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PubMed2004

Cellular engineering of conduits for coronary and lower limb bypass surgery: role of cell attachment peptides and pre-conditioning in optimising smooth muscle cells (SMC) adherence to compliant poly(carbonate-urea)urethane (MyoLink) scaffolds.

OBJECTIVE: We are developing a hybrid arterial bypass graft of compliant poly(carbonate-urea)urethane (MyoLink), endothelial and smooth muscle cells (SMCs). To enhance adhesion of SMCs we assessed various attachment factors and the effect of pre-conditioning on cell retention. METHODS: MyoLink segments were coated with either RGD, superfibronectin, fibronectin, fibronectin-like engineered polymer protein (FEPP), FEPP plus or type 1 collagen overnight. (111)Indium-radiolabelled SMCs were placed onto MyoLink segments for 48 h before being aspirated, then lavaged off. All grafts, aspirates and lavages were counted in a gamma counter. SMC viability on the MyoLink segments was also assessed for viability using the Alamar blue redox assay. Separately, MyoLink grafts lined with radiolabelled SMCs were divided into a pre-conditioned group, exposed to subarterial pulsatile flow whilst another group were held in static culture. After 1-week, grafts were exposed to arterial pulsatile flow whilst radioactivity was assessed using a gamma camera. RESULTS: Only FEPP plus significantly enhanced SMC attachment: mean of 32+/-6% cell attachment compared to 21+/-5% for uncoated control. Cell viability was enhanced by all attachment factors except fibronectin. Pre-conditioning was shown to significantly enhance the retention of SMCs onto the MyoLink once exposed to pulsatile arterial flow: the final attachment was 57+/-7% for the static and 76+/-7% for the pre-conditioned group. CONCLUSIONS: FEPP plus enhances SMC attachment to MyoLink. We believe this is because of its repeating sequences of RGD and its positive charge. Pre-conditioning enhances the retention of SMCs to MyoLink once exposed to pulsatile arterial flow.

Blood Vessel Prosthesis↗
PubMed1983

Carbohydrate metabolism during pulsatile cardiopulmonary bypass under profound hypothermia.

Procedures related to profound hypothermia and circulatory arrest have produced a great improvement in the operative results of cardiac repair in neonates and infants. As we already obtained data on the effects of these procedures on cerebral metabolism, we focussed our attention on carbohydrate metabolism to determine whether or not cardiopulmonary bypass with pulsatile flow would improve the results of bypass method for core cooling and rewarming. In 12 mongrel dogs under conditions of hypothermia, plasma levels of glucose, insulin and glucagon as well as cortisol and noradrenaline were monitored in both pulsatile and non-pulsatile bypass groups. The hyperglycemia was significantly depressed and insulin levels increased in cases of pulsatile flow. Thus, even under conditions of hypothermia, pulsatile flow results in an improvement of the blood flow in the pancreas and there is a more extensive utilization of glucose and a greater protective effect on the function of the visceral organs during bypass.

Animals↗
PubMed2004

Noninvasive measurement of steady and pulsating velocity profiles and shear rates in arteries using echo PIV: in vitro validation studies.

Although accurate measurement of velocity profiles, multiple velocity vectors, and shear stress in arteries is important, there is still no easy method to obtain such information in vivo. We report on the utility of combining ultrasound contrast imaging with particle image velocimetry (PIV) for noninvasive measurement of velocity vectors. This method (echo PIV) takes advantage of the strong backscatter characteristics of small gas-filled microbubbles (contrast) seeded into the flow. The method was tested in vitro. The steady flow analytical solution and optical PIV measurements (for pulsatile flow) were used for comparison. When compared to the analytical solution, both echo PIV and optical PIV resolved the steady velocity profile well. Error in shear rate as measured by echo PIV (8%) was comparable to the error of optical PIV (6.5%). In pulsatile flow, echo PIV velocity profiles agreed well with optical PIV profiles. Echo PIV followed the general profile of pulsatile shear stress across the artery but underestimated wall shear at certain time points. However, error in shear from echo PIV was an order of magnitude less than error from current shear measurement methods. These studies indicate that echo PIV is a promising technique for noninvasive measurement of velocity profiles and shear stress.

