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Biomedical subjects

S Gabbay

Publications and source records attributed to S Gabbay.

At least 37 records · Page 2Linked to original sources
PubMed1984

Haemodynamics and durability of mitral bioprostheses--an in vitro study.

The haemodynamic characteristics and durability of mitral bioprostheses were evaluated and compared in vitro in a pulse duplicator and in a fatigue test system. Porcine xenografts were shown to be the most stenotic of all bioprostheses, studied at rates simulating both rest and exercise; on the other hand the new generation of biological valves showed a clear improvement in haemodynamics compared with the standard porcine and pericardial prostheses so far used clinically. Durability tests performed at a rate of 1600 to 1800 beats per minute and with a closing pressure ranging from 80 to 100 mmHg showed that the Ionescu-Shiley and Edwards pericardial xenografts last significantly longer than the Hancock and Carpentier Edwards porcine valves and Hancock pericardial bioprosthesis. Correlation between the mode of failure of pericardial and porcine valves in vitro and in vivo clearly demonstrates that a major role in valve failure is played by mechanical stress. This can be either a consequence of the continuous trauma sustained by the tissue hitting against the bare dacron cloth of the sewing ring during the movements of the cusps. or a result of fatigue occurring and the bending points of the leaflets. The results of this study underline the importance of a continued in vitro evaluation of both haemodynamics and durability of bioprostheses, since some of the pericardial valves which had the best haemodynamic performance showed the worst resistance to fatigue-induced failure. A careful selection of the tissue, modification of the stent design and avoidance of a dacron covered frame are suggested to improve long-term durability of biological prostheses.

Bioprosthesis↗
PubMed1984

Acclimation of the euryhaline toad Bufo viridis to hyperosmotic solution (NaCl, urea and mannitol).

Bufo viridis were acclimated to hyperosmotic solutions of NaCl, urea or mannitol. The toads could not be acclimated to mannitol solutions of osmotic strength higher than 300 mosmol kg-1 H2O, but could be acclimated easily to NaCl and urea higher than 500 mosmol kg-1 H2O. Water uptake diminished under mannitol acclimation while the apparent osmotic permeability under NaCl and urea acclimation increased. Urea and sodium influx across the isolated skin changed inversely upon hyperosmotic acclimation, but they did not seem to depend on one another. The adaptational advantages of the observed changes are discussed.

Adaptation, Physiological↗
PubMed1984

Immunological reactivity to a new glutaraldehyde tanned bovine pericardial heart valve.

The presence of pericardial specific antibodies directed against prosthetic bovine tissue heart valves was quantified by use of an indirect immunofluorescence technique. Serum samples containing antibodies displayed bright fluorescence when tagged with a secondary layer conjugated to FITC. Specific antibody production was undetectable in dogs or sheep who had undergone heart valve replacement (mitral or tricuspid) with a new unicusp prosthesis (Meadox Medicals Inc., NJ), as long as 17 mos following implantation. Similarly, anti-pericardial IgG was not detected in the serum of patients grafted with an analogous commercially available tissue heart valve, although in one patient the presence of low affinity IgM was suggested. This study documents the low immunological reactivity of this new tissue heart valve. Clinically valvular dysfunction due to an immunological response is not expected.

Animals↗
PubMed1984

Long-term follow-up of the Ionescu-Shiley mitral pericardial xenograft.

In a group of 40 patients discharged from the hospital after mitral valve replacement with an Ionescu-Shiley pericardial xenograft from January, 1977, to December, 1980, seven instances of valve failure occurred. This unprecedented incidence of bioprosthetic dysfunction after mitral valve replacement with the Ionescu-Shiley pericardial xenograft led us to update the follow-up of our patients receiving this valve in the mitral position. The results of our survey showed, at 6 years postoperatively, an actuarial survival rate of 72%, an actuarial probability of being free from emboli of 62%, and an actuarial freedom from prosthetic failure of 60%. The explanted valves showed complete absence of the neoendothelial lining of the Dacron-covered frame and lesions resembling those observed in Ionescu-Shiley pericardial xenografts removed from our fatigue test system after a mean of 29 +/- 17 X 10(6) cycles. This similarity prompted a classification of tears occurring in the mitral Ionescu-Shiley pericardial xenograft, which is of extreme importance, since the clinical presentation and outcome of patients with a failing valve differs according to the type of rupture. The lesions of the cusp observed in clinical specimens were possibly related to the continuous trauma of the tissue against the bare Dacron cloth during closure of the valve. It is concluded that (1) actual durability and thrombogenicity of the Ionescu-Shiley pericardial xenograft in the mitral position needs to be carefully reassessed, (2) close follow-up of such patients by clinical and two-dimensional echocardiographic evaluation is advisable after the third postoperative year, and (3) failure of the mitral Ionescu-Shiley pericardial xenograft may occur suddenly, and awareness of this complication is the clue to prompt recognition and treatment of such patients.

