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Biomedical subjects

W G Austen

Publications and source records attributed to W G Austen.

At least 19 recordsLinked to original sources
PubMed1992

Postinfarct ventricular septal defect repair: effect of coronary artery bypass grafting.

Between June 1968 and April 1991, 75 patients who had undergone coronary angiography underwent repair of a postinfarction ventricular septal defect. Group 1 (n = 33) includes patients who had two- or three-vessel serious (> 75% narrowing) proximal coronary artery disease and underwent complete revascularization in addition to repair of the ventricular septal defect. Group 2 (n = 19) patients also had two- or three-vessel coronary artery disease but bypass grafting was not performed; only the ventricular defect was repaired. Group 3 (n = 23) patients had only single-vessel coronary artery disease that corresponded to the region of the infarct; they underwent ventricular septal defect repair only. Follow-up of hospital survivors was 96% complete at a mean of 86.2 months (range, 1 to 288 months). Hospital mortality after ventricular septal defect repair was 21.2% in the cohort with bypassed coronary artery disease (group 1), 26.3% in those with unbypassed disease (group 2), and 26.1% in those with only single-vessel coronary artery disease (group 3) (p = 0.88). With follow-up after 5 and 10 years, the actuarial survival was 72.2% +/- 8% and 47.8% +/- 10%, respectively, in the bypassed group, 29.2% +/- 11% and 0%, respectively, in the unbypassed group, and 52.2% +/- 10% and 36.5% +/- 11%, respectively, in the cohort with single-vessel disease. Bypassing associated coronary artery disease significantly increased long-term survival when compared with patients with unbypassed coronary artery disease (p = 0.0015).

Aged↗
PubMed1992

Ultra-pure polymerized bovine hemoglobin blood substitute: effects on the coronary circulation.

The effects of stroma-free hemoglobin (SFHgb) on the coronary circulation remain unclear. An intact canine model utilizing intracoronary adenosine to abolish the confounding effect of autoregulation was used to study maximal myocardial oxygen delivery during progressive hemodilution with polymerized bovine SFHgb. The circumflex coronary artery was instrumented with a flow probe, hydraulic constrictor, and proximal and distal catheters for adenosine infusion and distal pressure measurement, respectively. This preparation was used to generate diastolic coronary pressure-flow relations during maximal vasodilation. Maximal coronary conductance and maximal myocardial oxygen delivery were determined in two groups of 7 dogs each following hemodilution, first with 6% hetastarch (Control), followed by further hemodilution with ultra-pure, polymerized, bovine SFHgb. After hemodilution with SFHgb, maximal coronary flow increased slightly without evidence of coronary vasoconstriction. Since hemodilution with this material increases oxygen carrying capacity, maximal oxygen delivery is greater than Control, despite the very low canine hematocrit. These findings suggest: 1) SFHgb can provide adequate oxygen delivery to the myocardium despite extreme degrees of hemodilution, and 2) in this intact model, there is no evidence of adverse coronary vasomotion.

Animals↗
PubMed1990

Late results with Carpentier-Edwards porcine bioprosthesis.

From 1977 to 1984, 429 patients underwent aortic valve replacement (AVR), and 339 underwent mitral valve replacement (MVR) with a Carpentier-Edwards bioprosthesis. Early mortality for AVR was 4.6% (isolated AVR, 1.9%) and for MVR was 5.3% (isolated MVR, 4.1%). Follow-up was 99.3% complete at a mean of 5.9 years. Actuarial event-free rates at 10 years for AVR and MVR were, respectively, 1) for structural valve deterioration, 91.4 +/- 3.2% versus 75.1 +/- 4.0% (p less than 0.01); 2) for nonstructural dysfunction, 100% versus 97.8 +/- 1.6% (p = NS); 3) for thromboembolism, 90.6 +/- 2.3% versus 87.3 +/- 2.6% (p = NS); 4) for anticoagulant-related bleeding, 95.3 +/- 1.1% versus 88.6 +/- 2.4% (p = 0.05); 5) for endocarditis, 87.8 +/- 5.7% versus 90.6 +/- 2.4% (p = NS); 6) for reoperation, 91.0 +/- 2.5% versus 74.4 +/- 3.7% (p less than 0.01); 7) for valve-related mortality, 76.1 +/- 6.9% versus 71.4 +/- 5.2% (p = 0.01); 8) for permanent physical impairment, 85.0 +/- 3.0% versus 71.5 +/- 3.6% (p less than 0.01); and 9) for combined operative mortality, valve-related mortality, and reoperation, 68.7 +/- 6.4% versus 51.5 +/- 4.9% (p = 0.01). No structural valve dysfunction was observed in any AVR patient whose valve was inserted after age 70. Age at operation was the only factor that predicted structural valve deterioration (p less than 0.01).

