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Biomedical subjects

J H Donachy

Publications and source records attributed to J H Donachy.

At least 19 recordsLinked to original sources
PubMed1995

Hemolytic differences among artificial cardiac valves used in a ventricular assist pump.

Ventricular assist devices (VADs) required for cardiac support may produce clinically significant hemolysis. VAD valves differ in both mechanics and hemodynamics. Therefore, we examined a ball valve, a modified tilting disc (MTD) valve, a polyurethane trileaflet valve, and a Björk-Shiley monostrut valve to determine their degrees of hemolysis. The valves were tested in a Pierce-Donachy VAD which pumped fresh bovine blood through a mock loop. Blood samples were analyzed for hematocrit and plasma hemoglobin, from which the indices of hemolysis were calculated. A one-way analysis of variance indicated significant differences between certain valves. The MTD was the most hemolytic. No significant hemolytic difference was found between the trileaflet and monostrut valves despite their different designs. The monostrut valve and the MTD valve were hemolytically very different despite their similar design. This study suggests that the valve type significantly affects the hemolysis produced by the VAD.

Animals↗
PubMed1990

An electric artificial heart for clinical use.

Advances in microelectronics, high-strength magnets, and control system design now make replacement of the heart using an implantable, electrically powered pump feasible. The device described herein is a compact, dual pusher plate unit with valved polyurethane sac-type ventricles positioned at either end. The power unit consists of a small, brushless direct current motor and a motion translator. A microprocessor control system is used to regulate heart beat rate and provide left-right output balance. Bench studies lasting for as long as 1 year have been performed. Heart replacement with the electric heart has been performed in 18 calves since 1984. The longest survivor lived for more than 7 months. Among the causes of termination were component failure, thromboembolic complications, and bleeding. No major problem has been identified that precludes prolonged use of the electric heart. In the future the patient with end-stage heart disease will have an electric artificial heart as one therapeutic option.

Animals↗
PubMed1987

Postoperative cardiac support with a pulsatile assist pump: techniques and results.

Since 1980 this group has employed a pulsatile assist pump(s) in 23 patients. Postoperative survival was 39% (9/23). In this group, 16 patients have required left ventricular support; 9 have been weaned from the pump, and 7 have survived (44%). Three patients required right ventricular support, and two have survived (66%). Four patients required biventricular assistance, but none survived. There have been four late deaths in this group. Of the five patients alive and well, all are New York Heart Association Class I or II. Important conclusions include the following: The pulsatile pump can adequately support the pulmonary or systemic circulation for a period of days; dramatic improvement in ventricular function is frequently observed in patients with univentricular failure; adequate right ventricular function is a major determinant of survival in a patient with pulsatile left ventricular support; preoperative cardiogenic shock and/or a prolonged time on cardiopulmonary bypass (CPB) predispose the patient to diffuse intravascular coagulation and a poor result; considerable information remains to be learned regarding the selection of assist pump candidates, optimal CPB techniques, and intraoperative identification of biventricular failure, which will further improve these results.

Adult↗
PubMed1984

The compliance problem: a major obstacle in the development of implantable blood pumps.

The compliance problem represents a major obstacle in the development of implantable blood pumps. The motor-driven pumps are enclosed in an airtight casing with gas in the motor space. The trapped gas in the motor space either increases the load on the motor during systole or impedes blood sac filling. Potential solutions to the compliance problem include the use of a conventional blood pump with a compliance chamber, a blood pump with an isolated blood sac and accumulator, or a volume-compensated blood pump. Most experimental studies designed to investigate this problem have been performed with compliance chambers. An ideal compliance chamber should accept 100 ml gas with less than a 15-mm Hg increase in pressure and should automatically compensate for changes in atmospheric pressure. To date, two designs have been shown to be effective in laboratory and animal studies: a collapsible rectangular sac design developed by our group, and a lenticular chamber developed by Nosé and associates. Compliance chambers of the former design have now been employed to provide the required compliance for motor-driven assist pumps in long-term calf studies.

Assisted Circulation↗
PubMed1983

Clinical effectiveness of mechanical ventricular bypass in treating postoperative heart failure.

