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PubMed2004

Flow-induced platelet activation in bileaflet and monoleaflet mechanical heart valves.

A study was conducted to measure in vitro the procoagulant properties of platelets induced by flow through Carbomedics bileaflet and Bjork-Shiley monoleaflet mechanical heart valves (MHVs). Valves were mounted in a left ventricular assist device, and platelets were circulated through them under pulsatile flow. Platelet activation states (PAS) were measured during circulation using a modified prothrombinase method. Computational fluid dynamics (CFD) simulations of turbulent, transient, and non-Newtonian blood flow patterns generated by the two valve designs were done using the Wilcox k - w turbulence model, and platelet shear-stress histories (the integral of shear-stress exposure with respect to time) through the two MHVs were calculated. PAS measurements indicated that the bileaflet MHV activated platelets at a rate more than twice that observed with the monoleaflet MHV. Turbulent flow patterns were evident in CFD simulations for both valves, and corroborated the PAS observations, showing that, for particles close to the leaflet(s), shear-stress exposure in the bileaflet MHV can be more than four times that in the monoleaflet valve.

Aortic Valve↗
PubMed1983

Pulmonary prostacyclin production with increased flow and sympathetic stimulation.

We evaluated the effects of an abrupt increase in flow and of a subsequent sympathetic nerve stimulation on the pulmonary production of prostacyclin (PGI2) and thromboxane A2 (TXA2) in canine isolated left lower lobes perfused in situ with pulsatile flow. When flow was abruptly increased from 50 +/- 3 to 288 +/- 2 ml/min, mean pulmonary arterial pressure (Ppa) increased by 15 +/- 2 Torr and then declined by 2.4 Torr over the next 5 min. This secondary decrease in Ppa was associated with a significant 0.26 +/- 0.11 ng/ml increase in the pulmonary venous concentration of the stable PGI2 hydrolysis product 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) as determined by radioimmunoassay. Stimulation of the left stellate ganglion usually resulted in an increase in Ppa which peaked at 1.1 +/- 0.6 Torr above its prestimulus level and then declined over the next 5 min. Associated with this decline was a 0.24 +/- 0.11 ng/ml increase in 6-keto-PGF1 alpha at 1 min. We suggest that the decline in Ppa is due to the synthesis and release of PGI2 by the endothelial cells in response to an increase in perfusion pressure.

6-Ketoprostaglandin F1 alpha↗
PubMed1990

An in vitro study of the onset of turbulence in the sinus of Valsalva.

During systole a small portion of the mainstream aortic flow is intercepted by the sinus ridge, or downstream corner of the sinus of Valsalva. This fluid curls back toward the ventricle to form a large eddy, or vortex, that spins within the sinus cavity. The fluid motion within similar recirculating flows is known to be unstable with an early transition to turbulence. The stability of the aortic sinus vortex was examined in the current study in an in vitro pulsatile flow rig. The geometry of the experimental test section was the same as the geometry of the natural aortic root. Different model valves, including a natural valve, were placed in the test section, and different flow conditions were studied. Point velocities were measured by hot film probes placed at two locations within the sinus vortex. The velocity waveforms and their power spectra were used to determine the stability of the sinus flow. The experimental results revealed that the aortic sinus vortex becomes turbulent under simulated exercise conditions. Turbulent intensities were highest near the sinus ridge, which is the location of the coronary ostia. Despite the transition to turbulence within the vortex, the mainstream aortic flow upstream from the valve remained laminar. The turbulence within the vortex was also associated with vibration of the valve leaflets under exercise conditions. These vibrations may be related to the systolic ejection murmurs that are heard clinically. Furthermore, the localized turbulence may explain the location of atherosclerotic lesions and dissecting aneurysms, as well as the distribution of the lesions of bacterial endocarditis.

Animals↗
PubMed2006

Turbulent flow as a cause for underestimating coronary flow reserve measured by Doppler guide wire.

