In vitro evaluation of control strategies for an artificial vasculature device

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. An artificial vasculature device (AVD) that may better facilitate myocardial recovery than VAD by controlling the afterload seen by the ejecting heart is being developed. The AVD concept is to enable any user-defined input impedance (IM) with resistance (R) and compliance (C) components. In this study, a pulse duplicator was used to test the efficacy of the AVD concept for two control strategies in an adult mock circulation: (1) R-C in series and (2) 2-element Windkessel (R-C in parallel) using instantaneous impedance position control (IIPC) to maintain a desired value or profile of R and C. In vitro experiments were performed and the resulting cardiovascular pressures, volumes, flows, and the afterload (R and C) seen by the LV during ejection for simulated cardiac failure were recorded and analyzed. Our results indicate that setting the AVD to lower IM reduced LV volume and pressure, restored LV stroke volume, and increased coronary flow. The IIPC control algorithms are better suited to maintain any instantaneous IM or an IM profile, but are susceptible to measurement noise.

Hemodynamic and left ventricular pressure-volume responses to counterpulsation in mock circulation and acute large animal models

Alternative therapies for treating heart failure patients are being explored to provide effective options for patients with progressive heart failure. Cardiac assist devices that promote myocardial recovery may be a potential solution. Ventricular assist devices (VAD) have demonstrated long-term efficacy and intraaortic balloon pumps (IABP) have shown short-term successes. In this paper, testing of a hybrid counterpulsation device (CPD) that couples the attributes of device longevity (VAD) with less invasive surgery (IABP) is presented. Hemodynamic and ventricular pressure-volume responses to a 40 ml CPD and 40 ml IABP were evaluated in vitro in an adult mock circulation and in vivo in a large animal heart failure model. The CPD is a flexing diaphragm ventricle with a controlled stroke volume up to 85 cc through a single, valveless cannula. In this study, the CPD was cannulated to the brachiocephalic artery to provide 40 ml of counterpulsation support. The CPD effectively provided diastolic augmentation increasing coronary flow and afterload reduction. These results were comparable to IABP. These preliminary studies suggest that CPD may be an effective therapy for treating patients with early stage heart failure.

In vitro evaluation of the effect of aortic compliance on pediatric intra-aortic balloon pumping

OBJECTIVES: To evaluate the effect of aortic compliance on pediatric intra-aortic balloon pumping (IABP). DESIGN: In vitro study using a mechanical model of the pediatric left heart circulation. SETTING: Cardiovascular fluid dynamics research laboratory. SUBJECT: Pulsatile flow system simulating the pediatric left heart circulation and two different aortas with compliances comparable to those of the pediatric aorta (0.12 and 0.07 mL/mm Hg). INTERVENTIONS: Measurements were made at a baseline peak aortic flow of 4 L/min, at simulated shock (1.7 L/min), and with 1:1 IABP (rates, 130 and 150 bpm; balloon volumes, 2.5 and 5.0 mL). MEASUREMENTS AND MAIN RESULTS: Peak flow rates were measured in the ascending aorta, coronary arterial system, and brachiocephalic arterial systems. Aortic pressure was measured in the ascending aorta. For both aortas (0.12 and 0.07 mL/mm Hg), IABP resulted in diastolic augmentation (38 +/- 8 and 43 +/- 16 mm Hg) and afterload reduction (4 +/- 2 and 6 +/- 3 mm Hg). For both aortas, compared to shock, IABP resulted in significant increases in coronary arterial and brachiocephalic arterial flow and aortic pressure for both aortas. Aortic flow significantly increased only in the less-compliant aorta. CONCLUSIONS: In a laboratory model of pediatric left heart circulation, IABP results in diastolic augmentation, afterload reduction, and improved hemodynamics, even in aortas of greater compliance.

Aortic input impedance in infants and children

Flow and pressure measurements were performed in the ascending aortas of six pediatric patients ranging in age from 1 to 4 yr and in weight from 7.2 to 16.4 kg. From these measurements, input impedance was calculated. It was found that total vascular resistance decreased with increasing patient weight and was approximately one to three times higher than those of adults. Conductance per unit weight was relatively constant but was approximately three times higher than for adults. Strong inertial character was observed in the impedance of four of the six patients. Among a three-element and two four-element lumped-parameter models, the model with characteristic aortic resistor (R(c)) and inertance in series followed by parallel peripheral resistor (R(p)) and compliance fitted the data best. R(p) decreased with increasing patient weight and was one to three times higher than in adults, and R(c) decreased with increasing patient weight and was 2 to 15 times higher. The R(p)-to-R(c) ratio differed significantly between infants and children vs. adults. The results suggested that R(p) developed more rapidly with patient weight than did R(c). Compliance values increased with increasing patient weight and were 3 to 16 times lower than adult values.

Feedback control of mean aortic pressure in a dynamic model of the cardiovascular system

Orbital measurements of the cardiac function of Space Shuttle crew members have shown an initial increase in cardiac stroke volume upon entry into weightlessness, followed by a gradual reduction in stroke volume to a level approximately 15% less than preflight values. In an effort to explain this response, it was hypothesized that gravity plays a role in cardiac filling. A mock circulatory system was designed to investigate this effect. Preliminary studies carried out with this system on the NASA KC-135 aircraft, which provides brief periods of weightlessness, showed a strong correlation between cardiac filling, stroke volume, and the presence or absence of gravity. The need for extended periods of high quality zero gravity was identified to verify this observation. To accomplish this, the aircraft version of the experiment was reduced in size and fully automated for eventual integration into a Get Away Special canister to conduct an orbital version of the experiment. This article describes the automated system, as well as the development and implementation of a control algorithm for the servoregulation of the mean aortic pressure in the orbital experiment. Three nonlinearities that influence the ability of the apparatus to regulate to a mean aortic pressure of 95 mm Hg were identified and minimized. In preparation for a Space Shuttle flight, the successful function of the servoregulatory scheme was demonstrated during ground tests and additional test flights aboard the KC-135. The control algorithm was successful in carrying out the experimental protocol, including regulation of mean aortic pressure. The algorithm could also be used for the automated operation of long-term tests of circulatory support systems, which may require a scheduled cycling of the pumping conditions on a daily basis.

