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Biomedical subjects

E M Breznock

Publications and source records attributed to E M Breznock.

At least 19 recordsLinked to original sources
PubMed1999

Strut fracture mechanisms of the Björk-Shiley convexo-concave heart valve.

Investigations of convexo-concave (C/C) valve outlet strut fractures (OSFs) were initially confounded by knowledge that the strut was subject to bending forces in arresting the opening disc. Pulse duplicator studies subsequently showed that closing loads were all born by the inlet strut, along with an understandable focus on the nature of the welds, where most fractures occurred. As observations of explanted valves accumulated, certain features pointed to unusual closing loads that might be contributory factors, but these hypothetical forces could not be verified. Epidemiological extrapolations and case-matched control studies have shown that certain valve and patient characteristics were each associated independently with increased OSF risk, leading to clinically valuable risk stratification, but little additional understanding of why OSFs continued to occur. Detection of the causative, highly transient (< 0.5 ms), outlet-strut-tip impacts due to closing disc over-rotation that have almost ten times the force of disc opening, and the capability of inducing leg-base bending stresses beyond the strut wire's fatigue endurance limit had to await the development of computer-controlled pulse duplicators and strut-leg strain gaging. Exercised young animals easily achieved such strut loading, but most human patients would probably have more difficulty. The actual OSF mechanism is a long-term, valve-patient interaction that requires the concurrence of susceptible valve geometry and sufficient ventricular contractility potential to develop the isovolumic, high dP/dt needed for forceful disc over-rotation. Critical strut tip loading must then occur often enough to fatigue fracture both strut legs within the patient's lifetime with the valve.

Animals↗
PubMed1997

Removal of a cholesteatoma in a dog, using a caudal auricular approach.

A new surgical method for treating cholesteatoma in dogs is described. Although rarely reported in dogs, cholesteatomas may be more common than previously believed. Complete excision of a cholesteatoma is associated with low recurrence and good long-term prognosis. Surgical intervention, with total ear canal ablation and lateral bulla osteotomy, has been recommended in dogs with tumors of the middle ear; however, this technique often results in conductive hearing loss. Through a caudal auricular approach to the tympanic bulla, we were able to preserve the external ear canal, reconstruct the auditory ossicles, and graft the tympanic membrane. Results of brain stem auditory-evoked response tests in the dog revealed intact conduction potentials. A caudal auricular approach to the tympanic bulla is technically possible, preserves normal appearance, and may maintain, or even improve, hearing conduction of affected ears in dogs.

Animals↗
PubMed1995

A computer-controlled, continuously circulating, hot irrigating system for endometrial ablation.

OBJECTIVE: This study evaluated the efficacy of a computer-controlled thermal catheter system to ablate the endometrium by use of 5 to 15 ml of hot saline solution. STUDY DESIGN: Five in vivo sheep uteri and 32 freshly excised human uteri were studied by inserting a self-contained heater catheter equipped with thermocouples and circulating hot saline solution for 15 minutes within the uteri at various temperature settings ranging from 60 degrees C to 80 degrees C. The uteri were grossly examined and microscopically evaluated by hematoxylin and eosin and reduced nicotinamide adenine dinucleotide-diaphorase stains for degree of acute destruction, depth of thermal injury, and predicted viability. RESULTS: All 80 degrees C sheep treatments resulted in complete loss of viability at mucosal, submucosal, and myometrial levels. In human uteri temperatures > or = 80 degrees C produced grossly recognizable thermal damage to the endometrium. Full-thickness irreversible damage was seen in the endometrium. Loss of viability was also demonstrated 1 to 3 mm deep in the superficial myometrium. Intrauterine pressure was demonstrated to range from 20 to 40 mm Hg, with a mean of 26 mm Hg. No leakage of fluid from the oviducts was observed. CONCLUSION: The data presented here demonstrate that a simple technique coupled with a sophisticated monitoring control system could successfully ablate the endometrium without the vagaries associated with individual operator skill levels.

