Arterial pressure pulsation during nonpulsatile biventricular bypass experiments: possible idioperipheral pulsation

During nonpulsatile biventricular bypass (NPBVB) experiments, regular fluctuations of arterial pressure were observed in all five long-term animals whose ventricles were fibrillated. Analysis of the characteristics of this fluctuation was performed retrospectively. The pulse pressure of this fluctuation increased gradually after the first 2 weeks. They were 6.7, 7.6, 10.2, and 12.4 mm Hg on the fortieth, sixtieth, eightieth, and ninetieth postoperative day, respectively, in the animal surviving for 99 days. Cycle rate was generally high for the first 40 days, and then decreased to approximately 40 cycles/min in calves alive for greater than 90 days. The beat rate of these arterial pressure fluctuations was lower than atrial but similar to respiratory cycle rates. However, no flow fluctuations were observed in conjunction with the arterial pressure oscillations. Therefore, neither atrial contractions nor the mechanical effects of respiration were causing the pressure pulsations. Though further investigations are necessary, it is highly suggestive that this phenomenon was derived from the vasomotor center and can be called "idioperipheral pulsation." It is conceivable that the NPBVB animals adapted to the nonpulsatile condition by adding active pulsatile components of their own to maintain adequate peripheral circulation.

Totally implantable artificial organ: cardiac prosthesis

This article reviews the current status of completely implantable cardiac prostheses, with an emphasis on those systems presently under development at The Cleveland Clinic Foundation (CCF). Such devices have been one of the final goals of artificial heart research since 1957, when Dr. Kolff initiated these studies in Cleveland. Although earlier plans aimed at using radioisotopes as the energy source, more recently, due to public opinion and sociopolitical influences, the shift has been towards exclusive use of electrically activated energy converters. These systems can be roughly broken down into two groups according to the powertrain configuration. In the first group, electric heating coils maintain liquid salts in thermal batteries at temperatures close to 500 degrees C. This thermal energy is then converted (through a Stirling cycle) to mechanical motion of the pusher plate (PP) which in turn acts on the blood. Two such systems (emphasized in this article) are under development here at CCF in joint efforts with Nimbus Corporation and the University of Washington, respectively. In the second group of ventricular assist systems, electric energy is converted directly to PP motion through rotating cams, solenoids, or electrohydraulic transmission systems. At least four American contractors are working at the preclinical stage on this group of devices. One in particular, the CCF-Nimbus system, consisting of a biolized surface blood pump, an electrohydraulic energy converter, and a compliance chamber to handle the variable volume behind the PP, is described in depth in this discussion. In terms of future prospects, it is forecasted that by 1988, the completely implantable VAS will be used clinically, and that by 1994, a specially designed total artificial heart (nontethered patient) would be ready for human use.

Clinical thermofiltration: initial application

The first clinical thermofiltration procedures (plasma filtration near or above normal physiologic temperature) were performed on a secondary hypercholesterolemia patient. The intent of this filtration scheme is the selective removal of low density lipoproteins (LDL) and maintenance of high density lipoproteins (HDL) and other essential plasma proteins including albumin. The EVAL 4A filter, at a filtration temperature of 37 degrees C, was selected for on-line thermofiltration. The sieving coefficients of LDL + very low density lipoproteins (VLDL) cholesterol, HDL cholesterol, and albumin were 0.02, 0.75, and 0.78, respectively. These results are comparable to in vitro filtration tests using the plasma of the same patient. This system is simple to apply and does not require replacement solution. Compared with plasma exchange, a high return of HDL and other essential plasma solutes can be returned to the patient by this method.

Anatomical considerations in the design of a long-term implantable human left ventricle assist system