Successful repair of a ventricular assist system percutaneous lead

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.

Myocardial mechanics, energetics, and hemodynamics during intraaortic balloon and transvalvular axial flow hemopump support with a bovine model of ischemic cardiac dysfunction

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.

Estimation of timing errors for the intraaortic balloon pump use in pediatric patients

The use of the intraaortic balloon pump (IABP) for managing acute left ventricular failure in pediatric patients is less successful than in adults. It is often reported that rapid pediatric heart rates make accurate timing difficult to achieve. Traditional IABP theory requires that the balloon inflate during diastole (after aortic valve closure), for optimum coronary pressure and flow augmentation, and deflate just before the next systole for optimal ventricular afterload reduction. Errors in timing balloon inflation and deflation may result in the reduced IABP efficacy seen in children. To investigate timing errors when using the traditional IABP inflation and deflation markers in pediatric patients, six patients (age, 2.2+/-1.4 years; weight, 11.5+/-3.9 kg) were studied intraoperatively. Radial artery pressure (RAP) waveforms from a standard, fluid-filled pressure monitoring system were recorded on an FM data tape recorder simultaneously with high-fidelity, aortic root pressure waveforms, aortic root flow waveforms, and M-mode echocardiography. For each patient, a sequence of five recorded waveforms was analyzed. The mean +/- standard deviation of the time delay between aortic root and RAP markers and percentage delay of the corresponding part of the cardiac cycle were determined. When compared with aortic root waveforms, the RAP waveform consistently showed a delay in the IABP timing markers. A 107+/-23 msec (53+/-11%) delay in diastolic inflation and a 92+/-11 msec (40+/-4%) delay in presystolic deflation was found. If IABP timing to the RAP markers were to be used, the delay in IABP inflation would result in reduced diastolic augmentation, and the delay in IABP deflation into the systolic period would increase afterload. M-mode echocardiography provided timing markers that were identical to those provided by high-fidelity aortic root pressure waveforms. The combined effect of these delays on IABP function could substantially reduce the efficacy of the IABP in pediatric patients, indicating the need for more accurate indices for IABP timing in this patient group.

Neonatal piglet model of intraaortic balloon pumping: improved efficacy using echocardiographic timing

BACKGROUND

Pediatric intraaortic balloon pumping (IABP) has met with little success because of technical difficulty in tracking rapid heart rates. This study was designed to evaluate the efficacy of M-mode echocardiography for IABP timing in a neonatal piglet model.

METHODS

Two groups of piglets underwent mitral valve avulsion to create a model of shock. Group 1 (n = 8; mean weight, 7.7+/-1.8 kg) underwent IABP timed with both the ascending aortic pressure and M-mode echocardiogram. Group 2 (n = 6; mean weight, 7.5+/-1.4 kg) underwent two separate periods of IABP: one with echocardiographic timing and the second using standard timing points from the femoral arterial pressure tracing and electrocardiogram. Measurements included ascending aortic flow, left anterior descending arterial flow, ascending aortic pressure, left atrial pressure, and heart rate.

RESULTS

Mitral valve avulsion produced a shock model with a significant decrease in mean aortic pressure and aortic flow and a significant increase in left atrial pressure and heart rate. Compared with the shock state, IABP in group 1 animals resulted in a significant increase in aortic flow (353+/-152 versus 454+/-109 mL/min; p < 0.05) and a significant decrease in left atrial pressure (23+/-6 versus 17+/-7 mm Hg; p < 0.05). Group 2 animals with echocardiogram-timed IABP had significantly increased aortic flow (365+/-106 versus 458+/-107 mL/min; p < 0.05) and mean aortic pressure (43+/-11 versus 52+/-8 mm Hg; p < 0.05). However, standard-timed IABP failed to show any improvement.

CONCLUSIONS

In piglets with rapid heart rates, echocardiogram-timed IABP results in increased aortic flow and pressure and decreased left atrial pressure compared with standard-timed IABP.

Influence of gravity on cardiac performance

Results obtained by the investigators in ground-based experiments and in two parabolic flight series of tests aboard the NASA KC-135 aircraft with a hydraulic simulator of the human systemic circulation have confirmed that a simple lack of hydrostatic pressure within an artificial ventricle causes a decrease in stroke volume of 20%-50%. A corresponding drop in stroke volume (SV) and cardiac output (CO) was observed over a range of atrial pressures (AP), representing a rightward shift of the classic CO versus AP cardiac function curve. These results are in agreement with echocardiographic experiments performed on space shuttle flights, where an average decrease in SV of 15% was measured following a three-day period of adaptation to weightlessness. The similarity of behavior of the hydraulic model to the human system suggests that the simple physical effects of the lack of hydrostatic pressure may be an important mechanism for the observed changes in cardiac performance in astronauts during the weightlessness of space flight.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and The Society of Thoracic Surgeons: long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and Society of Thoracic Surgeons: long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

Compact compliance chamber design for the study of cardiac performance in microgravity

A need was identified for a Mock Circulation System (MCS) of small size and weight that could function in a microgravity environment for the investigation of cardiovascular response to the weightlessness of space flight. Part of the MCS development involved the redesign of the compliance chamber from a Penn State MCS using a coil spring instead of the leaf spring system employed in the Penn State system. The new compliance chambers achieve a weight reduction of 47% and a volume reduction of 64% over the original Penn State design. Testing showed the coil spring compliance chambers retained physiologic characteristics and adjustability by using coil springs of various stiffness, and functioned equivalently to the original Penn State design.

