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PubMed1999

Present status of the total artificial heart at the University of Tokyo.

At the University of Tokyo, various types of total artificial heart (TAH) systems have been studied since 1959. At the present time, 2 types of implantable TAH have been developed. One is an undulation pump TAH (UPTAH) and the other is a flow transformed pulsatile TAH (FTPTAH). Using the UPTAH, 14 cases of implantation were performed in goats and 10 days' survival obtained. The new type of FTPTAH is under a prototype study. To prevent ring thrombus, a polyurethane membrane valve, a jellyfish valve, has been developed. The longest in vivo experiences with this valve in the TAH blood pump have been 312 days in the left side blood pump and 414 days in the right side blood pump. Conductance and arterial pressure based control (1/R control) can realize the physiological control of the TAH. Using 1/R control, 532 days of survival could be obtained in a goat with a paracorporeal TAH. The technique required to apply this control method to a implantable TAH is under development. We have proposed a new 5 year research project of the implantable TAH entitled "Comprehensive Basic Research on the Development of a Japanese Original Implantable Total Artificial Heart" to The Ministry of Welfare.

Animals↗
PubMed2001

A hybrid compliant vascular graft seeded with microvascular endothelial cells extracted from human omentum.

We report the development of a hybrid vascular graft using an innovative compliant poly(carbonate-urea)urethane unlike any previous polyurethane MyoLink as a permanent scaffold. The engineered graft has a hierarchical arterial structure: a monolayer of oriented microvascular endothelial cells (MVECs) and 3-D matrix (human collagen Type 4/dermatan sulfate) bonded onto MyoLink. The grafts' clinical feasibility was evaluated by determining optimal MVEC seeding density, incubation time, viability, and adhesion of these cells when exposed to arterial shear stress. MVECs from human omentum were isolated by a new centrifugation protocol, radiolabeled and seeded onto hybrid graft 2 to 18 x 105 cells/cm(2) for 24 h at 37 degrees C and for 1 to 5 h at 6 x 105 cells/cm(2), washed 3 times, and gamma counted. Qualitative assessment of seeding density/incubation was also undertaken with scanning electron microscopy (SEM) and viability tested with a modified Alamar Blue assay. A pulsatile flow phantom was used to subject the hybrid graft (200 mm length, 5 mm internal diameter) seeded with radiolabeled MVECs (6 x 105 cells/cm(2) at 2 h) to arterial shear and dynamic scintigraphy images acquired in real time using a nuclear medicine gamma camera system during 14 h of perfusion (n = 6). The optimal seeding density was 6 x 105 cells/cm(2), and qualitative SEM confirmed this. Incubating cells for 2 h produced significantly greater cell attachment than was seen for 1 h incubation (p < 0.05), and there was no significant difference in adhesion between cells incubated over the 2 h. Exposure of grafts to acute shear stress resulted in significantly higher proportions of initial cells attached to hybrid grafts compared to native MyoLink grafts (67 +/- 3% versus 55 +/- 2%, p < 0.001). As shown here, tissue engineering of native Myolink grafts significantly reduces the seeding density and incubation time to produce a monolayer onto which cells adhere to better.

Cell Adhesion↗
PubMed2002

Strain rate imaging: an in vitro "validation" study using a physiologic balloon model mimicking the left ventricle.

BACKGROUND: Strain rate imaging (SRI) can be implemented from digital ultrasound loops of tissue Doppler imaging (TDI) data and is performed as an autocorrelation solution of the distance between intramyocardial targets. As such, it should have better resolution along longer distances of wall segments that are imaged at the length of individual ultrasound scan lines. METHODS: We used a new left ventricular double-balloon phantom with a tissue-mimicking gel between the walls. Mounted in a water bath and connected to a pulsatile flow pump at four-stroke volume (30-50 ml/beat), the high frame rate, digital, multiple two-dimensional/tissue/TDI loops of balloon wall motion were recorded using a GE VingMed system FiVe (3.5 MHz phased array transducer), with the model scanned longitudinally from the apex. The strain rate (SR) values were measured at the apex and the lateral wall using an offline measurement program, and mean SR values for every 100 msec were calculated by averaging three determinations at each point. The excursions of the apex and lateral wall also were measured directly by high speed digital video imaging, and consecutive velocity profiles were calculated every 100 msec. A total of 40 data points for four-stroke volumes were analyzed. RESULTS: While our balloon model had enough gel targets between the walls to produce a good mimic of myocardial speckle with walls that thickened and thinned, samples immediately across the apex and apex SR values (Hz) varied substantially. In contrast, systematic signals could be obtained from lines imaged >15 degrees from the true apex and crossing a longer length of myocardium. At the lateral wall, there was a close correlation between the video velocities and SR values, as well as a close overlap of the phasic patterns. CONCLUSIONS: SRI produces more reliable data from wall segments parallel to scan lines.

