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PubMed1984

Characteristics of flow velocities in the umbilical arteries, assessed by Doppler ultrasound.

Measuring blood velocities by Doppler ultrasound has introduced a new noninvasive technique into obstetrical diagnostics. This study evaluates the information about fetoplacental hemodynamics that can be extracted from Doppler signals obtained from umbilical arteries. The most significant blood flow characteristic is blood flow pulsatility expressed as pulsatility index (PI). The PI is the difference between systolic and diastolic velocity, divided by the mean velocity. The PI strongly correlates with downstream impedance to flow. It is demonstrated that sophisticated spectral analysis of the Doppler signals has no practical advantages over the simple zero-crossing technique for establishing PI values, since blood flow in umbilical arteries has a blunt-to-flat profile. This study shows that the PI is a gestational-age-related, intra- and inter-observer-reproducible variable. The significant decrease of PI values with advancing gestational age reflects a progressive reduction of placental vascular resistance to umbilical blood flow. The PI holds promise as a simple method for early diagnosis of impaired umbilical circulation.

Blood Flow Velocity↗
PubMedDate not supplied

Technical note: a durable impeller pump with rolling bearing and purge system.

Our former works demonstrated that the authors' impeller pump could support the circulation of experimental animals for several months without harm to blood elements and organ function of the animals. The termination of the experiments was mostly related to wear of the mechanical bearing and the thrombosis along the bearing. To solve the bearing problem, a magnetic bearing was investigated in our laboratory, resulting in some new problems, such as complicated design and control, considerable energy consumption and lower reliability. Progress in developing an impeller pump for long-term application has been achieved recently. Instead of using a slide bearing, a rolling bearing system has been devised. Its service life is more than ten years due to a wear-proof roller made of ultra-high molecular weight poythene. In order to avoid thrombus formation, a special purge system was introduced to the bearing, thus saline with heparin can be infused through the bearing into the pump. Therefore, the bearing keeps working in the saline, and no thrombus will be formed along the beating. The animal experiments demonstrated that 30 cc fluid infusion per hour continuously or interruptedly is enough to prevent the thrombus formation. With these improvements, the impeller pump was continuously run for one year and no bearing wear was measured in the endurance test. The device weighing 150g is fully implantable, consumes around 9.6 W electric energy by delivering 9 l min(-1) blood flow against 120 mmHg mean pressure and reaches a highest total efficiency, 24.7%, of motor (including controller) and pump at this point, which can produce both pulsatile and non-pulsatile flow according to the requirements.

Animals↗
PubMed1984

Neonatal cerebral blood flow velocity I. An in vitro validation of the pulsed Doppler technique.

A combined pulsed and continuous Doppler instrument was used to assess flow velocities in an in vitro model designed to simulate small deeply lying arterial vessels. Diameters of the model vessels, depth under the transducers and the pulsatile flow patterns were chosen to simulate the corresponding conditions that can be expected when cerebral blood flow velocities are measured with this technique through the anterior fontanel in newborn infants. Computer analysis of the space average velocity signal from the pulsed Doppler mode, showed that the area under this curve, which corresponds to distance, was closely correlated to true flow over a wide range of flows in vessels of different diameters. This variable is suggested to be the closest estimate of true flow, when the diameter of the vessel under study cannot be accurately measured.

Blood Flow Velocity↗
PubMed1983

Quantitative evaluation of the pattern of shunt flow in the right ventricle and pulmonary artery of dogs with experimental ventricular septal defect.