In vitro evaluation of forward and reverse volumetric flow across a regurgitant aortic valve using Doppler power-weighted mean velocities

To determine the accuracy of using power-weighted mean velocities for quantitating volumetric flow across a cardiac valve, we equipped pulsatile flow-tank systems with a 25 mm porcine or a 27 mm mechanical valve with various sizes of regurgitant orifices. Forward and reverse volumetric flows were measured over a range of hemodynamic conditions using two insonating angles (0 and 45 degrees). Pulsed Doppler power-weighted mean velocity measurements were obtained simultaneously with electromagnetic or ultrasonic transit-time probe measurements. For the porcine valve, Doppler measurements correlated well with electromagnetic flow measurements for all (r = 0.75 to 0.97, p < 0.05) except the smallest (2.7 mm) orifice (r = 0.19). For the mechanical valve, power-weighted mean velocity measurements correlated well with ultrasonic transit-time measurements for each hemodynamic condition defined by pulse rate, mean arterial pressure, and insonating angle (r = 0.93 to 0.99, p < 0.01), but equations varied unpredictably. Thus, although power-weighted mean velocity volumetric flow measurements correlate well with flow probe measurements, equations vary widely as hemodynamic conditions change. Because of this variation, power-weighted mean velocity data are not useful for quantitation of volumetric flow across a cardiac valve at this time. Further investigation may show how different hemodynamic conditions affect power-weighted mean velocity measurements of volumetric flow.

Variation in artificial heart acceleration and sound production with prosthetic valve selection in vitro

In an attempt to explore methods to reduce total artificial heart (TAH) acceleration and sound production, in vitro measurements of TAH acceleration and sound were made when using a variety of prosthetic valves in a test ventricle. A miniature, uniaxial, high fidelity accelerometer was glued to the housing of a UTAH-100 left ventricle adjacent to the inflow and outflow ports and parallel to the axis of diaphragm excursion. A miniature, high fidelity contact microphone was glued to the opposite side of the ventricular housing between the inflow and outflow ports. Data was collected over a range of heart rates, ventricular filling volumes and control modes while using tilting disc valves (TDV) and polymer trileaflet valves (PTV). For both valve types, the peak systolic acceleration impulse was lower (approximately equal to 50%) when the ventricle was fully rather than partially filled and the peak diastolic acceleration impulse was lower (approximately equal to 50%) when the ventricle was fully rather than partially ejected. The magnitude of the acceleration with PTVs was approximately equal to 20x less than the TDVs (0.5 to 2.2 g vs. 10 to 49g). The magnitude of the sound production was also considerably less with the PTVs (28 to 49 db vs. 50 to 64 db). Diastolic acceleration and sound production was approximately twice the systolic value for the TDVs; the reserse was true for PTV sound production. These data demonstrate the substantial reduction in TAH impulse acceleration and sound production by selecting PTVs over TDSs. With PTVs, the TAH impulse acceleration is the same as the natural heart. Consequently, this ability to lower TAH acceleration and sound production to the level of the natural heart may lead to a reduction in component wear, patient discomfort and other undesirable consequences of TAH implantation.

Markers of thromboembolization in a bovine ex vivo left ventricular assist device model

The production of blood microemboli (BME) was studied using an ex vivo exteriorized left ventricular assist device (LVAD) model in calves. Each of eight calves received a series of three LVADs, each operating for 24 hr. Blood microemboli were measured directly by a laser (624 nm and 828 nm) light scattering microemboli detection (LSMD) system through the LVAD outflow cannula and by constant pressure filtration (CPF) of blood samples from the LVAD outflow cannula. Hematologic parameters were also measured. After LVAD removal, perivalvular thrombi were evaluated using polar coordinate mapping. The average LSMD and CPF results correlated. For example, in one series of three calves, one ventricle exhibited significantly greater thrombogenesis than did the other ventricles, as indicated by both the LSMD and CPF results. In a series of five calves, one calf developed an abnormally high activated thromboplastin time (APTT), even in the absence of heparin. For two of the three ventricles tested in that calf, microemboli concentration (CPF), Factor XII activity, level of fibrin degradation products (FDP), and accumulated thrombus were significantly lower than for the other calves. The whole blood viscosity (WBV, at 230 s-1) in this calf also decreased to lower values than were seen with the other calves.

Oxygen metabolism in animals with total artificial hearts

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.

A justification for high resolution hematocrit measurement

The purpose of this study was to determine the feasibility of using a 6" digital caliper and a 20x viewing microscope to measure hematocrit (HCT) from microhematocrit tubes. The reliability and validity of the digital caliper technique (DC) was simultaneously compared with that of the conventional "turntable" style microhematocrit method (MC) and the Coulter Counter hematocrit (CC) for a comprehensive comparison of the three methods. The reliability of the three methods was assessed by computing the standard error of the measurement (SEm) on triplicate readings of human blood samples. The SEm for MC, CC, and DC methods were 0.3555, 0.3004, and 0.1491, respectively. Validity was assessed by comparing the average of the triplicate HCT readings for each method with HCT determined by densitometry. Average HCT values (+/- SE) for the MC, CC, DC, and densitometry methods were 42.3 +/- 3.2, 42.4 +/- 3.4, 43.1 +/- 3.4, 43.7 +/- 3.3, respectively. Only the DC HCT values were not different from the densitometry HCT (P > 0.05). The MC and CC values were significantly lower (P < 0.01). It is concluded that accurate, highly precise measurements of HCT are obtainable using the digital caliper. The significance for this is the increased ability to perform extremely accurate measurement of changes in plasma volume. With this information, research labs can reliably measure smaller changes in plasma than was previously possible with commercial procedures.

