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A nonlinear III-V field-effect transistor model is proposed for designing microwave antenna switches and related circuits, off-state gate and drain capacitance values of a pseudo-morphic high-electron-mobility transistor (HEMT) derived from pulsed S-parameters with a deep OFF-state quiescent gate voltage are found to be much less voltage dependent than capacitance values measured by a nonpulsed bias owing to trap-induced dispersion effects. Our device model based on pulsed-bias CV characteristics accurately simulates switch nonlinearity. Both gate and drain capacitance values are assumed to be nonlinear, and a charge expression is developed for model implementation. For both capacitance values, a nonpulsed-bias CV curve is also utilized to maintain accurate capacitance at the quiescent voltage and, thus, accurate simulation of off-switch isolation. Additional terms are introduced to an existing drain current model to improve accuracy at high Vgs/low Vds and subthreshold regions. Furthermore, the model is extended to multiple-gate devices. Harmonics generated from both OFF- and ON-state switches, insertion loss, and isolation are accurately predicted for both single- and multiple-gate HEMTs.

An automatic measuring system for the partial pressure, pCO2, of atmospheric and oceanic carbon dioxide was developed. The system was mounted on a moored buoy for routine observation of maritime meteorology in the East China Sea. CO2 observations were conducted from June 29, 1997 to January 6, 1998. During the observation period, the atmospheric pCO2 showed little variation (341–365 μatm), whereas pCO2 in the surface water varied significantly (308–408 μatm). In the summer, pCO2 was higher in the surface water than in the overlying atmosphere, implying that this area was a source for atmospheric CO2, though it became a sink after late September. Time-series data clearly exhibited significant short-term variations in the oceanic pCO2, i.e. sudden variations during the passage of typhoons, and diurnal variations driven by the diurnal variations in the sea-surface temperature under calm conditions. The effects of typhoons on ocean–atmosphere CO2 exchange at the surface could differ, depending on the relative position of the mooring site with respect to the center of the moving typhoons. These differences result from the different contributions of sea-surface cooling, entrainment, and upwelling. The efflux enhanced by three typhoons accounted for 60% of the efflux of CO2 in the warm season. It is suggested that typhoons have a significant impact on the carbon cycle in the western subtropical North Pacific.

Crank angle-resolved measurements of gas temperature and water vapor concentration are made during the compression stroke of an internal combustion (IC) engine with a novel diode laser absorption sensor. The temperature is determined from the ratio of optical absorption for two overtone transitions of water vapor in the intake gas mixture, and the H2O concentration is determined from this inferred temperature and the absorption for one of the transitions. The measurements sample a short-path region (6 mm) of the in-cylinder gases near the spark plug, which has been modified to provide optical access. Hence, the sensor can be installed in nearly any engine via the spark plug port. Wavelength modulation spectroscopy is employed with second harmonic detection (WMS-2f) to enable the short-path measurements over a range of temperatures and pressures from 500 to 1050 K and 1 to 50 atm at a bandwidth of 7.5 kHz. The accuracy of the sensor is validated in a static cell, giving RMS errors of less than 3% in temperature and less than 3.6% in H2O concentration over a wide range of conditions. Crank angle-resolved measurements are performed in unfired and fired engine cylinders, illustrating the potential of this sensor for investigating a range of difficult-to-model trends in current and proposed IC engine combustion schemes.

To clarify environmental effects of the Chemobyl radionuclides, long-lived Chernobyl radioactivity (239,240Pu,238Pu,241Pu and90Sr) in deposition samples in May 1986 was measured at 11 stations in Japan. Temporal variation of weekly deposition of90Sr differed from that of volatile radionuclides such as131I and137Cs, which may reflect the released process at Chernobyl. On the other hand, the geographical distributions of the monthly deposition of long-lived radionuclides were similar to those of volatile radionuclides, in which maximum deposits of90Sr and plutonium were observed in Akita, a northwestern Japan Sea coast site of Honshu Island. Higher241Pu deposition in most of the stations, as well as high238Pu/239,240Pu activity ratios were observed. The241Pu/238Pu activity ratios in deposition samples were nearly equal to that in the total release, which is clear evidence that Chernobyl-derived plutonium was transported to Japan in May 1986 together with volatile radionuclides although the contribution of Chernobyl Pu was about three orders of magnitude lower than137Cs.