Animals↗
PubMed1995

The effect of hypovolemic shock and reperfusion on the hepatic oxygen supply-uptake relationship in the dog.

The hepatic oxygen supply-uptake relationship was investigated during hypovolemic shock using a right heart bypass technique. The results were dissimilar to those previously reported in that the ratio of liver oxygen delivery to systemic oxygen delivery was significantly decreased during shock. The decreased ratio was due to a significant decrease in the portal venous oxygen delivery when compared to the decrease in the systemic oxygen delivery. The decrease in portal venous oxygen delivery was caused not only by the decrease in portal venous blood flow, but also by the decrease in oxygen content of portal blood. The ratio of hepatic arterial oxygen delivery, on the other hand, was significantly increased during shock. Hypovolemic shock increased the liver oxygen extraction ratio to nearly 100% of the pre-shock value. These findings suggest a hepatic protective mechanism for matching oxygen uptake to rising hepatic oxygen requirements. Liver oxygen delivery returned to pre-shock value after correction of hypovolemia primarily due to a significant increase in hepatic arterial oxygen delivery. A significant negative correlation between the liver oxygen extraction ratio and the oxygen content of hepatic venous blood was observed. The hepatic venous oxygen content appears to be a simple and appropriate index of liver oxygenation in clinical medicine because it is difficult to evaluate the liver oxygen extraction ratio directly.

Animals↗
PubMed1995

Effects of hypovolemic shock and reperfusion on liver blood flow in the dog.

Liver blood flow was investigated in hypovolemic shock using a modified right heart bypass technique which can obtain accurate portal blood flow. Findings were similar to those previously reported: hepatic blood flow accounted for 34% of cardiac output in this study; 76% of hepatic blood flow was delivered from the portal vein and 24% from the hepatic artery. Hypovolemic shock markedly decreased total liver blood flow by a reduction in portal venous blood flow. The findings of this study provide evidence that mesenteric blood flow is a peripheral circulation circuit where blood flow is restricted during reduced circulatory volume. Development of a hepatic arterial buffer response during hypovolemic shock was confirmed by an increased ratio of hepatic arterial flow to cardiac output. Reduced total hepatic blood flow during hypovolemic shock returned to control flow by an increase in hepatic arterial flow after reperfusion. The results of this study demonstrate that compensated reactions for maintaining liver blood flow mainly due to the hepatic arterial buffer response were functioned both during hypovolemic shock and after elimination of shock.

Animals↗
PubMed1994

Tricuspid and mitral valvular disease: valve replacement.

Using the methods described, the author has performed AV-valve replacement surgery in seven clinical dogs with AV valve dysfunction. Two dogs received autologous tissue tricuspid valves, three dogs received autologous tissue mitral valves, one dog received a mechanical mitral prosthesis, and one dog received a mechanical mitral and autologous tricuspid prosthesis. The two dogs that received a tricuspid prosthesis recovered from surgery, one dog is normal nearly 3 years after valve replacement surgery, and the second dog was euthanized 3 weeks after replacement surgery because of complications related to other congenital cardiovascular defects (ie, pulmonary artery coartations). The dog that received the mechanical mitral valve prosthesis made a complete immediate postoperative recovery but died from hemorrhage complications related to a femoral artery catheter removal 3 days after surgery. Hemorrhage from the left atrium resulted in the death of one dog after implantation of a bioprosthetic mitral valve. Two dogs with mitral valve bioprostheses and one dog with a mitral and tricuspid valve replacement could not be weaned from the cardiopulmonary bypass pump, even with pharmacological support. Although the initial results in this small clinical trial have not been spectacular, it is apparent from the few clinical cases operated on that the equipment, supplies, and techniques have advanced sufficiently in veterinary surgical practice to perform AV-valve replacement surgery in companion animals. Prosthetic valves are available presently to perform such surgery even in small animal patients (5 kg). However, a significant obstacle that must be overcome before such techniques become routine is the selection of animal patients that have sufficient myocardial reserve to undergo valve replacement surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Experimental evaluation of an autologous tissue heart valve.

