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Biomedical subjects

L N Scotten

Publications and source records attributed to L N Scotten.

13 recordsLinked to original sources
PubMed1999

The new St. Jude Medical regent mechanical heart valve: laboratory measurements of hydrodynamic performance.

BACKGROUND AND AIM OF THE STUDY: The St. Jude Medical (SJM) mechanical heart valve was the first bileaflet valve with leaflets and orifice all fabricated from pyrolytic carbon. In 1992, a supra-annular cuff configuration, the SJM mechanical heart valve Hemodynamic Plus Series (HP), was introduced, which gave a one-size gain in orifice area over the standard valve. In a continuing effort to improve hydrodynamic performance, a new enhanced configuration of the mechanical valve - the SJM Regent valve - has been developed. The blood-contacting components of the SJM Regent valve have the same design features as those of the standard or HP valve, but the orifice lumen area has been increased, without compromising structural integrity, by a shift in the cuff-retaining orifice rims. METHODS: Valve performance has been measured using a laboratory simulation of the left heart system. Three samples of both valve types (SJM Regent, HP) for sizes 17 mm to 27 mm, were tested at a cardiac output of 5 l/min. Supplementary steady-flow measurements were made at flow rates between 5 and 30 l/min. Pressure and flow signals were recorded and several performance parameters, including pressure gradient, effective orifice area (EOA), insufficiency (regurgitant volume as a percent of forward flow volume) and energy loss, were computed. RESULTS: All sizes of the SJM Regent valve showed improved hydrodynamic performance compared with the HP valve. For the small sizes (17, 19, 21 mm), the pressure gradient of the SJM Regent decreased by 37%, 36% and 39%, respectively; the EOA increased by 22%, 22% and 21%; and the total transaortic energy loss decreased by 33%, 31% and 31% compared with the HP valve. The regurgitation for both valves ranged between 4% and 8% of forward flow volume over the 17-27 mm size range. CONCLUSIONS: Hydrodynamic measurements confirm the gain of the SJM Regent valve over the HP valve that is expected based on the increased geometric orifice area. Given its basic similarity of design, but with an increased EOA as demonstrated in vitro, the SJM Regent valve is anticipated to provide an increased level of clinical benefit.

Biocompatible Materials↗
PubMed1994

A database obtained from in vitro function testing of mechanical heart valves.

The in vitro function of the CarboMedics, Medtronic Hall, Omniscience, Starr-Edwards, St. Jude and Sorin (formerly Shiley) Monostrut heart valves have been compared using a pulsatile flow model left heart and load system. A wide range of flows and heart rates were used. The above valves in all sizes and in both aortic and mitral positions were tested. Results for transvalvular pressure, regurgitation and effective orifice area are presented. The small size St. Jude valves showed the least transvalvular pressure and largest effective orifice area. For large valves, the least regurgitation was exhibited by the Starr-Edwards valve. The data provides a reference for the range of normal performance that can be expected of mechanical prosthetic heart valves.

Aortic Valve↗
PubMed1991

Discrimination in vitro between the acoustic emissions from Bjork-Shiley convexo-concave valves with and without a broken minor strut.

A statistical pattern recognition technique is used to learn and recognise the frequency spectra of the closing sounds emitted by Bjork-Shiley convexo-concave heart valves, with and without fractured minor struts, when operating in vitro. The sounds are generated with test valves operating under a variety of conditions in a model left ventricle. It is found in the learning stage that the discriminant functions generated correctly classified almost all of the cases within the learning set. When applied to cases outside the learning set, including a recording of a clinically implanted valve, the functions correctly classify the valves. These preliminary results, for a limited number of valves, lead us to believe that the discriminant analysis of heart valve sounds is a promising noninvasive method for screening patients with implanted Bjork-Shiley convexo-concave valves.

Heart Valve Prosthesis↗
PubMed1990

Balloon dilatation of the stenosed aortic valve: how does it work? Why does it fail?

The hemodynamic changes that may occur in patients undergoing aortic balloon valvuloplasty were examined in the circulatory model. Four conclusions were reached. (1) Significant transvalvular pressure gradients appear only if the orifice is severely narrowed. (2) The magnitude of this gradient is highly flow dependent. (3) At critical narrowings, minute alterations in orifice size may induce most significant changes in the transvalvular gradient. (4) In low flow states significant gradients appear only if the stenosis is extreme. In patients with aortic stenosis, especially those with failing hearts and low cardiac output, the pressure gradient may be effectively decreased by minimal dilatation of the aortic orifice. These patients, however, remain in jeopardy because recurrent narrowing may cause a gradient incompatible with life.

Aortic Valve↗
PubMed1985

The Mitroflow pericardial heart valve. In vitro assessment over a range of sizes in aortic and mitral positions.