Blood Flow Velocity↗
PubMed2000

Tissue engineering of vascular grafts: human cell seeding of decellularised porcine matrix.

OBJECTIVES: To develop a biocompatible and mechanically stable vascular graft combining human cells and a xenogenic acellular matrix. DESIGN/MATERIALS: Decellularised matrix tubes were obtained by enzymatic cell extraction of native porcine aortas. Endothelial cells and myofibroblasts were isolated from human saphenous veins and grown in cell cultures. The inner surface of the tubes was seeded with endothelial cells or myofibroblasts and exposed to pulsatile flow. RESULTS: After cell extraction, the absence of cellular components, as well as the maintenance of matrix integrity, was demonstrated by means of light microscopy and scanning electron microscopy. Furthermore, the porcine matrix was successfully seeded with human endothelial cells, which grew to a monolayer under flow conditions. Stable biomechanical properties were achieved at physiological perfusion pressures in vitro. CONCLUSIONS: Cellular components can be extracted from native porcine blood vessels. Vascular grafts can be generated in vitro of animal acellular matrix and human cells.

Animals↗
PubMed2001

The use of impedance index in the surveillance of PTFE femorodistal grafts.

BACKGROUND: Impedance is the equivalent in pulsatile flow of resistance in steady flow. The impedance index has been used successfully in the surveillance of vein grafts, but its use has not been reported in the context of PTFE femorodistal grafts. METHODS: Twenty-eight patients (median age 68 years (IQR 59-73 years) and 20 men) undergoing 28 PTFE femorodistal grafts with a vein cuff were evaluated prospectively comparing the impedance index with standard duplex graft surveillance. All grafts were performed for critical ischaemia. At risk grafts were identified and treated appropriately after angiography. RESULTS: The primary patencies at 1 and 2 years were 82% and 50% respectively. Duplex identified 11 at risk grafts of which 9 had an identifiable correctable lesion. Impedance analysis overpredicted at risk status when compared with duplex in the immediate postoperative phase and was unsuccessful in detecting inflow disease or low flow relating to cardiac failure. Using a threshold index of 0.5, impedance analysis has a sensitivity of 87%, specificity of 88%, with positive and negative predictive values of 76% and 94% respectively. CONCLUSIONS: Impedance index is a non-invasive method of graft surveillance which is applicable to PTFE femorodistal bypasses and may be a useful alternative to duplex although formal validation studies will be required.

Aged↗
PubMed1999

In vitro analysis of coronary atheromatous lesions by intravascular ultrasound; reproducibility and histological correlation of lesion morphology.

AIM: To determine the reproducibility and histological correlation of qualitative intravascular ultrasound imaging of atheromatous coronary arteries using the recently proposed European Society of Cardiology classification of plaque composition in conditions approximating the clinical setting. METHODS: Atheromatous lesions (n=21), identified from 30 post-mortem human coronary arteries, were imaged using intravascular ultrasound in a pulsatile flow system which simulates coronary flow. Fifty sites (21 x minimum lumen area and 29 x distal reference sites) were selected independently by two observers from continuous video recordings. Atheromatous plaque was classified as echodense, echolucent, heterogeneous or calcified by each observer and by one observer on separate occasions. Arterial specimens were histologically sectioned at these sites and similarly analysed by a third observer blinded to the intravascular ultrasound appearances. RESULTS: Overall inter- and intra-observer reproducibility for plaque-type (Kappa 0.87[0.80-0.94] and 0.89[0. 85-0.93 respectively]) and focal calcification (0.78[0.74-0.82] and 0.88[0.84-0.92]) was high. Differences in site selection significantly influenced reproducibility particularly at reference sites. Agreement for overall plaque type between intravascular ultrasound and histology occurred in 89% of sites (Kappa 0.73[0.69-0. 77]). Specificity and positive predictive values for individual plaque types were greater than 90%. CONCLUSION: Using modern intravascular ultrasound technology in an in vitro system which approximates the clinical setting the proposed ESC classification of plaque composition by intravascular ultrasound is reproducible and correlates well with histology. It should therefore perform reliably in diagnostic intravascular ultrasound examinations and in the guidance of percutaneous coronary interventions.

