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ASAIO Journal 02/2003; 49(2):187. · 1.39 Impact Factor
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ABSTRACT: There is no well-established therapy for treating infections of heart-assist or artificial heart devices, a serious problem with life-threatening consequences. We used a promising new approach in which antibiotic-impregnated polymethylmethacrylate beads were placed around an implanted left ventricular assist device to control an external blood pump infection in a bridge-to-transplant patient. In this case report, we describe the potential of antimicrobial-impregnated polymethylmethacrylate beads for in situ control of infections involving external surfaces of cardiovascular devices.
The Annals of Thoracic Surgery 03/1999; 67(2):554-5. · 3.74 Impact Factor
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ABSTRACT: Current algorithms for control of the total artificial heart are directed at maintaining hemodynamic homeostasis. Future control systems will also need to modify cardiac output in response to metabolic needs. This study was undertaken to evaluate oxygen metabolism monitoring as an indicator of the adequacy of organ and tissue perfusion. Following recovery from implantation of the Utah-100 pneumatic total artificial hearts, five calves (85 to 95 kg) underwent placement of fiberoptic oximetry catheters to determine mixed venous and arterial oxygen saturations. By continuously measuring oxygen consumption with a gas analyzer, oxygen utilization and delivery were determined. In the awake calves, at-rest cardiac output was varied to produce hyperperfused and hypoperfused conditions while the adequacy of tissue perfusion was assessed with continuous mixed venous oximetry and confirmed with serum lactate (Lact) levels. Inadequate tissue perfusion (Lact > 1.0 mmol/L) was evidenced by a mixed venous oxygen saturation < 40%, oxygen delivery of < 200.0 milliliters/minute/m2), and oxygen delivery to utilization ratio of < 1.8 during the hypoperfusion conditions of the experiment. By accounting for oxygen consumption, the ratio of oxygen delivery to oxygen utilization was predictive of the adequacy of tissue perfusion. These results suggest that continuous oxygen metabolism monitoring may be useful as a physiologic control modifier to maintain total artificial heart output sufficient to meet physiologic needs, while avoiding hyperperfusion, unnecessary wear and deterioration of the implanted device due to excessive heart rates.
The International journal of artificial organs 03/1993; 16(3):135-40. · 1.86 Impact Factor
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ABSTRACT: Pharmacological therapy for congestive heart failure includes drugs that have both inotropic and vasoactive effects, although it is sometimes difficult to differentiate between the two effects. An animal with an implanted total artificial heart (TAH) allows the investigation of the vascular effect of these drugs in the absence of the effect on the myocardium. An advantage of the TAH model is its sensitivity to changes in right and left ventricular preload and afterload. Four instrumented TAH calves were given vasoactive drugs and the response was compared to control. Epinephrine, dopamine, isoproterenol, and nitroprusside were selected because of the predictability of their responses. Epinephrine caused a significant increase in systemic vascular resistance (SVR), and dopamine caused a significant increase in Pulmonary vascular resistance (PVR) and Isoproterenol caused a significant decrease in PVR. TAH implanted calves can thus serve as a pharmacological model to study the vascular response, which may be useful in investigation of new agents with inotropic and vascular effects.
The International journal of artificial organs 01/1992; 14(12):775-80. · 1.86 Impact Factor
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ABSTRACT: Pneumatically powered artificial hearts readily accommodated the higher net stroke volumes by the right ventricle than from the left ventricle. We published that this discrepancy was approximately 8% of the left ventricular cardiac output. A variety of methods have been used to achieve balance between the right and left atrial pressures. Relatively large volume-displacement chambers (VDC) present potential problems, but do provide balance. The VDC in volumetrically coupled right-left stroke volumes was eliminated by using a small-diameter interatrial shunt (IAS). Preliminary studies demonstrated excellent balance in contracted and expanded blood volume (preload) and by hypotension and hypertension created with vasoactive drugs (afterload). At a mean aortic pressure of 120 mmHg, heart rate of 120 BPM, cardiac output of 8 L/minute and right atrial pressure of 13 mmHg, the peak IAS flow was 3.2 ml/beat in a right to left direction and 8.0 ml/beat in a left to right direction. The net left to right flow was 4.8 ml/beat. Over a wide range of preload (2 to 20 mmHg) and afterload (45 to 180 mmHg), the left atrial pressure was routinely 5 mm Hg more than the right atrial pressure. Elimination of the VDC reduces the number of components, volume, and weight of the totally implantable artificial heart. The IAS offers a simple solution to a very complex problem and provides a device that is simpler to implant and is possible to explant.