This article reviews the optical techniques applied to the determination of intravascular hemoglobin oxygen saturation as well as the noninvasive estimation of arterial and tissue saturation. Although in skeletal muscles and brain tissues myoglobin and cytochrome analyses have been demonstrated (F.F. Jobis et al., 1977; K. Kariman et al., 1983), their effects upon absorption and reflection spectra of tissues are small. Thus, this review is focused only upon measurement of hemoglobin saturation. >

A photon-cell interactive Monte Carlo (" pciMC ") model was developed to quantify the intracellular optical propagation in a 3-dimensional biconcave red blood cell (RBC) model having a finite volume and intracellular hemoglobin. The orientation of RBCs with respect to the incident photons was randomized to allow either extra- or intra-cellular propagation depending on the incident point and angles where the photon propagation at the plasma-cell interface was determined by the Snell's law and Fresnell's law. In this study, the photon propagation through single RBC using the pciMC was compared against the Henyey-Greenstein phase function. The absorption dependent intracellular optical path length was evaluated in comparison to Mie theory. Both results showed good agreement. The pciMC can contribute to photo-spectroscopy of blood and tissues by quantifying both extra- and intra-cellular optical propagation.

The design of a noninvasive reflectance pulse oximeter that uses the same principle of transmittance pulse oximeter and analyses the oxygen saturation of arterial blood was described. Four sets of red and infra-red LEDs were used as light sources. The respective reflectance photoelectric outputs were used to make an internal calibration curve of the instrument relative to the arterial oxygen saturation values measured with a Co-Oximeter (OSM-3) in five healthy nonsmoking subjects during steady-state hypoxaemia. The accuracy of the present instrument was studied in six patients with respiratory failure. From 22 samples, a good correlation coefficient (0.98) with a standard deviation of 1.42 was obtained in the range between 73 and 100 per cent between the arterial oxygen saturation measured with the present instrument and that with the Co-Oximeter. The result strongly suggests the usefulness of this oximeter in monitoring patients with hypoxaemia.

A fully-MMIC 77 GHz T/R module has been developed, which is incorporated with microstrip-patch planar antennas to constitute a one-body antenna/transceiver (A/T) unit for automotive forward-looking radars. The module employs a single-cavity structure for low cost manufacturing to house a dielectric interconnecting sheet and four MMIC chips consisting of a 77 GHz fundamental frequency VCO, a power amplifier and two receivers. A newly developed filtering lid for the cavity facilitates a 90 dB isolation between the Tx and Rx ports of the module to avoid undesirable interference. When combined with signal processing electronics, the A/T unit achieved a >120 m maximum detection range and a 16 deg. azimuth angle coverage.

i-AlGaAs/n-GaAs heterostructure FETs with n/sup +/-GaAs source and drain regions selectively grown by MOCVD (metal-organic chemical vapor deposition) were developed. Diode I-V characteristics and TEM (transmission electron microscope) observations showed that the epitaxial structures are preserved in the present process. A small source resistance (0.35 Omega -mm) and a minimal threshold voltage shift at a short gate-length 0.3- mu m gate showed a high K value of 650 mS/mm. The high current drivability and the small threshold voltage shift at short gate-lengths suggest the potential of the DC-HIGFETs for LSI applications. >

The objective of this study was the development of a reflectance pulse oximeter sensor for broader clinical applications, specifically for broader arterial oxygen saturation (SaO/sub 2/) measurement from various body portions. To enhance the reflectance pulse amplitude from any body surface and eliminate the effect of tissue inhomogeneity, the new sensor incorporated ten LED chips for each wavelength mounted symmetrically at the radial separation distance of 7 mm around a photodiode chip. Based on the photon diffusion theory, the wavelength combination, 730/880 nm, was determined to obtain a linear relationship between the reflectance ratio and broader SaO/sub 2/ range from 100% to 30%. The improved linearity of the new sensor was evaluated in dogs (n=5) in comparison to the 665/910 nm conventional wavelength sensor. Additionally, this new reflectance sensor was applied to various body surfaces in healthy human adults (n=30). The relative reflectance pulse amplitudes from the fingertip, forehead, and chest were 1.0, 0.3, and 0.1 as normalized to the fingertip at each wavelength. These results will broaden the application sites of the reflectance pulse oximeter sensor in the hospital and home healthcare.

