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PubMed1992

Anastomotic intimal hyperplasia: mechanical injury or flow induced.

All anastomotic intimal thickening may not be the same, and the underlying mechanism(s) regulating the different types may vary. We investigated the localization of experimental anastomotic intimal thickening in relation to known biomechanical and hemodynamic factors. Bilateral iliofemoral saphenous vein and polytetrafluoroethylene grafts were implanted in 13 mongrel dogs. The distal end-to-side anastomotic geometry was standardized, and the flow parameters were measured. After 8 weeks, seven of 10 animals (group I) with patent grafts were killed and the anastomoses fixed by perfusion. Histologic sections from each anastomosis were studied with light microscopy, and regions of intimal thickening were identified and quantitated with use of oculomicrometry. To characterize the anastomotic flow patterns, transparent silicone models were constructed from castings of the distal anastomosis of three animals (group II), and flow was visualized with use of helium-neon laser-illuminated particles under conditions simulating the in vivo pulsatile flow parameters. Histologic sections revealed two separate and distinct regions of anastomotic intimal thickening. The first, suture line intimal thickening, was greater in polytetrafluoroethylene anastomoses (0.35 +/- 0.23 microns) than in vein anastomoses (0.15 +/- 0.03 microns, p less than 0.05). The second distinct type of intimal thickening developed on the arterial floor and was the same in polytetrafluoroethylene (0.11 +/- 0.11 microns) and vein anastomoses (0.12 +/- 0.03 microns). Model flow visualization studies revealed a flow stagnation point along the arterial floor resulting in a region of low and oscillating shear where the second type of intimal thickening developed. High shear and short particle residence time were observed along the hood of the graft, an area devoid of intimal thickening.(ABSTRACT TRUNCATED AT 250 WORDS)

Anastomosis, Surgical↗
PubMed1995

Dynamic characteristics of prosthetic heart valves.

The relation between flow rate (Q) and transvalvular pressure-drop (DP) is of fundamental importance for a prosthetic heart valve tested in steady flow conditions. The Q-DP plot can thus be called the static characteristic of the valve. While in pulsatile flow, with time (t) as a parameter, the instantaneous Q(t)-DP(t) relation can also be obtained. The Q-DP relation forms a phase graph on an X-Y plane during a whole cardiac cycle, and can be regarded as the dynamic characteristic, which to our knowledge has never been systematically explored before. With in vitro experiment the Q(t)-DP(t) relations are presented for five different aortic valves. Properly modelling the characteristics of heart valves is a key link in modelling the interactions between the ventricle and arterial system. Treatments for valves, such as diode analogue and orifice area assumption governed by the Gorlin formula, are found unsatisfactory. A simple one-dimensional flow equation is used to further examine the Q-DP graph, and both the dynamic resistance characteristic and the dynamic flow characteristic can be obtained. It is found that the dynamic characteristic differs from the static one not only in the inertance effect but also in the transient process, which can be quite energy-consuming and therefore important. Geometric relations of these phase graphs with the transvalvular power loss are discussed. The method of dynamic characteristics provides a new way to evaluate the performance of a tested valve.

Biomedical Engineering↗
PubMed1989

Effect of prosthetic mitral valve geometry and orientation on flow dynamics in a model human left ventricle.

Pulsatile flow dynamics through bileaflet (St Jude and Duromedics), tilting disc (Bjork-Shiley and Omniscience), caged ball (Starr-Edwards), pericardial (Edwards) and porcine (Carpentier-Edwards) mitral valves in a model human left ventricle (LV) were studied. The model human ventricle, obtained from an in situ diastolic casting, was incorporated into a mock circulatory system. Measurements were made at various heart rates and flow rates. These included the transvalvular pressure drop and regurgitation in percent and cm3 beat-1. The effect of valve geometry and the orientation of the valve with respect to the valve annulus was analyzed using a flow visualization technique. Qualitative flow visualization study indicates certain preferred orientations for the tilting disc and bileaflet valve prostheses in order to obtain a smooth washout of flow in the LV chamber.

Heart↗
PubMed1998

Validated computation of physiologic flow in a realistic coronary artery branch.

