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Biomedical subjects

W E Richenbacher

Publications and source records attributed to W E Richenbacher.

35 records · Page 2Linked to original sources
PubMedDate not supplied

Recurrent pulmonary embolism after inferior vena caval interruption with a Greenfield filter.

Twenty-six patients have undergone inferior vena caval interruption with a Greenfield filter. One patient (3.8%) developed a fatal, recurrent pulmonary embolism. Postmortem examination documented the presence of thrombus within the filter, proximal extension of thrombus beyond the filter apex, and fresh pulmonary emboli. In a combined series of 556 patients, 12 patients (2.2%) developed recurrent pulmonary emboli, 2 (0.36%) of which were fatal. Including case reports, 18 patients have had documented recurrent pulmonary emboli following Greenfield filter insertion. In 4 patients, the recurrent embolism was fatal. Six (60%) of 10 patients had a concomitant malignancy. A work-up and treatment plan for patients having recurrent pulmonary emboli after the insertion of a Greenfield vena caval filter is proposed.

Hemofiltration↗
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In vivo performance of a transcutaneous energy transmission system with the Penn State motor driven ventricular assist device.

A transcutaneous energy transmission system (TETS) has been used to power the Penn State motor driven ventricular assist device in nine calf experiments, for a total of 316 days of cumulative in vivo experience. This is seen as an important step toward a completely implantable ventricular assist system and total artificial heart. The TETS converts an external 12 volt DC source via inductive coupling to a regulated 14 volt output voltage for use by the motor controller. A maximum output power of 70 watts is available. In calf experiments, the TETS output power averaged between 8 and 12 watts. The motor controller was not implanted in these experiments, awaiting further development of the miniaturized electronics. The TETS output was returned percutaneously to the external motor controller, allowing the TETS output to be monitored directly. System efficiency, from DC source to DC output, and including losses in 12 feet of cable, ranged from 55% to 70%, depending upon supply voltage, motor load, and degree of coil coupling. The subcutaneous coil was well tolerated, demonstrating only temporary, mild, superficial induration.

Animals↗
PubMedDate not supplied

Time course of cytokine release and complement activation after implantation of the HeartMate left ventricular assist device.

Pro-inflammatory mediators, including interleukin-6 (IL-6), IL-8, and complement C3a, are released after cardiac surgery as part of the inflammatory response related to blood-biomaterial interaction in the cardiopulmonary bypass circuit. Post operative time course data for these mediators are not fully defined in patients receiving left ventricular assist device (LVAD) support. The authors performed enzyme linked immunosorbent assays for concentrations of IL-6, IL-8, and C3a in plasma in six HeartMate LVAD recipients at the following times: pre operatively; 4, 8, 16, 24, 36, and 48 hr post operatively; daily through the first week; and weekly thereafter for 6 weeks. All patients survived without major complications during the study. Pre operative concentrations of IL-6 and C3a in plasma were significantly increased compared with age matched controls. Post operatively, the concentrations of IL-6 and IL-8 in plasma took longer to return to baseline values after insertion of the LVAD than the trends reported in the literature after routine cardiopulmonary bypass alone. Concentrations of IL-6 and complement C3a continued to decrease to lower than baseline post operatively, reaching statistical significance after 6 weeks of LVAD support. The authors conclude that the presence of the HeartMate LVAD delays the return of pro-inflammatory mediator concentrations back to baseline values compared with routine cardiopulmonary bypass alone, but the device does not appear to be an ongoing source of cytokine release or complement activation.

Complement Activation↗
PubMedDate not supplied

In vivo demonstration of cavitation potential of a mechanical heart valve.