Our group has designed an air-powered, sac-type ventricular assist pump (VAP) that has a smooth polyurethane surface and Bjork-Shiley-type valves. This VAP has undergone extensive testing in calves and has been available for clinical use during the last 5 years. When properly employed, the circulatory support permitted immediate separation of the patient from bypass. Definite hemodynamic evidence of improved ventricular function has been observed during the period of unloading of the deranged ventricle by the VAP. However, during the first 3 years of our experience, the VAP was used in 11 patients with 1 survivor. During the last 2 years, specific attention has been directed to use of right, left, or biventricular assistance as indicated, to prompt application of the VAP when required, and to use of atrial rather than ventricular cannulation for VAP inflow. Accordingly, the survival rate over this 2-year period has increased to 50% (four of eight patients). The short-term assist pump is an important adjuvant for the surgeon who operates on seriously ill cardiac patients.

Aged↗
PubMed1981

Approaches to the artificial heart. Invited speaker.

Over the last two decades, the implantable artificial heart has evolved from an idea to a device capable of completely supporting the circulation for periods now exceeding 5 months. Although initial animal studies were limited by thromboembolism and device breakage, the usual causes of death in experimental animals are now infection, atrioventricular valve obstruction, elastomer bladder calcification, or inadequate cardiac output because of the relatively rapid growth of the young calves. As a result of the bulky nature of the energy converter and the substantial risk of infection with large diameter percutaneous tubes, clinical use of their air-powered artificial hearts will be limited to patients who are awaiting or being prepared for heart transplantation. Artificial hearts with implanted energy converters are being developed for permanent heart replacement. These devices require well-designed, durable mechanical components and sophisticated control systems. Although initial designs centered around thermal engines powered by a completely implantable nuclear energy source, the excessive cost and potential dangers have shifted the focus away from the nuclear system. Several electrically driven artificial hearts, based on samarium-cobalt magnet brushless direct-current motors, are now undergoing bench testing and will be ready for long-term animal studies within 2 years. This research will culminate with the availability of an "off-the-shelf" electrically powered artificial heart for use in patients with a wide range of nonrepairable forms of end-stage heart disease.

Animals↗
PubMed1980

Calcification inside artificial hearts: inhibition by warfarin-sodium.

Intracavitary calcium phosphate deposits were observed in smooth, elastomeric blood pump sacs implanted in male calves for periods of 115 to 166 days. These deposits occurred predominantly on the flexing surface of the sacs. In contrast, similar pump sacs remained generally free of mineral deposits for up to 150 days in calves treated with the anticoagulant warfarin-sodium. These results implicate a vitamin K-dependent process in calcium phosphate deposition on elastomeric sacs.

Animals↗
PubMed1980

Mechanical circulatory assistance for postoperative cardiogenic shock: a three year experience.

Retrospective analysis of 14 patients undergoing circulatory support for postcardiotomy cardiogenic shock during the past 3 yrs has demonstrated the ability of the profoundly depressed myocardium to recover. Four patients were totally weaned from circulatory support and 2 are long-term survivors. Our results suggest that improved survival is dependent on the absence of certain peri-operative complications. To improve future clinical results we suggest that prompt application of assist pumping is necessary to eliminate prolonged cardiopulmonary bypass times and subsequent massive bleeding; those circulatory support systems requiring systemic anticoagulation are of no value in the treatment of postcardiotomy cardiogenic shock; the use of atrial cannulation may be advantageous in certain patients to eliminate critical inflow obstruction, further prolongation of cardiopulmonary bypass, and additional myocardial damage; and that the high incidence of right ventricular failure that is refractory to medical therapy makes the ability to support both ventricles mandatory.

Adult↗
PubMed1979

Total artificial heart implantation in calves with pump on an angled port design.