A permanently implantable left ventricle assist system (LVAS) is being developed and is planned to be implanted in the left chest cavity against the chest wall with the electrohydraulic energy converter placed in a resected rib space. The inflow and outflow pump ports are connected to the left ventricle (LV) apex and to the descending aorta, respectively. Three additional major components of this system consist of the transcutaneous energy transmission system (TETS) (Thermedics), the variable volume device (VVD), and the internal battery. To finalize the design of this integrated system, key anatomical information was obtained by a special radiographic and angiographic study of 31 adult men with a varying degree of coronary artery disease and myocardial dysfunction. These data were combined with the previous computed tomography study by using a standard vertical reference system. The resultant integrated data, which consist of the three-dimensional chest model, the LV apex and axis orientation, rib orientation, chest wall thickness, and the descending aorta location, were used to define the design and anatomical locations of the inflow and outflow pump ports, the VVD, the pump and energy converter orientation, the TETS, and the internal battery. The most critical component for the design was found to be the inflow system. With regard to the average coronary disease patient, an anatomically practical configuration was demonstrated to exist for the presently proposed LVAS. Design flexibility was allowed for some of the critical components in order to fit the system in a large number of patients regardless of the stage and type of the underlying disease.

Anatomicomechanical study for the hydraulic line of a thermal left ventricular assist system

A thermal left ventricular assist system currently under development consists of two separate major components, i.e., a pump/actuator module and an engine/thermal battery module. The possible implantation site of the engine/battery module is tentatively determined to be the iliac fossa, which requires a flexible interconnecting line to the pump/actuator module. A quantitative and biomechanical study was done on the effect of the implanted hydraulic line on the bendability of the torso. It revealed that the semirigid interconnecting line would not severely restrict the movement of the patient provided it has the proper prebend configuration. The cadaver fitting study proved the anatomical feasibility of the retroperitoneal iliac fossa as the implant site of the Thermal Ventricular Assist System 8 (TVAS 8) engine/battery module. The location and configuration of the interconnecting line of the TVAS 8 were determined using biomechanical analysis so that the restriction of the body movement due to the line could be minimized. The main route of the line was the left side of the trunk, and the line is W shaped in configuration. The line elongation is the most critical resistive factor and accordingly there may still be rigidity during lateral flexion.

Use of the anaerobic threshold for evaluating various total artificial heart control algorithms in calves

In the total artificial heart (TAH) project, choosing the best control mode is an important factor in the design of a completely implantable TAH. Four different control modes for the TAH were evaluated in the same calf using the anaerobic threshold (AT) as an assessment of aerobic capacity, where AT was defined as the oxygen consumption (VO2) at which the relationship between blood lactate measurements and VO2 became nonlinear during progressive treadmill exercise. This new approach tests the integrated response of the central, peripheral, and metabolic regulatory mechanisms to physiological workloads. Preliminary data showed AT in the left master alternatively ejecting mode to be slightly higher than in the other three modes.

Human thoracic anatomy based on computed tomography for development of a totally implantable left ventricular assist system

Human thoracic anatomy was studied using computed tomography (CT) for the development of a totally implantable electrohydraulic left ventricular system [Nimbus, Inc., and The Cleveland Clinic Foundation (CCF)]. To obtain statistical dimensional information for the chest wall, apex of the heart, and aorta, routine calibrated CT scans of 18 men and 17 women were analyzed. A special radiopaque vest was worn by the patient just prior to the scanning and X-ray procedures, so that each transverse scan could be assigned to a specific chest level after combination with a standard vertical referencing system set on the patient's radiogram. A polar coordinate system and direct measurement of transverse distances from the vertical column to points on the chest wall were employed to define collectively the shape and size of the intrathoracic surface of the chest wall. Locations of the aorta and apex were described by measuring their normalized distances from the midline and vertical column to the intrathoracic surface of the lateral and anterior chest wall. The radius of curvature of the intrathoracic wall lateral to the left ventricle was determined to be approximately 10.4 cm for the average adult male chest. The present CCF intrathoracic pump with this curvature fits fairly well in both the average and individual thoraxes of these adult males. The location of the aorta, particularly of the descending aorta, was used to determine the optimal outlet design. The most critical anatomical area was the apex location. For adult males, an average distance of 2.8 cm from the apex to the internal chest wall was found. Because of this small dimension, careful design of the inflow port is being performed to avoid anatomical mismatch.