The pulsatile flow field in an anatomically realistic model of the bifurcation of the left anterior descending coronary artery (LAD) and its first diagonal branch (D1) was simulated numerically and measured by laser Doppler anemometry. The inlet velocity profiles used in the computer simulation and in the physical experiments were physiologically realistic. The computational geometric model was developed on the basis of a digitized arterial cast. The curvature of the LAD over the cardiac surface leads to axial velocity profiles which are slightly skewed towards the epicardial wall. Downstream of the bifurcation, a strong skewing occurs towards the flow divider walls as a result of branching. Locally, the wall shear stress component caused by the complex secondary velocity can be as high as the axial component. The wall shear stress representation from a cell-based perspective exhibits low shear stress and large deviation from the time-averaged shear stress direction during systole. In diastole, the instantaneous wall shear stress direction nearly corresponds to the mean direction. The comparison of computed and measured axial velocity results shows generally good agreement. In contrast to computed flow patterns in simpler geometries constructed from cylindrical tubes, the flow field is found to be smoother, presumably reflecting the adaptation of the vascular contour to the contained flow.

Algorithms↗
PubMed1992

Plethysmography. A treatise on its evolution, differential methodology and clinical utilization. 1973.

Plethysmography is the observation and use of volume changes in physiologic entities. The most influential short-term effect is caused by the pulsatile flow of blood. Attempts to convert these pulsatile volume changes into minimum required blood flow per unit of time have been successful clinically. Plethysmography can be accomplished by encapsulating digits, limbs and entire bodies. Volume changes in the member cause volume changes in the fixed chamber which then influences an observational medium. Plethysmography can also be accomplished with a strain gauge, direct application of electricity to flesh, changing opacity effects on tissue, ultrasound (the Doppler effect) or the piezoelectric method. The piezoelectric plethysmograph was successfully tested on 55 patients.

Blood Circulation↗
PubMedDate not supplied

[Pulsations of the umbilical vein: pathophysiologic aspects and fetal outcome].

Continuous forward flow to the fetal heart in the umbilical vein is a normal Doppler finding. Altered fetal hemodynamics can cause a pulsatile flow pattern in the umbilical vein. Pulsations in the umbilical vein were diagnosed in 14 pregnancies complicated by fetal hydrops, cardiac malformations, arrhythmia or severe intrauterine growth retardation. To document the fetal outcome, the results were analysed retrospectively. Compared with a normal Doppler group (N = 56), a significantly higher rate of perinatal death (Alpha < 1%), (64% vs 1.75%) was diagnosed, when pulsations in the umbilical vein were present. The Apgar-score was significantly lower (4.5 vs 8.4) (p < 0.0002) in the group with pulsations in the umbilical vein. There was no significant difference of pH between the newborns of the two groups. Eight fetuses developed hydrops. Thirteen fetuses had increased reverse flow in the inferior vena cava. The vena cava of the acardiac fetus could not be identified. The knowledge of the poor outcome and the pathophysiologic relationships of fetal hemodynamics may be useful in clinical management. Therefore Doppler examination of the umbilical vein should be performed in high-risk pregnancies.

Female↗
PubMed1999

Pulmonary and caval flow dynamics after total cavopulmonary connection.

OBJECTIVE: To assess flow dynamics after total cavopulmonary connection (TCPC). DESIGN: Cross-sectional study. SETTING: Aarhus University Hospital. PATIENTS: Seven patients (mean age 9 (4-18) years) who had previously undergone a lateral tunnel TCPC mean 2 (0. 3-5) years earlier. INTERVENTIONS: Pressure recordings (cardiac catheterisation), flow volume, and temporal changes of flow in the lateral tunnel, superior vena cava, and right and left pulmonary arteries (magnetic resonance velocity mapping). RESULTS: Superior vena cava flow was similar to lateral tunnel flow (1.7 (0.6-1.9) v 1. 3 (0.9-2.4) l/min*m2) (NS), and right pulmonary artery flow was higher than left pulmonary artery flow (1.7 (0.6-4.3) v 1.1 (0.8-2. 5) l/min*m2, p < 0.05). The flow pulsatility index was highest in the lateral tunnel (2.0 (1.1-8.5)), lowest in the superior vena cava (0.8 (0.5-2.4)), and intermediate in the left and right pulmonary arteries (1.6 (0.9-2.0) and 1.2 (0.4-1.9), respectively). Flow and pressure waveforms were biphasic with maxima in atrial systole and late ventricular systole. CONCLUSIONS: Following a standard lateral tunnel TCPC, flow returning via the superior vena cava is not lower than flow returning via the inferior vena cava as otherwise seen in healthy subjects; flow distribution to the pulmonary arteries is optimal; and some pulsatility is preserved primarily in the lateral tunnel and the corresponding pulmonary artery. This study provides in vivo data for future in vitro and computer model studies.