Animals↗
PubMed2000

Color Doppler sonography for evaluating response to transcatheter arterial embolization and percutaneous ethanol injection therapy and for detecting recurrence of hepatocellular carcinoma.

Eighty-six patients (mean age, 63 years) with 92 hepatocellular carcinomas (2.0 cm or greater in diameter; mean +/- SD, 3.5 +/- 1.6 cm) underwent color Doppler sonography before and after transcatheter arterial embolization and after subsequent percutaneous ethanol injection for (1) identification of pulsatile flow in the residual tumor area after transcatheter arterial embolization, (2) evaluation of therapeutic effectiveness of combined transcatheter arterial embolization and percutaneous ethanol injection, and (3) detection of recurrence during follow-up evaluation. Before and 2 weeks after transcatheter arterial embolization, color Doppler sonography revealed pulsatile flow in 76 (82.6%) and 43 (46.7%)lesions, respectively. After percutaneous ethanol injection, tumor stains in these lesions completely disappeared on digital subtraction angiography (gold standard). During follow-up study (3 to 45 months), digital subtraction angiography revealed recurrence in 73 patients (38 local recurrences and 19 new lesions [2.0 cm or greater]), whereas color Doppler sonography revealed pulsatile flow in 76.3% (local) and 63.2% (new) (not significant). Color Doppler sonography was useful for complying with our three objectives, especially for detecting local recurrence during follow-up evaluation.

Aged↗
PubMed1976

Some physical properties of the pulmonary arterial bed deduced from pulsatile arterial flow and pressure.

This study aimed to quantify changes of vascular compliance and resistance of the proximal and the peripheral pulmonary arterial vessels when vascular smooth muscle was stimulated. These above vascular characteristics were derived from registrations of pulsatile pressure and flow in the pulmonary artery (PA). An in situ cat lung preparation was used, with the right heart by-passed by a pulsatile blood pump. Vascular input impedance was derived from PA pulsatile pressure and flow recordings, and impedance characteristics were used for calculation of the variables of a simple lumped analog representation of the arterial bed. PA smooth muscle was stimulated by infusions of collagen suspension, by general hypoxia and by noradrenaline injections. Collagen caused 40% reduction of vascular compliance (C), no changes in proximal arterial resistance (R1) and 180% increase in peripheral vascular resistance (R2). Hypoxia caused 50% reduced C, 20% increased R1 and 7u% increased R2. Noradrenaline caused 20% reduced C and 30% increased R1 and R2. These results, together with results derived from simulation of the observed impedance changes in a computer model of the lung arterial bed, indicated that collagen infusion elicited contraction of small and medium-sized arteries, with increased arterial volume as result of increased distending pressure. Hypoxia and noradrenaline, seemed both to cause contraction of the total arterial bed. This effect being most pronounced during hypoxia.

Animals↗
PubMed1993

Experimentally induced changes in heart rate alter umbilicoplacental hemodynamics in fetal sheep.

In the anesthetized sheep fetus, we have accelerated heart rate by atrial pacing (n = 6) or caused decelerations by stimulating the vagus nerve (n = 7). Alterations in heart rate were linearly related to changes in the ratio of the diastolic minimum (D) to systolic maximum (S) of flow and velocity, and to changes in the flow pulsatility index in the umbilical artery. Decelerations slightly increased vascular resistance, and decreased blood flow and mean arterial pressure, but accelerations had no significant effect. The index of impedance was unaltered by either intervention. The major factor mediating the influence of heart rate on blood flow pulsatility in the umbilical artery was the aortic blood pressure pulsatility. An equation was derived to adjust flow D/S to a standardized heart rate. Results showed that heart rate correction can affect the interpretation of experimental data.