Adaptive responses of total artificial heart animals to treadmill exercise

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.

Quantitative bacterial analysis of porous, fabric, and smooth non-blood contacting implant surfaces and their tissue interfaces in a 169 day pneumatic total artificial heart animal recipient

All long-term total artificial heart (TAH) survivals are subject to sepsis. Survival can be prolonged, but the source of the infection cannot be eliminated with any known course of antibiotics or treatment regimen. Sambo, a U-100 pTAH calf, survived 169 days. At week 6, he became septic, growing a Pseudomonas species (Ps). Weekly blood cultures were intermittently positive until week 13 when they became continuously positive until his demise, from a ruptured left ventricular pumping diaphragm. Spatially specific porous silicone rubber (SSP) was used for surface modifications on the drive lines and as cuffs around the Dacron TAH graft to large vessel anastomoses. This gave an excellent opportunity to examine two types of porous implants surfaces (Dacron grafts and SSP) to the smooth Biomer ventricular surfaces with their respective adjoining tissue interfaces for bacterial colonization. Nine tissue samples and 13 implant surfaces were processed with Costerton's quantitative bacterial techniques. The largest numbers of bacteria (> 10(6)/cm2 Ps.) were grown from the smooth ventricular surface and in the cul-de-sac where the SSP delaminated from the driveline (two smooth implant surfaces in contact but without tissue apposition). The Dacron grafts were intermediate in bacterial concentrations and SSP surface modified drivelines and tissues were sterile. In this model, the more intimate biointegration found in the porous implants showed improved bacterial resistance in a chronically infected pTAH. The more completely biointegrated and neo-vascularized porosity SSP was the only implant surface and opposing implant tissue interface sampled to remain sterile.

Influence of viscosity and pressure on prosthetic valve regurgitation

Blood viscosity varies during the course of artificial heart implants and is affected by pathological conditions. To gauge the potential effect of changing viscosity on valve performance, leakage rates were measured across a closed Medtronic-Hall valve with water, water/glycerol and fresh whole bovine blood for aortic and pulmonary pressure ranges. As might be expected from the low Reynolds numbers (< 140), losses across the valve were found to be primarily viscous. For the two Newtonian fluids, leakage was slightly less than linearly proportional to pressure. This is comparable with empirical data for orifice flow, which predicts three fifths power dependence on pressure. For blood, however, the greater than linear dependence on pressure found suggests that the pseudoplasticity (shear-thinning behavior) of blood is important. These data provide evidence that the viscous and non-Newtonian properties of blood must be taken into account in modelling prosthetic valve performance and may affect the test methods and flow regulation strategies for prosthetic blood pumps.

Measurement of oxygen consumption and arterial-venous oxygen saturation following total artificial heart implantation

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.

Thrombus with infection in total artificial heart animals

From January 1980 to December 1990, several types of total artificial hearts were implanted into 378 animals. In a retrospective study of these animals, 147 (39%) were found to have thrombus with infection (T&I). The criteria for diagnosis was thrombus formation in the artificial heart and a positive blood culture. The most common pathogen isolated from T&I animals was Pseudomonas species. Concurrent skin lesions and contamination from the pressure lines may be the primary sources of infection, but bacterial translocation from the intestine is another possible route. The main pathological findings at necropsies of artificial heart animals with T&I were associated with sepsis, congestive heart failure, infected thrombus, thromboembolism, and multiple organ infarctions. Most thrombi appeared to have originated from valve junctions and connectors. On the basis of these observations, a possible mechanism for pathogenesis of T&I has been proposed. The results suggest that design improvements and surface modifications to reduce thrombosis are important factors that should be carefully considered. Similarly, it is important to eliminate the route of entry of pathogenic microorganisms. These findings imply that bacterial interaction with thrombus, device related bacterial colonization, and host immunomodulation and gut barrier function following artificial heart implantation need further investigation.

Animal implantation results with the Utah-100 total artificial heart

The Utah-100 total artificial heart was designed to have increased reliability over the Jarvik-7 total artificial heart, achieve better fit, and minimize device associated thrombus formation, without decreasing the function. The Utah-100 heart was tested in 28 calves and 3 sheep. The smallest animal at the time of implantation weighted 54 kg. Mean survival duration was 78 days (range, 1-331 days), with 14 animals surviving longer than 60 days. Multiple organ function was maintained satisfactorily with the Utah-100 artificial heart, and mean plasma free hemoglobin values in the calves that survived longer than 100 days were less than 10 mg/dl. Hemorrhage was the main cause of death in animals dying within 30 days after implantation (5/13, 38%); infection was another primary cause of death or termination (4/31, 13%). Deaths due to mechanical failure occurred from valve or diaphragm failure in two cases, yielding a 91% reliability at a 90% confidence level for 60 days' support. No animal died because of driver or other technical failure. Utah-100 hearts showed superior antithrombogenicity in the connector and valve-related areas when compared with the results of the Jarvik-7 heart, which was also fabricated and implanted in our laboratory (p less than 0.01). With these test results, the authors anticipate that the Utah-100 heart will be a safe and effective device for interim use as a bridge to heart transplantation.