New sequential external counterpulsation for the treatment of acute myocardial infarction

Over a period of 6 years, 52 patients with acute myocardial infarction (AMI) were treated with sequenced external counterpulsation (SECP). Of the 23 patients who experienced severe chest pain, 22 had complete relief within 30 min of SECP, and 31 of the 52 patients showed remarkable improvement in their electrocardiogram after the first hour of treatment. Fifteen patients were studied using the 35-lead ST segment elevation-mapping method. sigma ST and NST, indicators of infarct size, showed decreasing trends in seven patients treated with SECP for a period of 6 days, whereas sigma ST and NST of the control group of eight patients increased during the same period. Our hemodynamic data indicate that in four of five patients with AMI and left heart failure, the central venous pressure and cardiac output increased after SECP, whereas the pulmonary wedge pressure decreased. Measurements of the P-wave terminal force of lead V1 also demonstrated that the application of SECP can improve left ventricular function in a majority of patients with AMI.

A new hollow-fiber oxygenator for clinical cardiopulmonary bypass

A new hollow-fiber oxygenator has become available for clinical cardiopulmonary bypass. It is available in three sizes for adult use, ranging from 3.3 to 5.4 m2. The surface area is dependent on the number of fibers, with blood and oxygen effecting very efficient gas transfer throughout the length of each of the fibers. The clinical experience now covers 100 patients, using the 3.3-m2 device in 16 patients, the 4.3-m2 device in 12 patients, and the 5.4-m2 device in 72 patients. In all cases, the oxygenator has proven highly efficient in gas transfer. The addition of an oxygen-blending unit was found to be necessary to prevent overoxygenation. It is a safe and effective device to use in routine clinical practice.

Ex vivo preclinical evaluation of membrane plasma separators

Four different types of hollow-fiber membrane plasma separators, constructed of cellulose acetate, polyvinyl alcohol, polyethylene, and polymethylmethacrylate membranes, were evaluated in ex vivo dog perfusions under conditions simulating their clinical use. An arteriovenous (A-V) fistula constructed in the dogs for blood access enabled repeated access to be achieved without surgical intervention. All modules produced transient leukopenia and a reduction of platelet counts. The polymethylmethacrylate module showed minimum reductions of white blood cell counts and CH50. The early leukocyte count reduction in membrane plasmapheresis is most likely related to the magnitude of complement activation by the membrane, as is seen with hemodialysis.

Characterization of polypropylene membrane for plasma separation

Plasma separators of two different types constructed with polypropylene membrane were evaluated. Characterization of the membrane indicated that these separators meet the desired clinical requirements for sieving, filtration, and blood compatibility. In vitro sieving coefficients for albumin and total protein were 0.97 and 0.90, respectively. These modules showed a filtration flux dependency on blood shear rate. The ET filter (0.2 m2) had a higher shear rate for a given blood flow and also a higher flux. Based on the anticipated clinical applications at lower blood flows (less than 100 ml/min), small surface area devices having high shear rates meet clinical needs. The higher surface area module (Plasmaflux) also gave a satisfactory performance.

Characterization of polyethylene membrane for plasma separation

Three types of polyethylene hollow fiber membranes (Mitsubishi, Tokyo) were evaluated for plasma separation: EHF-Type 1 (lowest porosity and smallest inner diameter), Type 2 (medium porosity and diameter), and Type 3 (highest porosity and largest inner diameter). Characterization of these membranes led to the selection of the Type 3 membrane as the best, based on in vitro studies of filtration and sieving properties. Analysis of the data suggests that pore size and pore number (density) are more optimal for this membrane. Ex vivo studies of the Type 3 membrane showed high sieving (greater than 0.9) for albumin, total protein, and total cholesterol; each was stable over time. No significant hemolysis was observed.

Experimental results for chronic left ventricular assist and total artificial heart development

After more than 20 years of research on the artificial heart, it is now accepted that the pneumatically actuated total artificial heart can maintain near-normal physiology in experimental animals for several months. Such systems are clinically acceptable for short-term application (a few months) in patients waiting for a suitable heart transplant. However, realistically, a cardiac prosthesis that has the capability of being totally implantable for over 2 years must be available. Based on this premise, our group initiated the development of a mechanically actuated total artificial heart, capable of coupling with either a thermal or electrical actuation system. Since 1977, under the National Institutes of Health chronic left ventricular assist program, we have used two different pusher-plate pumps and electrical systems. Taking advantage of technology generated in these programs, we began developing a prosthesis to replace the total cardiac function. This paper is a summary of both the chronic left ventricular assist and total artificial heart development progress in this laboratory.