Animals↗
PubMed1990

The effect of flow and mass transport in thrombogenesis.

The paper presents a mathematical analysis of the contributions of flow and mass transport to a single reactive event at a blood vessel wall. The intent is to prepare the ground for a comprehensive study of the intertwining of these contributions with the reaction network of the coagulation cascade. We show that in all vessels with local mural activity, or in "large" vessels (d greater than 0.1 mm) with global reactivity, events at the tubular wall can be rigorously described by algebraic equations under steady conditions, or by ordinary differential forms (ODEs) during transient conditions. This opens up important ways for analyzing the combined roles of flow, transport, and coagulation reactions in thrombosis, a task hitherto considered to be completely intractable. We report extensively on the dependence of transport coefficient kL and mural coagulant concentration Cw on flow, vessel geometry, and reaction kinetics. It is shown that for protein transport, kL varies only weakly with shear rate gamma in large vessels, and not at all in the smaller tubes (d less than 10(-2) mm). For a typical protein, kL approximately 10(-3) cm s-1 within a factor of 3 in most geometries, irrespective of the mural reaction kinetics. Significant reductions in kL (1/10-1/1,000) leading to high-coagulant accumulation are seen mainly in stagnant zones vicinal to abrupt expansions and in small elliptical tubules. This is in accord with known physical observations. More unexpected are the dramatic increases in accumulation which can come about through the intervention of an autocatalytic reaction step, with Cw rising sharply toward infinity as the ratio of reaction to transport coefficient approaches unity. Such self-catalyzed reactions have the ability to act as powerful amplifiers of an otherwise modest influence of flow and transport on coagulant concentration. The paper considers as well the effect on mass transport of transient conditions occasioned by coagulation initiation or pulsatile flow. During initiation, instantaneous flux varies with diffusivity and bulk concentration, favouring the early adsorption/consumption of proteins with the highest abundance and mobility. This is akin to the 'Vroman effect' seen in narrow, stagnant spaces. The effect of flow pulsatility on kL has the potential, after prolonged cycling, of bringing about segregation or accumulation of proteins, with consequences for the coagulation process.

Biomechanical Phenomena↗
PubMed2004

Impella Recover 100: successful perioperative support for off pump coronary artery bypass grafting surgery in a patient with end-stage ischemic cardiomyopathy.

The authors present the successful use of the Impella recover 100 intracardiac left ventricular assist device in a 55-year old man suffering from end-stage ischemic cardiomyopathy. The pump was implanted preoff pump coronary artery bypass grafting (OPCAB) and it was successfully weaned 5 days postoperatively. In addition, an intra-aortic balloon pump (IABP) was implanted to convert the non-pulsatile flow of the Impella into a pulsatile flow. In this paper benefits and risks of this technique are shown.

Cardiomyopathy, Dilated↗
PubMed1981

Haemodynamic aspects of lower limb arterial reconstruction using Dacron and Goretex prostheses.

We have studied some haemodynamic consequences of vascular grafts of less than 8 mm diameter by animal studies on dogs before and after aortofemoral bypass with either knitted Dacron 5 mm internal diameter (6 dogs) or Goretex 6 mm internal diameter (7 dogs) prostheses between 17 and 24 cm in length. Both materials gave an increased velocity of pulse wave transmission for pressure and flow and an increase in resistance to pulsatile flow. The effects were more severe with Dacron than with Goretex. Pressure index and pressure pulsatility were not significantly altered, but flow pulsatility index, peak flow rate, and peak flow acceleration were all significantly reduced after both implants. These results are due to mismatching of mechanical properties leading to an increased impedance to pulsatile flow.

Animals↗
PubMedDate not supplied

[Changes in hemodynamic indices during perfusion with pulsatile and steady currents in aortocoronary bypass surgery].