The International journal of artificial organs 07/1991; 14(6):359-64. · 1.86 Impact Factor
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ABSTRACT: Unlike the mechanisms of intraaortic balloon pump (IABP) support, the mechanisms by which transvalvular axial flow Hemopump (HP) support benefit dysfunctional myocardium are less clearly understood. To help elucidate these mechanisms, hemodynamic, metabolic, and mechanical indexes of left ventricular function were measured during conditions of control, ischemic dysfunction, IABP support, and HP support. A large animal (calf) model of left ventricular dysfunction was created with multiple coronary ligations. Peak intraventricular pressure increased with HP support and decreased with IABP support. Intramyocardial pressure (an indicator of intramyocardial stress), time rate of pressure change (an indicator of contractility), and left ventricular myocardial oxygen consumption decreased with IABP and HP support. Left ventricular work decreased with HP support and increased with IABP support. During HP support, indexes of wall stress, work, and contractility, all primary determinants of oxygen consumption, were reduced. During IABP support, indexes of wall stress and contractility were reduced and external work increased. These changes were attributed primarily to changes in ventricular preload, and geometry for HP support, and to a reduction in afterload for IABP support. These findings support the hypothesis that both HP and IABP support reduce intramyocardial stress development and the corresponding oxygen consumption, although via different mechanisms.
ASAIO Journal 45(6):602-9. · 1.39 Impact Factor
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ABSTRACT: A patient with an implanted, electrically powered, ventricular assist device (Thermo Cardiosystems VE HeartMate) experienced a partial break of the percutaneous lead 5 months after implantation. The break (limited to the Silicone rubber tube) occurred at the junction of the lead with the Y-connector to the controller and vent, leaving approximately 5 cm of exposed lead from the skin exit site to the connector. Electronic and pumping functions of the pump continued, but the opening in the lead (which went more that half way around the circumference) prevented the use of pneumatic actuation as a back-up mode for pump operation, and placed the pump at risk for contamination. Repair of the lead without surgical intervention was desirable, with ease of repair and minimal risk to the patient being the top priorities. The use of multiple layers of heat-shrink tubing or external metal stents was ruled out in favor of a three stage repair procedure. The first stage involved the removal of the Dacron velour in-growth material from the lead to expose the underlying Silicone rubber tube. While the opening in the tube was held shut, a coating of medical grade Silicone rubber adhesive was applied to the tube, then wrapped with a woven Dacron mesh, followed by two layers of plastic wrapping material to protect the adhesive. This initial layer was secured by an external stent of tubing with cable ties. After several days to allow for complete curing of the adhesive, the adhesive coating with mesh was repeated. The final step involved a double layer wrap of a 1 mm thick Silicone rubber sheeting with mesh incorporation and adhesive secured in place with cable ties. After completion of the repair and verification of the ability to operate the device with pneumatic actuation, the patient was discharged with no recurrence of the problem after 8 months of weekly follow-up. This experience demonstrates the need to clinically anticipate component repair or replacement without total device replacement in future implantable blood pump systems.
ASAIO Journal 45(6):619-21. · 1.39 Impact Factor
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ABSTRACT: Test methods and results of in vitro assessment of a centrifugal pump with a magnetically suspended impeller are provided. In vitro blood tests have been completed with a resulting normalized milligram index of hemolysis (NmIH) of 12.4 +/- 4.1, indicating that hemolysis is not a problem. Hydraulic characterization of the system with water has shown that a nominal pumping condition of 6 L/min at 100 mmHg was met at 2,200 rpm. Maximum clinically usable cardiac output is predicted be 10 L/min. The magnetic bearing supported impeller did not contact the housing and was shown to be stable under a variety of pumping conditions. The driving motor efficiency is 75% at the nominal condition. Finally, a description of the clinical version of the pump under development is provided.