Aged↗
PubMed2002

Clinical evaluation of reflectance spectrophotometry for the measurement of gastric microvascular oxygen saturation in patients undergoing cardiopulmonary bypass.

OBJECTIVE: To evaluate the impact of cardiopulmonary bypass (CPB) on gastric mucosal oxygen saturation assessed by reflectance spectrophotometry in patients undergoing coronary artery bypass graft surgery. DESIGN: Prospective, observational study. SETTING: A division of cardiothoracic anesthesia in a university hospital. PARTICIPANTS: Twelve consecutive patients undergoing CPB. INTERVENTIONS: Monitoring, anesthesia, surgical procedure, and CPB for the patients followed routine clinical protocol as established in the departments. Microvascular oxygen saturation in gastric mucosa was assessed by reflectance spectrophotometry before, during, and after CPB. MEASUREMENTS AND MAIN RESULTS: Gastric mucosal oxygen saturation averaged 65 +/- 7% (mean +/- SD) before CPB, decreased significantly to 57 +/- 9% during CPB (p < 0.01), and was 59 +/- 8% after CPB. These changes in regional oxygen saturation were not mirrored in variables of systemic oxygenation. Gastric mucosal oxygen saturation always showed instantaneous reactions to various surgical and pharmacologic interventions. CONCLUSION: Reflectance spectrophotometry allowed the authors to assess gastric mucosal oxygen saturation with a high repetition rate, regardless of spontaneous circulation with pulsatile flow or nonpulsatile flow during CPB. This technique provided the means to monitor on-line the course of tissue oxygen saturation throughout the operative procedure. Reflectance spectrophotometry is an appropriate and sensitive assessment tool to monitor gastric mucosal oxygen saturation in patients undergoing CPB.

Aged↗
PubMed2006

Seeding of human vascular cells onto small diameter polyurethane vascular grafts.

INTRODUCTION: Thrombogenicity of small diameter vascular prostheses might be reduced by complete coverage of the luminal surface with vascular cells. We investigated cell seeding on polyurethane vascular prostheses (PUVP). METHODS: 45 PUVP were divided into three groups of n = 15 each: Group A (diameter 20 mm, gamma-sterilized), Group B (diameter 4 mm, gamma-sterilized), and Group C (diameter 4 mm, ethylene oxid [Eto]-sterilized). Human smooth muscle cells (SMC), fibroblasts (FB), and endothelial cells (EC) were isolated from saphenous vein segments and expanded in culture. PUVPs were pre-seeded with a mixed culture of FBs and SMCs (mean 7.7 +/- 2.3 x 10(6) cells) followed by EC seeding (mean 4.4 +/- 0.9 x 10(6) cells). Seven days after cell seeding, PUVPs were perfused under a pulsatile flow. Flow definitions were as follows: adaption phase: low flow, resulting pressure: 60/30 mm Hg; high flow: resulting pressure: 160/50 mm Hg, lasting for 4 hours in all groups. Three subgroups were defined out of each group, differing in the perfusion strategy: high flow immediately, adaption phase of 15 minutes followed by high flow, and adaption phase of 30 minutes followed by high flow. Specimens were taken after each seeding procedure, prior to and after perfusion, and then examined using a scanning electron microscope (SEM) and immunohistochemical staining procedures. RESULTS: Pre-seeding with the mixed culture revealed a better initial adhesion in Groups A and B compared to group C (76% vs. 41%). In Groups A and B, EC seeding (adhesion 72%) resulted in a confluent EC layer. Immunohistochemical stainings were positive for collagen IV, laminin, CD31, and factor VIII, but negative for eNOS. In Group C, only isolated cells were found after each seeding procedure, which rounded up and vanished during the next days. When perfused with high-flow immediately, Group A and B prostheses revealed small defects (< 10% of the surface) of all cell layers. After perfusion with an adaption phase of 15 minutes only few defects were found within the EC layer with an intact basement membrane. An adaption phase of 30 minutes resulted in a confluent cell layer without significant cell defects. After perfusion, the endothelial cells also stained positive for eNOS. CONCLUSION: Seeding of a mixed culture consisting of FBs and SMC resulted in an excellent EC adhesion and resistance to shear stress. Cell attachment was better on gamma-sterilized PUVPs compared to Eto-sterilization. The cells obviously maintained their ability to adapt to shear stress.

