flow increased. In the presence of LAD stenosis, the TCBF (97.7+/-36.1 mL/min) decreased when the continuous flow LVAD support increased to 2.0 L/min (83.9+/-22.1 mL/min, P = 0.029), 2.5 L/min (83.2+/-25.2 mL/min, P = 0.012), and 3.0 L/min (87.6+/-23.4 mL/min, P = 0.005) because of decreases in LCX flow. CONCLUSION: Use of a continuous flow LVAD decreased TCBF, LAD flow, and LCX flow secondary to reduced systolic LAD flow and LCX flow, and decreased TCBF and LCX flow in the presence of LAD stenosis. These findings are potentially relevant to understanding the physiology of myocardial blood perfusion during continuous flow LVAD support especially in patients with coronary artery disease.

Animals↗
PubMed1986

Pulsatile flow of Casson's fluid through stenosed arteries with applications to blood flow.

The effects of non-Newtonian nature of blood and pulsatility on flow through a stenosed tube have been investigated. A perturbation method is used to analyse the flow. It is of interest to note that the thickness of the viscous flow region is non-uniform (changing with axial distance). An analytic relation between viscous flow region thickness and red cell concentration has been obtained. It is important to mention that some researchers have obtained an approximate solution for the flow rate-pressure gradient equation (assuming the ratio between the yield stress and the wall shear to be very small in comparison to unity); in the present analysis, we have obtained an exact solution for this non-linear equation without making that assumption. The approximate and exact solutions compare well with one of the exact solutions. Another important result is that the mean and steady flow rates decrease as the yield stress theta increases. For the low values of the yield stress, the mean flow rate is higher than the steady flow rate, but for high values of the yield stress, the mean flow rate behaviour is of opposite nature. The critical value of the yield stress at which the flow rate behaviour changes from one type to another has been determined. Further, it seems that there exists a value of the yield stress at which flow stops for both the flows (steady and pulsatile). It is observed that the flow stop yield value for pulsatile flow is lower than the steady flow. The most notable result of pulsatility is the phase lag between the pressure gradient and flow rate, which is further influenced by the yield stress and stenosis. Another important result of pulsatility is the mean resistance to flow is greater than its steady flow value, whereas the mean value of the wall shear for pulsatile flow is equal to steady wall shear. Many standard results regarding Casson and Newtonian fluids flow, uniform tube flow and steady flow can be obtained as the special cases of the present analysis. Finally, some applications of this theoretical analysis have been cited.

Arterial Occlusive Diseases↗
PubMed1996

Prediction of cerebral blood flow in fetal lambs by carotid artery ultrasonic flow transducer.

To determine whether common carotid artery blood flow measured with an ultrasonic flow transducer would predict brain blood flow in fetal sheep, we measured unilateral common carotid artery blood flow and compared this to simultaneous measurements of total brain blood flows made by radioisotope-labelled microsphere techniques. We studied anaesthetized, exteriorized fetal sheep with intact umbilical circulation after ligation of extracranial, extracerebral arteries and placement of a common carotid artery flow transducer; five fetuses at 120 d gestation had 19 total comparison measurements. As measured by microsphere technique, mean basal blood flow during undisturbed conditions to regional brain areas were similar to normal values reported for the exteriorized ovine fetus; these flows were highly correlated to fetal PaCO2 and successfully varied over a wide range (total brain 9.1-200.4 ml/min/100g and total cortex 6.1-153.1 ml/min/100g) in subsequent experimental conditions of hypercapnia or occluded blood flow. Blood flow as measured by flow transducer significantly correlated (P < or = 0.01) with microsphere measurements of blood flow to total brain (r = 0.56) and total cortex (r = 0.62); regional flow to cerebellum (r = 0.70) and thalamus (r = 0.60) also correlated to transducer measurements. Stronger correlations were observed at low-flow conditions to total brain (r = 0.83) and to total cortex (r = 0.90). As measured by microsphere technique, right and left cortical blood flows were highly correlated (P = 0.0001, r = 0.97), indicating that the flow transducer or surgical manipulation did not disturb the distribution of cerebral blood flow. The mean values for zero flow reference of the transducer were < 1.5% of mean basal flow values. It is concluded that the common carotid artery flow transducer technique developed in this study provides an accurate prediction of blood flow to total brain and total cortex over a wide range of values in fetal sheep. This technique provides a methodologic advantage to sequential experimental interventions and may prove advantageous to studies of fetal sheep cerebral circulation.