Highly selective etching of InAlAs over InGaAs by ArF excimer laser with Cl/sub 2/ gas was demonstrated. The etching rate of InAlAs relative to that of InGaAs increased as the laser fluence decreased and the Cl/sub 2/ pressure increased, and the highest observed etching rate ratio exceeded 70. The very fast InAlAs etching rate is speculated to be due to the higher reactivity of Al than that of Ga.

The effect of the surface Fermi level position on the dc characteristics of InP-base heterostructure bipolar transistors (HBTs) is examined. The Fermi level of an InP surface covered with silicon oxide was located at an energy position close to the conduction band minimum of InP. This implies formation of an electron accumulation layer at the interface, which acts as a surface leakage path. The HBT passivated with silicon-oxide film showed a huge excess base current and poor current gain. In contrast, the Fermi level position at the silicon-nitride/InP interface was found to be near the midgap, and no electron accumulation layer formed at the interface. The HBT passivated with silicon-nitride film showed excellent dc characteristics with a very small excess base current.

The objective of this research was to develop a method of estimating central aortic pressure (AA) waveform from the noninvasive radial tonometry (TRA) waveform. In order to attain this goal, the Fast Fourier Transform (FFT) and Auto-Regressive eXogenous (ARX) models were used to develop the transfer function (TF) between the AA (input) and TRA (output). The inverse TF was then derived to generate the AA waveform from the TRA waveform. To test the accuracy of the model, the aortic pressure waveform using a Millar catheter tip transducer and noninvasive radial artery waveform using a Colin tonometer were simultaneously obtained in 5 patients who were undergoing cardiac catheterization at Yamagata University. The inverse TF based on the FFT model did not accurately reconstruct the AA waveform. On the contrary, ARX model resulted in accurate estimate of AA with the estimation error of approximately 3% for systolic, diastolic and mean pressure levels. The noninvasive radial tonometry in combination with the ARX model may offer a potential of noninvasive estimation of aortic pressure waveform.

A fully MMIC 5 GHz-band transceiver module has been developed, which demonstrated high-speed modulation capability of 48 Mbps OFDM/64QAM with 5-7% error vector magnitude (EVM) for 5-6 GHz operations. The module is assembled on a multi-layer ceramic substrate with land grid type RF/DC terminals and measures 11.0/spl times/13.75/spl times/1.1 mm/sup 3/. The module incorporates four MMIC chips operating from /spl plusmn/3 V power supplies and supports a wide range of IF frequencies from 200 MHz to 1.8 GHz.

