Search PubMed⌕ Search

Biomedical subjects

R E Clark

Publications and source records attributed to R E Clark.

395 records · Page 22Linked to original sources
PubMedDate not supplied

Development of an implantable centrifugal blood pump.

The efficacy of centrifugal pumps for short-term (0-30 days) ventricular support has been widely reported and favorably compared with pulsatile systems. A small, durable, implantable centrifugal blood pump is being developed for medium-term use (up to 6 months). The pump is based on the Medtronic Hemadyne system that has existed in multiple forms over the past 30 years. The pump is approximately the size of a tennis ball, weighs 240 g, and is comprised of a 2.5 cm plastic impeller driven by a radially coupled brushless DC motor. In vitro hydraulic performance was recorded over a wide range of flow conditions on a mock circulatory loop. The pump generated 7 L/min flow against an afterload of 100 mmHg pressure, with a maximum power draw of 10.4 watts. Pulsatile flow was preserved when placed in conjunction with a simulated left ventricle. In vivo testing was performed in 10 healthy sheep for 10-292 hr. Heparin was used to facilitate cannulation, and no anticoagulation was administered after pump implantation. Blood chemistries reflecting hematologic, pulmonary, renal, and hepatic functions were recorded and demonstrated no adverse effects with normal pump operation. Complications were related to kinking of blood conduits and thrombus formation within the cannulae. These results are encouraging and warrant further studies to prove feasibility of this pump as a medium-term implantable ventricular assist device.

Animals↗
PubMedDate not supplied

A comprehensive cardiovascular waveform analysis program for IBM-compatible personal computers.

Computerized cardiovascular waveform processing has become a necessary and fundamental tool in the analysis of physiologic data. The availability of numerous commercial data-analysis programs has significantly enhanced the efficiency of waveform analysis. Many such programs come with their own programming language, which enables the researcher to create an application program suited to a specific series of calculations. Once written, an application program can significantly increase the efficiency with which data from a specific experiment can be analyzed. However, creating or modifying a program for each new experimental protocol can be time-consuming, especially in the error-detection and verification stages. Single-purpose programs also prove somewhat inflexible to unexpected changes in experimental formats. These problems suggested the need for a more flexible program, but one that is nevertheless specifically suited to the analysis of cardiovascular signals. This need led to the development of a program designed in collaboration with surgeons and physiologists. This program addresses some important analysis problems in cardiovascular research, and allows the user to survey and manipulate cardiovascular waveforms in an intuitive and spontaneous manner.

Algorithms↗
PubMedDate not supplied

In vitro quantification of regurgitant jet flow by color Doppler ultrasound and conservation of momentum.

Prosthetic valve regurgitant jets can be imaged with color Doppler ultrasound (CDU), but clinical quantitation remains elusive. An equation based on an integrated conservation of momentum analysis was implemented for CDU quantitation of regurgitation. This was compared with a simple, non-CDU momentum balance analysis recently reported that requires only a pulsed Doppler ultrasound (PDU) reading within the jet and a continuous wave Doppler (CWD) reading of the orifice velocity. For in vitro steady flows, the simple, non-CDU method was accurate only with PDU readings taken 5 cm from the orifice; flows were underestimated when readings 1 and 3 cm from the orifice were used. The CDU method was accurate, even when flows calculated from readings between 0.5 and 6.0 cm from the orifice were averaged together.

Blood Flow Velocity↗
PubMedDate not supplied

In vitro ultrasound characterization of a polyurethane trileaflet valve.

Polyurethane synthetic trileaflet valves were compared with commercial prostheses in vitro, in a pulse duplicator using ultrasound to characterize the flow velocities and patterns. Flow-pressure drop behavior was in the middle range of other prosthetic valves. Diastolic regurgitant jets were located by color Doppler ultrasound, and there appeared to be some leakage through the leaflet fold at the commissure. Nevertheless, the closing volumes and closed valve leakage volumes were, on average, lower than other prosthetic valves. Systolic 20 Hz spectral oscillations detected with pulsed Doppler and continuous wave Doppler were attributed to leaflet flutter in the open valve.

Aortic Valve↗
PubMedDate not supplied

A computerized physiologic pulse duplicator for in-vitro hydrodynamic and ultrasonic studies of prosthetic heart valves.

