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PubMedDate not supplied

Results of animal experiments using an undulation pump total artificial heart: analysis of 10 day and 19 day survival.

An undulation pump is a special rotary blood pump in which rotation of a brushless DC motor is transformed to an undulating motion by a disc in the pump housing attached by means of a special link mechanism. In the blood pump, a closed line between the disc and housing moves from the inlet to the outlet by this undulating disc motion, which sucks and pushes the blood from the inlet to the outlet. Because the same phenomena occurs at both sides of the disc, a continuous flow is obtained when the motor rotational speed is constant. The pump flow pattern can be easily changed from continuous flow to pulsatile flow by controlling the motor drive current pattern. A seal membrane made of segmented polyurethane protects the blood from invading the link mechanism as well as the motor. UPTAH is fabricated with two undulation pumps and two brushless DC motors. Its size is 75 mm in diameter and 80 mm long, and it has one of the great advantage of no compliance chamber required in the system. UPTAHs were implanted under cardiopulmonary bypass (CPB) into the chest cavities of 16 goats, each weighing between 41 and 72 kg. No anticoagulant and antiplatelet agent was used after the surgery. The left atrial pressure was automatically controlled to prevent its elevation and sucking of the atrial wall into the atrial cuff. The following results were obtained: (1) UPTAHs fit well into all the goats; (2) the longest survival was 19.8 days, the cause of death was bleeding from the aortic anastomosis; (3) No thrombus was observed in the blood pump despite no anticoagulant use. Hemolysis depended upon the length of CPB during surgery. When CPB time was within 2 hours, hemolysis level returned to baseline within a few days of the surgery. UPTAH is a promising implantable TAH, because of its small size and easy controllability.

Animals↗
PubMed1983

Development and evaluation of pulsatile roller pump and tubing for cardiac assistance.

In our laboratories we have developed a roller pump for cardiopulmonary bypass and circulatory assistance that has the ability to produce steady or pulsatile flow. The pulsatile mode can also be used for counterpulsation. The roller pump has been tested both experimentally and clinically. Studies have also been performed in vitro and in vivo to evaluate and select the best medical-grade roller pump tubing to be used in the pump for short- and long-term support. In vitro tests included rebounding of tubing volume versus revolutions per minute, rebounding over time with continuous pumping, flex life, and spallation. In vivo testing was performed in mongrel dogs using heparinless left heart bypass pumping for 6 h. Hematologic studies were performed during the procedure. Postmortem examination was performed, looking especially for thromboembolism. The tubing and connectors were also inspected. The results of the in vivo and in vitro tests of all tubings were then compared.

Animals↗
PubMed1989

Urethral responses to sacral stimulation in chronic spinal dog.

Urethral activity was investigated in the awake chronic spinal-injured canine using urodynamic recordings, video cystofluoroscopy, and urethral pressure recordings without anesthesia. Bladder contractions and voiding were induced by electrical stimulation with epidural electrodes inserted into the sacral canal. Urethral pressure remained elevated during stimulation and for 1-3 s afterward. Poststimulation voiding occurred with three different patterns: 1) pulsatile voiding in which squirting of urine was associated with contractions in the membranous urethra; 2) "on and off" voiding in which pulsatile flow was interrupted for brief periods of time; and 3) steady-stream voiding in which nonpulsatile flow was followed by pulsatile flow. Viewing these voiding patterns with fluoroscopy indicated that the proximal membranous urethra was important in all of the patterns. We conclude that in the chronic spinal-injured canine the skeletal muscle within the membranous urethra (rhabdosphincter) is involved in responses to sacral stimulation and various voiding patterns.

Animals↗
PubMed1983

Numerical study on post-stenotic dilatation.

