John Kennedy

Infective endocarditis in drug addicts. Experiences with medical and surgical treatment.

Isolated tricuspid valvular endocarditis is no longer rare, and its increasing incidence has paralleled the rise in heroin addiction. In the period between December, 1969 and December, 1971, 16 episodes of bacterial endocarditis occurred in 13 individual drug abusers at the Ben Taub General Hospital, Houston. The tricuspid valve (TV) was involved in all cases. Two patients required surgery during the acute infection; one underwent total excision of the TV without replacement, and one received aortic and TV prostheses because of progressive heart failure. Antibiotic therapy was individualized and guided by tube dilution sensitivities and serum bactericidal levels. In view of the excellent response to antibiotic therapy, surgery for infected prosthetic or natural valves is presently reserved for those patients with progressive cardiac failure or infections unresponsive to medical therapy.

Arterial baroreceptor responses to intraaortic balloon assistance

Abstract Alteration in arterial baroreceptor output (BRO) by intraaortic balloon assistance (IABA) was studied in acute experiments in normal dogs. Baroreceptor impulses originating in the aortic arch and in the carotid sinus were recorded. Without balloon assistance a single BRO volley accompanies each pulse wave. IABA produced two sharply delineated BRO volleys, one caused by left ventricular ejection and the other by diastolic pressure augmentation. Although BRO during cardiac systole fell, the addition of a second BRO volley during balloon inflation in diastole led to a net increase in BRO. The magnitude of BRO in each phase responded to changes in balloon inflation pressure and in timing of events. As expected from the known rate sensitivity of baroreceptors, the electroneurographic wave form correlated poorly with simultaneous pressure wave forms. When recorded simultaneously, BRO from aortic arch and carotid sinus baroreceptors responded similarly to IABA. The marked alterations of BRO observed in this study emphasize the need to consider system factors in the design and operation of mechanical circulatory devices; induced neurohumoral responses are likely to contribute significantly to the final therapeutic result.

Criteria for selection of patients for mechanical circulatory support.

Abstract The experience with 36 patients referred for possible mechanical circulatory assistance is reviewed. The criterion for assisted circulation in the 32 patients so treated was either cardiac arrest or a decreasing cardiac output, estimated by the indicator-dilution technique or inferred from a progressively increasing arteriovenous oxygen difference, in spite of vigorous supportive treatment. Although at present the heart-lung machine is the only method of wide clinical applicability, other promising devices are undergoing limited clinical trial. It will be necessary to identify mechanisms of preterminal cardiac failure and to select a method appropriate to the physiologic abnormality.

Stress Analysis of Normal Human Aortic Valve Leaflets during Diastole

Geometry of the normal human aortic valve leaflets during diastole were measured carefully by several different techniques. It was found that each of the three semilunar valve leaflets can be closely approximated by two principal radii of curvature with a limited range of subtending angles. Membrane theory is applied to analyze the stress distribution in the valve leaflets. The computed results are presented to cover ranges of the subtending angle

Use of a paracorporeal left ventricular bypass pump in experimental heart failure

tH1 between 180 and 230°, for subtending angle

Neointimas cultured in vitro for circulatory assist devices: I-Comparison of cultured cells derived from autologous tissues of various organs☆☆☆

tH2 between 70 and 260°, and for radii of curvature ratio R2/R1 between 0.6 and 0.9. An alternative method applying the theory of thin shells is also comprehensively discussed. Since the method involves extremely complicated computation procedures, and yet the actual thickness of the valve leaflets is so thin that they behave more like membranes than shells, no effort was made to compare the two methods numerically.

Mechanical and histological study of aortic valve tissue from a patient with Marfan's disease

Abstract Pneumatically powered Baylor-Rice diaphragm pumps designed for paracorporeal left ventricular bypass were studied in a mock circulatory system, and the modified swirl model exhibited the most desirable flow characteristics. This pump, lined with Dacron velour and incorporating cageless hollow metallic inflow and outflow ball valves, was attached to exteriorized connectors sutured to the left atrium and descending thoracic aorta in 15 healthy calves and 15 calves with cardiac decompensation as a result of experimentally induced mitral stenosis, mitral insufficiency, aortic stenosis or coronary artery insufficiency. Relatively few hemodynamic changes were detected in healthy calves during chronic left ventricular bypass pumping. Mean aortic pressure, mean left coronary arterial flow, mean left renal arterial flow and heart rate did not change; however, the pulsatile contours of these pressure and flow measurements were altered as one would expect with pump ejection. Mean left atrial and pulmonary arterial pressures decreased slightly and effective cardiac output increased slightly with pumping. Significant hemodynamic changes occurred during left heart bypass in the animals with heart failure. Left ventricular bypass pumping caused marked reductions in left atrial, pulmonary arterial and left ventricular end-diastolic pressures, and it increased cardiac output and left coronary arterial flow.

Effects of the carotid sinus reflex upon coronary vessel tone.

Abstract In order to develop an antithrombogenic surface for cardiovascular prostheses, neointimas were produced from various autologous tissues on velour-lined and flat prosthetic surfaces. Twenty-four mongrel dogs and six calves were used and three modalities of tissue culture techniques, i.e. explant culture, subculture, and direct trypsinization followed by in vitro culture, were applied. It was found that good neointimas can be made in vitro from autologous skeletal muscle, vein, omentum and granulation tissue on velour-lined prostheses. For the silicone rubber prosthesis with flat surface, the omentum was the only usable tissue to produce a living cell lining in vitro because of easy procurement, short preparation time, formation of uniform and thin cell layers, and least incidence of bacterial contamination.

Progress toward an Orthotopic Cardiac Prosthesis

A comparison between a normal and a Marfans disease aortic valve has been attempted in terms of their tissue stress-strain characteristics and their histology. The diseased valve tissue was found to be more compliant by an order of magnitude than the normal valve, which is related to the disorientation of its collagen fibers, and the proliferation of mucopolysaccharides.

Analysis of a variable volume intra-aortic balloon pump in a mock circulatory system

Abstract 1. 1. The authors have investigated the effects of the stimulation of dogs carotid sinus on coronary flow in an open-loop experiment where aortic pressure and heart rate were kept constant. 2. 2. While determination of myocardial oxygen consumption demonstrates that the metabolic state of the myocardium was unaltered by the procedure, there was a significant decrease in the coronary resistance (p 3. 3. Dependence of coronary vessels upon carotid sinus perfusion pressure was similarly demonstrated during cardiopulmonary bypass.