Adolescent↗
PubMed1995

Estimation of average flow in ungated 3D phase contrast angiograms.

Three dimensional (3D) phase contrast angiograms contain velocity data, which is discarded after the reconstruction of the projections. In extension to earlier work on velocity quantification with ungated 2D phase data, this paper shows that a useful estimate of the average velocity and flow rate can be extracted from ungated 3D phase contrast angiograms. Simulations and experiments in a phantom and in vivo were performed. For pulsatile flow and strong spin saturation, an over-estimation of the flow rate at the net in-flow end of the imaging volume and underestimation at the net out-flow end was observed. Imaging at lower RF tip angles yielded flow rates close to the correct value within the entire imaging volume. In contrast to ungated 2D experiments, the flow rates determined by repeated 3D experiments showed no variation.

Adult↗
PubMed1992

Ductus venosus blood flow velocity waveforms in the human fetus--a Doppler study.

Successful human fetal ductus venosus flow velocity waveform recording was achieved cross sectionally in 48 out of 60 women at 19-22, 27-30 and 36-39 weeks of gestation. The ductus venosus shows a pulsatile flow pattern consisting of a systolic and diastolic forward component without a late diastolic reverse component as demonstrated in the inferior vena cava. Peak systolic velocities as high as 40-80 cm/s were observed. A statistically significant increase in time-averaged velocity, peak systolic and peak diastolic velocity with advancing gestational age was established.

Blood Flow Velocity↗
PubMed2002

Endothelial nitric oxide production during in vitro simulation of external limb compression.

External pneumatic compression (EPC) is effective in preventing deep vein thrombosis (DVT) and is thought to alter endothelial thromboresistant properties. We investigated the effect of EPC on changes in nitric oxide (NO), a critical mediator in the regulation of vasomotor and platelet function. An in vitro cell culture system was developed to simulate flow and vessel collapse conditions under EPC. Human umbilical vein endothelial cells were cultured and subjected to tube compression (C), pulsatile flow (F), or a combination of the two (FC). NO production and endothelial nitric oxide synthase (eNOS) mRNA expression were measured. The data demonstrate that in the F and FC groups, there is a rapid release of NO followed by a sustained increase. NO production levels in the F and FC groups were almost identical, whereas the C group produced the same low amount of NO as the control group. Conditions F and FC also upregulate eNOS mRNA expression by a factor of 2.08 +/- 0.25 and 2.11 +/- 0.21, respectively, at 6 h. Experiments with different modes of EPC show that NO production and eNOS mRNA expression respond to different time cycles of compression. These results implicate enhanced NO release as a potentially important factor in the prevention of DVT.

Blotting, Northern↗
PubMed1993

[Duplex ultrasound evaluation of Basedow struma treated with iodine therapy].

Over a period of 18 months the thyroid gland of 31 patients suffering from Grave's disease was examined by Duplex ultrasound for changes in blood perfusion. In 24 of these patients a follow-up study was achieved immediately after a presurgical iodine therapy. For estimation of the perfusion the "Pulsatile Flow Index (PFI)" was calculated. Compared to the normal group (22 volunteers, mean: 0.46 +/- 0.11) changes of 41 and 22% were highly significant for this pre (mean: 0.65 +/- 0.08, p < 10E-6) and post therapy (0.56 +/- 0.1, p < 5E-5). Therapy was unsuccessful in 3 cases on a single, in one case on both sides. Altogether PFI yielded semiquantitative information on blood perfusion of the gland as well as on the rate of success.

Adolescent↗
PubMed1989

An in vitro comparative study of St. Jude Medical and Edwards-Duromedics bileaflet valves using laser anemometry.