Steady flows and pulsatile flows of a Newtonian fluid through a channel with a rectangular hump were numerically studied as a two-dimensional model of blood flow in a constricted artery. From the numerical calculation, it was shown that one of the hydrodynamic causes of endothelial lesion of artery and post-stenotic dilatation can be found in the large temporal variation of shear stress behind a constricted portion of artery. Local maximum of the pressure there can be seen as secondary factor for the post-stenotic dilatation.

Arterial Occlusive Diseases↗
PubMed2000

[Development of a control and monitor system for the cardiopulmonary cerebral resuscitation(CPCR) device].

A novel idea in developing cardiopulmonary-cerebral resuscition(CPCR) device has been developed, using a combination of membrane artificial lung(oxygenator), mild-hypothermia, and centrifugal blood pump technologies. A control system for the CPCR has been introduced, using converter control and sensor monitor, with 8031 chips as the controller. Pressure, flow rate and temperature monitors were installed in the system. Two modes of blood pump regulation have been adopted, i.e. continous flow and pulsatile flow. The in vitro evaluation tests showed that the two modes were reasonable and feasible.

Animals↗
PubMed2001

Comparative hydrodynamic evaluation of bioprosthetic heart valves.

BACKGROUND AND AIM OF STUDY: Pressure gradients across cardiac valve prostheses have been identified as one of the most important performance measures in valve replacement surgery. Specifically in aortic valves, these gradients influence reduction of left ventricular hypertrophy and are postulated to influence long-term survival. The correct choice of replacement valve is hampered by a lack of uniform measures of valve performance. The aim of this study was to compare in-vitro hydrodynamic performance of commercially available bioprosthetic valves under identical test conditions. METHODS: In-vitro steady forward flow and pulsatile flow tests were performed on aortic and mitral bioprosthetic valves in accordance with ISO/FDA guidelines at two different institutions to obtain objective hemodynamic performance measures. Measurements were recorded at various flow rates, flow and pressure to obtain mean pressure gradients and effective orifice areas (EOAs). RESULTS: Wide variation in pressure gradients was found among tested valves of each size. For a given size, differences of 200 to 400% were observed; in general, the valve models' relative rankings in pressure drop were independent of size. CONCLUSION: The Carpentier-Edwards Perimount valve showed superior performance at all sizes tested. While the mean pressure gradients and EOAs reported by each institution differed for a given valve, the performance of valve models relative to each other was similar. The testing of valves under identical conditions is a valuable comparative indicator of valve hemodynamic performance.

Animals↗
PubMed1978

Comparative studies of pulsatile and nonpulsatile flow during cardiopulmonary bypass. I. Pulsatile system employed and its hematologic effects.

A new, commercially available roller pump system able to deliver pulsatile and nonpulsatile flow has been studied in patients undergoing elective open-heart surgical procedures. The pulsatile pump (Stöckert Instrumente) may be used with standard extracorporeal circuit equipment and consistently produces a peripheral arterial pulse pressure of 25 to 30 mm. Hg at mean flow rates of 3.5 to 4.0 L. per minute. Twenty patients, arbitrarily allocated to pulsatile or nonpulsatile groups, have been studied. There were no significant differences between the groups in respect of age, weight, bypass time, pump flow, or mean arterial pressure during bypass. Comparative studies of the hematologic effects of pulsatile and nonpulsatile perfusion were carried out. There was no evidence of increased hemolysis with pulsatile flow, nor was there increased depletion of red blood cells (RBC's) or platelets in the pulsatile group. This pulsatile pump system may therefore be used to produce pulsatile perfusion during cardiopulmonary bypass without the fear of producing excessive blood cell trauma.

Adult↗
PubMed2001

The role of the Womersley number in pulsatile blood flow a theoretical study of the Casson model.