BACKGROUND: Doppler-tipped coronary guide-wires (FW) are well-established tools in interventional cardiology to quantitatively analyze coronary blood flow. Doppler wires are used to measure the coronary flow velocity reserve (CFVR). The CFVR remains reduced in some patients despite anatomically successful coronary angioplasty. It was the aim of our study to test the influence of changes in flow profile on the validity of intra-coronary Doppler flow velocity measurements in vitro. It is still unclear whether turbulent flow in coronary arteries is of importance for physiologic studies in vivo. METHODS: We perfused glass pipes of defined inner diameters (1.5-5.5 mm) with heparinized blood in a pulsatile flow model. Laminar and turbulent flow profiles were achieved by varying the flow velocity. The average peak velocity (APV) was recorded using 0.014 inch FW. Flow velocity measurements were also performed in 75 patients during coronary angiography. Coronary hyperemia was induced by intra-coronary injection of adenosine. The APV maximum was taken for further analysis. The mean luminal diameter of the coronary artery at the region of flow velocity measurement was calculated by quantitative angiography in two orthogonal planes. RESULTS: In vitro, the measured APV multiplied with the luminal area revealed a significant correlation to the given perfusion volumes in all diameters under laminar flow conditions (r2 > 0.85). Above a critical Reynolds number of 500--indicating turbulent flow--the volume calculation derived by FW velocity measurement underestimated the actual rate of perfusion by up to 22.5 % (13 +/- 4.6 %). In vivo, the hyperemic APV was measured irrespectively of the inherent deviation towards lower velocities. In 15 of 75 patients (20%) the maximum APV exceeded the velocity of the critical Reynolds number determined by the in vitro experiments. CONCLUSION: Doppler guide wires are a valid tool for exact measurement of coronary flow velocity below a critical Reynolds number of 500. Reaching a coronary flow velocity above the velocity of the critical Reynolds number may result in an underestimation of the CFVR caused by turbulent flow. This underestimation of the flow velocity may reach up to 22.5 % compared to the actual volumetric flow. Cardiologists should consider this phenomena in at least 20 % of patients when measuring CFVR for clinical decision making.

Artifacts↗
PubMedDate not supplied

Hydrodynamics of a long-body bileaflet mechanical heart valve.

A new bileaflet substitute mechanical heart valve (MHV) that incorporates an optimal length-to-annulus ratio for improved hydrodynamic efficiency was recently introduced. Efforts have been made on this new prosthesis to use the current advances in carbon materials and design technology to achieve higher net forward flow with minimal energy loss for the smaller aortic valves, while reducing regurgitant closure volume for the larger size valves by an elongated orifice. Benchtop experiments performed in a pulsatile flow loop, under simulated physiologic conditions, substantiated these improvements as claimed.

Aortic Valve↗
PubMed2003

Unrecordable pulsatile ocular blood flow may signify severe stenosis of the ipsilateral internal carotid artery.

AIM: To examine the relation between stenosis of the internal carotid artery (ICA) and pulsatile ocular blood flow (POBF). METHODS: In 57 eyes of 30 patients who were referred for Doppler ultrasound examination of the ICA we measured POBF and analysed the correlation with degree of ipsilateral ICA stenosis. RESULTS: There was a significant negative correlation between POBF and ipsilateral ICA stenosis (Pearson correlation coefficient, r=-0.516, p<0.0001). In 14 eyes POBF could not be measured by the OBF tonometer, and in 11 of these cases (79%) severe stenosis (>75%) of the ipsilateral ICA was present. When these eyes were excluded from analysis, there was no correlation between POBF and ICA stenosis (r=-0.02, p=0.91). Among these 43 eyes in which POBF could be measured it ranged 667-2095 microl/min with a mean of 970.72 microl/min. CONCLUSION: Low or unrecordable POBF may signify severe stenosis of the internal carotid artery. POBF is not a direct reflection of ipsilateral ICA blood flow.

Aged↗
PubMed1994

Clinical application of pulsatility index of flow volume to detect the hemodynamic changes in IUGR fetus.

We attempted to assess feto-placental circulation in fetuses with intrauterine growth retardation (IUGR) by calculating the pulsatility index of flow volume (PIQ) based on the quantitative measurement of blood flow. Doppler sound was processed by an analog to digital converter and a frequency analyzer. Multiplication of frequency and signal strength of the Doppler sound at a certain time theoretically represents a value proportional to flow volume. Using this value, we calculated PIQ of the descending aorta, umbilical artery, and middle cerebral artery in normal fetuses, IUGR fetuses, and distressed fetuses during 24-41 weeks gestation. The PIQ of the fetal descending aorta in the IUGR fetus was significantly higher than that of the normal fetus. When cutoff value was set to mean +1 SD, abnormal PIQ was observed in 88% of IUGR fetuses. In contrast, the abnormal pulsatility index of maximal flow velocity (PIV) of the descending aorta was observed in only 62% of IUGR fetuses. In the distressed fetuses, both PIQ and PIV of the umbilical artery increased, and these indices of the middle cerebral artery markedly decreased. It is suggested that the increased PIQ of the descending aorta is an early indicator of changes in the fetal circulation in IUGR fetuses.