An in vitro comparative study of St. Jude (SJ) and Edwards-Duromedics (DM) Bileaflet valves was performed under steady and physiological pulsatile flow conditions in an axisymmetric chamber using Laser Doppler Anemometry (LDA). LDA measurements were conducted in two different orientations; in the first orientation, the LDA traverse was perpendicular and, in the second orientation, parallel to the tilt axis of the leaflets. The axial velocities were measured in both orientations at two different locations distal to the valves. The velocity profiles at peak systole show the presence of stronger vortex in the sinus region for flow past SJ valve in the first orientation compared to the DM valve. Velocity profile distal to the SJ valve in second orientation was relatively flat where as for the DM valve, a jet-like flow was present. The differences found in the velocity profiles between the two valves can be attributed to the differences in geometry with thicker leaflets, smaller angle of leaflets opening and the presence of the leaflet curvature for the DM valve. The results obtained in this study do not show any fluid dynamic advantages due to the curved leaflet geometry of the DM valve.

Biomechanical Phenomena↗
PubMed1993

Fundamental flow studies in models of human arteries.

Atherosclerosis is the principal cause of myocardial and cerebral infarction. Atherosclerotic lesions are present in localized regions of the vasculature where abrupt changes in vessel geometry occur, such as bends and bifurcations. In order to develop features of the risk profile, flow systems which simulate closely the pertinent anatomy and surface properties of the human vasculature are used with test fluids which mimic the physicochemical properties of blood. Analysis of the flow regimes were made by one-, two- or three-dimensional laser Doppler anemometry. Rigid and elastic model vessels with simple flow geometry as well as true-to-scale models of human arterial casts were used. Viscous pseudoplastic and viscoelastic fluid suspensions were employed under both steady and pulsatile flow. From the measured velocity profiles, the shear rates were estimated and with the local viscosity the shear stresses calculated. Flow behaviour was visualized using dyes and birefringent solutions. It was found that the geometry and flow rate ratio at bifurcations greatly influence the flow separation zones. It is also important to consider elasticity, pulsatility and non-Newtonian flow behavior in large blood vessels in zones where secondary flow is developed and flow separation zones are formed.

Arteries↗
PubMed1993

Effect of stenosis geometry on the Doppler-catheter gradient relation in vitro: a manifestation of pressure recovery.

OBJECTIVES: This study investigated the effect of stenosis geometry on the Doppler-catheter gradient relation. BACKGROUND: Although gradient estimation by Doppler ultrasound has been shown to be accurate in various clinical and in vitro settings, there have also been reports of substantial discrepancies between Doppler and catheter gradients. These conflicting results may be due to differences in geometry and hemodynamic characteristics of flow obstructions. METHODS: Stenoses of various geometry were simultaneously studied with continuous wave Doppler and catheter technique in a well controlled pulsatile flow model. RESULTS: Doppler and catheter gradients correlated very well regardless of stenosis geometry and site of distal catheter measurement (r = 0.98 to 0.99, SEE = 1.8 to 5.3 mm Hg). When the catheter was pulled back through the stenosis, the highest gradients were found in or close to the stenosis. When these catheter gradients were compared with Doppler gradients, the agreement between the two techniques was excellent regardless of stenosis geometry (slope 0.97; mean difference 0.6 +/- 2.0 mm Hg). However, when distal pressures were measured 10 cm downstream from the stenotic segment, the slope of the regression line, and therefore the agreement between Doppler and catheter gradients, differed for the different stenosis types (slopes from 0.98 to 1.69). In stenoses with abrupt narrowing and abrupt expansion, agreement was acceptable. Doppler gradients were only slightly greater than catheter gradients (mean difference 4.5 +/- 5.2 mm Hg). In stenoses with a gradually tapering inlet and outlet, the Doppler-catheter gradient relation was dependent on the outflow angle. Good agreement was found for an angle of 60 degrees (mean difference 0.6 +/- 1.8 mm Hg). In stenoses with a 40 degrees outflow angle, Doppler gradients exceeded the catheter gradients by 13% on average; for stenoses with a 20 degrees outflow angle, Doppler gradients exceeded catheter gradients by 46 +/- 11.4%, with differences as great as 65 mm Hg. These results were identical for stenoses gradually tapering outward to the distal tubing diameter and those with abrupt expansion after 2 cm of gradual expansion. The results were also not affected by changing the inflow angle from 20 degrees to 60 degrees. However, an abrupt narrowing instead of a tapering inlet significantly altered the Doppler-catheter gradient relation (p < 0.001); Doppler gradients exceeded the catheter gradients by 34 +/- 10% for this stenosis type. CONCLUSIONS: Doppler gradients accurately reflect the highest gradients across flow obstructions that occur in the vena contracta. However, these gradients may be significantly greater than catheter gradients that are measured farther downstream, as is usually the case in clinical catheterization studies. These discrepancies are due to pressure recovery. The magnitude of pressure recovery is highly dependent on the stenosis geometry, which therefore significantly affects the Doppler-catheter gradient relation. It is the outflow geometry that predominantly influences this relation, but the shape of the inlet may affect the results as well. Although pressure recovery occurs even in stenoses with abrupt narrowing and abrupt expansion, the phenomenon is most likely to become clinically relevant in stenoses with a gradually tapering inlet and outlet with an outflow angle < or = 20 degrees.