Cavitation is implicated as the cause of pitting and erosion of explanted mechanical heart valves that failed. Previous in vitro studies demonstrated transient negative pressure spikes upstream of mechanical heart valves at the instant of leaflet closure. When the magnitude of the transient negative pressure spike is below the vapor pressure of the fluid flowing across the mechanical valve, cavitation bubbles have been documented near the valve housing or occluder disc. To test for the presence of transient negative pressure spikes that are conducive to cavitation in vivo, we measured left atrial pressure at the valve orifice after mitral valve replacement. Mitral valves were replaced with 27 mm prostheses in 10 goats (50-60 kg). Control animals (Group 1, n = 5) received pericardial valves. Study animals (Group 2, n = 5) received bileaflet pyrolytic carbon valves. Pressure was recorded from a high frequency atrial transducer at hyperdynamic and hypodynamic states. Transient negative pressure spikes did not occur in any Group 1 animal. Transient negative pressure spikes below the vapor pressure of blood (-713 mm Hg) were recorded in four of five Group 2 animals at the hyperdynamic state: -900, -950, -800, -400, and -1,400 mm Hg (p = 0.048 Group 1 versus Group 2, Fisher's exact test). No cavitation potential exists in vivo after bioprosthetic valve implantation. Transient negative pressure spikes below the vapor pressure of blood occur in vivo at hyperdynamic physiologic states when this bileaflet pyrolytic carbon valve is implanted in the mitral position. These studies demonstrate the potential for cavitation with implanted mechanical valves in vivo.

Animals↗
PubMedDate not supplied

Clinical trial: a clinician's perspective.

As a result of my participation in several clinical trials at The University of Iowa, I have now redrawn what I perceive to be the algorithm for conduct of a clinical trial. Of note, I have excluded the development of the new device, in vitro device testing, in vivo animal experimentation, clinical protocol development, granting of an Investigational Device Exemption, and the process by which clinical sites are selected. Following my algorithm I have made no mention of the commercialization of an experimental device, including the Pre-Market Approval process and FDA panel meetings. In summary, I believe there are a variety of reasons why a principal investigator would choose to participate in a clinical trial. With tongue in cheek, I would offer fame and fortune as two possible motivating factors. Obviously, both are double-edged swords. Should a trial not turn out as hoped, celebrity can instantly turn to notoriety. With respect to fortune, administrative and clinical activity performed by the principal investigator on behalf of the clinical trial does not generate income, and, in fact, can place a considerable financial drain on the investigator's department. I believe that investigators are strongly driven by intellectual curiosity, but it is important to maintain perspective when participating in a clinical trial. The real reason we seek clinical trial site designation is to allow us to offer new, innovative therapeutic modalities to our patients. By so doing, it is imperative that we conduct the clinical trial in as thoughtful and as safe a manner as possible, with our patients' well being always foremost in our minds.

Clinical Trials as Topic↗
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Hospital discharge for the ventricular assist device patient: historical perspective and description of a successful program.

Patients who are supported with an implantable ventricular assist device (VAD) as a bridge to cardiac transplantation are potential candidates for hospital discharge. Hospital discharge rates in reported clinical series vary from 27% to 60%. Many of the patients included in these series, however, were subjects of premarket approval clinical trials and as such, are bound by rigid eligibility criteria for discharge. According to a voluntary registry maintained by Thermo Cardiosystems, Inc., the postmarket discharge rate in patients supported with the HeartMate VE LVAS is approximately 25%, a number that is artificially low due to incomplete reporting. The postmarket discharge rate at the busiest Thermo Cardiosystems HeartMate VE LVAS centers is 53%. Clearly, discharge rates need to increase if the VAD is ever to be considered a viable destination therapy for end-stage heart failure. The discharge program instituted at The University of Iowa incorporates patient and family training as well as community services education. Between January 1999 and April 2001, fourteen patients received VAD support as a bridge to transplantation with the HeartMate VE LVAS. Thirteen patients (93%) were discharged from the hospital. Eight of the 13 patients have been transplanted after having spent 65.8% +/- 31.4% of their period of blood pump support as an outpatient. Eight of 13 patients (62%) required a total of 20 unplanned repeat hospitalizations. A well defined, aggressively implemented discharge program can adequately prepare the VAD patient for the transition from hospital to home.