Perioperative mechanical circulatory support for transplantation

Mechanical circulatory assistance has become a necessary supplement to more conventional means of hemodynamic support as a shortage of donor organs and associated increase in waiting time have contributed to an increased incidence of hemodynamic deterioration in potential transplant recipients. This review summarizes the experience with circulatory support before and after transplantation of the Utah Transplantation Affiliated Hospitals (UTAH) Cardiac Transplant Program and draws conclusions on the efficacy of one program's use of mechanical circulatory support. Between March 1985 and October 1990, 401 patients were accepted for first-time heart transplantation by the UTAH program. One hundred and eighty patients (46%) were supported before transplantation with conventional hemodynamic therapies, 72 patients (18%) with oral enoximone, 96 patients (25%) with intravenous inotropes, and 34 patients (9%) with an intraaortic balloon; nine patients (2%) required centrifugal blood pump circulatory support. Not included in these statistics are 10 patients awaiting transplantation as of October 10, 1990. Thirty-eight candidates (10%) died awaiting transplantation, 329 (84%) received transplantation, and 24 (6%) were removed from the transplantation list for other reasons. Ten patients (3%) required mechanical circulatory support after transplantation with 38% of this group surviving 1 year after after transplantation. No single factor, including either hemodynamic support before transplantation or donor heart ischemic time, was found to be predictive of the need for mechanical circulatory support after transplantation. One-year survival rates after transplantation of patients requiring mechanical circulatory support before transplantation (86%) were not significantly different than for all transplant patients (88%). The experience of the UTAH Cardiac Transplant Program shows that with the judicious use of mechanical circulatory support transplant patients with advanced forms of hemodynamic support can have as equal a probability of survival as patients who undergo elective transplantation.

Calves chronically implanted with a total artificial heart as a pharmacological model

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.

Cardiac output requirements and maximum dimensions for a neonate total artificial heart

Two equally important issues need to be addressed during the early stages of the design of an implantable total artificial heart (TAH): proper anatomical fit and cardiac output capacity. As part of a first-time feasibility study to develop a neonate-size TAH, two studies were conducted to establish useful anatomical and physiological standards. The first (Study A) was conducted to determine the maximum dimensions of a neonate-size TAH. Twelve preserved hearts from full-term neonates with the hypoplastic left heart syndrome were examined. A second study (Study B) was designed to determine the acceptable minimum stroke volume compatible with minimum neonate cardiac output requirements. This study was based on a combination of: a) reported cardiac output studies in healthy term neonates, and term neonates with heart failure, b) body weight range, and c) limiting factors of TAH technology, e.g., valvular regurgitation and leveling off of the maximum cardiac output value at a specific heart rate and filling pressure. The proposed neonatal standards for TAH technology are presented.

Determination of critical pericardial dimensions in patients with dilated cardiomyopathy

The development of orthotopically positioned cardiac replacement devices requires a knowledge of the space available to guide the design of the blood pumping system. Pericardial dimensions from in vivo and cadaver studies of normal subjects have been reported, but little information is available on in vivo pericardial dimensions in patients with dilated cardiomyopathies. The critical pericardial dimensions were determined in 13 men who were cardiac transplant recipients (age, 42 +/- 13 years; body mass, 72 +/- 11 kg; three with ischemic and 10 with idiopathic cardiomyopathy) by comparison of corresponding pericardial axes on chest radiographs to measurements obtained during orthotopic cardiac transplant in the context of a total artificial heart fit trial. The main pericardial dimensions measured intraoperatively were found to be the T10 midline anteroposterior (AP) axis (12.3 +/- 1.4 cm), the aortic root to diaphragm length (9.7 +/- 1.5 cm), the T10 total cardiac lateral axis (18.1 +/- 2.3 cm), and the tricuspid annulus to left ventricular apex (12.1 +/- 1.7 cm). All patients had cardiomegaly as indicated by a greater than normal cardiothoracic ratio. These data described the limited dimensions of the pericardial space available for orthotopic cardiac replacement devices. Chest film dimensions can be corrected using 0.92 and 0.88 as reduction factors for the (AP) and lateral axis dimensions, respectively. In this patient sample, there was little or no correlation between pericardial dimension and patient body mass or diagnosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of microsphere and intraoperative quantitation of bronchial blood flow

Although significant variation in bronchial blood flow (BBF) has been reported, precise quantitation is difficult because of the small sized vessels and variable anatomy. Ventricular balance is critical to the function of the total artificial heart (TAH), and variation in BBF can alter this balance in the bovine model. Bronchial blood flow was measured in 12 calves by two methods: six by the radioactive labeled microsphere technique (MBBF), and six intraoperatively (IBBF) during cardiopulmonary bypass (CPB). In the MBBF group, BBF ranged from 1.9 ml/kg to 16.0 ml/kg, whereas IBBF varied from 2.6 ml/kg to 10 ml/kg (NS). Cardiac output (CO) was significantly higher (p less than 0.0005) in the MBBF group. Bronchial blood flow in both groups was highly variable. The higher flow in the MBBF group may be attributed to the arteriovenous shunting of microspheres, whereas lower flow in the IBBF group may be secondary to physiologic changes during CPB. This technique, described to measure IBBF, can estimate large variations in the natural right to left shunt that contributes to imbalance in the TAH.

Atrial compliance changes in animal total artificial heart recipients

Right atrial compliance of chronically implanted total artificial heart animals was calculated from the pressure-volume relationships acquired at autopsy and compared with those of a control animal. The chronically implanted animals showed right atrial dilatation and low compliance. Even though atrial dilatation and decreased compliance have an opposite direct effect on atrial pressures, these changes may, in turn, disturb stretch-dependent volume regulatory processes, resulting in high atrial pressure.