Blood Pressure↗
PubMed2004

Differences in pulsatile ocular blood flow among three classifications of diabetic retinopathy.

PURPOSE: Choroidal blood flow may be determined by pulsatile ocular blood flow (POBF) measurements. In the present study, the POBF of diabetic patients with increasingly severe retinopathy was compared with that in nondiabetic control subjects. METHODS: The study was a masked cross-sectional analysis. Seventy-seven diabetic subjects, including 13 with mild or no retinopathy, 36 with moderate to severe retinopathy, and 28 with proliferative diabetic retinopathy (PDR), previously treated with panretinal photocoagulation (PRP). Fifty-six nondiabetic control subjects served as the comparison group. All subjects underwent masked measurement of POBF in the right eye by Langham pneumotonometry. Analysis of variance (ANOVA) determined whether differences existed between groups. Pair-wise comparisons between groups were conducted by Student's t-test. RESULTS: The main outcome measures were ophthalmic pulse amplitudes, intraocular pressure (IOP), heart rate, and POBF. Patients with moderate to severe nonproliferative diabetic retinopathy (NPDR) had POBF 18% higher than the control (mean OBF, 943 microL/min). Among PRP-treated subjects with PDR, ocular blood flow was 22% below the control (mean OBF, 619 microL/min), and 34% less than moderate to severe nonproliferative diabetic retinopathy. Diabetic patients with no retinopathy or mild NPDR had OBF indistinguishable from the control (785 vs. 797 microL/min). Differences between the four groups were statistically significant by ANOVA (P < 0.0001). CONCLUSIONS: POBF is unaffected early in diabetic retinopathy, but increases significantly in eyes with moderate to severe NPDR. POBF is decreased in eyes with laser-treated PDR. These experimental data represent the largest published assessment of POBF in NPDR. This is the first study to examine POBF in subjects with PRP-treated PDR.

Aged↗
PubMed1998

In vitro evaluation of the long-body On-X bileaflet heart valve.

BACKGROUND AND AIMS OF THE STUDY: In order to optimize the length-to-diameter ratio, a series of circular aluminum rings with flared inlet and varying ring lengths, with internal diameters corresponding to that of 19 mm replacement prosthetic heart valve orifices, were tested in a steady-flow hydraulic system. The study aim was to determine the ring length-to-internal diameter ratio that produces the best hydraulic efficiency (i.e. lowest pressure gradient) within the physiologic flow rate range. METHODS: Each ring was tested at flow rates of 10, 15, 20, 25 and 30 l/min and length-to-diameter ratio effect on hydraulic efficiency determined experimentally. The hydraulic effect was most significant for a ratio of about 0.6, with an increase to 1.2 providing little additional benefit. Thus, a ratio of about 0.6 was considered optimum in terms of hydraulic efficiency and incorporated into the design of the On-X bileaflet mechanical heart valve (BHV) series. An in vitro hydrodynamic study of the smallest (19 mm) and largest (25 mm) clinical On-X aortic valves was performed at two independent laboratories. Standard St. Jude Medical BHVs were used as the study controls. RESULTS: Steady-flow experiments showed that the pressure gradient in the On-X valve was about 50% less than that of the comparable size control. The pulsatile flow study demonstrated a similar pressure gradient advantage. Laser Doppler anemometer velocity profiles taken downstream of the On-X valve at the aortic root showed typical characteristics of bileaflet valves, with three velocity peaks. The peak velocity reached 1.6 m/s for the On-X and 1.75 m/s for the control valve. A recirculating vortex was seen in the sinus cavity during the ejection period. This vortex, found in most aortic valves (including bioprostheses), is believed to provide a beneficial wash-out of the valve region and assist in valve closure. CONCLUSIONS: These two independent studies clearly demonstrated that the elongated valve body and comparably larger flow area helped to improve the valve hydrodynamic performance, which is especially beneficial in the smallest (19 mm) size valve.