This paper reviews the current status and future perspectives of the artificial heart research that was started in 1957 by Akutsu and Kolff. During the 1960's, although not much progress was made in increasing animal survival time with artificial hearts, clinical applications were already made for both a ventricular assist device in 1962 and total artificial heart (TAH) in 1969 followed by a second TAH application in 1981. Both TAH applications were done as bridges to heart transplantation. Meanwhile, the animal survival time improved during the 1970's because of the availability of better biomaterials, better understanding of the circulatory system, and improvement in surgical techniques. Continuous flow pumps were also investigated during the 1970's, which demonstrated feasibility for chronically supporting circulation in healthy animals. Four permanent cases of TAH application were done early 1980's for patients who could not be the candidates for heart transplantation. Although the patients were tethered to the external drive-console, one of them survived for nearly two years. Complications due to thromboembolism and infection were the major causes of death in these patients. The patients' quality of life was questionable and the permanent application of the TAH was then stopped to make improvements in the system in terms of implantability and biocompatibility. During the 1980's, efforts were then switcthed to development of totally implantable VAD and TAH systems, which led to the first discharge of a VAD patient from the hospital in 1992. In the early 1990's, implantable electric VADs, Novacor and ThermoCardio System (TCI), became available to support the circulation of end-stage cardiac patients until a donor heart could be found. The transplantation rate of the VAD patients ranged around 70% with the average waiting time of 80 to 100 days. The number of patients transplanted with VADs are more than 5000 and those with the pneumatic TAH exceed 200. Because of the larger size, requirement of heart valves, and complicated control mechanism of the pulsatile VADs, continuous flow pumps have been gaining popularity among clinicians. The clinical applications of the continuous flow devices have just begun, demonstrating remarkable performance in bridging to heart transplantation. In, the 21st century, we will see prevalent clinical applications of various circulatory support devices from pulsatile VAD, pulsatile TAH to continuous flow VAD. These devices will be combined with genetic treatment to re-generate the myocardium and recover the failing heart. Complete recovery of the myocardium may become possible through therapy combining circulatory assist devices and biotechnology.

The anatomic constraints and design parameters for a heart prosthesis have not yet been defined in heart transplant recipients (i.e., the population most eligible for total artificial heart implantation). The parameters regarding anatomic constraints were measured in 26 consecutive patients undergoing orthotopic heart transplantation (median body surface area 1.9 m2) after cardiectomy. A full-sized contour model of the cylindric total artificial heart (diameter 97 mm; width 81 mm) was inserted into the pericardial cavity to decide the pump configuration and to verify its fit. The dimensions of this model were based on the miniature electromechanical total artificial heart that is currently under development. Fit was found to be adequate in most of the cases with no identifiable compression of adjacent vascular structures. The median intraoperative measurements that define pericardial constraints for a heart prosthesis were pericardial length (130 mm), width (160 mm), and depth (140 mm). We also took measurements from the excised hearts, which should provide a useful reference for other prosthetic devices. The current dimensions of our implantable total artificial heart were found acceptable for orthotopic implantation. Length of the pericardium and cardiothoracic ratio were identified as variables related to adequacy of fit.

To test the durability of each part or assembled component of the Baylor-ABI total artificial heart (TAH), the authors performed an endurance test under severe conditions. The TAH was immersed in a saline bath at 42 degrees C, which is 4-5 degrees C higher than normal body temperature. This is an accelerated endurance test because of the elevated temperatures. In this accelerated endurance test loop, the 42 degrees C heated saline was circulated not only in the pump but also outside the pump. During pumping, temperatures of the motor and outside surface of the centerpiece were continuously measured. This testing showed that during almost 4 months of pumping no electromechanical troubles were observed. Both inside (motor) and outside temperatures were stable and the differences in both temperatures were only 3-4 degrees C, demonstrating that heat generation is not a problem. The voltage and current required in this system remained constant, indicating stable and reliable performance. Based on these results, this pump is expected to run continuously over a long duration in a normal physiologic environment. This accelerated endurance test system is very suitable for estimating the influence of heat generation by the actuator of blood pumps. It is also quite useful in validating the durability of various cardiac prosthesis.

An electro-mechanical VAS intended for totally implantable and permanent use has been developed at Baylor College of Medicine. It consists of a pusher-plate pump with a 63-ml stroke vol. and a compact actuator utilizing a direct current (DC) brushless motor with a roller-screw. The pumping unit weighs 620 g, and has a total vol of 360 ml, which is the smallest among implantable devices. With a filling pressure of 10 mmHg, the pump can provide 81/min of flow against an afterload of 120 mmHg. The pump is biolized by dry gelatin with tissue valves. Five subacute in vivo studies were conducted in calves for up to 3 weeks to validate easy implantability and sufficient hemodynamics. Excellent hemodynamics were obtained in the fill-empty mode utilizing the Hall effect stroke sensor. This VAS unit is compact, has low-noise characteristics, is easy to control, and exhibits excellent biocompatibility. This system is capable of supporting a failed heart and of meeting the anatomical, physiological, and psychological needs of patients who may require not only temporary support during bridge use but also permanent support.

