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Biomedical subjects

A J Bryan

Publications and source records attributed to A J Bryan.

At least 55 records · Page 3Linked to original sources
PubMed1997

Changes in myocardial concentration of glutamate and aspartate during coronary artery surgery.

Myocardial ischemic arrest, using a cold crystalloid cardioplegic solution, decreases intracellular concentrations of glutamate (from 6.2 +/- 0.5 to 4.5 +/- 0.45 micromol/g wet weight, n = 19, P < 0.05) and ATP (from 3.0 +/- 0.4 to 1.9 +/- 0.3 micromol/g wet weight, n = 9, P < 0.05) but not aspartate. After 20 min of normothermic reperfusion, the fall in glutamate and ATP was maintained (4.5 +/- 0.52 and 2.0 +/- 0.2 micromol/g wet weight, respectively), and there was a fall in aspartate (from 1.32 +/- 0.12 to 0.9 +/- 0.1 micromol/g wet weight). Myocardial arrest with cold blood cardioplegic solution did not cause a significant fall in tissue ATP, glutamate, or aspartate. However, after reperfusion all three fell significantly. With the exception of a fall in tissue valine during ischemia with cold crystalloid cardioplegic solution and a rise in alanine during ischemia with cold blood cardioplegic solution, there were no significant changes in tissue alanine, valine, leucine, or isoleucine during ischemia or after reperfusion using crystalloid or blood cardioplegic solutions. This work documents the changes in the intracellular concentrations of important metabolites in the hearts of patients undergoing coronary artery surgery using different myocardial protection techniques.

Adenosine Triphosphate↗
PubMed1997

Hemodynamics of St. Jude Medical prostheses in the small aortic root: in vivo studies using dobutamine Doppler echocardiography.

BACKGROUND AND AIMS OF THE STUDY: The well known correlation between prosthetic valve orifice area and transvalvular pressure drop has raised concerns about the presence of significant residual gradients when only a small-sized prosthesis can be implanted, particularly in patients with a large body surface area. The aim of this study was to study the hemodynamic performance of small-size St. Jude Medical aortic prostheses using dobutamine echocardiography. METHODS: Fifteen patients (14 females, one male, of mean age 67 years) who had undergone aortic valve replacement with size 19 mm St. Jude Medical prostheses at a mean of 19 +/- 8 (SD) months previously were studied. Dobutamine infusion was started at a rate of 5 micrograms/kg/min and increased to 10 and subsequently to 20 micrograms/kg/min at 15-min intervals. Pulsed and continuous-wave Doppler studies were performed at rest and at the end of each stage. Effective orifice area (EOA) and mean gradient across each prosthesis were calculated, and cardiac output (CO) was determined by Doppler measurement of flow in the left ventricular outflow tract. RESULTS: Dobutamine-stress increased heart rate and cardiac output by 57% and 86% respectively (both p < 0.0005), and mean transvalvular gradient increased from 22.0 +/- 4.9 mmHg at rest to 41.9 +/- 9 mmHg at maximum stress (p < 0.0001). Regression modeling analyses demonstrated that maximum stress gradient was independent of all variables except resting gradient (p = 0.0068). Body surface areas had no effect on the changes in cardiac output, effective orifice area or transprosthetic gradient at maximum stress. CONCLUSIONS: These data demonstrate that the size 19 mm St. Jude Medical prosthesis exhibits favorable hemodynamic performance. Transvalvular gradients remained within a clinically acceptable range, both at rest and under stress conditions. Moreover, in the patient population studied, overall hemodynamic performance indicates that with St. Jude Medical aortic valves, patient-prosthesis mismatch is unlikely to be a problem of clinical importance.

Adult↗
PubMed1996

Experimental models of accelerated atherosclerosis syndromes.

The processes of angioplasty restenosis, vein graft failure, and transplant atherosclerosis, collectively termed 'syndromes of accelerated atherosclerosis', have been the focus of significant clinical and experimental research. Limitations of clinical studies have forced emphasis onto experimental animal models for the purpose of determining pathophysiology and evaluation of potential therapeutic strategies. However, the apparent failure of many in vivo animal models to predict interventional outcome in humans has raised doubt over their suitability as models of these pathophysiological states. Similar criticism has befallen the use of in vitro techniques for elucidating pathophysiology of the cellular elements. An awareness of the shortcomings of the various experimental models in use would therefore seem prerequisite both to a more critical evaluation of data generated from their use, and to the development of truly effective therapeutic strategies for humans.

Animals↗
PubMed1996

Influence of external stent size on early medial and neointimal thickening in a pig model of saphenous vein bypass grafting.