The goal of the autologous tissue heart valve (ATHV) prosthesis project has been the development of a non-antigenic, non-calcifying bioprosthesis of greater durability than heterograft or homograft bioprostheses. It is made in the operating room, at a sterile work bench, during surgery for heart valve replacement. Autologous pericardium is used for valve construction after a five minute immersion in 0.6 per cent glutaraldehyde buffered to pH 7.4 with phosphate. The stent-mounted trileaflet prosthesis can be made in five minutes with a semi-automated method that uses two concentric mating stents that substitute clamping for sewing of the tissue. In vitro testing, to include pulse duplicator, accelerated wear tester, static testing for leakage and tensile strength testing, has been performed with ATHVs made with glutaraldehyde-tanned bovine and ovine pericardium. Transvalvular pressure gradients were measured at 3.3-7.3 mmHg at flow rates of 4-5 l/min. Six valves have been tested beyond 800,000,000 cycles with full opening and closing at differential closing pressures of 125 mmHg. One of the valves developed a 2mm leaflet tear after 26,000,000 cycles but the remaining five survived intact. No fractures were seen in the Dacron covered Delrin stents. Six ATHVs were implanted in juvenile sheep for five months. One animal died after five months of infective endocarditis secondary to an unrecognized deep wound infection and the other five were electively sacrificed at the same time interval. Four valves were fully competent at terminal elective cardiac catheterization and one showed minimal insufficiency attributed to a paravalvular leak. The leaflet tissue was free of generalized calcification in all instances. There was no evidence of leaflet tissue thickening or shrinkage. The mean calcium content at necropsy of the 15 leaflets from the five valves was 8.357 mg/g of tissue. There is experimental evidence that an ATHV made of pericardium treated briefly with glutaraldehyde may achieve the goal of a non-calcifying, more durable bioprosthesis.

Animals↗
PubMed1987

Pleurovenous shunting technique for treatment of chylothorax in three dogs.

The operative technique for placement of a pleurovenous shunt catheter is described. Pleurovenous shunting was used in the surgical treatment of 3 dogs with chylothorax refractory to medical management. Chylothorax in 2 of the dogs was palliated, but because of severe restrictive fibrous pleuritis, the third dog was euthanatized during follow-up surgery.

Animals↗
PubMed1986

Congenital feline portosystemic shunts.

Five young cats with portosystemic communications, 2 with single intrahepatic and 3 with single extrahepatic portosystemic communications, were managed surgically. One cat with a ductus venosus was treated successfully by surgery. Ptyalism and behavioral changes were similar in all 5 cats. Biochemical abnormalities included low BUN values, increased blood ammonia values, and increased sulfobromophthalein retention. None of the cats had portal hypertension at the time of surgery. Seemingly, single portosystemic shunts should be considered a surgical disease in the cat.

Ammonia↗
PubMed1984

Constrictive pericardial disease in the dog.

The clinicopathologic features of constrictive pericardial disease in 13 dogs were reviewed. The causes were infection (3 dogs), metallic foreign body (1 dog), and idiopathic (9 dogs). Owner complaints included abdominal enlargement, tachypnea, weakness or syncope, exertional fatigue, and weight loss. Ascites and jugular venous distention were consistently observed, whereas abnormalities of arterial pulses and heart sounds were variable and inconsistent. Diminished QRS voltages were common. Mild to moderate cardiomegaly, rounding of the cardiac silhouette, and variable and nonspecific angiographic findings were frequently observed. Cardiac catheterization consistently showed elevation and equilibration of atrial and ventricular diastolic pressures, but a prominent early diastolic (y) descent was uncommon. Fibrosis was confined to the parietal pericardium in 8 dogs, and included the epicardium in 5 dogs. Parietal pericardectomy was successful in relieving the syndrome in 6 of 10 dogs. Pulmonary thrombosis was the most common cause of early postoperative mortality.

