Fujimoto Lk

Long-term in vivo study of gas diffusion in bilaminar compliance chambers.

The problem of gas diffusion from compliance chambers in long-term pulsatile blood pump implantation continues. To evaluate and predict gas diffusion at the intrathoracic tissue interface, eight air-filled static bilaminar compliance chambers were implanted in four calves for a mean duration of 191 days. Mean volume loss was 40.3 +/- 6.2 ml (0.2 ml/day) compared with previous results of 1.2 ml/day for pure Hexsyn diaphragms. The residual gas in the chamber was analyzed as nitrogen = 89.6 +/- 0.6%; oxygen = 1.5 +/- 1.1%; and carbon dioxide = 8.8 +/- 0.6%. The resulting gas composition is assumed equivalent to that of the tissue interface and was used in developing a diffusion model. For a complete left ventricular assist system (LVAS), gas diffusion at the arterial blood and tissue interface was simulated. The predicted time to reach a minimum volume of 90 ml (compliance volume equal to full pump stroke volume) was in excess of 1 year.

In vitro and in vivo performance evaluation of a totally implantable electrohydraulic left ventricular assist system.

The biolized electrohydraulic left ventricle assist devices were tested in 14 calves with an average survival time of 162 days and as long as 250 days without the use of anticoagulants. In vitro, the system pumped 4.1 L/min at a low 4.8 mmHg fill pressure with a mean afterload of 100 mmHg and rate of 46 bpm. A flow rate of 13.5 L/min was observed at 155 bpm and 110 mmHg afterload. Motor frequency and current increased with increasing flow rate (162 Hz, 0.67 amp at 2.5 L/min; 484 Hz, 2.43 amp at 13.5 L/min). Flow rate did not change significantly with afterload pressure. The complete system was implanted in a 100 kg calf. Synchronization of the blood pump with the natural heart was demonstrated at heart rates of 85 to 167 bpm. The synchronized flow rate varied from 6 to 10.5 L/min despite the considerable heart rate changes and stroke variations. The system hemodynamic performances were acceptable and met NIH requirements.

A simple and compact total artificial heart for temporary use

Thromboembolism and anatomic fit are the major issues to be addressed in the design of a heart replacement device for total circulatory support. In an attempt to overcome these problems, a simple 70 mm3 displacement pusher plate, low pressure, pneumatically driven TAH was developed for temporary use. For optimal anatomic fit, easy implantation, and better flow patterns, the 5.7 X 10.7 cm total artificial heart (1) TAH was made of two essentially flat pumps integrated into a single unit. This single package approach avoids the dead space that occurs between the two pieces of conventional TAH and thus minimizes overall volume. It was designed to be positioned in the pericardial sac in a fashion similar to the natural ventricles and, based upon previous anatomic studies, fit in the average sized adult patient. In contrast to conventional free diaphragm pumps, the diaphragms of this TAH are supported by pusher plates that have a unique guide mechanism at the center to ensure a linear-controlled diaphragm motion and consequent uniform blood flow distribution. The guide of each pusher plate nests into the other, resulting in minimal thickness of the package. By using a simple displacement transducer, reliable output monitoring, with the possibility of selection of various pumping modes and adjustment of stroke volume, is possible. The authors anticipate this efficient and practical TAH to be a suitable temporary heart replacement device.

Study of heat dissipation to the lung from a thermal ventricular assist system.

The thermally powered left ventricular assist system (LVAS) requires that heat be dissipated to surrounding lung tissue and blood. This acute study was conducted in three anesthetized calves (weighing 84.3 +/- 14.3 kg) to evaluate the mechanisms involved in the dissipation of heat to the lung tissue. The heaters were placed in contact with the left lung surface and skeletal muscle tissue. Compared to the muscle tissue, heat flux to the lung was approximately three times higher for the same surface temperatures. For a constant heat flux, lung interface temperature tended to vary inversely with the cardiac output and ventilatory flow. This preliminary study demonstrated that the level of heat generated by the thermal LVAS can be effectively dissipated to the lung, with the convection mechanisms of airflow and blood flow playing a major role.

Methods for volume assessment of an air filled compliance chamber.

The air-filled (120 ml) compliance chamber employs a Dacron covered Hexsyn-butyl bilaminar diaphragm to minimize gas diffusion. Finite permeability dictates the need for a means to detect the remaining air volume and a refill port for gas addition. X-ray studies were used to detect radiopaque chamber markers in cadavers. Tangential X-ray cinematography enabled detection of chamber volumes less than 100 ml and diaphragm center deflection predicted volume to within +/- 6 ml of the actual volume. An electrically driven left ventricular assist pump (90 cc) was used to evaluate motor current (MC) and intracompliance pressure (IP) as indicators of low compliance volume. Peak MC was a function of both hemodynamic output power and compliance volume. Thus, if the peak current for a given hemodynamic output is known, variances may be indicative of low compliance volumes. The cyclic minimum IP vs. volume was +1, -3, and -13 mmHg for compliance volumes of 120, 90, and 80 cc, respectively. Ejection velocity did not significantly affect IP. In conclusion, X-ray studies and MC are useful as noninvasive means of assessing the need for compliance refill. IP, though measured invasively, is the most sensitive volume-dependent parameter.

A biolized implantable ventricular assist device compatible with IABP console.

A low pressure pneumatic pusher plate blood pump was developed for temporary right, left, or biventricular assist. Important features of this pump are its 1) driveability by the standard, easily available intraaortic balloon pump (IABP) console; 2) gelatin coated internal surface for blood compatibility; 3) essentially flat disc shape, 3 cm thick and 11 cm in diameter, for optimal anatomic fit; and 4) unique pusher plate guide mechanism to ensure linear motion without deflections of the diaphragm, and consequent uniform flow distribution into the pump. The guide telescopes into itself to avoid a housing protrusion for easy implantability; this controlled movement also provides a number of performance, control, and diagnostic benefits. The pumps 60 ml displacement gives up to 4.7 L/min at 80 bpm and 6.7 L/min at 120 bpm outputs in a mock loop. This VAD has been implanted in two calves for 43 to 84 days, continuously driven by a Datascope IABP console. An average 5 L/min pump output has been observed in both synchronous and fixed rate modes. No anticoagulation was required. We expect extensive clinical use of this VAD, based on its reliability, low cost, and simplicity.