Animals↗
PubMed2006

Effects of low abdominal blood flow and dobutamine on blood flow distribution and on the hepatic arterial buffer response in anaesthetized pigs.

Low cardiac output impairs the hepatic arterial buffer response (HABR). Whether this is due to low abdominal blood flow per se is not known. Dobutamine is commonly used to increase cardiac output, and it may further modify hepatosplanchnic and renal vasoregulation. We assessed the effects of isolated abdominal aortic blood flow changes and dobutamine on hepatosplanchnic and renal blood flow. Twenty-five anesthetized pigs with an abdominal aorto-aortic shunt were randomized to 2 control groups [zero (n = 6) and minimal (n = 6) shunt flow], and 2 groups with 50% reduction of abdominal blood flow and either subsequent increased abdominal blood flow by shunt reduction (n = 6) or dobutamine infusion at 5 and 10 microg kg(-1) min(-1) with constant shunt flow (n = 7). Regional (ultrasound) and local (laser Doppler) intra-abdominal blood flows were measured. The HABR was assessed during acute portal vein occlusion. Sustained low abdominal blood flow, by means of shunt activation, decreased liver, gut, and kidney blood flow similarly and reduced local microcirculatory blood flow in the jejunum. Shunt flow reduction partially restored regional blood flows but not jejunal microcirculatory blood flow. Low-but not high-dose dobutamine increased gut and celiac trunk flow whereas hepatic artery and renal blood flows remained unchanged. Neither intervention altered local blood flows. The HABR was not abolished during sustained low abdominal blood flow despite substantially reduced hepatic arterial blood flow and was not modified by dobutamine. Low-but not high-dose dobutamine redistributes blood flow toward the gut and celiac trunk. The jejunal microcirculatory flow, once impaired, is difficult to restore.

Abdomen↗
PubMedDate not supplied

Instantaneous cross-sectional flow velocity profiles: a comparative study of two ultrasound Doppler methods applied to an in vitro pulsatile flow model.

Two methods based on different techniques for construction of cross-sectional flow velocity profiles from Doppler ultrasound signals were compared: an intraluminal method using pulsed-wave Doppler echocardiography and an extraluminal method using two-dimensional (color) Doppler ultrasound. The methods were applied to an in vitro pulsatile flow model. With the intraluminal method, pulsed Doppler recordings obtained throughout several flow pulses at different positions across a tube were digitized, and cross-sectional flow velocity profiles were obtained by matching the onset of flow velocity at the various positions. With the extraluminal method, cross-sectional flow velocity profiles were obtained by time interpolation between the digital flow velocity data obtained from several flow velocity maps. The first flow velocity map was recorded at onset of flow and the following maps were incrementally delayed with 20 msec from one flow pulse to the next. The time lag caused by the time needed to update each of the flow velocity maps was compensated for by time interpolation between the sequentially recorded flow velocity maps. The cross-sectional flow velocity profiles obtained with the two methods were compared at identical positions within the tube model at equal flow settings and throughout the pulsatile flow periods. At three different flow settings with peak flow velocity of 0.3, 0.5, and 0.7 m/sec, the difference (mean +/- SD) between the obtained velocities were 0.01 +/- 0.04, -0.01 +/- 0.05, and -0.03 +/- 0.07 m/sec, respectively. The findings suggest that cross-sectional flow velocity profiles from pulsatile flow velocity recordings can be obtained equally well with both methods.

Blood Flow Velocity↗
PubMed1995

Effect of extracorporeal membrane oxygenation flow on pulmonary capillary blood flow.