Animals↗
PubMed1983

Radiocolloid scintigraphy as an aid to the diagnosis of congenital portacaval anomalies in the dog.

Five clinically normal dogs and 5 dogs in which portacaval anomalies were diagnosed angiographically were utilized to evaluate differences in the appearance of the radiocolloid liver scan between the 2 groups. The liver was clearly visualized in all dogs, allowing subjective evaluation of size. In the dogs with portacaval shunts, scintigraphy revealed an obviously small liver as well as pulmonary uptake of radiocolloid. The utility of this technique was then tested in a group of dogs with liver disease and was shown to be of value in differentiating dogs with primary portacaval shunts from other types of liver disease.

Animals↗
PubMed1983

Valved apico-aortic conduit for relief of left ventricular hypertension caused by discrete subaortic stenosis in dogs.

A double-outlet left ventricle (LV), with a valved conduit interposed between the LV apex and the aorta, was created in 7 dogs with subaortic stenosis. Of 8 dogs in which the implantation was attempted, 1 died following thoracotomy but before conduit implantation could be performed, 1 died from hemorrhage 24 hours after surgery, 1 died from septicemia as a sequel to pneumonia 10 days after surgery, 1 died from "shock-lung" 4 days after surgery, and 4 were functionally normal 22, 12, 6, and 2 months after surgery. In the 7 dogs in which the implantation was completed, the mean LV to aorta (LV-Ao) pressure gradient was significantly (P less than 0.01) reduced by the implantation. Diastolic and systolic murmurs were detected over the prosthetic valve area in 3 of the 4 surviving dogs 1 to 4 days postoperatively, but the murmurs gradually decreased in intensity until they disappeared after 1 month. The 4 survivors had no angiographic evidence of prosthetic valve insufficiency at 2 months or at 1 year. In 3 of the survivors, the LV-Ao pressure gradients 2 months postoperatively were 45, 20, and 0 mm of Hg, as compared with 120, 90, and 50 mm of Hg preoperatively. Postoperative pressure measurements were not obtained on 1 surviving dog.

Animals↗
PubMed1983

alpha-Adrenoreceptor stimulation of the systemic circulation in dogs.

The influence of phenylephrine (an alpha-adrenoreceptor agonist) on the arterial and venous systems of the systemic circulation was studied in 10 anesthetized dogs during a right ventricular bypass procedure. Phenylephrine (1 microgram X kg-1 of body weight X min-1) produced a significant (P less than 0.001) increase in arterial resistance, no change in venous resistance, and a mild decrease in venous compliance. Seemingly in the clinically normal dog, a dose of phenylephrine sufficient to double total peripheral resistance will redistribute a small amount of blood volume from the venous to arterial systems with a slight decrease in venous return and concomitant attenuation of cardiac output.

Animals↗
PubMed1982

Blood volume of nonsplenectomized and splenectomized cats before and after acute hemorrhage.

Blood volume (BV) was determined in awake, nonsplenectomized (NSPX) and splenectomized (SPX) cats before and after hemorrhage (6 ml/kg). Each NSPX cat had a determined BV at least 10 ml/kg greater than the same cat after splenectomy. The mean BV of SPX cats was 43.4 +/- 8.94. ml kg (4.3% of body weight). The calculated RBC masses of NSPX and SPX cats were 17.0 +/- 4.07 and 12.2 +/- 1.12 ml/kg, respectively. Each NSPX cat had apparent RBC masses of 5 ml/kg greater than that of the same cat after splenectomy was done. At 1 hour after a hemorrhage, the BV and RBC masses determined in SPX cats were 46.7 +/- 12.1 and 9.7 +/- 1.90 ml/kg, respectively. Extravascular-to-intravascular fluid flux (calculated from RBC masses and plasma protein dilution) was approximately 0.80% of body weight. The indirect method with 51Cr-labeled RBC for BV determination was accurate and precise in awake, SPX cats; in awake, NSPX cats, the 51Cr-labeled RBC dilution method was precise, but not accurate. The spleen in the cat resulted in marked overestimations of BV and RBC masses.