Aorta↗
PubMed2002

Effect of treatment by medicine or surgery on intraocular pressure and pulsatile ocular blood flow in normal-pressure glaucoma.

PURPOSE: To study the effect of trabeculectomy and monotherapy with topical betaxolol, brimonidine and latanoprost on intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) in patients with normal-pressure glaucoma (NPG). METHODS: In this retrospective study NPG patients attending the glaucoma research unit at Moorfields Eye Hospital were reviewed. Patients treated by surgery or topical medication (betaxolol, brimonidine or latanoprost) who had pre- and post-treatment IOP and POBF measurements were studied. For those patients who were having treatment to both eyes, one eye was selected at random for analysis. RESULTS: A total of 147 patients were reviewed. Forty-three eyes were receiving betaxolol 0.5%, 58 eyes latanoprost 0.005%, 23 eyes brimonidine 0.2% and 23 eyes had undergone trabeculectomy surgery. There were more female than male patients in all four groups, and the groups were similar with regards age. Pre-treatment IOP and POBF values were similar among the groups ( P=0.27, P=0.08 respectively). Post-treatment IOP values tended to be lower than pre-treatment values for all four groups. All groups had an increased POBF except for betaxolol, where POBF decreased. CONCLUSION: Patients treated by trabeculectomy and those receiving topical latanoprost and brimonidine had lower IOP and higher POBF following treatment. The betaxolol-treated group, despite a slight decrease in IOP, had a decreased POBF. Lowering IOP by treatment may not necessarily be associated with an increase in POBF.

Administration, Topical↗
PubMed1988

Patterns of blood flow in episcleral vessels studied by low-dose fluorescein videoangiography.

The blood supply of the ocular anterior segment arises from a saggittal arterial ring composed of the long posterior ciliary arteries, the muscular and anterior ciliary arteries and perforating scleral arteries. This ring supplies coronal arterial circles within and outside the globe. Low dose anterior segment fluorescein videoangiography demonstrates arterial and venous flow, recording its characteristics and direction. Videoangiograms were performed at low and high magnification in 15 normal subjects. Episcleral arteries and veins were distinguishable by the presence or absence of pulsatile flow and by their fluorescence intensity. Arteries usually perfused earlier than veins, and with higher flow velocity. Twenty-five of 40 arteries flowed away from scleral perforations close to the limbus. All 8 veins drained away from the limbus. The communication between two arteries may be demonstrated by a static, pulsating column of non-fluoresceinated blood. This sign arose at a point of scleral perforation, at the junction between muscular and anterior ciliary arteries and in the episcleral anterior circle. It supports the concept of arterial shunting, both in the saggittal plane and in the superficial coronal circle. Perforating scleral arteries lay anterior to the episcleral arterial circle in superior angiograms and posterior to it in inferior studies. Vessels that had been characterised by videoangiography were identified in stereo colour photographs of angiographic fields. Arteries were best distinguished from veins by their high tortuosity and thick walls. Using these photographic characteristics, the distribution of arteries and veins over the rectus muscles was surveyed in 13 subjects. The incidence of arteries is lowest over the lateral rectus muscle. Veins were concentrated in the vertical meridian and were absent over lateral rectus in 8 subjects. Five intra-operative videoangiograms are reported. Retraction of conjunctiva facilitated imaging of the episcleral vessels and demonstrated arterial communication through a shared capillary bed.

Adult↗
PubMed1990

Flow measurements in a model of the mildly curved femoral artery of man.

Steady flow observations in a smooth curved femoral artery model with a gradual bend revealed a flow pattern like that observed in coiled pipes. A double helical type flow was found to develop, with converging streamlines in the wall vicinity from the upper and lower plane of curvature merging asymptotically along the inner curvature in a stable manner. The helical or swirl angle of the labeled fluid particle paths increased with flow rate and thus Dean number. Flow in the wall vicinity was altered by centrifugal effects almost immediately downstream of the transition from the straight to curved segment for steady flow, although the propagation of this effect was observed farther downstream along the inner curvature side. This observed distance along the inner curvature became shorter with increasing Dean number. Pressure measurements for steady flow revealed progressively larger pressure drops with distance along the entrance region of the curved segment relative to that for a straight lumen. The overall pressure drop or flow resistance increased in a nonlinear way with increasing flow rate and thus Dean number. Time average pressure drop measurements across another similar smooth curved femoral model were found to be about the same for simulation of femoral artery pulsatile flow as for steady flow.

Blood Flow Velocity↗
PubMedDate not supplied

Monitoring regional cerebral oxygen saturation using near-infrared spectroscopy during pulsatile hypothermic cardiopulmonary bypass in a neonatal piglet model.