Actuarial Analysis↗
PubMed1990

Hemodynamic effects and oxygen transport properties of a new blood substitute in a model of massive blood replacement.

Recent concerns regarding the safety of the national blood supply have rekindled interest in the development of blood substitutes. Clinical studies have dampened the initial enthusiasm for fluorocarbon solutions as blood substitutes. The potential of hemoglobin solutions as blood substitutes has continued to stimulate investigations. However, the development of an ideal hemoglobin-derived blood substitute has eluded investigators for the past century. A persistent problem has been the inability to develop hemoglobin solutions that provide adequate oxygen and carbon dioxide exchange, while avoiding toxicity that precludes clinical safety and long-term survival. Traditionally, investigators have focused on human hemoglobin solutions. The use of outdated banked blood or pedigree human donor blood as a hemoglobin source poses continued disease transmission risks and a prohibitively limited supply. We evaluated the hemodynamic and gas transport effects of a new purified, polymerized bovine hemoglobin preparation. Bovine hemoglobin oxygen affinity is regulated by chloride ion. The concentration of chloride ions in human plasma results in excellent oxygen transport properties in a stroma-free environment. In addition, unlike human blood, bovine blood is a more disease-free hemoglobin source that is available in large supply. We exchange-transfused eight conscious sheep with this new polymerized bovine hemoglobin solution. All animals tolerated greater than or equal to 95% exchange transfusion to reach a final ovine hematocrit of 2.4 +/- 0.5% with stable hemodynamics and no clinical evidence of distress. The exchange transfusion with bovine hemoglobin polymer resulted in a final plasma hemoglobin concentration of 6.1 +/- 1.6 gm/dl, which supported oxygen consumption at baseline levels. All animals that were exchange transfused with this preparation survived long term with rapid resynthesis of ovine erythrocytes.

Animals↗
PubMed1989

Ultrapure, stroma-free, polymerized bovine hemoglobin solution: evaluation of renal toxicity.

Because of recent concern about the safety of our national blood supply, there is increased interest in finding safe and effective blood substitutes. One option is the use of stroma-free hemoglobin (SFH) solutions. Recently, a SFH solution based on ultrapure, polymerized bovine hemoglobin (UPPBHg) has been shown to be effective in oxygen transport. We examined the potential renal toxicity of this material. Sprague-Dawley rats were infused with UPPBHg at doses of 25, 50, 75, and 100 ml/kg. Additional groups of rats were infused with UPPBHg at these doses with the addition of bicarbonate at a dose adequate to alkalinize the urine. Further groups of rats received UPPBHg intentionally contaminated with raw bovine blood lysate. Renal function was examined by subsequent determination of serum creatinine. UPPBHg infusion up to 50 ml/kg caused no significant change in serum creatinine; at higher doses, there was a reversible rise in creatinine at 24 hr following infusion. Addition of bicarbonate diminished the amount of reversible toxicity seen, even at doses of 100 ml/kg. In contrast, with hemolysate-contaminated UPPBHg, there were sharp increases in creatinine 24 hr after infusion of all doses tested, even at 25 ml/kg; these did not decrease significantly by 48 hr following infusion. At the higher doses tested, death occurred. These observations were not affected by simultaneous bicarbonate infusion. This study shows that UPPBHg may be administered in very large doses with only mild, reversible renal toxicity. The observation that urine alkalinization ameliorates this toxicity suggests that this may occur by hemoglobin precipitation or by a toxic effect in the renal tubules.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

The effect of colloid osmotic pressure on the survival of sheep following cardiac surgery.