Academic Medical Centers↗
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Education of the ventricular assist device patient's community services.

Two implantable, electric left ventricular assist systems have received approval from the Food and Drug Administration (FDA) for use outside a hospital environment. As patients supported with these systems are discharged from the hospital, it is important that various community services and agencies be involved in the care of this unique patient population. Between January 1999 and May 2001, The University of Iowa Hospitals and Clinics (UIHC) implanted 14 HeartMate VE LVAS (Thoratec Corporation, Pleasanton, CA) in patients as a bridge to cardiac transplantation. Of these 14 patients, 13 were discharged home from the hospital. On the basis of our 3 year experience, a discharge program has been developed to educate the ventricular assist device (VAD) patient's community services. Ten community services most critical to a safe home discharge program are identified. Timing of service contact, mechanism of contact, community education method, education content, education materials, and outpatient community service usage are described.

Ambulatory Care↗
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Lobar pulmonary edema due to mitral regurgitation: diagnosis by echocardiography.

One etiology of unilateral lobar pulmonary edema is mitral regurgitation. Echocardiography is able to demonstrate the retrograde flow of blood into the pulmonary veins and allows timely diagnosis and treatment planning. Correction of mitral regurgitation is followed by resolution of the radiographic abnormality.

Echocardiography, Transesophageal↗
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Negative pressure transients with mechanical heart-valve closure: correlation between in vitro and in vivo results.

Negative pressure transients (NPT) recorded in a single closing event of mechanical valves in the mitral position in an in vitro setup are compared with data recorded in the left atrium in vivo with the valves implanted in the mitral position in an animal model. The loading at valve closure (dP/dtCL) computed from the in vivo ventricular pressure recording (ranging from 700 to 2300 mm Hg/s) agreed with the magnitudes predicted in our earlier in vitro experiments (750-3000 mm Hg/s). The NPT signals and the corresponding power spectral density plots from the in vivo data were in qualitative agreement with those recorded in vitro. The NPT magnitudes were found to be below the vapor pressure for blood in mechanical valves with rigid occluders suggesting a potential for the valve to cavitate in vivo. Our in vivo results also suggest that the valves with flexible occluders are less likely to cavitate. The correlation of the in vitro and in vivo data also suggests that the flexibility of valve housing used in the in vitro studies is not an important factor in the dynamics of mechanical valve closure in vivo.

Animals↗
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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.

Adult↗
PubMedDate not supplied

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)

Adult↗
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Roller screw electric motor ventricular assist device.

The roller screw electric VAD is easier to manufacture and 25% lighter than the previously described drum cam model. This device requires 12 to 15 W to pump 6 to 8 l/min with minimal hemolysis. The motor drive has functioned for periods up to 93 days in vivo with no measurable wear. The compliance chamber volume varies by 100 cc during VAD function but does so while maintaining pressure variations below 15 mmHg. Compliance chamber volume loss of 2 to 5 cc/day is explained by gas transport through SPU. The subcutaneous sampling port provides ready access to the sealed system.

Animals↗
PubMedDate not supplied

Clinical spectrum of mechanical circulatory assistance.

Mechanical blood pumps can provide effective circulatory support in a variety of clinical settings. Ventricular assist devices are single ventricle blood pumps designed to work in parallel with the natural heart. These devices can be powered by air pulses or an electric motor to provide temporary or permanent circulatory assistance, respectively. Unlike ventricular assist devices, artificial hearts replace the natural heart. In doing so, they provide complete support of both the systemic and pulmonary circulation. Air-driven artificial hearts will primarily support patients with profound biventricular failure prior to heart transplantation. Electrically assisted artificial hearts with their implantable energy converters are in the earliest stages of development. These devices will ultimately serve as permanent heart replacements in patients who do not qualify for heart transplantation.

Animals↗