Adaptation, Physiological↗
PubMed1986

In vitro evaluation of six mechanical and six bioprosthetic valves.

The in vitro function of 6 tissue valves and 6 mechanical valves (all size 29) was assessed in a purpose-built pulse duplicator under different pulsatile flow conditions. Valve function was analyzed by measuring the mean pressure difference across each valve during forward flow, and the reverse flow through each valve during valve closure (dynamic regurgitation) and in the fully closed position (static regurgitation). Although valves of the same type showed similar characteristics, there were significant differences in function between different types of valves. Porcine valves showed much higher forward flow pressure gradients than pericardial, tilting disc, or bileaflet mechanical valves. However, the porcine valves showed least regurgitation, with pericardial valves having less regurgitation than mechanical valves.

Bioprosthesis↗
PubMed1984

Hormonal and electrolyte responses during and after open heart surgery.

Maintenance of the balance of electrolytes and hormones within their normal range is necessary for normal myocardial metabolism. Open heart surgery involving cardiopulmonary bypass produces metabolic disturbances which affect normal metabolic homeostasis. Several studies have suggested that pulsatile cardiopulmonary bypass causes less severe metabolic disturbance than non-pulsatile bypass and that non-pulsatile bypass causes hypofunction of the anterior pituitary and adrenal glands. The present study, however, with non-pulsatile flow showed that there was no evidence of hypothalamo-pituitary-adrenal axis hypofunction when the hormonal values of corticotrophin (ACTH), cortisol and cortisone were corrected for the hemodilution involved in cardiac surgery. Electrolytes, particularly calcium, play an important role in myocardial contractility. The levels of ionized calcium are normally controlled by parathyroid hormone (PTH) with a negative feedback of calcium controlling the system. However, this study showed that significant increases in bioactive PTH during cardiopulmonary bypass were not related to the calcium concentration, but appeared to be influenced by low blood pH values and by the degree of hypothermia.

Adrenocorticotropic Hormone↗
PubMed1998

[Neuropsychological and psychopathologic changes following cardiac surgical procedures].

Neuropsychological and neuropsychiatric disorders following open heart surgery are estimated to occur in as many as 80 per cent of all patients. They have been recognised from the very beginning of modern heart surgery. Despite a huge amount of scientific literature, data concerning incidence, the phenomenology and duration of symptoms diverge. This finding may be explained by heterogeneous aetiopathogenetic concepts and methodological and terminological problems associated with the investigation of postoperative delirium or neuropsychological and psychopathological sequelae of cardiac surgery. Nowadays, most authors agree in respect of a multifactorial pathogenesis of cognitive deficits following cardiac surgery. Factors influencing the psychopathological and neuropsychological outcome of cardiac surgery can be divided into pre-, intra- and postoperative variables. Advanced age, degree of cardiovascular impairment and other case histories, as well as history of drug abuse, are those preoperative variables that may be responsible for a postoperative cognitive decline. The predictive value of personality traits (depression and/or anxiety), however, is most controversial. Among the intraoperative variables related to the postoperative cognitive state, are e.g. the type of operation and technical procedure (micro-/macroembolism due to the way of oxygenation, pulsatile/-non-pulsatile flow) and duration of extracorporeal circulation. In the postoperative period, the duration of intubation or ICU stay and related variables (like sleep or sensory deprivation/hyperstimulation) were identified as significant predictors of neuropsychological and psychopathological alterations. Modern research focusses on neurobiochemical markers of brain injury which may serve as early predictors of a postoperative cognitive decrease. These parameters may indicate an early postoperative diagnosis and neuroprotective treatment in patients at risk.

Cardiac Surgical Procedures↗
PubMed1997

In vitro training model for endovascular embolization of cerebral aneurysms.