The occurrence of late complications in implanted cardiac prosthetic valves has emphasized the need for the development of an animal model in which these complications are reproducible. Sheep constitute an excellent model for chronical and pathological studies of prosthetic devices. In our experience, survival of sheep following implantation of prosthetic valves is closely related to postoperative serum colloid osmotic pressure (C.O.P.). The normal range as measured in 28 healthy sheep was 16.67 +/- 0.55 mm Hg. A protocol was developed to maintain the colloid hydrostatic pressure gradient (C.H.P.G.) as close as possible to the normal physiological range, and to delay the extubation until the C.O.P. was within this range, and the C.H.P.G. greater than 7 mm Hg. Using the above protocol, a new tri-leaflet polyurethane valve was inserted into eight, five to seven month old sheep in place of the mitral and tricuspidal valves. One hour after terminating the extacorporeal circuit, the C.O.P. was measured at 13.10 +/- 0.96; but within five to six hours, it rose to 17.1 +/- 1.1. During the same period, the C.H.P.G. increased from 3.02 +/- 0.96 to 7.6 +/- 0.50 mm Hg. The postoperative period was uneventful, and all animals survived. We have thus concluded that the routine measurement and monitoring of C.O.P. constitutes a guide of great clinical importance.

Animals↗
PubMed1987

Aortic dissection.

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Aortic Dissection↗
PubMed1987

The superiority of cold oxygenated dilute blood cardioplegia.

It has been clearly shown, both in a laboratory model and in humans, that oxygenation of crystalloid cardioplegic solutions markedly enhances myocardial preservation. The addition of a small volume of red cells to a crystalloid perfusate improves capillary perfusion. Based on these results, we have changed our cardioplegic solution from cold crystalloid to cold oxygenated dilute blood. In the present study we retrospectively evaluate the results of 400 operative procedures to determine whether the addition of oxygenation and a small volume of blood to the cardioplegic solution enhances myocardial protection in the clinical setting. Two hundred consecutive patients who underwent operation with cardioplegic arrest using a cold crystalloid cardioplegic solution (group 1) were compared with a subsequent 200 patients who underwent operation with cold oxygenated dilute blood cardioplegia (group 2). Patients in group 2, who received cold oxygenated dilute blood cardioplegia, had a significantly reduced need for postoperative intraaortic balloon pump counterpulsation and for atrioventricular pacing. Also, patients in group 2 had a lower incidence of perioperative myocardial infarction and had improved early outcome. None of the 200 patients in group 2 had electrocardiographic evidence of perioperative infarction. We conclude that cold oxygenated dilute blood cardioplegia provides better preservation than does a nonoxygenated crystalloid solution during elective ischemic arrest, because a cold crystalloid solution is able to deliver oxygen and the red cells are able to enhance capillary perfusion.

Blood↗
PubMed1987

Liver regeneration during immunosuppression.

As a preface to studies on the feasibility of liver segment transplantation, we studied the course of liver regeneration in immunosuppressed rats. Partial hepatectomies were performed in young adult male rats who were then treated with daily cyclosporine, dexamethasone, the combination of both agents, or vehicle. Body weight, liver weight, and liver DNA content were measured in subgroups of rats studied at various times after partial hepatectomy. All treated animals experienced weight loss, a phenomenon most marked in animals treated with both dexamethasone and cyclosporine. The DNA content of regenerating liver increased initially after partial hepatectomy in all animals. Restoring their original hepatic DNA in a fashion indistinguishable from controls, animals treated with cyclosporine increased liver DNA four fold within the first six days after partial hepatectomy. Animals treated with dexamethasone and both dexamethasone and cyclosporine increased their complement of liver DNA 2.5 fold, to 80% of that originally present. After day 6, the combined cyclosporine and dexamethasone treatment group became extremely catabolic and experienced a sharp decline in liver DNA. We conclude that despite the deleterious effects of cyclosporine and dexamethasone, especially in combination, on weight gain following partial hepatectomy, these agents do not prevent DNA synthesis and the accretion of new liver mass. We are encouraged by these studies to proceed with experimental studies on the normal growth and repair of liver segments transplanted into an immunosuppressed host.

Animals↗
PubMed1987

Myocardial temperature variation: effect on regional function and coronary flow in dogs.