Aortic Valve↗
PubMed1991

Impedance analysis to identify the at risk femorodistal graft.

Computer-assisted impedance analysis is a newly developed technique to identify femoropopliteal and distal vein graft stenoses before failure. Pulsatile flow is measured from the proximal and distal graft by use of an 8Mhz Doppler velocimeter. A pulse volume recorder measures pulsatile pressure within the thigh and calf. Fourier transfer analysis is performed on paired Doppler pulse volume recorder waveforms and an impedance score derived for the thigh and calf, respectively. In a retrospective review of 50 nonreversed femoropopliteal/distal grafts performed for limb salvage, postoperative biplanar intraarterial digital subtraction arteriography was compared with impedance analysis. Arteriography showed graft or runoff stenoses in 22 grafts (at risk) and 28 normal grafts (controls). Impedance scores were significantly higher in the at risk group (0.58 + [0.43 to 0.72]*), when compared with the controls (0.34 + [0.30 to 0.38], p less than 0.001*). A thigh or calf impedance score of greater than 0.45 was able to detect 20 of 22 stenoses, including 6 lesions in grafts with normal resting and postexercise ankle pressures. This score was then applied prospectively and compared with serial biplanar digital subtraction arteriography in a further 56 femoropopliteal/distal bypasses for limb salvage. Thirty-three of 34 lesions were successfully predicted and impedance scores were significantly higher in the at risk limbs (0.56 + [0.44 to 0.68]*) when compared with the controls (0.38 + [0.35 to 0.41], p less than 0.001*). In this series impedance analysis proved more sensitive than resting or stressed ankle pressures and, unlike Duplex scanning, was able to detect runoff as well as graft stenoses.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMedDate not supplied

The effects of low flow, low pressure pulsatile bypass.

The effects of low flow low pressure pulsatile bypass were studied in 90 consecutive patients undergoing coronary artery surgery. Overall pump flow rate (OFR) was 19-49 (mean 31 +/- 7) ml/kg/min at all temperatures. Moderate (28 degrees C) hypothermia was used. When cross-clamped flow was 17-49 (mean 27 +/- 7) ml/kg/min and mean perfusion pressure 50-60 mmHg. Priming volume (PV) was reduced to 1.45 +/- 0.02 L (range 1.2-2.0 L) PV, cardioplegia and volume additions were considered as total bypass crystalloid (TBC) and this correlated positively with increased post-operative positive water balance (r = 0.58, P less than 0.001). Bypass urine output averaged 135 +/- 24 ml (range 0-1,000 ml) was unrelated to OFR and correlated only with TBC (r=0.47, P less than 0.001). In 86 a single cardioplegia dose of 0.7 L (range 0.4-0.8 L) sufficed for this ischaemic period (mean 46 +/- 16 min). Four required a further 0.2-0.3 L. Their ischemic times were 44-74 min (mean 59 +/- 13 PNS). Inotropes were used in only 3 patients. Post-operatively 7 required diuretics for low hourly urine flow. Of the 76 with normal pre-operative renal function urea rose transiently in 15. Three had raised urea for over 9 days. Creatinine rose transiently in 7 but persisted in only one. Plasma cortisol (n=78) rose in 67 and fell in 11, indicating, overall, an adequate metabolic response. Plasma free haemoglobin before and after bypass varied widely and did not correlate with flow rate or perfusion time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