A fit study was conducted to define anatomic constraints to total artificial heart (TAH) insertion in 26 human orthotopic cardiac transplant recipients, and the parameters necessary for designing a totally implantable TAH were obtained from the excised heart. A multiadjustable fitting device was made (height, 118 mm; width, 81 mm; diameter, 97 mm), and with this model, 15 fitting and measuring studies were conducted to validate the design and demonstrate anatomic compatibility. Satisfactory fit of the contour model was observed in all cases. The model was placed through a sternotomy wound in the pericardial space. In addition to this mock-up fit study, the anatomic dimensions of the connection points to the TAH and the excised hearts also were measured. With the prototype model based on these data, a fit verification study was done in 11 recipients. Satisfactory fit in the pericardial space without compression of adjacent structures was observed in seven of 11 patients. This study suggests that the newly designed model of an anatomically and surgically practical configuration could be implanted in most patients in this population as a completely implantable cardiac prosthesis.

A completely implantable, one piece electromechanical total artificial heart (TAH) intended for permanent human use was developed. It consisted of left and right conically shaped pusher-plate blood pumps sandwiching a thin centerpiece with a compact, efficient electromechanical actuator. The actuator consisted of a direct current brushless motor; a planetary roller screw fit the space between the two conically shaped pusher-plates. The rotational motion of the motor was converted to the rectilinear motion of the rollerscrew to displace the left and right pusher-plates in the left master alternate mode. The diameter of the assembled TAH was 97 mm, with a central thickness of 82 mm. The overall weight was 620 g, with a displaced volume of 510 ml. The pump provided flows of 3-8 L/min with a preload of 1-15 mmHg against an afterload of 100 mmHg. The net efficiency ranged from 15% to 18%. This model showed good fit in the pericardial space of heart transplant recipients (body weight, 77 kg).

An implantable electromechanical ventricular assist system (VAS) intended for permanent human use was developed. It consisted of a conically shaped pumping chamber, a polyolefin (Hexsyn) rubber diaphragm attached to a pusher-plate, and a compact actuator with a direct current brushless motor and a planetary rollerscrew. The outer diameter was 97 mm, and the total thickness was 70 mm. This design was chosen to give a stroke volume of 63 ml. The device weighs 620 g, with a total volume of 360 ml. The pump can provide 8 L/min flow against 120 mmHg afterload with a preload of 10 mmHg. The inner surface of the device, including the pumping chamber and diaphragm, was made biocompatible with a dry gelatin coating. To date, two subacute (2 and 6 day) calf studies have been conducted. The pump showed reasonable anatomic fit inside the left thorax, and the entire system functioned satisfactorily in both the fill-empty mode using the Hall effect sensor signals and the conventional fixed rate mode. There were no thromboembolic complications despite no anticoagulation therapy. The system now is being endurance tested greater than 10 weeks (9 million cycles). This VAS is compact, low noise, easy to control, and has excellent biocompatibility.

The anatomic constraints to mediastinal fit of a total artificial heart (TAH) were largely neglected during the early developmental stages, precipitating failure due to compression or torsion of intrathoracic conduits and vascular structures. Cadaveric studies quantifying anatomic constraints are limited by postmortem factors causing distortion of critical structures. This study defines the anatomic constraints and parameters necessary for designing an implantable TAH. Importantly, these parameters were measured in 12 consecutive patients undergoing orthotopic cardiac transplant (mean body surface area, 2.0 +/- 0.1 m2) after native heart amputation. A full sized contour model of the cylindrical TAH (diameter, 97 mm; width, 78 mm) was inserted into the pericardial cavity to verify fit, which was found adequate in each case, with no identifiable compression of adjacent vascular structures. Intraoperative measurements obtained define intrathoracic and pericardial constraints for a cardiac prosthesis (mean pericardial dimensions: length, 133.0 mm; width, 154.0 mm; depth, 129.0 mm). The parameters measured will provide useful reference for other prosthetic devices, since they were obtained intraoperatively rather than postmortem. The current dimensions of our TAH were found to be acceptable for orthotopic implantation.