The performance of a three leaflet pericardial heart valve over a range of sizes in both the aortic and mitral position has been assessed in vitro. A pulse duplicator was used to test valves under conditions simulating normal and abnormal cardiac rhythms. The forward and regurgitant flow energy loss across each valve has been added to give an overall measure of valve hydrodynamic performance. This energy loss ranges from approximately 3% of the ventricle energy for large size mitral valves at low heart rates, to 22% for the smallest aortic valves operating at 120 beats per minute.

Aortic Valve↗
PubMed1984

New generation tissue valves. Their in vitro function in the mitral position.

The in vitro function of six tissue valves from four manufacturers has been assessed. One porcine bioprosthesis (Carpentier-Edwards supra-annular) and five pericardial valves (Edwards, Hancock, Ionescu-Shiley, Ionescu-Shiley low-profile, and Mitral Medical Mitroflow) were tested. Valve function was measured in a pulse duplicator simulating conditions of sinus rhythm (60, 80, and 120 beats/min and stroke volume 70 ml) and supraventricular tachycardia (200 beats/min and stroke volume 30 ml). Under each of these test conditions, mean transvalvular pressure, regurgitation, and transvalvular energy loss were determined and used to compare valve function. The porcine valve showed the largest mean transvalvular pressure during forward flow. The total energy loss of this valve, however, was not the largest for the valves tested. The total transvalvular energy loss ranged between 3% and 12% for all valves and conditions. For all valves, energy loss and regurgitation were greatest during simulated tachycardia.

Bioprosthesis↗
PubMed1983

The Björk-Shiley and Ionescu-Shiley heart valve prostheses. In vitro comparison of their hydrodynamic performance in the mitral position.

Shiley Scientific Inc., are now manufacturing six types of prosthetic heart valves. There are four different models of the Björk-Shiley and two versions of the Ionescu-Shiley pericardial heart valve. The Björk-Shiley valves are those with a spherical disc, 60 degrees and 70 degrees opening convexo-concave discs, and the latest monostrut model. The Ionescu-Shiley valves are the original titanium stent model and the latest Delrin stent low profile model. The hydrodynamic performance of these valves in the mitral position all having a tissue annulus diameter of 29 mm, has been measured. Tests were performed in a pulse duplicator simulating sinus rhythm at heart rates of 60, 80 and 120 beats per minute (BPM) with a stroke volume (SV) between 69 and 73 ml and at a heart rate of 200 BPM with SV between 27 and 34 ml. The latter test condition simulates a situation of supraventricular tachycardia. Mean transmitral pressure, regurgitation, and transmitral energy loss for each valve under each set of conditions were compared. All the Björk-Shiley valves were tested in two orientations with the major flow orifice oriented either anteriorly (A) or posteriorly (P). For all valves, it was found that the major contribution to the total transmitral energy loss, most apparent at 200 BPM, was caused by regurgitation and that at 60, 80 and 200 BPM, the forward flow phase contributed only a small amount to the total energy loss. The small intentional leakage across the Björk-Shiley valves is minor compared to closing regurgitation but is a major contributor to transmitral energy loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Output↗
PubMed1980

In vitro assessment of mitral valve prostheses.

The performance of five prosthetic mitral valves (Ionescu-Shiley, Hancock, Carpentier-Edwards, Starr-Edwards, and Björk-Shiley), all of the same nominal size (29 mm), has been assessed in a hydromechanical simulation of the left heart at three pulse rates. The mean and maximum transvalvular pressure differences, the observed and/or calculated area, and the energy loss for each valve were compared. It was found that each measure of performance rates the valves in the same order or merit, with the Ionescu-Shiley valve performing the best and the Hancock the worst among the valves tested.

Biomechanical Phenomena↗
PubMed1979

Construction and evaluation of a hydromechanical simulation facility for the assessment of mitral valve prostheses.

A hydromechanical simulator of the human left heart and systemic circulation system has been built for evaluating the dynamic actions of mitral valve prostheses. The facility includes a transparent and compliant model ventricle pumping into a simulation of the systemic circulation impedance. Transparent materials permit detailed high speed photography of valve action from the left ventricular aspect. This action has been analyzed by digitizing the valve open area and computing the variation of area with time. Additionally, pressures across and flows through the valves have been measured. Comparison has been made between the maximum observed valve open areas and the areas computed using the appropriate pressure and flow measurements substituted in clinically used equations.

Heart Valve Prosthesis↗
PubMedDate not supplied

The in vitro function of 19-mm bioprosthetic heart valves in the aortic position.

1. The new pericardial valves tested showed better hydrodynamic performance than the porcine and the St. Jude Medical mechanical valves. 2. The Ionescu-Shiley III valve exhibited the best hydrodynamic performance, with the least transvalvular energy loss. 3. Transvalvular energy loss shows that the major loss across the 19 mm valves occurs during the forward-flow phase. 4. Our data compares well with data from other in vitro tests performed using different test apparatus. 5. The pericardial bioprostheses, in particular, function well in the 19 mm size and therefore offer an alternative to the increased operative risk associated with valve over-sizing or orifice enlarging procedures. 6. The performance of the two porcine valves tested were comparable with each other.

Animals↗