We present a new in vitro model for the training of endovascular embolizations of cerebral aneurysms. The technique and laboratory set-up described allow the embolization of thin-walled, transparent silicone aneurysm models under "semi-physiologic" conditions, i.e., in a closed circulation with pulsatile flow and pressure, simulating the hemodynamic conditions encountered in biologic systems.

Embolization, Therapeutic↗
PubMed2001

Simple method for estimating regurgitant volume with use of a single radius for measuring proximal isovelocity surface area: an in vitro study of simulated mitral regurgitation.

The proximal isovelocity surface area (PISA) color Doppler method with use of a hemielliptic formula is reported to be accurate for quantitating regurgitant volume (RV). However, this formula ideally requires the measurement of 2 or 3 radii and therefore is not widely used clinically. The purpose of this in vitro study was to derive a simple PISA formula for estimating RV with use of a single radius axial to the valve orifice and to compare it with the clinically used single-radius hemispherical formula (2 x pi R(2) x AV x TVI/Vp), where AV is the apparent color Doppler aliasing velocity, R is the PISA color Doppler aliasing radius, TVI is time-velocity integral of the jet by continuous wave Doppler, and Vp is the peak velocity of the jet by continuous wave Doppler. Pulsatile flow studies were performed across a convex curvilinear surface, which more closely approximates the shape of the mitral valve than does a planar surface. Pulse rates (60 to 80 bpm), peak flow velocities (4.0 to 6.0 m/s), and regurgitant orifice areas (0.2 to 1.0 cm(2)) were varied to simulate mitral regurgitation. The AVs were varied from 11 to 39 cm/s, and a single PISA aliasing radius was measured at each AV. Excellent linear correlations were obtained between the PISA radius and the actual RV measured with use of a beaker (r = 0.94 to 0.97, P <.0001). A series of simplified formulas was derived from the regression line of the PISA radius versus the RV. For example, with an AV of 21 cm/s, RV was estimated by a simplified PISA formula (where RV[mL] = 10 x R [mm] - 30) with an accuracy of 3.3 +/- 6.3 mL versus -20.3 +/- 8.7 mL for the standard single-radius PISA method (P <.0001). By using the standard single-radius hemispherical PISA formula, RV was underestimated if the radius was <20 mm. By using simplified regression equations, the PISA radius accurately estimated RV at a PISA radius <20 mm. Clinical studies are necessary to validate this concept.

Echocardiography, Doppler, Color↗
PubMed1985

Evaluation of the patient with intermittent claudication.

The most common cause of intermittent claudication is atherosclerotic occlusive arterial disease. Differentiation of the common musculoskeletal and neurologic conditions that may mimic intermittent claudication is often possible with a careful history, but when insufficient detail is provided or multiple conditions exist, the findings on physical examination and noninvasive studies are useful. While physical examination provides a rough estimate of the degree of ischemia, assessment of functional impairment produced by occlusive arterial disease is best made with noninvasive studies before and after standard exercise. Arteriography is reserved for the patient for whom restoration of pulsatile flow is planned.

Angiography↗
PubMedDate not supplied

Axial reciprocation of rotating impeller: a new concept of antithrombogenecity in centrifugal pump.

For long-term application, rotary pumps have to solve the problems of bearing wear and thrombosis along the bearing. Most investigators choose the magnetic bearing to realize zero-friction and no contact between the rotor and stator; the former avoids the mechanical wear and the latter eliminates the possibility of thrombus formation. The authors have tried and found, however, that it is difficult to apply a magnetic bearing to the rotary pump without disturbing its simplicity, reliability and implantability, and have therefor developed a much simpler and much more creative approach to achieve the same results. Instead of using a sliding bearing, a rolling bearing has been devised for the pump, and its friction is about 1/15 of the sliding bearing. Furthermore, a wear-proof material of ultra-high-molecular weight polythene has been adopted to make the rollers, and its anti-wear property is 8 times better than metal. Thereby, the service life of the bearing has been prolonged to ten years according to the documents provided by the producer. In order to prevent the thrombus formation along the bearing, the impeller reciprocates axiallly as the impeller changes its rotating speed periodically to produce a pulsatile flow. The reciprocation is the result of the effects of a magnetic force between the motor rotor and stator, and a hydraulic force between the blood flow and the impeller. Similar to a piston pump, the oscillating impeller can make the blood flow in and out of the bearing, resulting in wash-out once a circle. This obviously helps to prevent thombosis along the bearing and in the pump. The endurance tests with saline of this novel pump demonstrated the durabililty of the device. It promises to be able to assist the circulation of patients permanently, and to be able to replace heart transplantation in the future.