A completely implantable total artificial heart (TAH) is being developed based on many years of research performed at the Cleveland Clinic Foundation and Nimbus, Inc. The pumping unit consists of biolized surface-treated pusher plate blood pumps powered by an interventricular electrohydraulic energy converter. A variable volume device references the back side of the pusher plates to lung pressure. Electrical power is supplied by a transcutaneous energy transmission system, integrated with a wearable external battery pack. An implanted internal battery provides back-up power. System design and optimization efforts have resulted in a compact pumping unit package and an overall TAH that meets anatomic, physiologic, and engineering requirements. Overall pumping unit basic dimensions are 98 mm diameter and 80 mm thick. The blood pumps have a truncated conical shape and are separated by a thin interventricular septum 21 mm thick. Theoretical stroke volume is 64 ml, and maximum stroke length is 13.2 mm. Normal pump operation is at 90% of full stroke, which yields a net output of 53 ml, with valve regurgitation taken into account.

Surface composition of and CO chemisorption on a partially oxidized titanium foil covered with 120 A of nickel was examined by Auger electron spectroscopy (AES) after various amounts of hydrogen reduction at 700 K. AES and sputter-profiling showed the segregation of submonolayer amounts of reduced titanium oxide on the nickel surface after 10–40 min of hydrogen reduction at 700 K. The maximum CO uptake at room temperature was reduced to 30–40% of the pre-reduction value after 30 min of hydrogen reduction. These observations suggest that the commonly reported phenomenon of strong metal-support interaction (SMSI) is a result of partial coverage of the metal catalyst surface by titanium oxide.

The details of a relatively low‐cost, low‐noise, 16‐bit interface between a digital‐to‐analog converter and an Apple II computer are presented.

We conducted chronic experiments to determine how to treat profound biventricular failure systematically with ventricular assist devices (VADs) and to analyze the factors that affect prognoses for this condition. Anoxic arrest was induced in ten goats by aortic cross-clamping under normothermic conditions (38.5 degrees C) for 30 (n = 3), 45 (n = 1), and 60 (n = 6) minutes. A left ventricular assist device (LVAD) was implanted in eight animals, and a biventricular assist device (BVAD) was used in two. Three goats--two of which had undergone anoxic arrest for 30 minutes and one for 60 minutes--whose right atrial pressure (RAP) was approximately 18 mm Hg during the acute stage, recovered in two to three weeks, and the pumps were successfully removed. Pathological findings in these animals showed scattered areas of surviving myocardium, with connective tissue replacing the degenerated myocardium. The remaining five LVAD goats required higher RAPs to maintain circulation and died from various causes. Maintaining circulation without volume loading, even in the presence of arrhythmias, was easier with the BVAD. One BVAD animal that underwent 45 minutes of anoxic arrest recovered from right ventricular failure, and the right pump was removed. The second goat (anoxic arrest, 60 min) on the BVAD failed to recover. Autopsy of the myocardium revealed a thin ventricular wall. Our studies show that the use of VADs allows time for a failing heart to recover, but the potential for healing is affected by the severity of myocardial damage prior to VAD application.(ABSTRACT TRUNCATED AT 250 WORDS)

