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Biomedical subjects

G A Prophet

Publications and source records attributed to G A Prophet.

At least 19 recordsLinked to original sources
PubMed2001

Modifications in surgical implantation of the Penn State electric total artificial heart.

BACKGROUND: Two modifications of the surgical implantation protocol for the Penn State Total Artificial Heart (ETAH) were evaluated: Phrenic nerve ischemia was prevented by minimizing dissection and traction; and hemostasis was augmented and ETAH cuff anastomoses reinforced by using fibrin glue. METHODS: Thirteen Holstein calves underwent orthotopic surgical implantation of the Penn State ETAH between February 1998 and August 2000. Mean hemodynamic and laboratory chemistry variables from the first postoperative week were compared between calves receiving the original (n = 7) and modified (n = 6) protocol. RESULTS: Calves assigned to the modified protocol displayed an improvement in the Po2/FiO2 ratio compared to original (419.4 +/- 17.5 vs 336.3 +/- 35.4, respectively; p = 0.05). All additional parameters were equivalent between groups. The percent survival of animals receiving the modified protocol at 2, 4, and 12 weeks was higher than that of animals that underwent the original protocol. Original-protocol calf deaths consisting of hemothorax (n = 3), and respiratory failure (n = 1) were prevented in the modified protocol. CONCLUSIONS: Our results suggest that manipulations in surgical protocol may promote increased survival in calves implanted with the Penn State ETAH.

Animals↗
PubMed1999

Potassium-channel opener cardioplegia is superior to St. Thomas' solution in the intact animal.

BACKGROUND: In isolated hearts, the potassium-channel opener pinacidil is an effective cardioplegic agent. This study tested the hypothesis that pinacidil is superior to St. Thomas' solution in the more clinically relevant intact animal. METHODS: Sixteen pigs were placed on full cardiopulmonary bypass. Hearts underwent 2 hours of global ischemia (10 degrees to 15 degrees C). Either St. Thomas' or 100 micromol/L pinacidil was administered every 20 minutes (10 mL/kg). Preischemic and postreperfusion slopes of the preload-recruitable stroke work relationship were determined. Changes in myocardial adenine nucleotide levels and cellular ultrastructure were analyzed. RESULTS: Pinacidil cardioplegia resulted in an insignificant change in the slope of the preload-recruitable stroke work relationship (40.6+/-2.1 mm Hg/mm before ischemia and 36.5+/-3.7 mm Hg/mm after ischemia; p = 0.466). In contrast, St. Thomas' solution resulted in a significant decrease in the slope after reperfusion (34.3+/-5.5 mm Hg/mm and 13.5+/-2.3 mm Hg/mm; p = 0.003). Adenine nucleotide levels, myocardial tissue water, and ultrastructural changes were similar between groups. CONCLUSIONS: Pinacidil ameliorated myocardial stunning associated with traditional hyperkalemic cardioplegia without causing significant differences in cellular metabolism.

Adenine Nucleotides↗
PubMed1999

Computer-assisted endoscopic coronary artery bypass anastomoses: a chronic animal study.

BACKGROUND: With traditional instruments, endoscopic coronary artery bypass grafting (ECABG) has not been possible. This study was designed to determine the feasibility of using a robotically-assisted microsurgical system to perform ECABG in a chronic animal model. METHODS: Nine calves were placed on cardiopulmonary bypass after harvesting the left internal mammary artery (LIMA). Subxiphoid endoscopic ports (2 instrument, 1 camera) were placed, and a robotic system was used to perform ECABG between the LIMA and left anterior descending coronary artery. LIMA graft flow (LIMAQ) was measured. Animals were sacrificed at 1 month, and hearts underwent angiographic and histologic analyses. RESULTS: Acute graft patency was 89% (8/9). Two animals died suddenly within the first 48 hours. There was no significant difference in mean acute and chronic (n = 6) LIMAQ (40.9+/-4.7 and 38.5+/-5.0 ml/min, respectively). Survivors had an angiographic patency rate of 100% (6/6), confirmed by histology. CONCLUSIONS: This study shows that ECABG is feasible in a chronic animal model with excellent results.

Anastomosis, Surgical↗
PubMed1998

Dynamic in vitro and in vivo performance of a permanent total artificial heart.

In vivo characterization studies were performed to compare the dynamic in vivo performance of the Penn State/3M Health Care electric total artificial heart to existing in vitro data. Fully implanted systems were utilized including the artificial heart, controller, backup batteries, compliance chamber, and transcutaneous energy transmission. Catheters were implanted to measure central venous pressure (CVP), left atrial pressure (LAP), right atrial pressure (RAP), pulmonary artery pressure (PAP), and aortic pressure (AoP). Cardiac output (CO) was determined from the implanted controller, and systemic vascular resistance (SVR) was calculated. Steady state data were collected for each animal along with data regarding the transient responses to changes in preload and afterload. Preload was manipulated through volume changes. Afterload changes were accomplished through vasoactive agents. Increased preload caused little change in cardiac output because the pump output was nearly maximum at baseline. LAP, AoP, and SVR increased with increasing RAP. Decreased preload caused a reduction in CO, LAP, and SVR. Afterload increase resulted in a slight decrease in flow and an increase in system power and SVR. Afterload reduction was accompanied by a decrease in preload and a concomitant reduction in flow. Overall, the system response was similar to the response observed in vitro.