The purpose of this Note is to clarify the meaning of the Womersley number alpha in pulsatile blood flow in small vessels. In particular. we explain why the use of alpha as aperturbation parameter to obtain approximate solutions of the Casson model (frequently used in the literature) is not appropriate. Using the techniques of dimensional analysis and scaling, we show that alpha is the product of the Reynolds and Strouhal numbers. Since the latter is very small for physiological flows, the result is that alpha < 1 even at relatively high values of the Reynolds number (i.e., for non-negligible inertia) and we validate our perturbation theory results by comparison with a numerical integration of the full model. Although this analysis is based on the Casson model, our method has general validity and may be applied to other models which describe more accurately the rheological properties of blood.

Blood Circulation↗
PubMed1994

[Analysis of blood flow in hepatic tumors by color Doppler ultrasonography].

We evaluated the diagnostic significance of blood flow pattern and velocity in hepatic tumors detected by color doppler ultrasonography. Fifty seven patients with hepatocellular carcinoma (HCC) and 12 patients with hepatic hemangioma (HEM) were studied with ultrasonographic apparatus equipped with color doppler system (Toshiba SSA-270A, 3.75MHz sector scanner). Furthermore 12 patients with HCC were studied repeatedly after transcatheter arterial embolization (TAE) and/or percutaneous ethanol injection (PEI). Blood flow was measurable in 2 of 12 patients with HEM (17%). Pulsatile flow with low speed (7 cm/sec) and low amplitude was detected in one patient, and continuous flow with low speed (5 cm/sec) in the other. Blood flow was measurable in 43 of 57 patients with HCC (75%). The detection rate of blood flow in HCC was significantly higher than in HEM. Pulsatile flow was detectable in 42 of 43 patients (98%). Average maximum velocity of pulsatile flow was over 40cm/sec. Analysis of blood flow after treatment provided us useful information on the effect of treatment. In conclusion, analysis of blood flow in hepatic tumors on US with color doppler system may provide useful information on differential diagnosis between HCC and HEM, the assessment of the therapeutic effect of TAE or PEI, whether additional treatment is required or not, and when it should be done if required.

Adult↗
PubMed1994

Cochlear blood flow measured by averaged laser Doppler flowmetry (ALDF).

This report describes a new approach to estimate the hydromechanical properties of a vascular system. Averaged laser Doppler flowmetry (ALDF) was developed by averaging the flux signal of a laser Doppler flowmeter (LDF) synchronized to the heart cycle. The usefulness of this method was verified by manipulation of the cochlear microvasculature. Twelve pigmented guinea pigs under pentobarbital/fentanyl anesthesia were used. The cochlea was surgically exposed and the LDF probe placed on the bony surface of the first turn to monitor cochlear blood flow (CBF). The LDF flux signal (0.2 s time constant) was sampled by an A/D board at 2 kHz for 255 ms and averaged with synchronization to the heart beat. The mean blood flow, peak to peak amplitude, and time (phase) delay of pulsatile flow were measured from the averaged signal. According to a transmission line model of the vascular system, under a given perfusion pressure, mean flow reflects resistance while amplitude and time delay of the pulsatile flow are related to the reactance component of the impedance of the vascular system. During the formation of photochemically-induced thrombosis in the cochlear microvasculature, there was a dramatic mean flux decrease (90.1 +/- 3.4% from baseline (BL), N = 6). Additionally, a time-dependent decrease in amplitude and time delay of pulsatile flow were indicated by ALDF. These results suggest a large increase in vascular resistance and significant decrease in compliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

In vitro validation of a thermodilution right ventricular ejection fraction method.

A thermodilution catheter and computer system has been developed to measure right ventricular ejection fraction and volumes. To evaluate the performance of this method, the thermodilution system was evaluated in an in vitro pulsatile flow model. Thermodilution measurements of ejection fraction (EF), cardiac output (CO), stroke volume (SV), end-diastolic volume (EDV), and end-systolic volume (ESV) were compared with known values in a pulsatile flow bench. Thermodilution EF measurements correlated very well with the pulsatile flow model (r2 = 0.95, m [slope] = 0.85, SEE = 4.0 EFU). Thermodilution CO and SV were highly predictive of actual pulsatile flow (r2 = 0.99, m = 0.99, SEE = 187 ml/min and r2 = 0.98, m = 0.96, SEE = 2.5 ml, respectively). Thermodilution end-diastolic and end-systolic volume measurements resulted in low mean eror, -1.8% and 0.6%, respectively. The standard deviations of the error for EDV and ESV were 11.0% and 16.4%. The thermodilution measurements were repeatable, with CO, SV, and EF coefficients of variation of 3.2%, 3.3%, and 4.7%, respectively. EDV and ESV were slightly more variable, with coefficients of variation of 5.5% and 7.2%, respectively.