BACKGROUND: Late saphenous vein graft failure results from intimal and medial thickening due to migration and proliferation of vascular smooth muscle cells and superimposed atheroma. These changes may represent an adaptation by the vein to its insertion into the arterial system. Using a porcine model of arteriovenous bypass grafting, we recently demonstrated that supporting the graft with a nonrestrictive external Dacron velour stent significantly reduced intimal hyperplasia and total wall thickness. In the present study, we investigated the influence of different external stent sizes on graft wall dimensions and cell proliferation. METHODS AND RESULTS: Three stent sizes were tested: mildly restrictive, nonrestrictive, and oversized (5, 6, and 8 mm in diameter, respectively). Four weeks after grafting, total wall thickness was decreased 40% by 5-mm stents (P = .02), 66% by 6-mm stents (P = .0004), and 81% by 8-mm stents (P = .02 versus unstented grafts). Neointimal thickness was reduced almost 62% by 6-mm and 72% by 8-mm stents (both P = .01) but not by 5-mm stents. As a result, the encroachment of the intima into the lumen was reduced approximately 70% by 6- or 8-mm stents (P = .02 and P = .01 versus unstented grafts, respectively). Both neointimal and medial cell proliferation were significantly reduced by all three stents compared with unstented grafts. CONCLUSIONS: External stenting of saphenous vein bypass grafts reduces early intimal and medial hyperplasia. Oversized stents give equally profound suppression of intimal thickening, obviating the need for precise size matching with the graft and greatly simplifying the surgical procedure.

Animals↗
PubMed1996

Effects of cardiopulmonary bypass temperature on pulmonary gas exchange after coronary artery operations.

BACKGROUND: Pulmonary dysfunction is one aspect of the postoperative morbidity associated with cardiopulmonary bypass. Normothermic systemic perfusion can result in shorter intubation times, which have been attributed to improved pulmonary gas exchange, but the influence of perfusion temperature on pulmonary gas exchange itself is not known. METHODS: Pulmonary gas exchange was assessed using alveolar-arterial oxygen pressure gradients in 45 patients undergoing routine coronary revascularization who were randomized to undergo cardiopulmonary bypass at 28 degrees C, 32 degrees C, or 37 degrees C. This was part of a more comprehensive study of the effects of temperature on bodily systems. The gradients were estimated preoperatively with the patients breathing air, again over a period between 2 and 4 hours postoperatively during mechanical ventilation with three different oxygen concentrations (30%, 40%, and 60%), and again 1 hour after extubation while breathing the same three oxygen concentrations. RESULTS: Preoperative alveolar-arterial oxygen pressure gradients on air were 24.4 +/- 8.2 mm Hg (mean +/- standard deviation) (28 degrees C), 24.5 +/- 20.4 mm Hg (32 degrees C), and 20.5 +/- 9.5 mm Hg (37 degrees C). Postoperatively, during ventilation and after rewarming, the gradients increased with the increase in inspired oxygen fraction concentrations (30% to 60%) from 67.1 +/- 12.0 mm Hg to 193.1 +/- 30.5 mm Hg (28 degrees C), from 76.4 +/- 20.6 mm Hg to 246.7 +/- 47.7 mm Hg (32 degrees C), and from 79.0 +/- 18.0 mm Hg to 222.9 +/- 40.5 mm Hg (37 degrees C), respectively. A similar pattern was noted 1 hour after extubation, when the gradients increased from 72.4 +/- 12.5 mm Hg to 256.6 +/- 26.5 mm Hg (28 degrees C), from 75.7 +/- 13.9 mm Hg to 252.7 +/- 38.3 mm Hg (32 degrees C), and from 69.1 +/- 19.3 mm Hg to 253.1 +/- 33.0 mm Hg (37 degrees C). There were no significant differences in alveolar-arterial oxygen pressure gradient between the three groups during ventilation or after extubation. CONCLUSIONS: Cardiopulmonary bypass perfusion temperature does not influence alveolar-arterial oxygen pressure gradients in the first 12 hours after routine coronary artery bypass grafting in patients with uncompromised pulmonary and left ventricular function.

Carbon Dioxide↗
PubMed1996

Reduced prostacyclin and increased leukotriene B4 synthesis in porcine venous-arterial grafts.