Equipment Design↗
PubMed2003

Nasal molds as predictors of fine and coarse particle deposition in rat nasal airways.

Respiratory particle toxicity and accompanying dosimetry are commonly studied in laboratory animals and results are extrapolated to humans. Nasal deposition in the rat has been studied experimentally using acrylic molds made from postmortem casts and in vivo techniques. A previous study (Martonen & Yang, 1993) found agreement between the deposition efficiencies of rat nasal airways and nasal molds for ultrafine particles (<0.1 micro m) but disagreement for particles greater than 1 micro m. In this work, the hypothesis that molds made from postmortem casts of rat nasal airways are suitable predictors of the deposition of particles greater than 1 micro m in live rats was reevaluated by considering data recently obtained in our laboratory. Comparisons of deposition data for steady and pulsatile flows in the inspiratory and expiratory directions from studies using an F344 nasal mold and Long-Evans rats were performed. The validity of comparing nasal deposition data derived from an F344 nasal airway with data from Long-Evans airways was supported by a comparison of the nasal morphologies of these strains. Graphical comparisons of data showed good agreement between deposition in a nasal mold and rat nasal airways for particles with diameters between 0.5 and 4 micro m; statistical comparisons indicated differences. Statistical findings were not considered conclusive because of differences in variability between the studies. The available data suggest that good estimates of total nasal deposition in rats can be obtained by using rat nasal molds as surrogates for their live counterparts in studies of the deposition of particles greater than about 0.5 micro m.

Algorithms↗
PubMed2003

Optimization of ECG gating in quantitative femoral angiography.

PURPOSE: To determine which phase of the heart cycle would yield the highest reproducibility in measuring atherosclerosis-related variables such as arterial lumen volume and edge roughness. MATERIAL AND METHODS: 35 patients with hypercholesterolemia underwent select- ive femoral angiography, repeated four times at 10-min intervals. The angiographies were performed with ECG-gated exposures. In angiographies 1 and 2 the delay from R-wave maximum to each exposure was 0.1 s, in angiographies 3 and 4 the delay was 0.1, 0.3, 0.5 or 0.7 s or the exposures were performed 1/s without ECG gating. Arterial lumen volume and edge roughness were measured in a 20-cm segment of the superficial femoral artery using a computer-based densitometric method. Measurement reproducibility was determined by comparing angiographies 1-2 and angiographies 3-4. RESULTS: When measuring arterial lumen volume and edge roughness of a 20-cm segment of the femoral artery, reproducibility was not dependent on ECG gating. In measuring single arterial diameters and cross-sectional areas, the reproducibility was better when exposures were made 0.1 s after the R-wave maximum than when using other settings of the ECG gating device or without ECG gating. CONCLUSION: The influence of pulsatile flow upon quantitative measurement in femoral angiograms seems to be the smallest possible in early systole, as can be demonstrated when measuring single diameters and cross-sectional areas. In variables based on integration over longer segments, measurement reproducibility seems to be independent of phase.

Adult↗
PubMed1986

Design of a function test apparatus for prosthetic heart valves. Initial results in the mitral position.

A test rig has been developed to investigate the function of prosthetic heart valves under pulsatile flow conditions. The rig uses a servo-controlled pump to produce a physiological flow waveform through the valve. The pressure difference across the valve and flow through the valves are measured to assess the valve function. The mean pressure difference, root mean square (RMS) forward flow and regurgitant volumes are calculated on a computer. In the initial study, seven popular mechanical prostheses (sizes 29 and 27 mm) were evaluated in the mitral position under five different flow conditions. The mean pressure difference was dependent on the position of the downstream pressure tapping, the orientation of the valve and the time interval used to average the signals. The orientation of some valves also affected the regurgitant volumes. These variations (10-25%) were similar in size to the differences measured between individual valves. Test conditions have to be specified very carefully for accurate comparison of valve function to be made.

Blood Flow Velocity↗