Cineangiographic studies in patients with ventricular septal defect (VSD) have occasionally demonstrated that part of the blood across the defect is ejected immediately into the pulmonary artery (PA) passing through the outflow tract of the right ventricle (RV), but without being trapped in it. We attempted to make a quantitative evaluation of the flow of a partial shunt pathway (a direct VSD-PA pathway) that drains that part of the blood from the defect. Our method depended on a thermal dilution technique to obtain the ejection fraction of the RV and to observe a simultaneous pair of dilution curves at the roots of the aorta and PA after introduction of tracer into the left atrium. An analytical process was specially designed by incorporating a stable one-pass deconvolution technique. The method was applied to eight anesthetized dogs with acutely produced experimental VSD on the entrance of the outflow tract of the RV. The flow through the direct VSD-PA pathway was, in most cases, greater than 50 and up to 85% (mean of the eight, 57 +/- 5% SE) of the total left-to-right shunt flow. This would imply that less than 50%, and down to as little as 15%, of the total amount of shunt flow contributed to extra work of the RV in these cases. In addition, the impact on the pulmonary vasculature due to such a large amount of pulsatile flow through the direct VSD-PA pathway may accelerate the development of hypertrophy of the pulmonary vessel wall.

Animals↗
PubMed1990

Correlation of laser Doppler wave patterns with underlying microvascular anatomy.

Laser Doppler velocimetry (LDV) was performed on the chest, back, and abdomen of four healthy volunteers. As the probe was moved over distances of 2-6 mm, the red-cell flux varied by 100%, but was associated with three distinctive wave patterns. Correlative skin biopsies showed that a high flux, pulsatile pattern superimposed on vasomotor activity was found when the probe was directly over an ascending elastic arteriole with its immediate branches; low flux, pulsatile flow with minimal or no vasomotor activity was found when the probe was off center relative to the ascending arteriole and its branches; and a low flux, non-pulsatile pattern occurred when the probe window was situated between ascending arterioles over an area in the upper horizontal plexus composed primarily of capillaries and post-capillary venules.

Humans↗
PubMedDate not supplied

Evaluation of biodegradable, three-dimensional matrices for tissue engineering of heart valves.

A crucial factor in tissue engineering of heart valves is the type of scaffold material. In the following study, we tested three different biodegradable scaffold materials, polyglycolic acid (PGA), polyhydroxyalkanoate (PHA), and poly-4-hydroxybutyrate (P4HB), as scaffolds for tissue engineering of heart valves. We modified PHA and P4HB by a salt leaching technique to create a porous matrix. We constructed trileaflet heart valve scaffolds from each polymer and tested them in a pulsatile flow bioreactor. In addition, we evaluated the cell attachment to our polymers by creating four tubes of each material (length equals 4 cm; inner diameter, 0.5 cm), seeding each sample with 8,000,000 ovine vascular cells, and incubating the cell-polymer construct for 8 days (37 degrees C and 5% CO2). The seeded vascular constructs were exposed to continuous flow for 1 hour. Analysis of samples included DNA assay before and after flow exposure, 4-hydroxyproline assay, and environmental scanning electron microscopy (ESEM). We fabricated trileaflet heart valve scaffolds from porous PHA and porous P4HB, which opened and closed synchronously in a pulsatile bioreactor. It was not possible to create a functional trileaflet heart valve scaffold from PGA. After seeding and incubating the PGA-, PHA-, and P4HB-tubes, there were significantly (p < 0.001) more cells on PGA compared with PHA and P4HB. There were no significant differences among the materials after flow exposure, but there was a significantly higher collagen content (p < 0.017) on the PGA samples compared with P4HB and PHA. Cell attachment and collagen content was significantly higher on PGA samples compared with PHA and P4HB. However, PHA and P4HB also demonstrate a considerable amount of cell attachment and collagen development and share the major advantage that both materials are thermoplastic, making it possible to mold them into the shape of a functional scaffold for tissue engineering of heart valves.

Animals↗
PubMed1999

Ethanol enhances basal and flow-stimulated nitric oxide synthase activity in vitro by activating an inhibitory guanine nucleotide binding protein.