Adult↗
PubMed1984

Calcification of implanted xenograft pericardium. Influence of site and function.

In a series of 23 dogs, glutaraldehyde-fixed xenograft pericardium was implanted as a left atrial wall patch (Group I, 11 dogs), as a substitute for the mitral valve chordae (Group II, 12 dogs), and as an external pericardial patch (Group III, five dogs, in which one of the two former procedures was associated). All dogs of Group I survived and were put to death after 12 months. The atrial patch appeared thickened and shrunken in all, with intense fibrous reaction, calcification, and even bone formation. The structural changes were minimal in the external aspect of the patch, not in contact with the host's endocardium and blood. Eight dogs of Group II survived from 7 months to 3 years. In all, the pericardial chordae were thickened and calcified with good healing at the suture lines; that their original length was retained, however, allowed for good valve function. In the dogs of Group III the pericardial substitute appeared well preserved after 12 months, not calcified, and without noteworthy degenerative changes. Minimal or absent epicardial adhesions were noted. We conclude that (1) the tendency for xenograft pericardial tissue to calcify is strongly influenced by the site of implantation and function and by contact with host blood and endocardium; (2) heterologous pericardium may be considered suitable for closure of pericardial defects after open cardiac operations, and (3) studies on calcification of biological tissue should be carried out by long-term evaluation of such tissues inside the heart.

Animals↗
PubMed1984

Fatigue-induced failure of the Ionescu-Shiley pericardial xenograft in the mitral position. In vivo and in vitro correlation and a proposed classification.

Four patients had signs of primary bioprosthetic dysfunction within the fourth postoperative year after mitral valve replacement with an Ionescu-Shiley pericardial xenograft; they represent approximately 9% of patients with Ionescu-Shiley pericardial xenograft mitral valves followed up for more than 3 years at our institution. Pathological investigation showed severe incompetence of all explanted valves due to cusp tears and lacerations. Histologic study of the pericardial tissue disclosed mild to moderate collagen degeneration, without infection or calcification. Neoendothelial formation on the Dacron cloth of the sewing ring was either absent or minimal. The high incidence of valvular incompetence prompted us to try to establish a correlation between the in vivo and in vitro modes of failure of the Ionescu-Shiley pericardial xenograft. For this purpose, 10 unimplanted Ionescu-Shiley pericardial xenograft valves were tested in a fatigue test system. Severe fatigue-induced lesions occurred in this group after an average of 29.09 +/- 17.26 X 10(6) cycles; initial failure could be recognized in six of them after an average of 16.94 +/- 20.12 X 10(6) cycles. Valves tested in the fatigue test system showed tears and lacerations similar to those noted in the Ionescu-Shiley pericardial xenografts obtained from the four patients (which were assumed to have functioned for more than 100 X 10(6) cycles in each case). Correlation between results of the fatigue testing and our clinical experience enabled us to recognize four types of tears which may occur in the Ionescu-Shiley pericardial xenograft. The results of this investigation showed the following: (1) Primary tissue failure of the Ionescu-Shiley pericardial xenograft may occur suddenly. (2) A classification of tears occurring in Ionescu-Shiley pericardial xenograft valves is useful since the clinical presentation of patients may differ according to type and location of the lesion. (3) In the manufacture of pericardial valves, particular care must be observed in selection of the tissue and in the frame design. (4) Improvement of the quality control is one of the clues to enhance durability of the Ionescu-Shiley pericardial xenograft.