ASAIO Journal 44(5):M733-6. · 1.39 Impact Factor
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ABSTRACT: A continuous flow centrifugal blood pump with magnetically suspended impeller has been designed, constructed, and tested. The system can be functionally divided into three subsystem designs: 1) centrifugal pump and flow paths, 2) magnetic bearings, and 3) brushless DC motor. The centrifugal pump is a Francis vane type design with a designed operating point of 6 L/min flow and 100 mmHg pressure rise at 2,300 RPM. Peak hydraulic efficiency is over 50%. The magnetic bearing system is an all active design with five axes of control. Rotor position sensors were developed as part of the system to provide feedback to a proportional-integral-derivative controller. The motor is a sensorless brushless DC motor. Back electromotive force voltage generated by the motor is used to provide commutation for the motor. No slots are employed in the motor design in order to reduce the radial force that the bearings must generate. Tests pumping blood in vitro were very encouraging; an index of hemolysis of 0.0086 +/- 0.0012 was measured. Further design refinement is needed to reduce power dissipation and size of the device. The concept of using magnetic bearings in a blood pump shows promise in a long-term implantable blood pump.
ASAIO Journal 42(4):275-81. · 1.39 Impact Factor
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ABSTRACT: The anaerobic threshold represents an objective measure of functional capacity and is useful in assessment of pulmonary and cardiovascular dysfunction. This study determined the anaerobic threshold in total artificial heart animals and evaluated the performance of the total artificial heart system. Five animals with total artificial hearts were put under incremental exercise testing after exercise training. The intensity of exercise ranged from 2.0 to 4.5 km/hr, with an increment of 0.5 km/hr every 3 min. The anaerobic threshold was 6.72 +/- 0.84 ml/kg/min as detected by the lactate method, and 6.48 +/- 0.79 by the CO2 method. The value of the anaerobic threshold in total artificial heart animals implies that the performance capacity of a total artificial heart is not sufficient to meet the oxygen requirements of vigorously exercising skeletal muscle. The protocol does not allow for driving parameter changes during exercise, and this situation, combined with the manual mode of the control system used, was inadequate to allow the total artificial heart animals to exercise more vigorously. Using an automatic control mode might be helpful, as well as considering the relationship between indices of oxygen metabolism, such as oxygen delivery, oxygen consumption, and oxygen extraction rate, in the control algorithms in total artificial heart control systems.
ASAIO Journal 40(3):M335-8. · 1.39 Impact Factor
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ABSTRACT: The relationship between indices of oxygen metabolism has been widely used in clinical practice to evaluate the adequacy of tissue perfusion, to predict the outcome of the critically ill patient, and to evaluate the effectiveness of therapies. This study quantitated and correlated the relationship between oxygen delivery (DO2), oxygen consumption (VO2), and oxygen extraction rate (EO2) in 14 animals with total artificial hearts (TAH) to investigate the oxygen metabolism in animals with TAH during different physiologic and pathologic conditions. These 14 animals were subdivided into healthy, critical, and exercise groups. There was a physiologic dependence of DO2 to VO2 in animals in the healthy and exercise groups, whereas a pathologic dependence of VO2 to DO2 appeared to occur in animals in the critical group. Reduced or inadequate VO2 leads to organ dysfunction, shock syndrome, multiple organ failure, and finally, mortality. Providing a higher level of DO2 by restoring circulating blood volume, increasing cardiac output, raising hematocrit levels, and improving pulmonary function to achieve a higher level of oxygen extract efficiency and oxygen consumption in animals with TAH that are in a critical condition might be helpful for the treatment of complications and result in decreasing mortality. Using the relationship between indices of oxygen metabolism as a physiologic modifier for TAH control algorithms also might improve the physiologic performance and quality of life of TAH recipients.