The aim of this study was to determine the effect of ethanol on endothelial nitric oxide synthase (eNOS), the enzyme responsible for the production of the important vasoactive agent nitric oxide. The effect of ethanol (0.8-160 mM) on both basal and flow-stimulated eNOS activity was determined using cultured bovine aortic endothelial cells (EC). In "static" EC ethanol dose-dependently increased basal eNOS activity with a maximum response (approximately 2.0-fold increase) achieved at 40 mM in the absence of any effect on cell viability or nitric oxide synthase protein expression. Pertussis toxin (PTX) pretreatment significantly inhibited the ethanol-induced increase in basal eNOS activity. EC exposed to steady laminar flow exhibited a flow- and time-dependent increase in eNOS activity. Ethanol significantly enhanced the laminar flow-induced eNOS response from 0.62 +/- 0.1 to 1.06 +/- 0. 06 pmol [14C]citrulline/mg/min, a response that was inhibited by PTX. PTX-catalyzed ribosylation of Gialpha substrates, an index of G-protein functional activity, was increased in laminar flow-exposed EC compared with static controls and was further enhanced by ethanol treatment. Likewise, EC exposed to low ( approximately 0.5 dynes/cm2) and high ( approximately 12 dynes/cm2) pulsatile flow demonstrated increased eNOS activity, an effect that was associated with increased PTX-catalyzed ribosylation of Gialpha substrates. Ethanol enhanced the low flow response in a PTX-sensitive manner. These data demonstrate a stimulatory effect of ethanol on basal and flow-stimulated eNOS activity, mediated in part by a mechanism involving a PTX-sensitive G protein.

Animals↗
PubMed1980

Hemolysis during pulsatile perfusion: clinical evaluation of a new device.

The degree of hemolysis occurring during cardiopulmonary bypass was evaluated in two groups of patients undergoing pulsatile and nonpulsatile perfusion. Results indicate that, with a newly developed method of creating pulsatile flow, both groups of patients compared favorably and had approximately the same degree of hemolysis. Because of its simplicity, low cost, reliability, and limited hemolytic activity, this pulsatile device warrants further clinical evaluation.

Cardiac Surgical Procedures↗
PubMed2005

Pulsatile ocular blood flow in patients with Graves' ophthalmopathy.

PURPOSE: Graves' ophthalmopathy (GO) is a cosmetically disfiguring and vision-threatening complication of Graves' disease (GD). We investigated the clinical application of pulsatile ocular blood flow (POBF) measurement for detection of clinically active GO. METHODS: In this prospective study, the OBF tonometer (OBF Labs, Wiltshire, UK) was used to measure POBF in 83 eyes of 83 patients with GD in two groups and 42 normal control subjects. Group A comprised 35 GD patients without ophthalmopathy, and group B composed 48 GD patients with ophthalmopathy. Results were compared with controls. RESULTS: Pulse amplitude, pulse volume, and POBF were significantly lower in group B than that in group A and controls (P<0.001). After adjusting for age, sex, systolic blood pressure, diastolic blood pressure, heart rate, intraocular pressure, and axial length, multivariate linear regression analysis showed that POBF was still significantly lower in eyes with GO (772.4 (SD 279.3) microl/min) than group A (1177.3 (SD 326.3) microl/min) and controls (1255.4 (SD 295.1) microl/min) (P<0.001). CONCLUSIONS: These data show that the pulsatile ocular blood flow differences between the groups are relevant to the presence of GO. POBF measurement is a clinically useful adjunct for assessing the haemodynamic change in GO patients.

Adult↗
PubMedDate not supplied

Depiction of carotid plaque ulceration and other plaque-related disorders by intravascular sonography: a flow chamber study.