Hemodynamic parameters were compared in 28 patients with ischemic heart disease subject to cardiopulmonary bypass surgery with non-pulsatile (group 1) and pulsatile flow (group 2). Systolic, diastolic and mean blood pressure (MBP) was assessed, total peripheral vascular resistance (TPVR) was calculated, esophageal, rectal and skin temperature was measured. Volumetric perfusion rate was the same in both groups. Pulse pressure was maintained at the level of 35 mmHg. MBP at the stage of hypothermia plateau and during warming decreased in both groups. It was significantly lower in group 1 at the beginning of warming and during clamp relief from the aorta. At the end of cooling period TPVR was lower with the use of pulsatile than non-pulsatile flow. It increased drastically towards the end of hypothermia plateau in group 1. During clamp relief from the aorta TPVR values did not significantly differ from baseline in group 2 and remained high in group 1. The warming rate happened to be greater in pulsatile than in non-pulsatile flow.

Coronary Artery Bypass↗
PubMed1990

Theoretical investigation of estimation of steady and pulsatile blood flow and blood vessel cross section by CW NMR excitation.

In this paper we show theoretically that when a magnetised blood bolus enters a CW NMR excitor coil of length Le at resonance and the signal from the T2-decaying, processing transverse magnetisation of the flowing blood spins is subsequently detected by a detector coil of length L separated from the excitor coil by a distance delta l, then by recording CW NMR signals at three positions such as delta l = 0, 0.5 and 1.0 cm one can eliminate the static tissue signal and measure non-invasively the steady component V0 as well as the total vessel cross section, beta accurately. The time dependent part of the CW NMR signal which depends on Vpulse(t), is also dependent on V0 non-linearly unless both L and Le are greater than 50 cm and delta l is zero. Finally, methods of obtaining true Vpulse(t) from the CW NMR signal after applying proper correction due to the steady flow are discussed.

Blood Circulation↗
PubMed2004

Plasminogen activator inhibitor-1 deficiency enhances flow-induced smooth muscle cell migration.

INTRODUCTION: We determined the role of smooth muscle cell (SMC)-derived plasminogen activator inhibitor-1 (PAI-1) in the flow-induced SMC migratory response. MATERIALS AND METHODS: Wild type (wt) or PAI-1 knockout SMC were cultured in the absence or presence of endothelial cells (EC) under static or pulsatile flow conditions in a perfused culture system. SMC migration was then assessed by Transwell assay. RESULTS: Pulsatile flow significantly increased SMC PAI-1 mRNA and protein levels, approximately 4- and 3-fold respectively (n = 4, p < 0.05). In the absence, but not in the presence of EC, pulsatile flow significantly increased ( approximately 2.4-fold) the migration of wt SMC when compared to wt SMC cultured under static conditions. PAI-1 -/-SMC migration was significantly increased under flow conditions as compared to wild-type controls (334 +/- 22% vs. 237 +/- 11%, n = 6, p < 0.05). This flow-induced migration was significantly attenuated, but not completely inhibited, when PAI-1 -/-SMC were cultured in the presence of EC (147 +/- 13%, n = 6, p < 0.05). The flow-induced PAI-1 -/-SMC migratory response was partially inhibited by an anti-urokinase plasminogen activator (uPA) antibody (#1189), and completely inhibited by both 1189 and the matrix metalloproteinase (MMP) inhibitor BB3103. In parallel PAI-1 -/-SMC cells, there was a greater flow-induced increase in proMMP-2 activity as compared to wild-type control cells. Moreover, under both static and flow conditions, tissue inhibitors of matrix metalloproteinases (TIMP)-2 activity was reduced in these PAI-1-deficient cells as compared to wild-type controls. CONCLUSIONS: These results suggest that SMC PAI-1 plays a role in limiting flow-induced SMC migration and thus may be an important mechanism for controlling the process of vascular remodelling.