Impairment of cerebral oxygenation in neonates and infants after hypothermic nonpulsatile cardiopulmonary bypass (CPB) support is well documented. The objectives of this study were: 1) using a neonatal piglet model to continuously monitor the regional cerebral oxygen saturation (rSO2) by near-infrared spectroscopy during pulsatile hypothermic CPB; and 2) to quantify the pulsatile flow in terms of energy equivalent pressure (EEP). After initiation of CPB, all piglets (n = 5) were subjected to 15 minutes of core cooling, reducing the rectal temperature to 25 degrees C, followed by 60 minutes of hypothermic CPB, then 10 minutes of cold reperfusion, and 30 minutes of rewarming. During CPB, mean arterial pressures (MAPs) and pump flow rates were maintained at 40-45 mm Hg and 150 ml/kg/min, respectively. During normothermic CPB, the rSO2 was significantly increased, compared with the pre-CPB level (56.8 +/- 5.2% vs. 41.8 +/- 5.5%, p < 0.01). At the end of cooling, the rSO2 level was 76.8 +/- 8.6% (p < 0.001 vs. pre-CPB). After 60 minutes of hypothermic CPB and 30 minutes of rewarming, the rSO2 level was decreased to 38.6 +/- 4.2%, which was not significantly different compared with the pre-CPB level. The average increase in pressure (from MAP to EEP) was 5 +/- 1%, and the average increase in extracorporeal circuit pressure (from ECCP to EEP) was 13 +/- 2%. This extra pressure may help to provide better regional cerebral oxygen saturation. During pulsatile CPB, there was no rSO2 deficiency in this high flow model. Near-infrared spectroscopy responded well to changes in rSO2 during different stages of these experiments and might be a helpful tool for intraoperative monitoring.

Animals↗
PubMed2004

A comparison of the effects of dorzolamide/timolol fixed combination versus latanoprost on intraocular pressure and pulsatile ocular blood flow in primary open-angle glaucoma patients.

PURPOSE: To evaluate the effects of dorzolamide/timolol fixed combination (D/T) compared to latanoprost on intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) in primary open-angle glaucoma (POAG) patients. METHODS: Thirty patients with POAG were randomized in an open-label, cross-over study. Intraocular pressure reduction was achieved by 4 weeks medical therapy with D/T twice daily or latanoprost 0.005% dosed once in the evening. During a 4-week run-in and a 4-week wash-out period between study arms, patients ceased use of all other glaucoma medications and used timolol maleate 0.5% twice daily. Primary efficacy variables were IOP and POBF. RESULTS: There was no difference in baseline IOP and POBF parameters between the two study arms. Both D/T and latanoprost statistically significantly reduced IOP by 4.6 mmHg (p < 0.0001) and 3.75 mmHg (p < 0.0001) and increased POBF by 2.048 microl/second (p = 0.0030) and 2.147 microl/second (p = 0.0009), respectively. Repeated measures anova detected significant changes in POBF with treatment (p = 0.0361). Dorzolamide/timolol fixed combination statistically significantly increased pulse volume by 0.767 microl (p = 0.0087), while latanoprost therapy had no significant effect (p = 0.2407). CONCLUSIONS: Both drugs had similar effects in terms of IOP reduction. Dorzolamide/timolol significantly increased pulse volume while latanoprost had no effect. Further studies are necessary to establish whether the enhancement of choroidal blood flow can prevent glaucoma progression.

Adult↗
PubMed1997

Effect of timolol and UF-021 (a prostaglandin-related compound) on pulsatile ocular blood flow in normal volunteers.

The effects of topically applied timolol (a nonselective beta-blocker) and UF-021 (a prostaglandin-related compound) on pulsatile ocular blood flow (POBF) were investigated in 9 healthy volunteers. One drop of either UF-021 or timolol was instilled in one randomly selected eye and the fellow eye received physiologic saline. Before and 90 min after drop instillation, we measured intraocular pressure (IOP), POBF, heart rate (HR) and blood pressure (BP). After a washout interval of at least 1 week, the other drug was instilled in the previously treated eye. IOP, POBF, HR, and PB were measured following the same protocol. After timolol administration, IOP and POBF decreased significantly in the treated eye (26%, p = 0.01, and 13%, p = 0.02, respectively) and in the fellow eye (11%, p = 0.01, and 11%, p = 0.03, respectively). HR also decreased (10%, p = 0.03), but BP did not change significantly. After UF-021 administration, no significant changes were found in IOP, POBF, HR, or BP. Our results suggest that in normal subjects timolol decreases POBF in both the treated and the untreated eyes, whereas UF-021 has no action on either IOP or POBF.