Hexsyn trileaflet valve: application to temporary blood pumps

A trileaflet valve, compression molded of Hexsyn rubber, was evaluated as a component in temporary blood pumps. A pair of valves was integrated into an LVAD which was tested in vitro and in vivo. The valve's hemodynamic performance was satisfactory and the blood compatibility was excellent in a three-week, in vivo experiment conducted to demonstrate performance in a short-term application. Hexsyn, which has excellent properties and produces high quality, complex components with ease of fabrication, offers a potential for low-cost blood pump valves.

Clinical results of mechanical support of the failing left ventricle

Six patients received mechanical support for a failing left ventricle after corrective cardiac operations. Despite intra-aortic balloon pumping and pharmacologic support, intractable failure persisted and cardiopulmonary bypass could not be withdrawn. The left ventricular assist device (LVAD) consists of a nonpulsatile centrifugal pump and two thromboresistant cannulas. Balloon counterpulsation added a pulsatile effect. LVAD support was continued for 72 to 168 hours and five patients were weaned from LVAD support. Two died of persistent low cardiac output within 3 days after pump removal, and a fourth died of multiple organ failure and pneumonia 8 weeks after LVAD removal. Autopsy studies in the first three patients showed myocardial necrosis greater than 50% of the left ventricular mass. Two patients survived after 72 and 74 hours of LVAD support. One patient is fully employed and active 27 months after a cardiac operation; the second is fully active 20 months after operation. Repeat cardiac catheterizations in both have shown all grafts patent and good ventricular function. These two long-term survivors justify the concept of LVAD support and its continued use in selected postoperative patients.

Volume compensation for left ventricle assist systems (LVAS): 18 month in vivo evaluation

The smooth surface cycled chambers, both Biomer and silicone rubber, developed thick tissue capsules and exhibited persistent active tissue reactions at the diaphragm-capsule interface. Textured surface chambers (dacron velour), both the cycled and control, developed a thin, stable capsule, with no active tissue reaction. Textured surface chambers have been explanted and examined after 210 and 494 days. One experiment is continuing, approaching 2 yrs in vivo with good performance. Although the number of textured surface compliance chamber studies as yet is limited, the dramatic improvement in performance and tissue response between the smooth and textured surface studies demonstrates the biological feasibility of this method of variable volume compensation for use in completely intracorporeal LVAS.

Axial changes of blood and plasma flow, pressure, and cellular deposition in capillary plasma filters

The ability to separate plasma on-line from whole blood by membranes has generated interest in applying this process to source plasma collection and to the therapeutic treatment of various disease states. The availability of capillary membrane devices in particular has prompted investigations in these areas. The deposition of blood cellular elements has required the investigation of those parameters related to fluid and mass flux. Analytical solutions relating blood flow rate, filtration rate, and pressure and deposition with respect to axial distance have been obtained. Comparison of these solutions with preliminary experimental results have been made. Results indicate that the deposition parameter versus distance from the inlet is a very sensitive function of capillary membrane properties and operating conditions. Plasma fluxes are also highly dependent on blood, membrane, and filter properties and operating conditions.

Pusher-plate type TAH system operated in the left and right free-running variable rate mode

A TAH system utilizing two pusher-plate type pumps was developed and tested in two calves for 45 and 108 days with excellent results. A Hall effect sensor was utilized to operate each pump with a full stroke at variable rates (VR); each pump was then allowed to run independently at different rates depending on its own preload and afterload. With this system, the animals' atrial pressures were kept to near-normal levels (less than 10 mmHg). However, significant differences in the left and right pump flows were observed (left higher than right) and they ranged from 5 to 30% of the left flow with a mean of 15%. These flow differences may be due to the bronchial circulation and related shunts. Right pump flows averaged 70 to 95 ml/min-kg and circulating blood volume ranged from 67 to 95 ml/kg. When various control modes including fixed rate and master-slave type simultaneously or alternatively ejecting VR modes were applied in the same animals and both pump flows were forced to be equal, unphysiological atrial pressures resulted. This result indicates that perhaps left and right flow differences are necessary physiological conditions to regulate the atrial pressures within normal ranges. Metabolic data also indicated that under simultaneously and alternately ejecting modes, A-V O2 content differences were increased due to decreased right pump flow as compared with those of the free-running VR mode. The left and right free-running VR mode of operation imposed minimal constraints on the animals' cardiovascular system and therefore yielded excellent hemodynamic and metabolic results.