Incremental changes in the temperature (28-42.5 degrees C) of the anterior left ventricular wall in a canine, working, beating right heart bypass preparation (constant preload, afterload, and heart rate) were produced to measure the effect of regional temperature on myocardial function and blood flow. Circumferential-axis segment lengths were measured with sonomicrometry in both the temperature-varied, left-anterior descending coronary artery (LAD)-supplied myocardium and the normothermic (38 degrees C) circumflex-supplied myocardium. Fast thermistors (time constant less than 0.25 s) continuously monitored midmyocardial temperature in both areas. A Silastic loop with heat exchanger, thermistors, strain gauge, and flow probe was inserted into the LAD and allowed precise control of regional myocardial temperature. Nine-micron microspheres injected into left atrium were used to evaluate coronary flow and distribution. In six anesthetized dogs, relative to normothermic control (38 degrees C), regional systolic shortening decreased 42.2 +/- 10% at 41 degrees C and increased 23.3 +/- 6% at 31 degrees C. There was no significant change in coronary blood flow or distribution at the three temperatures. Pressure-length areas varied inversely with myocardial temperature. These data demonstrate that there is a reversible inverse relationship between midwall T and ventricular function when heart rate, preload, and after-load are controlled.

Animals↗
PubMed1987

Augmentation of pulmonary blood flow by a right atrial balloon pump after the Fontan operation.

The Fontan principle of right ventricular exclusion is frequently applied to complex congenital lesions. Results are adversely affected by increases in pulmonary vascular resistance and/or ventricular end-diastolic pressure. Survival depends on means to increase pulmonary blood flow. To address this problem, we have developed a triple-balloon catheter that is passed via the femoral vein to the right atrium. Inflation is sequenced so that small balloons located at the junction of each vena cava with the atrium inflate first. Then the larger central balloon inflates, ejecting blood from the right atrium to the pulmonary arteries. The pump is timed to inflate during ventricular systole. In this study, we tested the catheter in vivo in eight dogs. Tricuspid atresia was created and right ventricular exclusion accomplished. Pulmonary blood flow was measured with a flow probe in the right atrium-to-pulmonary artery conduit, at central venous pressures of 15, 20, and 25 mm Hg. Pulmonary blood flow was increased by balloon pumping in every instance (p less than .05). Maximal augmentation of pulmonary blood flow (25.5%) was achieved at a central venous pressure of 15 mm Hg with a balloon ratio of 1:2. Less augmentation was achieved at a central venous pressures of 20 mm Hg (8.4% to 13.0%) and a 25 mm Hg (4.4% to 5.3%) and at balloon ratios of 1:4 and 1:8. We conclude that (1) a triple-balloon pump in the right atrium can significantly augment pulmonary blood flow after right ventricular exclusion and (2) most effective augmentation can be achieved without excessive volume loading. Pulsatile augmentation of pulmonary blood flow with this device should improve survival after Fontan operations.

Animals↗
PubMed1985

Myocardial revascularization with combined aortic and mitral valve replacements.

Although the results of coronary artery bypass grafting plus single aortic or mitral valve replacement have been documented, the risk of myocardial revascularization with combined aortic and mitral valve replacement is not well defined. We present a series of 33 consecutive patients undergoing myocardial revascularization with combined aortic and mitral valve replacement during a period of almost seven years. There were 21 men and 12 women with a mean age of 67 years. All patients had congestive heart failure, and 21 (64%) had angina pectoris. Mean New York Heart Association functional classification was 3.4; eight patients (24%) had ejection fractions less than 0.40, and 13 patients (41%) had cardiac indices less than 2.0 L/min/m2. All operations were performed with hypothermic crystalloid potassium cardioplegia. The number of coronary arteries grafted varied from one to four (mean, 1.7 grafts per patient). Four patients died while in the hospital (12.1%). There were no perioperative myocardial infarctions. At a follow-up of 2 to 80 months (mean 40.7 months), death had occurred in eight (27.6%) of the 29 hospital survivors. Actuarial survival rate at 72 months was 60.7%. Although no preoperative factors predicted late death, early deaths were related significantly to severe mitral regurgitation, low ejection fraction, high New York Heart Association classification and extensive coronary artery disease (p less than 0.05). Myocardial revascularization with combined aortic and mitral valve replacement can be performed with an acceptable early mortality rate but with an appreciable late mortality rate.

Actuarial Analysis↗
PubMed1979

The role of surgery on ambulatory patients in one teaching hospital.

The development of a program of one-day surgery for ambulatory patients in one hospital was stimulated by overloaded operating room facilities and a long waiting list of patients for hospital admission. This concept has received enthusiastic reception by the surgical staff and the number of operations has increased to over 7,500 per year. All of the surgical specialty services use the surgical day care unit, although the number of cases suitable for ambulatory surgical treatment varies greatly on the various services. There have been no deaths and about 1% of patients have been admitted to the hospital from the surgical day care unit for a variety of reasons that are summarized.

Ambulatory Care↗