Acute Disease↗
PubMed1982

Effects of the spleen, epinephrine, and splenectomy on determination of blood volume in cats.

Blood volume (BV), RBC mass, plasma protein (PP), and PCV were determined in (i) awake, nonsplenectomized (NSPX) cats before and after splenic contraction was induced by IV administration of epinephrine, (ii) in pentobarbital-anesthetized, NSPX cats before and after splenic contraction was induced by epinephrine and splenectomy, and (iii) in awake, splenectomized (SPX) cats before and after epinephrine was administered. Blood volume, absolute RBC mass in the spleen could not be determined accurately in awake or anesthetized, NSPX cats. Accurate BV and RBC mass determinations could only be obtained in cats without the spleen; mean BV and RBC mass of awake or anesthetized, SPX cats were 4.1% and 1.4% or body weight, respectively. The spleen was a dynamic sequestering organ for feline erythrocytes (RBC). Epinephrine (0.1 ml of 1:1,000) given IV resulted in the observed contraction of the spleen within 2 minutes. Relaxation of the spleen with RBC uptake began 3 minutes after epinephrine was given and it proceeded at a rate of approximately 0.93% of circulating PCV/min. At 20 minutes after epinephrine was given, a steady state of PCV occurred, and 20% of the maximum circulating PCV observed after the administration of epinephrine was stored within the spleen. At 60 minutes after epinephrine was given to awake, SPX cats, intravascular fluid influx of 4 ml/kg resulted in a decrease of PCV and PP. At 3 hours after splenectomy was done, intravascular fluid efflux resulted in hemoconcentration--a calculated fluid deficit of 2.5 ml/kg/hr occurring during the 3 hours after surgical removal of the spleen.

Anesthesia, General↗
PubMed1980

The systemic response of the traumatized patient: an overview.

A metabolic conflict occurs between increased production of easily used substrates and inhibition of their metabolism in any injured animal. The terms ebb and flow describe the dwindling and rising tides of such activity. The ebb may last 24 to 72 hours; the flow is usually over within two weeks but may last up to eight weeks or longer in more severe cases. The ebb phase corresponds to the traumatic and initial post-traumatic period when there usually is adequate substrate (oxygen, glucose, fatty acid) to meet the diminished demand of the tissues. The flow phase is the period of convalescence. The object of the organism's initial defense following injury seems to stabilize the situation during the ebb phase (preservation of the internal milieu). The longer the ebb phase can be maintained and the more substrates that can be conserved, the more likely the animal will recover during the flow phase. The ebb phase is set in motion by an injury such as hemorrhage, burns, fractures, soft tissue damage by crushing sepsis, or diarrhea. After the ebb phase, a variable, integrated response of nervous, endocrine, and metabolic systems begins, which compromises normal function to achieve specific survival objectives (that is, protection, stabilization and adaptation). Systemic changes (such as tissue catabolism) devoted to caloric needs and local growth (that is, wound repair) are all directed at the ultimate objective of survival.

Animals↗
PubMed1979

Surgical manipulation of portosystemic shunts in dogs.

Surgical manipulation to achieve stenosis or occlusion of portocaval shunts in 7 dogs resulted in disappearance of signs of central nervous, gastrointestinal, or urinary dysfunction. Results of blood chemical analyses and hepatic function studies as well as hepatic cellular architecture returned to normal or near normal within several months. Cranial mesenteric angiography was done on 4 dogs following corrective surgery; there was evidence of improved hepatic-portal circulation in 3 of the dogs and complete shunt obstruction in 1 dog.

Ammonia↗