Hemodynamic regulation in total artificial heart recipients

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.

On-line separation of macromolecules by membrane filtration with cryogelation

The use of cold filtration in the removal of macromolecules from disease state plasma is safe and simple. It overcomes the disadvantages of plasma exchange in chronic treatments and is specific in removal of those causative factors implicated in the disease.

Initial clinical experience with a new temporary left ventricular assist device

A new, simple left ventricular assist system has been developed and its use in experimental animals has been evaluated. The system achieves ventricular drainage by a transaortic valve cannula and utilizes a new centrifugal pump; the blood access is unique in requiring only a simple end-to-side synthetic graft anastomosis to the ascending aorta. Adequate pulsatility is obtained by concomitant use of an intraaortic balloon pump. This case report documents our initial clinical experience with this system in a postoperative patient with profound left ventricular failure unresponsive to all usual treatment. There was temporary recovery of left ventricular function upon decannulation after five and a half days of assist pumping. Despite the eventual death of the patient, the system functioned adequately, suggesting that it has good potential for use in a small, selected group of patients.

Bovine aortic and human dura mater valves: a comparative study in artificial hearts in calves

Thirty-one glutaraldehyde-treated bovine aortic valves (BAVs) and 105 glycerol-treated human dura mater valves (HDVs) were used in 51 various artificial hearts up to 316 days in calves. Multiple valves were implanted in the same animal under different hemodynamic conditions. A comparative study of these valves was performed in terms of blood compatibility and durability with relation to the different hemodynamic environments. Both BAVs and HDVs showed good blood compatibility. The degradation of collagen bundles of the valves began as early as 7 days in BAVs and 13 days in HDVs, and was seen in the hinged portions of the cusps. The fiber separation and resultant void formation were followed with insudation of blood elements and subsequent calcification. Calcification was dystrophic in nature and was encountered in 70.9% of BAVs and 7.6% of HDVs. All 17 BAVs used more than 30 days were calcified; in HDVs the earliest calcified lesion was seen in a 78 day specimen. The pathological changes were more severe in the left side than the right of the total artificial hearts. These results clearly indicated that the HDV is more durable than the glutaraldehyde-treated BAV. It was suggested that degradation of these tissue valves is greatly affected by the degree of hemodynamic stress on the valve cusp. Although glutaraldehyde treatment has increased the durability of tissue valves in general, the structure of the valve tissue also plays an important role in long-term durability.

The dura mater valve: in vitro characteristics and pathological changes after implantation in calves

Human dura mater valves of various sizes with rigid and flexible stents were tested in an in vitro pulsatile mock circulatory system. A 22-mm flexible stent valve incorporating a new fabrication technique showed almost the same pressure gradient as a 28-mm rigid stent valve. The backflow/stroke volume ratio was about 4% at a net flow of 10 L/min. One hundred and five rigid stent-mounted dura mater valves were used in 51 pump implantations for up to 316 days. Collagen fiber degeneration began three months after implantation. Microscopic and macroscopic calcification of the valve tissue was seen in eight out of 105 valves, giving an overall incidence of 7.6%. The calcified degeneration was dystrophic in nature, not accompanied by cellular reactions, and was seen in the areas of the valve under stress. The degenerative changes were more severe in the left side than in the right side of the total artificial heart. These findings suggest that mechanical damage to the tissue plays an important role in the pathogenesis of calcification.

The human dura mater valve. Fabrication methods

We have used a glycerol-treated human dura mater valve as a valve substitute of the blood pumps for more than 3 years. In comparative studies, it was shown that the dura mater valve is more durable than the glutaraldehyde-treated bovine aortic valves, and thought to be a very attractive valve material. Fabrication methods both for rigid and flexible stents were introduced.

Biological reactors as renal substitutes

The concept of using natural biological reactors for renal support has been investigated. Normal urine was used as the source of urinary wastes. Quantities of nitrogenous wastes approaching those produced in renal failure patients have been removed in batch reactors. Mixed strains of microorganisms are required. While further studies are required, it is conceivable that biological reactors can be useful in combination with other technologies in the design of future treatment modalities for renal failure.