Animals↗
PubMed1986

Arterial blood-flow waveform measurement in intact animals: new digital radiographic technique.

With a new radiographic method to determine the pulsatile flow pattern in an imaged artery, flow velocity is determined by tracking the movement of contrast material along the artery over time. Flow velocity is multiplied by an automatically determined cross-sectional area of the artery to determine blood flow. Pulsatile blood-flow waveforms were determined by radiographic and electromagnetic techniques in each femoral artery of four dogs while flow conditions were varied. Peak and average blood flows measured by the two techniques were highly correlated (r = .97 and .95, respectively). The closest agreement between the flow waveforms measured by the electromagnetic and radiographic techniques was found under normal flow conditions. The radiographically derived flow waveforms tended to be noisy at low blood-flow rates, and instantaneous blood-flow rates exceeding 700 ml/min were underestimated.

Animals↗
PubMed1991

Segmental vascular resistance during pulsatile and steady perfusion in 3- to 5-wk-old rabbit lungs.

To determine the mechanisms by which pulsatile perfusion reduces vascular resistance in isolated lungs, we compared the effects of pulsatile versus steady perfusion on total and segmental vascular resistance in isolated lungs of 3- to 5-wk-old rabbits. Lungs were perfused alternately with steady and pulsatile flow for 45-min periods at a constant total arteriovenous pressure drop. Blood flow was adjusted to keep mean pulmonary arterial pressure at 20 cmH2O, when left atrial and airway pressures were 8 and 6 cmH2O, respectively. We partitioned the pulmonary circulation into three longitudinal vascular segments, i.e., arteries, microvessels, and veins, by measuring pressures in 20- to 50-microns-diameter subpleural arterioles and venules by the micropipette servo-nulling method. We found that in the isolated, perfused 3- to 5-wk-old rabbit lung, in which arteries and veins are the main sites of resistance, pulsatile flow results in a 20-36% reduction in total vascular resistance, mainly due to a reduction in arterial and venous resistances. The decrease in total vascular resistance was similar in lungs that were untreated or treated with papaverine, indicating that the effect of pulsatile flow was not due to active vasomotion. The reduction in arterial resistance was greater than that in veins (31-55 vs. 19-22%), especially when pulse amplitude was high (5-10 vs. 20-30 cmH2O). Total vascular resistance was also lower after 45 min of pulsatile perfusion with a pulse rate of 200 pulses/min than 80 pulses/min (0.126 +/- 0.04 vs. 0.154 +/- 0.059 cmH2O.min.ml-1.kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

The effect of celiac and renal artery outflows on near-wall velocities in the porcine iliac arteries.

The effects of the outflow of aortic blood through the celiac and renal arteries on the flow field in the external iliac arteries were studied under steady and physiologically realistic pulsatile flow conditions. Laser Doppler velocimetry (LDV) measurements were made close to the medial, lateral, ventral, and dorsal walls of the external iliac branches of a clear, flow-through replica of a porcine aorta and its daughter vessels. The outflow from each branch of the replica was controlled so that the infrarenal aortic flow rate and the flow partition at the aortic trifurcation were the same for all experiments. LDV measurements were made with flow exiting through both the renal and celiac artery ostia, only the celiac ostium, and neither ostium. The steady flow results indicate that while the outflow through the renal arteries did not have a significant effect on near wall shear rate in the external iliac arteries, the flow through the celiac artery did. However, in pulsatile flow, three indices of near wall velocity in the iliac arteries were unaffected by celiac artery outflow, while a fourth showed a small effect that can be attributed to differences in minimum velocity. These results indicate that reliable simulations of blood flow in the external iliac arteries can be carried out without including the renal and celiac vessels, provided that the correct infrarenal flow wave is used. They also demonstrate that the flow field downstream of a region, such as a branch, that strongly alters the flow, can be nearly independent of the velocity field entering the region.

Animals↗