Aged↗
PubMed1983

Reproducible replacement of elongated or ruptured mitral valve chordae.

Anatomical rules that make it possible to accurately replace mitral anterior cusp chordae tendineae with tanned xenograft pericardium are defined. Anterior and posterior cusp chordae were replaced with xenograft and autologous pericardium in 11 patients who had ruptured or elongated chordae. The xenograft occasionally became calcified; however, because it did not become elongated or shortened, competence was maintained for up to 3 years. Insufficiency was corrected, and the correction maintained for up to 4 months. Degenerative disease proved easier to treat than rheumatic disease. Two-dimensional echocardiography was a valuable aid in both preoperative planning and postoperative evaluation.

Adult↗
PubMed1982

Physiologic mechanisms in aortic insufficiency. I. The effect of changing heart rate on flow dynamics. II. Determinants of Austin Flint murmur.

We studied the dynamic changes in mitral flow patterns and in mitral valve motion before and after producing acute, reversible aortic insufficiency (AI) in nine open-chest dogs. Phasic mitral flow, the mitral valve echocardiogram, and intracardiac phonocardiogram and other hemodynamic variables were measured. During moderate AI (mean regurgitant fraction 52 +/- 5%) (+/- SD), the antegrade filling volume decreased from 31 +/- 7 to 24 +/- 6 ml (p less than 0.01), but the peak protodiastolic mitral flow rate increased from 139 +/- 37 to 157 +/- 42 ml/sec (p less than 0.01), reflecting the shift of a larger fraction of total mitral filling volume to early diastole. In six dogs, atrial pacing was used to examine the hemodynamic effects of tachycardia. Increasing the heart rate from 90 to 120 beats/min increased cardiac output from 2.64 +/- 0.56 to 3.3 +/- 0.831/min (p less than 0.05) and decreased left atrial pressure from 24 +/- 8 to 17 +/- 7 mm Hg (p less than 0.05). Increasing heart rate to 150 beats/min compromised mitral filling, reduced cardiac output and increased left atrial pressure. Moderate tachycardia improves cardiac performance in AI by reducing regurgitant volume, without significantly reducing transmitral filling volume. The mitral valve echocardiogram showed only a small decrease in cusp opening amplitude during AI. A low-pitched left ventricular inflow tract murmur was recorded in protodiastole and corresponded in time to the rapidly increasing mitral flow. We conclude that the major determinant of the turbulence responsible for the creation of the austin flint murmur is the antegrade mitral flow stream and its mixing with the retrograde aortic flow.

Animals↗
PubMed1982

Pulmonary venous-bronchial fistula following left atrial pressure line insertion: iatrogenic cause of air embolism following cardiac surgery.

A 65-year-old patient sustained massive air embolism after the needle used for left atrial pressure line insertion punctured the posterior wall of the superior pulmonary vein, entering the middle lobe bronchus and causing a pulmonary venous-bronchus fistula. This is an apparently heretofore unrecognized potential cause of massive air embolism following cardiac surgery.

Aged↗
PubMed1979

Mechanism of reduction of mitral regurgitation with vasodilator therapy.

Acute mitral regurgitation was produced in six open chest dogs by excising a portion of the anterior valve leaflet. Electromagnetic flow probes were placed in the left atrium around the mitral anulus and in the ascending aorta to determine phasic left ventricular filling volume, regurgitant volume and stroke volume. The systolic pressure gradient was calculated from simultaneously measured high fidelity left atrial and left ventricular pressures. The effective mitral regurgitant orifice area was calculated from Gorlin's hydraulic equation. Infusion of nitroprusside resulted in a significant reduction in mitral regurgitation. No significant change occurred in the systolic pressure gradient between the left ventricle and the left atrium because both peak left ventricular pressure and left atrial pressure were reduced. The reduction of mitral regurgitation was largely due to reduction in the size of the mitral regurgitant orifice. Reduction of ventricular volume rather than the traditional concept of reduction of impedance of left ventricular ejection may explain the effects of vasodilators in reducing mitral regurgitation.

Animals↗
PubMed1979

Dynamic aspects of acute mitral regurgitation: effects of ventricular volume, pressure and contractility on the effective regurgitant orifice area.