BACKGROUND: Migration and proliferation of vascular smooth muscle cells in the intima and superimposed atheroma are the main changes underlying late failure of saphenous vein bypass grafts. There is evidence that these events are partly modulated by complex interactions between inhibitors of vascular smooth muscle cell proliferation, such as prostacyclin (PGI2), and mitogens, such as leukotriene B4 (LTB4). Because the relative balance between these eicosanoids may play a role in vein graft failure, the synthesis of PGI2 and LTB4 was measured in porcine saphenous vein-carotid artery grafts 4 weeks after implantation and compared with ungrafted vein and common carotid artery from the same animal. METHODS: Vessels were cut into 2-mm squares and preincubated in Dulbecco's minimum essential medium for 4 hours at 37 degrees C. Tissues were then further incubated with Dulbecco's minimum essential medium containing a range of concentrations of noradrenaline, arachidonate, and calcium ionophore A23187. Release of PGI2 and LTB4 into the supernatant was then assessed by radioimmunoassay. RESULTS: In response to all stimulators, PGI2 release was markedly diminished in vein grafts compared with ungrafted saphenous veins and carotid arteries. The patterns of responses were similar in each vessel type. In contrast, LTB4 release was significantly enhanced in vein grafts compared to ungrafted saphenous veins and carotid arteries. CONCLUSIONS: These data indicate that there is a down-regulation of cyclooxygenase or PGI2 synthase in porcine vein grafts, which may constitute a further phenotypic change that would augment the hyperplastic process. Local increases in LTB4 synthesis in the vein graft, which indicates an induction of lipoxygenase and LTB4 synthase enzymes (and possibly reflects release from leukocytes which have infiltrated the graft), may contribute to increased intimal proliferation by direct promitogenic effects on smooth muscle cells.

Animals↗
PubMed1996

Normothermic techniques during open heart operations.

There has been considerable interest in the use of normothermic techniques during cardiac operations, both as a means of myocardial protection and as a more physiologic environment for other organs during cardiopulmonary bypass. Although a limited number of uncontrolled studies have suggested superior clinical results compared with conventional hypothermic regimens, these claims have not been thoroughly investigated using randomized protocols. The limited available data suggest that the successful use of warm blood cardioplegia requires adequate delivery of the solution to all parts of the myocardium at optimal flow rates to maintain aerobic arrest, so those who advocate the use of normothermic arrest must pay particular attention to ensure that their myocardial protection is effective. The advantages of employing normothermic systemic perfusion in regard to factors such as improved hemodynamic performance and reduced blood loss postoperatively need to be balanced against concerns regarding the inadequacy of cerebral protection offered by this method.

Blood Coagulation↗
PubMed1996

The effects of cardiopulmonary bypass temperature on neuropsychologic outcome after coronary artery operations: a prospective randomized trial.

UNLABELLED: The effect of systemic perfusion temperature on postoperative cognitive function was investigated in 96 adult patients undergoing elective coronary revascularization with cardiopulmonary bypass at 28 degrees C, 32 degrees C, or 37 degrees C. Neuropsychologic performance was assessed 1 day before the operation and 6 weeks after the operation. Five tests were adapted from the Wechsler Adult Intelligence Scale and two from the Wechsler Memory Scale. RESULTS: No patients had major neurologic complications. Ninety-three patients completed the five Wechsler Adult Intelligence Scale tests, but only 70 went on to complete the Wechsler Memory Scale tests as well. In these, there was an effect of cardiopulmonary bypass temperature on the number of neuropsychologic tests in which there was a preoperative to postoperative deterioration (p = 0.021), the number with bypass at 37 degrees C being significantly greater than the number with bypass at 32 degrees C (p = 0.015). Subsidiary analyses using a multivariate linear model examined the effect of cardiopulmonary bypass temperature on the magnitude of change, with or without allowing for other possible confounding influences. There was an adverse effect of normothermic (37 degrees C) versus moderately hypothermic (32 degrees C) perfusion---more convincingly displayed in the analyses of all seven scores rather than just the Wechsler Adult Intelligence Scale scores. Further cooling to 28 degrees C conferred no additional benefit in terms of cognitive function. The importance of the deterioration is open to question.

Body Temperature↗
PubMed1996

External stenting reduces early medial and neointimal thickening in a pig model of arteriovenous bypass grafting.

The long-term clinical success of coronary artery bypass grafting with autologous saphenous vein is limited by progressive medial and neointimal thickening in the graft and superimposed atherosclerosis. We sought to reduce wall thickening by applying an external stent to experimental grafts in pigs. The diameter of the stent was designed to allow unrestricted initial expansion of the vein in response to arterial pressure and the stent material was highly porous so as to minimize adventitial [correction of advential] disruption. Four weeks after graft implantation, stented grafts had a larger lumen (11.2 +/- 6.2 [standard deviation] mm2 versus 7.6 +/- 3.4 mm2, p < 0.05, n = 9) and an almost fourfold thinner media (0.14 +/- 0.08 versus 0.49 +/- 0.22, p < 0.001) and neointima (0.10 +/- 0.07 versus 0.35 +/- 0.24, p < 0.001) than paired unstented grafts in the same animals. Cell proliferation was also greatly reduced by stenting in the neointimal and medial layers. The stenting procedure devised here is readily applicable to clinical coronary bypass grafts.