PURPOSE: To evaluate the ability of intravascular sonography to depict plaque ulceration and to identify the limitations of and the artifacts associated with this technique. METHODS: Twenty-eight human carotid arteries were mounted in a pulsatile flow chamber and examined with intravascular sonography. We compared 140 intravascular sonograms with gross pathologic and histologic sections. Ulcerations with a diameter or depth of at least 0.5 mm were sought. RESULTS: All eight arteries with ulcerated plaques and nine of 10 individual ulcerations were depicted by intravascular sonography. One artery (one of 140 arterial cross sections) with a small mural thrombus was misinterpreted as ulcerated. Our intravascular sonographic measurements underestimated the gross ulceration dimensions by 22% (depth) and 17% (orifice diameter). CONCLUSIONS: Intravascular sonography is highly accurate for the diagnosis of plaque ulceration. The central position of the high-frequency transducer within the target vessel facilitates high resolution of the arterial lumen-wall border, permitting more powerful definition of small ulcerations than available by other diagnostic methods. However, the utility of invasive intravascular sonography for detecting carotid ulcerations cannot be determined until the pathologic significance of plaque ulceration is clearly defined.

Aged↗
PubMed1994

Fluid flow increases membrane permeability to merocyanine 540 in human endothelial cells.

Fluid shear stress is a ubiquitous stimulus of mammalian cell metabolism; however, its signal transduction pathway is unknown. We hypothesized that shear stress may alter some physical properties of the cell membrane. Using primary human umbilical vein endothelial cells (HUVECs), we investigated the effects of shear on the cell membrane by monitoring flow-induced changes in the uptake of the amphipath merocyanine 540 (MC540). Under static conditions, MC540 was rapidly internalized by HUVECs at 37 degrees C, and so was the membrane impermeant dye lucifer yellow, suggesting that the MC540 uptake was partly due to endocytosis. However, exposure to steady flow for 5 min at 37 degrees C induced an increase in MC540 uptake while that of lucifer yellow was unchanged, suggesting that the flow-induced increase in MC540 uptake was not endocytosis-related. The increase in MC540 uptake was significant for levels of steady shear of 6 dyne/cm2 and above. Pulsatile flow was more stimulatory than steady flow at 2 dyne/cm2, but no significant difference between the two was seen at higher shear stress levels. We conclude that fluid shear stress enhanced the uptake of MC540 by a mechanism other than endocytosis, suggesting an increase in plasma membrane permeability during exposure of the cells to shear stress.

Cell Membrane↗
PubMed1996

Blood flow acceleration in the carotid and brachial arteries of healthy volunteers: respective contributions of cardiac performance and local resistance.

The influence of local resistance and cardiac performance on peripheral blood acceleration was investigated in 14 healthy male volunteers. Steady and pulsatile flow was studied in the brachial and in the common carotid arteries, ie, two territories that exhibit marked differences in resistive characteristics. Instantaneous blood velocity (V), mean blood velocity (Vm) and artery diameter (D) were evaluated at rest by an ultrasonic range-gated pulsed Doppler flowmeter using a double transducer probe, thus allowing the calculation of mean blood flow (Q). Mean local resistance (R) was obtained by dividing the mean arterial pressure by Q. The peak value of the local acceleration of the blood was obtained by computer-assisted calculation of the first derivative of instantaneous blood velocity (Gmax = +dV/dtmax). Peak aortic blood acceleration (GAo) was simultaneously measured from the suprasternal notch using a pulsed Doppler velocity meter. In the branchial and the common carotid arteries, Gmax was of a similar magnitude (551 +/- 30 and 555 +/- 44 cm/s2, respectively) despite major differences in the respective D, Vm, Q and R values. In neither artery was there a relationship between Gmax and either resting Q or R. At the brachial artery level, Gmax was positively related to GAo (r = 0.79, P = 0.0008). At the common carotid artery level, there was a weak, although non significant relationship between Gmax and GAo (P = 0.08). Our results indicate that the local acceleration of peripheral blood flow in the brachial artery is related rather to upstream central impulse than to downstream hemodynamics, and suggest some regional differences in the hemodynamic determinants of the local acceleration of peripheral blood flow.

Adult↗
PubMed1991

[Doppler echocardiographic determination of the effective orifice area of mechanical heart valve prostheses in a flow model].

