PubMed Health⌕ Search

Biomedical subjects

S Gabbay

Publications and source records attributed to S Gabbay.

45 records · Page 3Linked to original sources
PubMed1978

In vitro hydrodynamic comparison of mitral valve prostheses at high flow rates.

A pulse duplicator system for evaluating the hemodynamic performance of mitral prostheses is described. Under conditions stimulating normal resting physiology, all valves tested had measurable but acceptably small pressure drops. Under conditions simulating exercise, all were moderately to severely stenotic. Valves with nearly equal mounting diameters were compared. The Hancock, Beall, and Starr-Edwards valves (Group A) were found to be significantly more stenotic than the Björk-Shiley, Cutter-Cooley, Ionescu-Shiley, and Lillehei-Kaster valves (Group B). In the 29 to 30 mm. mounting diameter size at cardiac outputs of 5 and 9 L. per minute, Group A had average pressure drops of 3.2 and 10.5 mm. Hg and Group B, pressure drops of 1.6 and 5.3 mm. Hg, respectively. In the 24 to 26 mm. mounting diameter size, at cardiac outputs of 9 L. per minute, all the valves had critically large pressure drops (9 to 17.6 mm. Hg). The standard Gorlin formula is inappropriate for computing the orifice area of prosthetic valves. The discharge coefficient for a valve (a measure of how well the valve uses its primary flow area) and a performance index (a measure of how well the valve uses its mounting area) have been computed from a knowledge of the orifice size, without the necessity of assuming a value for the discharge coefficient required by the Gorlin formula. The biological valves (Hancock and Ionescu-Shiley) provide an efficient orifice for fluid flow at the free leaflet margins and have large discharge coefficients. On the basis of the fluid dynamic equation of motion, steady flow, root mean square (RMS) flow, and peak flow, combined with the appropriate transvalvular gradients, were all shown to yield equally accurate characterizations of valvular hydrodynamic performance. Mean flow, unfortunately the only value obtainable clinically, yielded effective orifice areas 10 percent smaller than either of the other three flow values.

Bioprosthesis↗
PubMedDate not supplied

A system for in-vitro characterization of heart valve bioprostheses under accelerated fatigue conditions and under physiologic conditions.

An accelerated fatigue testing system and a pulse duplicator (heart simulator) were used in a set-up in which pressure differences and pulsatile flow rates across prosthetic heart valves, as well as machine rates, could be measured using a real-time on-line data-acquisition system. With this information available, an immediate in-vitro characterization of the fluid dynamics of prosthetic heart valves could be obtained under both physiologic and accelerated conditions. In addition to the fatigue tester and the pulse duplicator, a signal conditioner, a DC amplifier, an analog-to-digital converter, and a digital microcomputer comprised the essential hardware. For the purpose of this study, special acquisition software was developed. By means of the same computational algorithms, all quantitative fluid dynamics data could be calculated using information from both the pulse duplicator and the fatigue tester, so that direct comparisons and correlations could be approached. Pressure difference-flow rate relationships for the two machines were comparable.

Bioprosthesis↗
PubMedDate not supplied

Reducing the variability in durability of heart valve bioprostheses. Key factor for future improvement.

Two observations concerning the Meadox unicusp bovine pericardial valve were presented. First, calcification has not been a major problem because of the relatively short implant durations (less than 5 years). The second observation was that thromboembolism was found to be practically nonexistent. The third observation was that the leaflets of certain valves that had been removed showed leaflet stretching, which resulted in excess stress in certain loci of the leaflet. The studies reported here showed that the bovine pericardial sac was distensible to various degrees. Strips from various sections of pericardium had a large spectrum of strain (5-45%), at very small stress levels (less than or equal to 4 g/mm2). Further, within any section the material was anisotropic, with strain differences of 25%. Finally, histologic studies of clinical grade Ionescu-Shiley bovine pericardial valves showed marked discrepancies in structure and staining characteristics, further documenting that this material is not homogeneous. New methods of tissue selection are mandatory and have been designed to improve uniformity and ultimately reduce the viability in performance in the clinical setting. This method can be applied to all pericardial valves.

Animals↗
PubMedDate not supplied

Degenerative changes in glutaraldehyde preserved pericardium used for the experimental replacement of anterior chordae of mitral valve.

Plastic repair of the mitral valve after rupture of the anterior chordae can only be performed when less that one third of the anterior leaflet has lost its chordal support. This experimental study was designed to examine a method for chordal replacement utilizing gluteraldehyde preserved pericardium (Bovine pericardium supplied by Hancock Laboratories). The correct length of the "new chorda" was determined by the use of anatomical rules. In applying these rules we adopted the hypothesis that the chordae were under tension throughout diastole. The anterior chordae were replaced in eight dogs. At the end of the procedure the valve was tested and found to be competent in every case. Two dogs died before restudy because of the development of bacterial endocarditis confirmed histologically. Five dogs were restudied four months to two years after chordal replacement. There was no evidence of mitral incompetence and the mean left atrial pressure was within the normal range in each of the five dogs restudied. Histological examination of the new chordae demonstrated both cartilage formation and calcification. Electron microscopy demonstrated excellent healing of both suture sites with ingrowth of native collagen fibres between the fibres of the preserved pericardium. We conclude that excellent haemodynamic results can be obtained after chordal replacement and are maintained in spite of degenerative changes. Early calcification is known to occur in biological materials implanted in dogs and the use of this technique in man will be determined by the specific biological environment.

Animals↗
PubMedDate not supplied

Comparative in-vitro fluid dynamics characterization of heart valve bioprostheses under accelerated fatigue conditions and under physiologic conditions.

An accelerated fatigue testing system and a pulse duplicator (heart simulator) were used to evaluate the fluid dynamics characteristics of 12 cardiac bioprostheses. Pressure differences and pulsatile flow rates across the valves, as well as machine rates, were measured using a real-time on-line data-acquisition system. All other valve hydrodynamic parameters were internally calculated. For the same pressure difference, the pulsatile flow rate was higher at higher pulse rates. Regurgitation fraction values were higher for valves tested at higher speeds. Closing volumes, however, remained fairly constant. Mean transvalvular pressure difference (delta p) and root mean square pulsatile flow rate (QRMS) under accelerated testing conditions were related according to the particular case of a parabolic regression through the origin of the form (type 1), delta p = Co Q2RMS. Prosthetic valves tested in the fatigue tester presented in general a more effective area for flow than did valves tested in the pulse duplicator. Calculated discharge coefficients and performance indexes were accordingly higher. In both testing devices pericardial valves had higher effective orifice areas, discharge coefficients, and performance indexes than did porcine xenografts, and large valves performed more efficiently than small valves. Differences among regression coefficients for the same valves tested in both machines appeared to be significant in 100% of the cases. There were differences in the degrees of stenosis among valves tested in the pulse duplicator and in the fatigue tester. Understanding of fluid dynamics data obtained for undamaged valves at accelerated speeds and their relation to data obtained at physiologic speeds permitted the detection and quantification of rupture and malfunctioning of these valves without removing them from the fatigue tester.

Bioprosthesis↗