Animals↗
PubMed1996

Comparison of hemodynamic performances of St. Jude Medical and CarboMedics 21 mm aortic prostheses by means of dobutamine stress echocardiography.

Dobutamine stress Doppler echocardiography was used to compare the hemodynamic performance of two small aortic bileaflet prostheses. Nineteen patients (14 female, mean age 64 years) who had undergone aortic valve replacement with 21 mm bileaflet valve prostheses (St. Jude Medical valve, n = 9, or CarboMedics valve, n = 10) were studied. Dobutamine infusion was started at a rate of 5 micrograms.kg-1.min-1 and increased to 10 and 20 micrograms.kg-1.min-1 at 15-minute intervals. Under maximum stress, heart rate and cardiac output increased by 70% and 120%, respectively, and mean arterial blood pressure decreased by 9%. Pulsed-wave and continuous-wave Doppler studies were performed at rest and at the end of each stage. Velocity ratio, effective orifice area, performance index, and discharge coefficient of the valve were calculated, and peak and mean velocities and pressure drops across the prostheses were measured. Dobutamine infusion produced similar increases in cardiac output in all patients. Effective orifice areas, discharge coefficients, and performance indexes were comparable for the two valve groups both at rest and maximum stress. Transvalvular velocities and pressure drops were also similar in the two valve groups. Transvalvular pressure drops were also comparable in patients with large body surface area. Dobutamine stress echocardiography is useful in the evaluation of the hemodynamic performance of prosthetic heart valves. St. Jude Medical and CarboMedics 21 mm prostheses have equally favorable hemodynamic performances in most patients under conditions of high cardiac output.

Aged↗
PubMed1995

Transesophageal echocardiography and adult cardiac operations.

Transesophageal echocardiography (TEE) now is used widely as a monitoring technique during and after cardiac operations. Widespread adoption of the technique has provided a wealth of new information. This review analyzes the influence of TEE on the routine conduct of cardiac operations and on surgical decision making in specific areas. Its use in routine hemodynamic monitoring and problem solving, both intraoperatively and postoperatively, is discussed. Transesophageal echocardiography has a particular role in valve operations, in guiding and assessing the immediate results of mitral valve repair. It also has found application in the grading and operative management of the severely atheromatous aorta, the diagnosis and management of aortic dissection, and other aspects of surgery of the thoracic aorta. In addition, management in specialized areas, such as cardiopulmonary transplantation and the insertion and monitoring of ventricular assist devices, have also been helped by the information provided by TEE.

Adult↗
PubMed1995

Evaluation of the hemodynamic performance of small CarboMedics aortic prostheses using dobutamine-stress Doppler echocardiography.

BACKGROUND: The well-known correlation between prosthetic valve orifice area and transvalvular gradients has raised concerns about the presence of significant residual gradients when the size of the prosthesis that can be implanted is limited by the presence of a small aortic annulus. METHODS: Dobutamine-stress Doppler echocardiography was used to evaluate the hemodynamic performance of small CarboMedics aortic prostheses (19 mm and 21 mm) in 18 patients (16 women; mean age, 64 years) who had undergone aortic valve replacement 23.5 +/- 19 months (standard deviation) previously. Dobutamine infusion was started at a rate of 5 micrograms.kg-1.min-2 and increased to 10 and 20 micrograms.kg-1.min-2 at 15-minute intervals. Pulsed and continuous wave Doppler studies were performed at rest and at the end of each stage. Effective orifice area, performance index, and discharge coefficient of both valves were calculated, and peak and mean velocity and pressure drop across the prostheses were measured. RESULTS: Heart rate and cardiac output increased by 74% and 94%, respectively, and mean arterial blood pressure decreased by 9% at maximum stress. Effective orifice area, discharge coefficient, and performance index were comparable in both valve sizes at rest and maximum stress. Also, there was no significant difference in mean transvalvular pressure drop (gradient) for 19-mm and 21-mm prostheses at rest (8.1 +/- 8.4 and 4.8 +/- 3.8 mm Hg) or maximum stress (15.1 +/- 14.2 and 8.8 +/- 5.8 mm Hg, respectively). No significant correlation could be demonstrated between transvalvular pressure drop and patient's body surface area. CONCLUSIONS: These data show that 19-mm and 21-mm CarboMedics aortic prostheses exhibit equally favorable hemodynamic performance with minimal pressure gradient, both at rest and under stress conditions.

Aged↗