The photon diffusion theory can yield quantitative estimation of tissue hemoglobin saturation, provided that the medium is homogeneous and that one calibration data is available. The error in detection of tissue OS of the gut mucosa ranged from 5 to 10% in oxygen saturation. In application to skin, the two-layer tissue model suggests that by properly designing the optical sensor and by appropriately selecting the illumination wavelengths, it is possible to capture mainly the light returning from the specific depth in tissue. Since the skin layer thickness is roughly in the order of 1 mm, the source and detector separation distance of approximately 3 mm or larger would ensure that the measured reflectance is truly returning from the deeper layer. When such reflectances are normalized to the blood-free reflectance obtained by squeezing the blood out of the tissue, the normalized reflectance truly represents the deeper layer characteristics. In application to head, since the skin and skull thickness is considerable large, separation distance of 40 mm or greater is required to ensure the reflectance is actually returning from the brain. Closely spaced optical sensor would measure the scattering and absorption characteristics of the skin and skull of the head. As for directional changes in optical propagation due to tissue inhomogeneities, multiple light sources at the equi-distance around the detector can be placed to average out the effect. The resultant reflectance can be analyzed based on the similar mathematical treatment as presented in this study. However, since the absolute reflectance level calculated by the theory and the actual reflectance for a given transducer geometry have some deviation, again one point calibration is required to close the gap between them. This can be accomplished through arterialization of the tissue and ventilating with pure oxygen to yield reflectance from tissue containing 100% saturated blood. As for hemoglobin content, isosbestic reflectance, for example at 805 nm, can be utilized to estimate tissue hemoglobin content. Once one point calibration is accomplished, reflectance changes thereafter due to changes in HbT and OST can be fairly accurately predicted by the photon diffusion theory in combination with linear analysis. Concerning separation of arterial and venous blood in tissue, the diastolic and systolic phases of the optical plethysmographic signal can be assumed to relate to venous or DC level, and to arterial or AC component. Since the four components, arterial and venous OS and Hb, are unknowns in the system, four equations or four wavelength measurements are required to sort out each effect.(ABSTRACT TRUNCATED AT 400 WORDS)

The long range goal is the development of a clinically useful, implantable, skeletal muscle powered cardiac assist device (MCAD). To accomplish this goal, two criteria must be met: good anatomic fit, and antithrombogenicity. Because of the relative locations of the latissimus dorsi (LD) muscle and aorta, there are two possible port arrangements: "crisscrossed" (C design), in which the ports are crossed to anastomotic sites, and "prong" shaped (P design), in which no crossover takes place. The purpose of this paper is to determine which of these designs is best from a fluid dynamic perspective, and hence has the best possibility for low thrombogenicity. Flow visualization (FV) techniques were used during two pumping conditions in a mock loop: worst case (MCAD off) and best case (MCAD driven optimally). Results of the MCAD off tests showed that both designs required immediate actuation (for example, an IABP console). However, FV studies under optimal conditions indicated superiority of the C design, most likely due to kinetic energy-induced rotary motion combined with a minimal interport distance. It is concluded that the C design provides ideal flow dynamics, even in valveless pumps, and also has application to valved devices.

Plasma atrial natriuretic polypeptide (ANP) levels and plasma renin activity (PRA) were measured in six left ventricular assist device (LVAD) goats, four single artificial heart (SAH) goats, i.e., LVAD animals with fibrillated hearts, and 3 total artificial heart (TAH) calves. During the 4 week experiment, the ANP levels in the SAH goats increased to 516 pg/ml from the control value of 61.8 pg/ml because of an elevated CVP of 13-21 mmHg, while those of the LVAD goats were near the lower limit of the control values. The TAH calves had slightly decreased ANP levels at 23-46 pg/ml after the third postoperative week, which did not increase after the steep increase in CVP induced by the changes in the driving conditions. The PRA levels were 10-50 times higher than control in the SAH goats and a TAH calf whose CVP rose to 19 mmHg, although the cardiac output was within normal limits.1) The secretion of ANP secondary to alteration in CVP was preserved in the LVAD recipients and enhanced diuresis, while it was compromised in the TAH cases. 2) The PRA levels in cases with elevated CVPs were high enough to suppress diuresis.

The right and left atrial pressures (RAP and LAP), circulating blood volume (CBV) and pump output were analyzed in 17 calves implanted with a free-diaphragm-type total artificial heart. A high RAP and increased CBV were common features in these animals, while the LAP was maintained in a nearly normal range throughout the course. Some correlation was seen between RAP, CBV and pump output, which was maintained in the range of 86.6 to 130.1 ml/min/kg. In the atrial myocardium various morphological changes were observed accompanied by thickening of the cell, which was conspicuous after one month of implantation. To improve this high venous pressure problem, an automatic controller for pusher-plate-type pumps wtih a greater sensitivity was introduced. A preliminary in vivo study using this new system is also reported.