A physiologic pulse duplicator for the simultaneous in-vitro hydrodynamic and ultrasonic evaluation of aortic prosthetic heart valves is described. The system is interfaced to a personal computer, which provides greater efficiency over manual techniques in system calibration, data acquisition, and analysis. The data analysis program aids selection of start and end systole and calculates pressure difference across the valve, the closing and regurgitant volumes, flow rates, and the Gabbay and Swanson performance indices. The pulse duplicator is designed to accommodate the ultrasonic measurement of fluid velocities, including pressure difference via the Bernoulli equation, and color-flow imaging. In tests of 19-mm, 23-mm, and 27-mm Bjork-Shiley spherical occluder valves, continuous-wave Doppler ultrasound was found to overestimate by about 50% the pressure difference measured directly by pressure transducers, a finding that is clinically important.

Aortic Valve↗
PubMedDate not supplied

The effects of anticalcification treatments on bioprosthetic heart valves implanted in sheep.

Several preimplantation processes have been shown to inhibit the calcification of pieces of porcine aortic valves and of bovine parietal pericardium implanted subcutaneously in rats. To investigate the effectiveness of these processes in modifying the calcification of bioprosthetic valves implanted in an intracardiac position, mitral and tricuspid valve replacements were performed in young sheep. Bioprosthetic valves treated with the following preimplantation processes were studied: 1) surfactants, including sodium dodecyl sulfate, polysorbate-80, Triton X-100 and N-lauryl sarcosine; 2) covalently bound aminohydroxypropane diphosphonic acid; 3) toluidine blue; and 4) incorporation of polyacrylamide into valvular tissues. Quantitative calcium analyses showed that only the surfactants substantially reduced calcification of bioprostheses implanted in intracardiac positions. This effect was evident only in porcine aortic valvular bioprostheses, and not in pericardial bioprostheses. Triton X-100 and N-lauryl sarcosine not only reduced calcification but also induced alterations that decreased the durability of the valves. Toluidine blue decreased calcification to a degree that was statistically significant but not biologically important, while polyacrylamide incorporation and diphosphonate binding increased calcification. Thus, data regarding anticalcification treatments obtained from subcutaneous implantation studies in small animal models should be interpreted cautiously and validated by studies with intracardiac valvular implantation in large animals.

Animals↗
PubMedDate not supplied

Human plasma causes rapid dysfunction in ex vivo pig hearts.

The use of hearts from large domestic animals represents a potential solution to the current human donor shortage. However, xenogeneic hyperacute graft rejection remains a major barrier to xenotransplantation. The purpose of this study was to use an ex vivo preparation to study variables that may correlate with hyperacute rejection in cardiac xenografts. Freshly excised hearts from 37 anesthetized pigs (10 to 37 kg) were perfused at 37 degrees C through the aorta with retrograde flow. The hearts functioned in a nonworking mode for 4 hours or until irreversible cardiac dysfunction occurred. Various perfusates were used: fresh whole autologous pig blood (n = 4), dog blood (n = 3), baboon blood (n = 5), human packed red blood cells (n = 2), human whole blood (n = 10), human whole blood and plasma (n = 3), and human plasma (n = 9), to which a modified Krebs-Henseleit bicarbonate buffer solution was added. Rapid loss of function was uniform and occurred most quickly (13 to 18 minutes) for hearts perfused with dog blood and human plasma. Isolated cardiac perfusion provided a means for the analysis of the cellular and plasma components of human blood to define which were required for rapid loss of function. The results indicated that the reaction was mediated by components present only in plasma.

Acute Disease↗
PubMedDate not supplied

The development of The Society of Thoracic Surgeons voluntary national database system: genesis, issues, growth, and status.

BACKGROUND: The purpose of this communication is to demonstrate the feasibility of a voluntary national cardiac surgical database. METHODS: The genesis of the Society of Thoracic Surgeons (STS) National Cardiac and General Thoracic Surgery Databases in the interval of 1986 to 1990 is described. The issues facing the Committee in the initial decision making processes are discussed choosing a society-based, in-house activity versus using an outside vendor, private practice needs versus academic ones; open versus closed membership and vendors, risk stratification; data quality; audit; and access to data. RESULTS: In the 6 years of operation the STS cardiac surgical database has grown from 41,000 to 706,000 patients. The number of practice groups, hospitals, and surgeons has increased from 26 to 624, 32 to 750, and 120 to 1850, respectively. All but one state is represented, as are more than 400 teaching hospitals, including 28 Veterans Administration hospitals and 60 university centers. CONCLUSIONS: The STS database system has become firmly established and is a model for other societies and associations. The data placed yearly in the public domain have become a national standard.

Cardiology Service, Hospital↗