Cardiac Catheterization↗
PubMedDate not supplied

Combined MRI and CFD analysis of fully developed steady and pulsatile laminar flow through a bend.

A combined MR and computational fluid dynamics (CFD) study is made of flow in a simple phantom laboratory flow rig consisting of a 180 degree bend with straight entry and exit sections. The aim was to investigate the potential of the use of MRI-linked CFD simulations for in vivo use. To this end, the experiment was set up for both steady and pulsatile laminar flow conditions, with Reynolds and Dean numbers and Womersley pulsatility parameter representative of resting flow in the human aorta. The geometrical images of the pipe and the velocity images at entry to the bend were used as boundary conditions for CFD simulations of the flow. The CFD results for both steady and pulsatile cases compared favorably with velocity images obtained at exit from the bend. Additional information such as pressure and wall shear stress, which either could not be measured adequately via MRI, or could not be measured at all, was also extracted from the simulation. Overall, the results were sufficiently promising to justify pursuing subsequent in vivo studies.

Aorta, Thoracic↗
PubMedDate not supplied

Some flow visualization and laser-Doppler-velocity measurements in a true-to-scale elastic model of a human aortic arch--a new model technique.

Flow studies were done in an elastic true-to-scale silicone rubber model of an aortic arch to study further hemodynamic influences on atherosclerosis. The model was prepared from a cast of a young woman. A revised model technique was used. The model had a compliance similar to that of the human aortic arch. Velocity measurements were done in the model with a two component laser-Doppler-anemometer in steady and pulsatile flow using a calcium chloride solution with a viscosity of eta = 3.18 mPas and density of rho = 1.28 kg/m3 at 20 degrees C. The time average Reynolds numbers over a whole cycle in the ascending aorta was Re = 1350. The Womersley parameter for pulsatile flow was a = 20. The pulse wave velocity in the ascending aorta was about c = 5.4 m/sec. The secondary flow behavior was discussed for steady and pulsatile flow. Reverse flows were found, especially along the inner radius of the aortic arch in the descending aorta in steady and pulsatile flow and also in small areas of the ascending aorta and at the branches of the aortic arch. The formation of atherosclerotic plaques at preferred local flow regions is discussed.

Aorta, Thoracic↗
PubMed1991

Gas transport in serpentine microporous tubes under steady and pulsatile blood flow conditions.

A serpentine gas exchange unit was built with cylindrical tubular microporous membranes featuring periodic arcs with a fixed curvature ratio (ratio of tube radius to radius of curvature) of 1/14 and circular angles between 30 and 360 deg. Oxygen transfer was measured under steady and pulsatile blood flow conditions in vitro and ex vivo to assess the design features which most effectively augment gas transfer. Under steady blood flow conditions, oxygen transfer increased with circular angles beyond 70 deg. Under pulsatile conditions, a wide range of geometrical and fluid mechanical parameters could be combined to enhance gas transfer performance, which eventually depended upon the secondary Reynolds number and the Womersley parameter.

Animals↗
PubMed2004

Mathematical modeling of fluid dynamics in pulsatile cardiopulmonary bypass.