OBJECTIVE: To validate a new application of the modified acetylene rebreathing method for pulmonary capillary blood flow in a swine extracorporeal membrane oxygenation (ECMO) model. DESIGN: Prospective, sequential measurements of pulmonary capillary blood flow, using a rebreathing technique, as affected by different flows through the ECMO circuit. SETTING: A cardiovascular hemodynamic research laboratory at a university medical center. SUBJECTS: Fifteen young mature farm swine (48 to 52 kg). INTERVENTIONS: Pulmonary capillary blood flow was measured using a modified rebreathing technique, and this measurement repeated at different flow rates through the extracorporeal membrane oxygenation circuit. Pulmonary artery flow rates were measured using both thermodilution and echo-Doppler techniques for comparison purposes. MEASUREMENTS AND MAIN RESULTS: Pulmonary capillary blood flow measurements, as assessed by modified acetylene rebreathing, compared well with both the thermodilution cardiac output measurement during normal circulation and the pulmonary artery flow probe measurement while the subjects received ECMO. Mean pulmonary capillary blood flow measured by acetylene rebreathing decreased from 89.72 +/- 6.97 (baseline) to 43.59 +/- 5.66 mL/kg/min as ECMO flow was maximized to 56.22 +/- 3.62 mL/kg/min. Decreasing the ECMO flow rate by half (to 28.23 +/- 3.45 mL/kg/min) caused an increase in mean pulmonary capillary blood flow to 53.79 +/- 6.16 mL/kg/min. When ECMO flow was discontinued, pulmonary capillary blood flow returned to a near baseline value of 71.68 +/- 7.05 mL/kg/min (mean values of pooled data for both closed- and open-chest animals [n = 15]). These measurements correlated well with both thermodilution cardiac output and pulmonary artery ultrasonic flow probe measurements. CONCLUSIONS: The modified acetylene rebreathing method is a valid and accurate method for the measurement of pulmonary capillary blood flow in the presence of ECMO flows. Pulmonary blood flow decreases as ECMO flow is increased, and the extent of decrease is directly proportional to the amount of flow through the extracorporeal circulation.

Animals↗
PubMed1996

Measurement of pulmonary blood flow by fractal analysis of flow heterogeneity in isolated canine lungs.

Regional heterogeneity of lung blood flow can be measured by analyzing the relative dispersion (RD) of mass (weight)-flow data. Numerous studies have shown that pulmonary blood flow is fractal in nature, a phenomenon that can be characterized by the fractal dimension and the RD for the smallest realizable volume element (piece size). Although information exists for the applicability of fractal analysis to pulmonary blood flow in whole animal models, little is known in isolated organs. Therefore, the present study was done to determine the effect of blood flow rate on the distribution of pulmonary blood flow in the isolated blood-perfused canine lung lobe by using fractal analysis. Four different radiolabeled microspheres (141Ce, 95Nb, 85Sr, and 51Cr), each 15 microns in diameter, were injected into the pulmonary lobar artery of isolated canine lung lobes (n = 5) perfused at four different flow rates (flow 1 = 0.42 +/- 0.02 l/min; flow 2 = 1.12 +/- 0.07 l/min; flow 3 = 2.25 +/- 0.17 l/min; flow 4 = 2.59 +/- 0.17 l/min), and the pulmonary blood flow distribution was measured. The results of the present study indicate that under isogravimetric blood flow conditions, all regions of horizontally perfused isolated lung lobes received blood flow that was preferentially distributed to the most distal caudal regions of the lobe. Regional pulmonary blood flow in the isolated perfused canine lobe was heterogeneous and fractal in nature, as measured by the RD. As flow rates increased, fractal dimension values (averaging 1.22 +/- 0.08) remained constant, whereas RD decreased, reflecting more homogeneous blood flow distribution. At any given blood flow rate, high-flow areas of the lobe received a proportionally larger amount of regional flow, suggesting that the degree of pulmonary vascular recruitment may also be spatially related.

Animals↗
PubMed1998

Flow dynamics of angiographically no-flow patent internal mammary artery grafts.