In a flow model the effective orifice areas (Ae) of 17 mechanical heart valve prostheses were determined. We measured the Ae-values of several sizes of three types of mechanical prostheses (Medtronic-Hall, St. Jude Medical, and Omnicarbon) under quasi-steady flow conditions using the continuity equation: Ae = flow/maximal transprosthetic velocity. The flow through the model could be determined exactly by directly measuring the decreasing fluid level within the feed tank, while the maximal velocities were calculated from CW-Doppler echocardiographic spectra. It was found that 1) over a range of 200-800 cm3/s Ae was constant for all prostheses and 2) in small aortic prostheses the Ae could be determined with only little scattering of the obtained values, while in large mitral prostheses there was a considerable variation within the results of repeated investigations. For example, in the 21- and 31-Omnicarbon-valves mean values of Ae were calculated as 1.41 and 4.03 cm2, respectively, with standard deviations of 0.05 and 0.49 cm2 as a result of about 70 single calculations in each valve. 3) The absolute values of Ae were smaller than those of comparable in vitro studies based on the Gorlin formula. We conclude that the effective orifice areas of prosthetic heart valves can be easily determined in a flow model by the combination of flow and Doppler echocardiographic measurements. As determinations are based on the same principle, the obtained values should clinically be referred to patients where the corresponding continuity equation for pulsatile flow is used as Ae = stroke volume/time integral of the maximal transvalvular velocity.

Aortic Valve↗
PubMed1985

The effects of fluid-mechanical factors on MR imaging in the arterial model.

Blood flow is a significant factor in MR imaging. The purpose of this investigation was to study fluid-mechanical effects on MR imaging. MR images generated by the pulsatile flow of bovine blood in an elastic model of the aorta with both renal arteries were studied. The high-frequency pulse sequence was synchronized to an ECG trigger signal. It was demonstrated that different flow velocities, laminar and turbulent flow, and backward flow can be visualized with MR imaging.

Aorta↗
PubMed2001

Intraocular pressure and pulsatile ocular blood flow after retrobulbar and peribulbar anaesthesia.

AIMS: This study investigated the effect of peribulbar and retrobulbar local anaesthesia on intraocular pressure (IOP) and pulsatile ocular blood flow (POBF), as such anaesthetic techniques may adversely affect these parameters. METHODS: 20 eyes of 20 patients who were to undergo phacoemulsification cataract surgery were prospectively randomised to receive peribulbar or retrobulbar anaesthesia. The OBF tonometer (OBF Labs, Wiltshire, UK) was used to simultaneously measure IOP and POBF before anaesthesia and 1 minute and 10 minutes after anaesthesia. Between group comparisons of age, baseline IOP, and baseline POBF were performed using the non-parametric Mann-Whitney test. Within group comparisons of IOP and POBF measured preanaesthesia and post-anaesthesia were performed using the non-parametric Wilcoxon signed ranks test for both groups. RESULTS: There was no statistically significant IOP increase post-anaesthesia in either group. In the group receiving peribulbar anaesthesia, there was a significant reduction in POBF initially post-anaesthesia which recovered after 10 minutes. In the group receiving retrobulbar anaesthesia, there was a persistent statistically significant reduction in POBF. CONCLUSIONS: Retrobulbar and peribulbar injections have little effect on IOP. Ocular compression is not needed for IOP reduction when using local anaesthesia for cataract surgery. Conversely, POBF falls, at least for a short time, when anaesthesia for ophthalmic surgery is administered via a retrobulbar route or a peribulbar route. This reduction may be mediated by pharmacologically altered orbital vascular tone. It may be safer to use other anaesthetic techniques in patients with ocular vascular compromise.

Aged↗
PubMed2001

Ocular hemodynamics during isometric exercise.