The design criteria of an extracorporeal circuit suitable for pulsatile flow are quite different and more entangled than for steady flow. The time and costs of the design process could be reduced if mutual influences between the pulsatile pump and other extracorporeal devices were considered without experimental trial-and-error activities. With this in mind, we have developed a new lumped-parameter mathematical model of the hydraulic behavior of the arterial side of an extracorporeal circuit under pulsatile flow conditions. Generally, components feature a resistant-inertant-compliant behavior and the most relevant nonlinearities are accounted for. Parameter values were derived either by experimental tests or by analytical analysis. The pulsatile pump is modeled as a pure pulsatile flow generator. Model predictions were compared with flow rate and pressure tracings measured during hydraulic tests on two different circuits at various flow rates and pulse frequencies. The normalized root mean square error did not exceed 24% and the model accurately describes the changes that occur in the basic features of the pressure and flow wave propagating from the pulsatile pump to the arterial cannula.

Cardiopulmonary Bypass↗
PubMed1983

On two-phase model of pulsatile blood flow with entrance effects.

A particle fluid suspension model is applied to the problem of pulsatile blood flow through a rigid circular tube with entrance effects. Flow is generated by an arbitrary (time and axial flow variable dependent) as well as a particular pressure gradient of physical importance. Fluid and particle phase velocities are explicitly determined for both, with and without entrance effects. Further, steady pulsatile velocities for both cases are deduced by taking time t -greater than . Several other limiting cases of physical and biological importance have been obtained and discussed in detail.

Animals↗
PubMed1998

Effects of amide and amine plasma-treated ePTFE vascular grafts on endothelial cell lining in an artificial circulatory system.

We sought to examine whether surface modification of expanded polytetrafluoroethylene (ePTFE) vascular grafts might extend graft patency without modifying the graft structure. Amide and amine plasma (butylamine) were applied to graft surfaces using radio frequency glow discharge. Surface analyses by Fourier transform infrared spectroscopy-attenuated total reflectance, X-ray photoelectron spectroscopy, and dynamic contact angle measurements revealed the presence of nitrogen-containing functional groups on the plasma modified graft surfaces, along with an increased surface hydrophilicity. Bovine aortic endothelial cells were seeded on amide and amine plasma coated ePTFE vascular grafts and placed inside an artificial circulatory system under well-defined flow conditions. The seeded endothelial cells were exposed to either constant or pulsatile flow condition for 5 days. Their corresponding maximum wall shear stresses were 1 dyn/cm2 under constant flow and 65, 108, and 259 dyn/cm2 under various pulsatile flows. Plasma modified ePTFE vascular grafts enhanced the endothelial cell lining under constant and pulsatile flow conditions. Fluorescence nuclear staining, scanning electron microscopy, and histological staining indicated the formation of an endothelial cell monolayer on the plasma coated graft surfaces.

Amides↗
PubMed2003

Flow in the early embryonic human heart: a numerical study.

Computational fluid dynamic (CFD) experimentation provides a unique medium for detailed examination of flow through complex embryonic heart structures. The purpose of this investigation was to demonstrate that streaming blood flow patterns exist in the early embryonic heart and that fluid surface stresses change significantly with anomalous alterations in fetal heart lumen shape. Stages 10 and 11 early human embryo hearts were digitized as calibrated two-dimensional (2D) cross-sectional sequential images. A 3D surface was constructed from the stacking of these 2D images. CFD flow solutions were obtained (steady and pulsatile flow). Particle traces were placed in the inlet and outlet portions of these two stages. Sections of the embryonic heart were artificially reshaped. CFD flow solutions were obtained and surface stress changes analyzed. Streaming was shown to exist, with particles released on one or the other side of the cardiac lumen tending not to cross over and mix with particles released from the opposite side of the cardiac lumen. Shear stress changes (stage 10) occur in the altered lumens. Streaming exists in steady and pulsatile flow scenarios in the embryonic heart models. There are differences in local shear stress distributions with surface shape anomalies of the fetal heart lumen. These observations may help shed light on the potential role of fluid dynamic factors in determining patterns of abnormal heart development.

Blood Flow Velocity↗