OBJECTIVES: This study sought to assess the flow dynamics of internal mammary artery grafts (IMAGs) in no-flow situations by use of a Doppler guide wire. BACKGROUND: Functionally no-flow and anatomically patent IMAGs have been reported by angiography in patients with a patent recipient coronary artery. METHODS: The study included 12 patients with an IMAG to the left anterior descending coronary artery (LAD) in whom no-flow patency of the graft was suspected angiographically. Thirteen patients with a normally functioning IMAG whose LAD was occluded in the proximal portion and was supplied only from the graft served as control patients. Phasic flow velocities were recorded in the distal portion of the graft and the recipient LAD using a 0.014-in., 15-MHz Doppler guide wire at rest and during hyperemia (0.14-mg/kg body weight per min intravenous adenosine infusion). RESULTS: There were no significant differences in systolic (15+/-3 vs. 19+/-6 cm/s, p = NS), diastolic (35+/-11 vs. 37+/-7 cm/s, p = NS) and time-averaged peak velocities at rest (20+/-5 vs. 21+/-5 cm/s, p = NS), during hyperemia (51+/-12 vs. 54+/-8 cm/s, p = NS) and in coronary flow velocity reserve (2.8+/-0.9 vs. 2.7+/-0.3, NS) in the native LAD in patients with a no-flow patent graft versus control patients. Within the graft, to and fro signals with systolic reversal and diastolic anterograde flow were seen in the no-flow patent grafts, although anterograde flow signals were recorded in systole and diastole in control patients. Systolic (-28+/-19 vs. 22+/-9 cm/s, p < 0.01), diastolic (18+/-17 vs. 44+/-14 cm/s, p < 0.01) and time-averaged (-2+/-6 vs. 26+/-9 cm/s, p < 0.01) peak velocities at rest were significantly smaller in the no-flow patent grafts than in control grafts. During hyperemia, anterograde flow became predominant, with a reduction in retrograde systolic flow signal and an increase in diastolic flow velocity and time-averaged peak velocity in the no-flow patent grafts, and no-flow situations disappeared temporarily. CONCLUSIONS: Functionally no-flow situations of IMAGs manifesting to and fro signals with systolic flow reversal and diastolic antegrade low flow velocity are temporary conditions in certain hemodynamic circumstances, and these grafts function as conduits during hyperemic states.

Adolescent↗
PubMed2005

Quantitative real-time blood flow estimation with intravascular ultrasound in the presence of in-plane flow.

Previously, we showed a source of error in blood flow estimation introduced by in-plane flow using a slow-time finite-impulse response (FIR) filter-bank method measuring blood flow through the image plane of an intravascular ultrasound (IVUS) catheter array. There is a monotonic relationship between flow velocity and the normalized second moment of the slow-time spectrum when flow is orthogonal to the image plane of a side-looking catheter array. However, this relationship changes in the presence of in-plane flow, as slow-time spectra shift and spread with varying in-plane and out-of-plane components. These two effects increase the normalized spectral second moment, resulting in flow overestimates. However, by resampling the received signal with variable time delay from pulse to pulse (i.e., tilting the slow-time signals), the slow-time spectrum shifts back to direct current (DC), and the orthogonal estimation method can be used. We present a method to correct this overestimation and accurately estimate blood flow through the image plane in real time. Initially, the tilt delay needed to shift the slow-time spectrum back to DC at each point within the flow field is calculated. Knowing this tilt delay, a tilted slow-time signal is obtained for the velocity component normal to the image plane, and its spectrum is estimated using a filter-bank. That spectrum then is used to estimate the flow speed using a mapping function closely related to the monotonic relationship between the slow-time spectrum and flow speed observed for orthogonal flow. To accurately estimate flow angles, we modified the filter-bank algorithm, applying slow-time filter coefficients in a tilted arrangement and studying the slow-time spectral energy as a function of tilt. The slow-time spectral estimate is constructed with the tilted output of eight narrow, band-pass filters from a filter-bank. Independent simulations show that, for blood slowing at angles between +/-6 degrees and +/-15 degrees at a speed of 300 mm/s, flow velocity would be overestimated by as much as 38.79% and 249%, respectively, using the direct filter-bank approach. However, this error can be corrected using the modified method presented here, reducing the maximum overestimation error by a factor of 2.69 and 10.88 for those angles, respectively. Although the remaining error is not negligible, the volume flow rate, calculated by integrating the flow velocity over the entire vessel lumen, differs by only 3% or less from the true value over the angular range considered here. This represents an improvement of a factor of 40 over uncompensated estimates at maximum flow angles. Consequently, the modified real-time method can quantitatively measure flow in most IVUS applications in which the catheter's image plane is not precisely orthogonal to the flow direction.

Algorithms↗