ASAIO Journal 40(3):M510-3. · 1.39 Impact Factor
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ABSTRACT: An electrohydraulic total artificial heart (EHTAH) has been developed and evaluated by long-term in vivo studies. The EHTAH is composed of blood pumps with an interatrial shunt (IAS), an energy converter, and electronics. The EHTAH with external electronics was implanted in four calves weighing from 81-90 kg. Two animals died on the 1st and 5th post operative days, the third animal survived for 32 days, and the fourth for 159 days. The IAS was free of thrombus at autopsy in all animals. The longest surviving animal increased in size from a pre operative weight of 81 kg to 134 kg on day 144. Cardiac output ranged from 9.3 to 10.5 L/min, whereas right and left atrial pressures increased with the calf's growth from 4-10 to 16-20 mmHg and from 8-14 to 18-22 mmHg, respectively. The animal favorably tolerated up to 3.4 km/hr of treadmill exercise, both hemodynamically and metabolically. The elevation of atrial pressures during treadmill exercise was significantly alleviated by employing an automatic control mode. It is concluded that the device has the potential to be a totally implantable system for permanent use.
ASAIO Journal 39(3):M373-80. · 1.39 Impact Factor
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ABSTRACT: The hemodynamic and metabolic adaptations to exercise in five calves implanted with the Utah-100 total artificial heart (TAH) were investigated. The outputs of the left and right ventricles (LCO, RCO) were measured with a cardiac output monitoring and diagnostic unit (COMDU). Arterial and venous oxygen content (CaO2, CvO2) and blood lactate levels (Lac) were measured by blood gas analysis and enzymatic methods. Oxygen consumption (VO2), oxygen delivery (DO2), oxygen extraction rate (EO2), index of metabolic adequacy (IMA), and systemic and pulmonary vascular resistance (SVR, PVR) were calculated. The intensity of exercise was categorized into three horizontal grades: low speed (LS) 0.7-1.0 mph, medium speed (MS) 1.0-1.4 mph, and high speed (HS) 1.4-1.8 mph, each for 30 min. During LS, MS, and HS exercise, the LCO, RCO, LAP, RAP, VO2, DO2, and EO2 all increased, and the SVR and PVR decreased. During exercise, there was a positive correlation between DO2, EO2, and VO2. The blood pH, BE, SBE, and lactate levels were within normal ranges, and the IMA exceeded 1.5, denoting that tissue perfusion was adequate and anaerobic metabolism did not occur. This study implies that Utah-100 TAH animals could physiologically accommodate to exercise with an intensity of up to 1.8 mph for 30 min by increasing cardiac preload, cardiac output, oxygen delivery, and oxygen extraction rate, and by decreasing systemic and pulmonary vascular resistance without transition to anaerobic metabolism.
ASAIO Journal 39(3):M381-5. · 1.39 Impact Factor
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ABSTRACT: An adaptive algorithm to detect full ejection points was developed for the automatic control of the electrohydraulic total artificial heart (EHTAH). To automatically control the EHTAH, systole in each ventricle is completed when a hyper-pressurization spike is detected on the oil side of that ventricle. A problem associated with the method of determining ventricular full ejection under variable afterload pressure is that a fixed level comparison method could fail to provide a normal full ejection condition. To increase system stability, safety, and efficiency, there is a definite need to vary the full ejection trigger level with changes in afterload. In this study, the full ejection trigger level for the current beat was changed based on the estimated afterload derived from the previous beat's pressure waveform. To increase this estimate's accuracy, an adaptive averaging window was used to determine which part of the previous pressure waveform would be used for the afterload estimation. With this enhanced control scheme, mock circulation tests with the EHTAH device demonstrated that estimated afterload tracked actual afterload. This scheme was also used successfully to control the EHTAH device implanted in three chronic calves.