Administration, Topical↗
PubMed1991

Cine phase-contrast magnetic resonance imaging for analysis of flow phenomena in experimental aortic dissection.

Using a 1.5 T magnetic resonance imaging (MRI) system, cine phase-contrast and magnitude images were obtained in three phantoms that simulated different anatomic configurations of aortic dissection. The dissection phantoms were made of compliant materials, and pulsatile flow was used in all experiments. Phantoms differed only in the location of the fenestration between the true and false lumens (I: an upstream "entry" only, II: both upstream "entry" and downstream "re-entry," and III: a downstream "entry" only). Flow jets, flap motion, and wave propagation were clearly visualized in cine MR images of each phantom, and quantitatively analyzed with reference to the stimulated cardiac cycle of the pump. Flow in the false lumen was always bidirectional. Upstream and downstream flow waves collided and dispersed within the false lumen. Flow through the false lumen was the same in phantoms I and II, and least in phantom III. The average area of the true lumen was largest in phantom III and smallest in I. Phantom I had the highest overall flow rate in the false lumen and greatest change in false lumen size during the cardiac cycle, while the downstream "entry" phantom had the lowest of both parameters. Flow phenomena in aortic dissections can be studied by cine phase-contrast MRI.

Aortic Dissection↗
PubMed1999

Pulmonary arterial Doppler velocimetry in fetuses with lung hypoplasia.

OBJECTIVE: The aim of the study was to examine Doppler flow velocity waveforms in the main stems of the pulmonary arteries in fetuses with autopsy-proven lung hypoplasia and to find out whether in these conditions typical patterns can be found. STUDY DESIGN: Doppler spectra were derived from the main stem of the right or left pulmonary artery in fetuses at high-risk for lung-hypoplasia. The following Doppler parameters were analyzed and compared to reference ranges: peak systolic velocity, acceleration time, time velocity integral, end-systolic reverse flow, pulsatility index (PI). Pulmonary hypoplasia was found in nine cases at autopsy after termination of pregnancy (19-23 weeks). According to etiology, three groups were considered: (A) bilateral renal malformations (n=4), (B) congenital diaphragmatic hernia (n=2), and (C) miscellaneous malformations including heart defects (n=3). RESULTS: The following Doppler parameters were found: normal values in end-systolic reversal flow in all cases, decreased peak systolic velocity and acceleration time in 3/9, decreased time velocity integral in 4/9 and increased pulsatility index in 6/9. Considering the etiology of pulmonary hypoplasia the pulsatility index was found to be the most sensitive, since all fetuses in groups A and B had an abnormal PI. CONCLUSIONS: Human fetuses with renal malformations and diaphragmatic hernia associated with lung hypoplasia show as early as 19-23 weeks of gestation an abnormal Doppler spectrum in the main stems of the pulmonary arteries. Increased PI is the best parameter to detect flow abnormality in this condition. Since the Doppler spectrum depends on cardiac anatomy and function, PI in lung hypoplasia seems to be reliable only when cardiac defects are absent.

Blood Flow Velocity↗
PubMed1987

Valvular obstruction of blood flow through saphenous veins.

To measure effects of vein valves upon blood flow through venous bypass conduits, 15 human saphenous veins (mean length 40.6 cm, 5.3 valves/vein) were perfused with normal saline at constant pressure (100 mm Hg). Flow through vein was measured before and after valve bisection. Vein valves were bisected using Leather's techniques. After valve bisection, flow in antegrade and retrograde directions was measured in seven veins. These data were analyzed using paired t tests. Antegrade flow through seven veins with intact valves averaged 317.1 cc/min. With valve bisection this increased significantly (P less than 0.001) to 474.3 cc/min. Retrograde flow through veins with valves bisected increased significantly (P less than 0.0001) to 428.3 cc/min. Eleven veins (mean length 42.2 cm, 5.6 valves/vein) perfused simulated capillary beds with banked blood using pulsatile flow (mean pressure 92 mm Hg). Flow, again, was measured before and after valve bisection. Data were analyzed using the paired t test. Antegrade flow increased from 124.4 cc/min in veins with valves intact to 142.5 cc/min once valves were bisected (P = 0.02). These data demonstrate that saphenous vein valves cause significant obstruction to blood flow under conditions similar to those in the arterial system. Bisection of vein valves significantly increases flow through vein. Improved patency of vein grafts using valve bisection techniques may be explained by increased blood flow alone.

Blood Flow Velocity↗