Microbially infected thrombus in animals with total artificial hearts

In a retrospective study of 330 animals with total artificial hearts (TAH), 103 (31%) had microbially infected thrombi (MIT). The incidence of MIT approximated 75% in the animals surviving more than 100 days. The most common pathogen isolated from animals with MIT was Pseudomonas. Most thrombi appeared to have originated from valve junctions and connectors. Methods to prevent MIT should be aimed at eliminating thrombus formation by improved design and materials and controlling the route of bacterial colonization. These findings suggest that bacterial interaction with the thrombus, device-related bacterial colonization, host immunomodulation, and gut barrier function after TAH implantation need further study.

Quantification of perivalvular thrombus formation in blood pumps by polar coordinate mapping

A polar coordinate mapping technique (PCMT) to quantitatively describe perivalvular thrombus formation was applied in the examination of prosthetic valves from paracorporeal assist devices. The method begins by photographing the upstream and downstream views of the freshly retrieved valves using transparency film. The valve images are then projected onto 10 x planforms of the valves, and the boundaries of the observable thrombi are traced. The radial thrombus length is then measured at 5 degrees increments and plotted on Cartesian coordinates as a function of polar coordinate. Mean radial thrombus length and incidence of thrombus are calculated. Statistical analysis can then be used to test for differences in the length, incidence, and pattern of thrombus formation between test groups. The effect of valve selection, anti-coagulant regime, and other factors that influence thrombus formation can be quantitatively compared with the PCMT. Consequently, the PCMT could be a valuable assessment tool for efforts being made to reduce thrombosis in prosthetic blood pumps.

Differential light scattering cuvettes for the measurement of thromboemboli in high shear blood flow systems

Newly developed optical scattering cuvettes were constructed as a modification of our existing 1.0 mm and 3.0 mm internal diameter (ID) cuvettes to facilitate the measurement of platelet microemboli ranging from 20 microns to 1,000 microns diameter in whole blood in 0.9 mm ID flows ranging from 250 to 4,000 ml/min. A perturbation solution to the one-speed radiative transport equation was used in the design and calibration of these cuvettes. A series of tests were performed with these cuvettes in an extracorporeal left ventricular assist device bovine model, and in a recirculating closed-loop flow system containing anticoagulated whole baboon blood, to determine to what extent they affect platelet and erythrocyte function ex vivo and in vitro. Serial hemolysis tests, thromboxane radioimmunoassay measurements, platelet counts, and activated partial thromboplastin times were measured. All of these tests with cuvettes in the extracorporeal and in vitro circuits were statistically indistinguishable from baseline measurements, suggesting the usefulness of this system for the measurement of microemboli in blood-contacting materials of extracorporeal circuits and cardiac assist devices.

A total artificial heart for neonates allowing bridging to transplantation

Since the early 1980s, a rapid increase in successful pediatric heart transplantation has improved the chance of survival for many children suffering from otherwise fatal cardiomyopathies or congenital cardiac defects. During the last 5 years, heart transplantation in neonates and infants (0-28 days and 1-12 months, respectively) has been the most rapidly growing area within the pediatric patient population. No adequate mechanical circulatory support system, designed to be used as a bridge to transplantation, is available for many of these pediatric patients. Neonates are the smallest candidates to potentially benefit from heart transplantation, and their often acute need for either heart transplantation or temporary circulatory support indicates that any new development of a pediatric bridging device should focus on this youngest group. Subsequently, such a device may be modified to any weight or age group. An innovative total artificial heart design was developed in an attempt to meet the anatomic and physiologic requirements of neonates and infants. This report discusses the rapidly growing pediatric heart transplantation patient population, as well as an innovative total artificial heart design.

Factors influencing the accuracy of the cardiac output monitoring and diagnostic unit for pneumatic artificial hearts

The Cardiac Output Monitor and Diagnostic Unit (COMDU) has been the most widely used method to noninvasively determine cardiac output in pneumatic ventricles for the past 10 years. Clinical observation has suggested a discrepancy between the COMDU and expected cardiac outputs. In vivo tests verified and quantified this error. The error sources were examined using in vitro test conditions, with both the inflow and outflow, as well as COMDU flow readings, being analyzed. Transducer and calibration error sources were also identified, and the accuracy of the method for determining cardiac output for the in vitro test conditions was quantified. With a more accurate calibration scheme, the in vitro average error was reduced from -16.2% (range of 0.1% to -41.1%) to 0.1% (range 4.8% to -3.65). The major error sources were identified as missed inflow, transducer calibration and drift, and system variance.

Design mediated thrombus reduction in the Utah-100 total artificial heart

The Utah-100 total artificial heart was initially designed and tested in 1983. General design goals, including improved fit for human application, improved reliability, and elimination of thrombus formation, were identified as improvements over the clinically used Jarvik-7 artificial heart, previously developed at the Institute for Biomedical Engineering, University of Utah. Specific design goals included 1) elimination of connector and valve-associated thrombus formation and 2) elimination of gross mineralization, thrombus formation, and creases on the blood-pumping diaphragm of the device. Explant retrieval results from 29 calves and sheep implanted with the Jarvik-7 artificial heart were compared with results from 25 calves and sheep implanted with the Utah-100 artificial heart. Macroscopic thrombus formation was found in 44% of the connectors of the Jarvik-7 artificial-hearts, compared with 2% (p less than or equal to 0.01) in animals with the Utah-100 artificial heart. Subvalvular and supravalvular thrombi were observed in 33% of the valves in the Jarvik-7 artificial heart and 10% (p less than or equal to 0.01) of the valves in the Utah-100 artificial heart. Mineralization of the pumping diaphragm was observed in 12% of the animals implanted with the Jarvik-7 artificial heart and in 4% of the animals with the Utah-100 diaphragms. Thrombus formation in the diaphragm-housing interface occurred in 2% of Jarvik-7 ventricles and in 6% of the Utah-100 ventricles. There were no identifiable diaphragm creases in the Utah-100 diaphragms, but a 10% incidence was found in Jarvik-7 devices. These results validate substantial progress toward improved design and fabrication methods in the Utah-100 total artificial heart.