ASAIO Journal 39(4):899-903. · 1.39 Impact Factor
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ABSTRACT: A prototype bench top model of a continuous flow ventricular assist device using an impeller suspended by magnetic bearings has been developed. Generation of a pulsatile pressure was studied using both a computer model and in vitro loop tests of the prototype. The motivation for developing a computer model for a blood pump in the natural circulation is two-fold. First, it allows simulation of the pump under a large variety of operating conditions. Second, it provides insight into what parameters of the system design are important for achieving a specific result. For example, in one case, an aortic pressure of 118/87 mmHg was generated by varying the speed from 2,000 to 2,600 rpm. The computer model was verified by coupling the centrifugal pump prototype to a mock circulatory system. The results of the model were verified by generating an aortic pressure of 113/78 mmHg while varying the speed from 2,000 to 2,600 rpm. These experiments have shown that it is possible to generate pulsatile pressure similar to that of native physiology using a centrifugal left ventricular assist device. Further tests will be required to quantify the effects on hemolysis.
ASAIO Journal 42(5):M620-4. · 1.39 Impact Factor
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ABSTRACT: In vitro tests were performed to evaluate the use of an interatrial shunt in balancing a dual energy converter, actively filled, volumetrically coupled, electrohydraulic total artificial heart. The in vitro atrial shunt was comprised of a 8 mm (PTFE) Teflon graft placed between the left and the right atrium. Other features under study were 1) cardiac output (CO) response to preload, 2) CO relationship to mean aortic pressure, and 3) balance of ventricular outputs. The tests were performed by varying the right filling pressure and monitoring ventricular output and inflow/outflow pressures. Effects of changes in afterload were simulated by varying the (AoP) pressure from 80 mmHg to 120 mmHg, and the (PAP) pressure from 15 mmHg to 40 mmHg. The test results indicated a rise in CO from 4 L/min to 9 L/min, with a change in mean right atrial pressure from 0 mmHg to 12 mmHg. No significant difference in CO was found as afterload pressures were varied. The interatrial shunt (IAS) was effective in establishing ventricular balance over a wide range of preload and afterload conditions, and a mean positive flow from left to right was maintained in the atrial shunt, even at conditions simulating an extreme left-right imbalance.
ASAIO transactions / American Society for Artificial Internal Organs 36(3):M254-7.
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ABSTRACT: An electrohydraulic total artificial heart (EHTAH), using an interatrial shunt (IAS) for right-left heart balance, was evaluated in acute, in vivo, open-chested calves. The EHTAH system demonstrated physiologic autoregulation with Starling-like responsiveness to preload. Output varied from 4 to 9 L/min, as right atrial pressure increased from 3 to 15 mmHg. Device output was minimally influenced by afterload. The efficacy of an IAS to balance the EHTAH was demonstrated over a wide range of preload and afterload conditions. Interatrial shunt flow rates, reflective of the degree of right-left imbalance, varied from 2% to 14% (IAS flow from left to right) of cardiac output. Left atrial pressures typically did not exceed right atrial pressures by more than 6-8 mmHg using an instrumented vascular graft such as the IAS. The simplicity and distinct anatomic, surgical, and engineering advantages of the IAS approach to right-left balance of implanted electrically powered artificial hearts justify further development toward a reliable long-term design.
ASAIO transactions / American Society for Artificial Internal Organs 36(3):M287-90.
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ABSTRACT: Left ventricular assist device (LVAD) pumping has hemodynamic and anatomic influences on right ventricular performance. A total artificial heart (TAH) model was employed to better understand the hemodynamic influence of an LVAD on the failing right ventricle. Biventricular failure was simulated by reducing both ventricular drive pressures of the TAH. After getting hemodynamic data, LVAD pumping in the case of right ventricular failure was simulated by increasing just the left ventricular drive pressure. In the LVAD-simulating condition, cardiac output increased and right atrial pressure decreased significantly (p less than 0.05) compared with the biventricular failure condition, whereas right ventricular function and minute work were the same in these two conditions. Even though changes were accompanied by adaptive increases in pulmonary resistance, substantially lower pulmonary artery and left atrial pressures resulted in the LVAD-simulating condition. From a hemodynamic perspective, these results indicate that an LVAD can increase right ventricular volume work by decreasing right ventricular pressure work, whereas right ventricular net pressure-volume work is unchanged and right ventricular failure is not worsened.
ASAIO transactions / American Society for Artificial Internal Organs 36(3):M538-41.