The APP was employed in our 21st TAH calf and has now been implanted in a total of 11 animals. The APP has a dynamic stroke volume of 105 ml, an ejection fraction of 75%, and a peak flow of 14 L/min. The TAH features 2 APPs which have polysulfone cases and contain smooth, seam-free polyurethane sacs. Concavoconvex Bjork-Shiley valves are used. The pumps are pneumatically driven but may be easily converted to pusher-plate drive. A pneumatic drive console and an automatic control unit complete the system. The automatic control unit permits independent control of the right and left hearts as a function of left atrial and aortic pressure respectively. The average survival of the APP TAH calves has been 65 days. Hematologic study has revealed basically normal results with minimal elevation of serum hemoglobin and lactic acid dehydrogenase (LDH), indicative of a low level of hemolysis. Elelvation of central venous pressure (CVP) and total blood volume continue to be a problem with some TAH calves but not all. The APP has led to a dramatic increase in duration of survival and decrease in thromboembolism.

Animals↗
PubMed1979

A two and one half year clinical experience with a mechanical left ventricular assist pump in the treatment of profound postoperative heart failure.

A sac-type paracorporeal left ventricular assist pump was implanted in 9 patients suffering from profound left ventricular failure following open heart surgery. Two patients had good recovery of left ventricular function and were weaned from assist. One survived 14 months postoperatively. Primary causes of death among the remaining patients were (1) primary right ventricular failure, (2) assist pump inlet cannula obstruction and (3) excessive bleeding. The strategies developed or proposed to deal with these problems include, respectively: (1) biventricular assist for patients with concomitant right ventricular failure; (2) cannulation of the left atrium to avoid inlet cannula obstruction by the left ventricular wall and intraventricular septum; (3) more rapid selection of left assist candidates and more rapid implantation techniques to reduce the coagulopathy associated with prolonged cardiopulmonary bypass, and an effective autotransfusion system to augment blood replacement.

Adult↗
PubMed1978

A new prosthesis for reconstruction of the left ventricular outflow tract.

A new left ventricular outflow tract prosthesis is described. It consists of a tightly woven Dacron graft with one end modified by being wrapped around a thin perforated stainless steel tube to form a rigid left ventricular insertion port and the other end anastomosed to a Hancock xenograft valved conduit for suture to the arterial system. The prosthesis is simple in design and flexible enough to permit anastomosis to any portion of the abdominal aorta. In addition, since the entire blood conduit consists of a porous woven arterial graft and a tissue valve, anticoagulants are not required. The prosthesis has been successfully employed in a 7-year-old boy who had undergone two previous open-heart operations for resection of a subaortic ring but who had persistent evidence of severe residual stenosis. We believe this conduit has advantages over present commercially available units.

Animals↗
PubMed1978

Prolonged mechanical support of the left ventricle.

An interdisciplinary group has developed a left ventricular assist pump system composed of a modified sac type pump, a pneumatic power unit, and a synchronizer. The pump fills from the left ventricle and discharges into the aorta. The system was employed for left ventricular assistance in a series of 12 normal calves, with an average pumping period of 70 +/- 8 days. The system was then evaluated in a series of calves in whom profound left ventricular failure had been produced. These studies indicate that the assist pump is effective in supporting the circulation and completely unloading the left ventricle. The assist system has now been employed in four patients who could not be weaned from cardiopulmonary bypass following cardiac valve replacement. The assist pump supported the circulation in three instances. In one patient, the assist pump was employed for 8 days until left ventricular function had improved sufficiently to permit pump removal; the patient was subsequently discharged from the hospital.

Aged↗
PubMed1977

The artificial heart. Progress and promise.

A multidisciplinary group has designed, fabricated, and evaluated an artificial heart. The heart consists of two smooth-surfaced sac-type pumps, two pneumatic power units, and an electronic control system. The artificial heart has been employed in 22 calves. A variety of problems have been encountered and overcome and a significant improvement in pump design has been made. As a result, a gradual increase in survival times has occurred. The last two calves in which the heart was tested lived for 60 and 42 days respectively. These animals ate well and gained weight. The ability of the control system to balance the output of the two pumps over long periods of time and to automatically increase cardiac output with treadmill exercise has been confirmed. No insurmountable problems in the development of the artificial heart have been identified. The date that an artificial heart will be available for clinical use depends on the availability of funds and on the tenacity of the investigators.

Animals↗