Right-left ventricular balance in implanted electrically powered artificial hearts

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.

Light scattering detection of microemboli in an extracorporeal LVAD bovine model

Thromboembolization studies were performed on two calves supported by extracorporeal left ventricular assist devices (LVAD) using a light scattering (He Ne Laser) microemboli detector (LSMD). The LSMD system was placed on the outflow cannula of the LVAD in the extracorporeal loop of each animal. The measurements included the size, number, and rate of production of circulating microemboli in the range 20 microns less than microemboli diameter less than 1,000 microns. These data were compared to independently and concurrently obtained measurements of emboli shear rate (CPF), platelet count, red blood count (RBC), leukocyte count (WBC), plasma free hemoglobin, factors XIII, X, and V, and sorbitol dehydrogenase. Embolic number and volume were seen to be most dynamic in the very early phases of acute thromboembolization (0-40 minutes) with a peak embolic response within the first 30 minutes. The dynamics of reduced emboli volume, rather than number, may be implicated in the later stages of the thromboembolic passivation of these ventricles. The LSMD results generally showed an inverse correlation of microemboli volume rate with CPF measurements for each ventricle. LSMD, CPF, and leukocyte and platelet counts, showed a direct correlation with reduced counts for each additional ventricle for both calves. Factor XII was seen to have a more direct correlation in time with LSMD measurements for each ventricle than other parameters under investigation. This study represents the first time laser scattering and filtration methods have been applied simultaneously with hematologic assays in order to study the dynamics of device associated thrombogenesis.

Pressure indices of myocardial oxygen consumption during pulsatile ventricular assistance

Left ventricular (LVP) and intramyocardial (IMP) pressure indices were compared with left ventricular myocardial oxygen consumption (MVO2) during pulsatile ventricular assistance to determine if MVO2 can be predicted under conditions of ventricular support. During five acute anesthetized calf experiments, IMP and LVP were recorded for control and six conditions of support. The assisted conditions were asynchronous and synchronous, 1:1 or 1:2; each control mode with atrial uptake only or combined atrial and ventricular uptake. IMP was measured by implantation of a miniature pressure transducer in the midanteriolateral wall of the left ventricle. MVO2 was determined using the radioactive microsphere blood flow technique and blood gas data. Mean values of peak systolic pressure, maximum dP/dt, and integral of Pdt were calculated for IMP and LVP for each condition. Pressure indicators of left ventricular function were found to correlate well with MVO2 during conditions of pulsatile support.

Mechanical failures of the pneumatic Utah-100 and Jarvik total artificial hearts. A comparative study

Jarvik-5 and Jarvik-7 total artificial hearts (TAHs) and Utah-100 TAHs were fabricated and implanted in calves and sheep. In the Jarvik series, 30.7% had mechanical failures (16.1% catastrophic). In the Utah-100 TAH series, 11.1% had mechanical failures (3.7% catastrophic). Failures were classified as: 1) diaphragm failures; 2) valve-holding ring failures; 3) air-leak failures; and 4) prosthetic valve failures. Marked reduction in mechanical failure for the Utah-100 TAH is attributed to progressive component redesign, material selection, and more stringent quality control criteria.

Scanning and transmission electron microscopic evaluation of the U-100 total artificial heart blood contacting surface

Thrombus formation, cell adhesion, mineralization, and the adsorbed protein layer have been investigated on blood contacting surfaces of the Utah-100 total artificial heart (TAH). Retrieval analysis was performed on two calves (at 7 and 97 days) and a sheep (at 21 days). Six locations on each ventricle were systematically evaluated by scanning electron microscopy. Transmission electron microscopy was used to measure the thickness and distribution of proteins (albumin, IgG, and fibrinogen) on the surface. Gross thrombus was detected only on the left atrial cuff in the 97 day calf. SEM demonstrated fairly clear surface morphology, with minimal platelet adhesion and activation, and little thrombus formation. At 97 days, calcium deposits were detected along the diaphragm-housing junction. Protein layer thickness on the diaphragm increased with implant time; dominant proteins detected on the surface were fibrinogen and IgG, rather than albumin. Improvements in design and fabrication techniques have demonstrated decreased intradevice thrombosis with the U-100 TAH. However, systemic thromboembolism still remains a problem, and further improvements in the blood contacting surface of the U-100 TAH are necessary to achieve a thrombus free TAH.