The dynamics of acute mitral regurgitation were studied in six open-chest dogs in whom a portion of the anterior leaflet was excised. Phasic mitral and aortic flows were measured electromagnetically and left ventricular filling volume, regurgitant volume (RV) and forward stroke volume (SV) were calculated. The systolic pressure gradient (SPG) between the left ventricle (LV) and left atrium (LA) was obtained from high-fidelity pressure transducers. The effective mitral regurgitant orifice area (MRA) was calculated from the hydraulic equation of Gorlin. Volume infusion resulted in significant increases in both left atrial and left ventricular pressures; thus, the SPG was unchanged and the increase in RV was due primarily to the increase in MRA. Angiotensin infused to raise arterial pressure resulted in greater increments in left ventricular than left atrial pressure, so that SPG rose significantly. The increase in RV was due to increases in both MRA and SPG. Norepinephrine infusion increased systolic left ventricular pressure and SPG, while left ventricular end-diastolic pressure and left atrial pressure diminished. Despite a significant increase in SPG, RV did not increase, due to a substantial decrease in MRA. Thus, angiotensin and volume infusion induced a substantial increase in regurgitation due to the increase in MRA, while augmentation of contractility after norepinephrine infusion resulted in a decrease in regurgitation through reduction of MRA. These findings support the clinical view that maintaining a small LV with sustained myocardial contractility will reduce mitral regurgitation. Alternatively, left ventricular dilatation can enhance mitral regurgitation by increasing the effective regurgitant orifice independent of SPG.

Angiotensin II↗
PubMed1979

In vitro hydrodynamic comparison of mitral valve bioprostheses.

With the use of the pulse duplicator built in our laboratory, the hydrodynamic characteristics of three sizes of the four commercially available mitral bioprostheses, Hancock, Carpentier-Edwards, Angell-Shiley, and Ionescu-Shiley, were studied and compared. A wide range of performance was found: for example, during pulsatile testing, at peak flow of 15 1/min (corresonding to a normal resting cardiac output) transvalvular gradients varied from as high as 20 mm Hg (Angell-Shiley) to 5 mm Hg(Ionescu-Shiley) in the 25 mm mounting diameter size. Effective orifice areas (EOA) are significantly different in valves of the same mounting size, e.g., at peak flows of 20 1/min, the Ionescu-Shiley 25 provides an EOA of 1.7 cm2 while the Angell-Shiley provides only 1.17 cm2. The EOAs of all bioprostheses have been found to increase with increasing flow (e.g., from 10--30 1/min peak flow, the Hancock 25 changed from 1.25 cm2 to 1.50 cm2). The Gorlin formula, as constituted for calculating the area of stenotic mitral valves, is inappropriate for prosthetic valves. But the discharge coefficients of the bioprostheses have been found to be around 1 when the planimetered area of the open valve orifice is determined at a given flow. By using this discharge coefficient, the Gorlin formula will give an excellent estimate of the true orifice area of mitral bioprostheses.

Bioprosthesis↗
PubMed1979

Dynamic changes in the canine mitral regurgitant orifice area during ventricular ejection.

We designed this study to test the hypothesis that in acute mitral regurgitation the mitral regurgitant area (MRA) is a dynamic quantity which varies with the time variation of ventricular volume. Mitral insufficiency was created in five open-chest dogs in which a portion of the anterior leaflet was excised. Phasic aortic and mitral flows were measured electromagnetically, along with left atrial and ventricular pressures. Filling, regurgitant, and stroke volumes, and systolic pressure gradient were determined by digital methods. MRA was calculated from the fluid dynamic equation of motion to give the temporal mean and the instantaneous value at three instants of time and at the time of peak flow (when inertia is negligible). Mean regurgitant fraction was 42 +/- 12% with no indication of left ventricular failure due to volume overload. MRA decreased monotonically with time to 59% of its initial value and closely paralleled the decrease in ventricular volume during systole. In a control study using a tilting-disc prosthesis with a hole 5 mm in diameter in the occluder, the calculated MRA was time invariant and equal to the measured area for regurgitation. We conclude that in acute mitral regurgitation the MRA is a function of ventricular volume.

Animals↗