Animals↗
PubMed1984

Pulmonary circulatory support. A quantitative comparison of four methods.

Profound right ventricular failure was produced in 16 goats by inducing ventricular fibrillation after the systemic circulation had been supported with a left atrial-aortic bypass pump. In each animal, four methods of providing pulmonary blood flow were compared quantitatively: passive flow through the pulmonary artery due to a right atrial to left atrial pressure gradient; pulmonary artery pulsation via a 40 ml intra-aortic type balloon within a 20 mm Dacron graft anastomosed to the main pulmonary artery; pulmonary artery pulsation via a 65 ml single-port, valveless, sac type pulsatile assist device; and right atrial-pulmonary arterial bypass via a valved pneumatic pulsatile pump. Average cardiac index of the 16 animals for each method was 31.1 +/- 12.9, 44.4 +/- 13.6, 64.3 +/- 16.9, and 102.0 +/- 20.7 ml/min/kg, respectively. Passive pulmonary artery flow alone provided inadequate pulmonary circulatory support. Addition of pulmonary artery pulsation via the intra-aortic balloon within a conduit increased cardiac index 13.3 ml/min/kg (43%) above passive pulmonary artery flow (p less than 0.0005); however, the cardiac index remained inadequate. Increasing pulmonary artery pulsation volume with a 65 ml sac device provided a 32.2 ml/min/kg (106%) increase in cardiac index above passive flow (p less than 0.0005) to a level that was marginally adequate. The valved right atrial-pulmonary arterial bypass pump increased cardiac index 70.9 ml/min/kg (228%) above passive pulmonary artery flow (p less than 0.0005) to a satisfactory level and is the recommended method of pulmonary circulatory support in profound right ventricular failure.

Animals↗
PubMed1982

Vascular anastomoses in growing vessels: the use of absorbable sutures.

Primary end-to-end infrarenal aortic anastomoses were performed in 36 piglets using two synthetic absorbable suture materials: polydioxanone and coated polyglactin. Animals were killed at 1, 4, and 11 weeks and 6 months following operation. Each aorta was removed, burst-tested to 300 mm Hg, radiographed, and examined histologically. All anastomoses were patent, and no burst-test failures occurred. Stenosis occurred in 14 of 17 animals at 1 and 4 weeks, respectively. One of 5 animals exhibited stenosis at 11 weeks, and none of the 14 animals had stenosis 6 months postoperatively. Histological examination revealed fibrosis replacing areas of disrupted elastica at 6 months in both suture groups. This study suggests that absorbable suture material, in particular polydioxanone, because of its excellent handling characteristics and prolonged tensile strength retention, will be useful for the repair of vascular and cardiac anomalies where growth of the suture line is required.

Absorption↗
PubMed1981

Primary vascular anastomosis in growing pigs: comparison of polypropylene and polyglycolic acid sutures.

Stenosis remains a significant problem in vascular anastomoses performed in the growing patient. This study compares the growth of vascular anastomoses performed with either polypropylene or polyglycolic acid sutures. End-to-end infrarenal aortic anastomoses were performed in 18 piglets. Twelve were performed with polypropylene; in six all sutures were placed in a continuous fashion (Group 1A), and in the other six the posterior sutures were continuous and the anterior were interrupted (Group B). Six anastomoses were performed with polyglycolic acid sutures placed in a continuous fashion (Group 2). The animals were killed 6 months following operation. The abdominal aorta was removed, measured, burst tested, and subjected to histologic studies. All anastomoses were patent. There were no burst failures at 300 mm Hg mean pressure. All polypropylene sutures in Group 1A and the continuous portion in Group 1B had straightened without breaking. Straightening without polypropylene suture breakage resulted in stricture in three Group 1A anastomoses and one Group 1B anastomosis; there was intraluminal polypropylene suture material in two Group 1A and five Group 1B anastomoses. Bowstring formation of the straightened, continuous portion of the polypropylene suture in two Group 1A anastomoses and one Group 1B anastomosis resulted in adherent thrombus. Group 2 anastomoses were without stricture and were grossly indistinguishable from adjacent normal vessel. Histologic examination showed varying degrees of chronic inflammation in the polypropylene anastomoses but negligible inflammation in the polyglycolic acid anastomoses. These results suggest that continuous suture techniques with polypropylene in growing vessels may result in stenosis and/or thrombosis. Moreover, synthetic absorbable polyglycolic acid sutures will be of use in vascular anastomoses in growing patients and in cases in which exacting technique with minimal postsurgical inflammation may be crucial to patency.

Animals↗
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

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

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↗