The autoregulatory capacity of the human retina is well documented, but the pressure-flow relationship of the human choroid is still a matter of controversy. Recent data, using laser Doppler flowmetry to measure choroidal blood flow, indicate that the choroid has some autoregulatory potential, whereas most data using other techniques for the assessment of choroidal hemodynamics indicate that the choroidal pressure-flow curve is linear. We used a new laser interferometric technique to characterize choroidal blood flow during isometric exercise. Twenty healthy subjects performed squatting for 6 min during normocapnia and during inhalation of 5% CO2 and 95% air. Ocular fundus pulsation amplitude, flow velocities in the ophthalmic artery, intraocular pressure, and systemic hemodynamics were measured in 2-min intervals. To gain information on choroidal blood flow fundus pulsation amplitude was corrected for changes in flow pulsatility using data from the ophthalmic artery and for changes in pulse rate. Ocular perfusion pressure was calculated from mean arterial pressure and intraocular pressure. The ocular pressure-flow relationship was calculated by sorting data according to ascending ocular perfusion pressure values. In a pilot study in 6 healthy subjects comparable ocular pressure flow relationships were obtained when choroidal blood flow was assessed with the method described above and with laser Doppler flowmetry. In the main study isometric exercise caused a significant increase in mean arterial pressure (56%, P < 0.001), pulse rate (84%, P < 0.001), and intraocular pressure (37%, P 0.004), but decreased fundus pulsation amplitude (-36%, P < 0.001). Significant deviations from baseline choroidal blood flow were observed only at ocular perfusion pressures >69% during normocapnia and 70% during hypercapnia. Our data indicate that during isometric exercise the choroid has a high capacity to keep blood flow constant despite changes in perfusion pressure and that this pressure-flow relationship is not altered by moderate changes in arterial carbon dioxide levels.

Adult↗
PubMed1997

Endogenous endotoxemia of intestinal origin during cardiopulmonary bypass. Role of type of flow and protective effect of selective digestive decontamination.

OBJECTIVE: To evaluate the possible related factors to endotoxemia and cytokine activation during the ischemic phase of extracorporeal surgery, and the effect of selective digestive decontamination (SDD) as a preventive measure. DESIGN: Prospective, open, randomized trial. SETTING: Two multidisciplinary ICUs (tertiary care hospitals). PATIENTS: One hundred consecutive patients undergoing cardiopulmonary bypass (CPB), randomly allocated to two groups; gut decontamination (group I = 50 cases) and controls (group II = 50 cases). INTERVENTIONS: Preoperative administration of oral non-absorbable antibiotics (polymyxin E, tobramycin and amphotericin B) versus no administration. MEASUREMENTS AND RESULTS: The assessment of decontamination by means of the bacteriologic control of rectal swabs. Determinations of gastric intramucosal pH (gastric pHi) and plasma endotoxin, tumor necrosis factor (TNF) aNd interleukin-6 (IL-6) before surgery and during the ischemic and reperfusion phases of bypass. Rectal aerobic Gram-negative bacilli (AGNB) were significantly reduced in the treated patients and in 56% total eradication was achieved. Endotoxin, TNF and IL-6 plasma levels were significantly lower in this group. By contrast, both endotoxin and TNF/IL-6 levels and gastric pHi correlated with the type of surgical flow (pulsatile versus non-pulsatile). CONCLUSIONS: SDD reduces the gut content of enterobacteria. This may explain the lower endotoxin and cytokine levels detected in decontaminated patients. In addition to SDD, the type of flow employed during bypass seems to influence endotoxemia and cytokine levels.

Amphotericin B↗
PubMed1989

Mathematical models of the flow in the basilar artery.

The flow in the basilar artery arises from the merging of the flows from the two vertebral arteries. This study deals with the question whether a parabolic (Poiseuille) profile will have been established before the basilar artery divides into both posterior cerebral arteries. The inlet length (that is, the downstream distance needed for the flow to become approximately equal to the limiting Poiseuille flow) and velocity profiles have been computed from two- and three-dimensional mathematical models in which flow pulsatility and vessel wall distensibility have been neglected and the complex geometry of the junction has been taken into account in a simplified form. The results show that the flow at the end of the basilar artery is far from being parabolic and that an asymmetry in the entrance flow will be carried along towards the end of the basilar artery, thus affecting flows in the circle of Willis.

Basilar Artery↗