Characterization of blood microemboli associated with ex vivo left ventricular assist devices in a bovine model

An ex vivo left ventricular assist device (LVAD) model was used in calves to study the production of blood microemboli (BME) and to evaluate possible correlations between constant-pressure filtration (CPF) measurements of flow-resistant BME, light-scattering microemboli detection (LSMD), observable thrombus accumulation, and hematologic markers. Aortic LVAD cannulae were implanted through the chest wall in two calves, and each calf received a series of LVADs, each operating 1-4 days. Blood samples from the LVADs underwent CPF through 20 mu pore filters at 20 mm Hg to produce estimates of occlusive BME concentration. Laser (He-Ne) light was directed through the outflow cannula, and the differentially-scattered light was detected for computer estimation of microemboli size, volume, and frequency. Blood chemistry and coagulation parameters were also analyzed. Removed LVADs were examined with polar coordinate mapping of accumulated perivalvular thrombi. One ventricle produced significantly greater CPF results, LSMD results, and Factor XII levels. During the use of that ventricle, the CPF results increased slowly with time after LVAD connection, while the LSMD results and Factor XII levels increased immediately after connection, followed by a later decrease. This contrast is explainable in terms of the dynamic development of BME strength. The calf model appears useful for the study of thrombogenesis, and the CPF and LSMD methods of BME analysis complement each other, and other measurements.

Development of smaller artificial ventricles and valves made by vacuum forming

Implantable prosthetic ventricles and trileaflet valves made by vacuum forming have been developed and implant tested. All components are made from Pellethane. Recognizing the need for smaller as well as larger ventricles, designs with effective stroke volumes of 50, 85, 100 and 130 cc have been tested with several valve types. The pneumatically driven Utah ventricular assist device (UVAD) can be used as a total artificial heart (TAH) or ventricular assist device (VAD) by using the appropriate inflow and outflow adapters. In vitro durability testing has demonstrated ventricular lifetime beyond two years and valve lifetime to nearly one and one half years. The polymer valves have lower regurgitation than mechanical valves. Animal implantation experience includes 21 TAH implants and 16 left ventricular assist device (LVAD) implantations. TAH survival ranges from 2 to 210 days. LVAD animals have lived up to 116 days before elective termination. The animal were healthy and grew normally. The devices exhibit a "Starling's Law" response. One TAH animal survived 72 days before successful explantation followed by transplantation. At autopsy, this animal had no renal infarcts. Hematology data has demonstrated the existance of little or no intravascular hemolysis (PF Hb less than 5 mg%). The "Philadelphia" version of the UVAD vacuum formed ventricles are small enough to be implanted without thrombus provoking connectors. Eight animals have received this TAH and survived up to 120 days. Vacuum forming offers a rapid and inexpensive way to produce reliable and effective total artificial hearts and valves for widespread, temporary clinical application in any size adult human.

Left ventricular oxygen consumption and organ blood flow distribution during pulsatile ventricular assist

One goal of left ventricular assistance is the reduction of left ventricular myocardial oxygen consumption while delivering adequate organ blood flow. The effect of assist device operation control mode and uptake cannulation method on the achievement of this goal was studied in six acutely prepared calves with healthy hearts. All combinations of left ventricular assistance significantly reduced the myocardial oxygen consumption; the reduction was independent of control mode. During ventricular assistance, regional organ blood flow distribution and myocardial endocardial/epicardial blood flow ratio were not different from values during the control, unassisted condition. Regardless of the left ventricular assist device uptake method or operational control mode, significant reduction in myocardial oxygen consumption was achieved while maintaining organ blood flow distribution.

Hemodynamic and energetic assessment of calves implanted with a left ventricular assist device (LVAD)

Hemodynamic and ventricular energetic parameters were measured in calves implanted with the air driven Utah Ventricular Assist Device (UVAD). Uptake site was varied to determine the effect of control mode and vacuum augmentation of filing. Uptake was drawn solely from the left atrium or combined with a left ventricular apical vent. LVAD outflow returned to the descending, thoracic aorta. Control modes examined included asynchronous pumping as well as 1:1 and 1:2 synchronous diastolic counterpulsation. The 85cc LVAD, vacuum formed from PELLETHANE, was implanted acutely in four animals and chronically in six (7, 49 and 116 days paracorporeally, 1, 28 and 32 days intrathoracically). Instantaneous blood pressures, intramyocardial pressure, aortic outflow, oxygen consumption, LVAD output and drive parameters were recorded. LVAD output was independent of control mode when the natural heart rate was greater than or equal to 80 beats per minute. Intrathoracically positioned LVADs pumped a mean flow of approximately equal to 5 liters/min without vacuum augmentation of filling. Paracorporeally positioned LVADs pumped approximately equal to 3 liters/min mean flow without vacuum augmentation and up to approximately equal to 6 liters/min with 38 mm Hg of vacuum augmentation of filling. Instantaneous ascending aortic pressure and flow showed distinct beat-to-beat variation depending on LVAD control mode. Lower average ventricular afterload was observed when pumping the LVAD asynchronously or 1:2 synchronously. In one acute preparation, left ventricular myocardial oxygen consumption was reduced from the unassisted average control level by 37% for the asynchronous and 1:1 synchronous control modes with left atrial uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Phonocardiographic evaluation of total artificial heart valve movement. Correlation with pressure waveforms

Two categories of inflow and outflow valve closure sounds are present in the Jarvick-7 model of the Utah total artificial heart. A presystolic inflow valve closure sound occurs at the end of ventricular filling, resulting from a transient rise in intraventricular pressure above that in the atrium. A second inflow valve closure sound follows, associated with the onset of mechanical systole with a rapid rise in intraventricular pressure. A mid- to late systolic outflow valve closure sound occurs at the end of ventricular ejection, resulting from a transient fall in intraventricular pressure below that in the aorta. A second outflow valve closure sound follows, associated with the onset of mechanical diastole with a rapid fall in intraventricular pressure. Under operating conditions where either ventricular filling or ejection is not complete, the presystolic and midsystolic sounds are absent. Thus, regulated heart driver parameters as well as preload and afterload to the extent that they influence ventricular filling and emptying will determine the presence and sequence of valve sounds.