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Biomedical subjects

N A Silverman

Publications and source records attributed to N A Silverman.

At least 19 recordsLinked to original sources
PubMed1991

Transesophageal echocardiographic features of normal and dysfunctioning bioprosthetic valves.

Transesophageal and transthoracic echocardiography and color flow Doppler were performed in patients with 42 normal and 20 dysfunctioning bioprosthetic mitral and aortic valves. Transesophageal echocardiography was superior to the transthoracic approach in delineating bioprosthetic valve cusps and the presence of valve thickening due to valve degeneration. In 27 clinically normal bioprosthetic mitral valves, regurgitation was demonstrated in three patients by the transthoracic approach and in seven by transesophageal study. Both transesophageal and transthoracic color flow Doppler demonstrated mitral regurgitation in 17 clinically regurgitant valves. The severity of mitral regurgitation was accurately assessed by the transesophageal study in all 13 patients who underwent angiography, whereas the transthoracic imaging underestimated valvular regurgitation in 7 of the 13 cases (54%). Bioprosthetic aortic valves were normal on clinical examination in 15 patients and were regurgitant in three others. Both transthoracic and transesophageal color flow Doppler were of equal value in observing and quantifying aortic regurgitation. In five clinically normal and regurgitant mitral and aortic valves, transesophageal color flow Doppler revealed eccentric regurgitant jets suggestive of paravalvular leak. This feature was not evident by the transthoracic approach. In conclusion, transesophageal echocardiography and color flow Doppler are superior to transthoracic imaging in estimating bioprosthetic mitral, but not aortic regurgitation, in differentiating valvular from paravalvular regurgitation, and in demonstrating thickened valves due to cusp degeneration.

Aortic Valve↗
PubMed1991

Porcine bioprosthetic aortic valve endocarditis with ring abscess and aortic stenosis.

Porcine bioprosthetic valve endocarditis is an infrequent but serious complication of valve replacement surgery. Ring (or annular) abscess is a frequent finding in mechanical valve endocarditis. In contrast, porcine valve endocarditis most often involves the cusps, and annular infection is uncommon. Porcine valvular dysfunction secondary to endocarditis usually takes the form of incompetence, whereas stenosis is less frequent. We report a case of a 76-year-old female who developed endocarditis with Staphylococcus epidermidis nine months after placement of a Carpenter-Edwards porcine aortic valve. Her initial presentation included complete heart block and moderate aortic stenosis. Transesophageal echocardiography aided the diagnosis by demonstrating large vegetations, while transthoracic echocardiography showed only slight thickening of the valve leaflets. At operation, there was a circumferential abscess around the sewing ring causing valve dehiscence and virtual discontinuity of the aorta from left ventricle. Valve degeneration and organisms within the cusps were observed on microscopy. This case illustrates two infrequent complications of porcine aortic valve endocarditis, namely massive annular abscess with invasion of the conducting system and aortic stenosis. It also demonstrates the utility and limitations of transesophageal echocardiography in the diagnosis of this disorder.

Abscess↗
PubMed1990

Carcinoid tumors of the thymus.

Carcinoid tumors arising in the thymus are rare. Since Rosai and Higa in 1972 distinguished these neoplasms from thymomas, fewer than 100 cases have been reported in the world literature. In a 38-year review (1950 to 1988) of surgically treated thymic tumors at Henry Ford Hospital, only 7 cases of thymic carcinoids were identified. These 6 men and 1 woman ranged in age from 27 to 70 years (mean, 48 years) at diagnosis. Follow-up was available in all patients with the longest survival being 12 years in 2 patients, and the shortest, 1 year, in 1. Recurrences and/or metastases developed in 4 of 7 patients between 1 and 9 years after initial resection. Recurrences were treated by reexcision in addition to radiation treatment and chemotherapy in 3 patients and reexcision with radiation treatment alone in 1 patient. A review of the literature along with our experience suggests that thymic carcinoids have a biological behavior distinct from thymoma in terms of cell origin, associated syndromes, neoplastic behavior, and prognosis. An aggressive surgical approach with complete initial excision of the tumor and of subsequent recurrences, along with radiation and probably chemotherapy, is the best available treatment today.

Adult↗
PubMed1990

Ventriculoarterial coupling influences regional contractility.

The purpose of this study was to adjudicate whether concomitant manipulation of inotropic state and arterial elastance influences linear indices of regional contractility. Fifteen autonomically denervated open-chest porcine hearts were instrumented with midmyocardial ultrasonic crystals and aortic and left ventricular chamber microamanometers. Linear left anterior descending coronary artery regional stroke work vs preload relationships (RSW) were generated by 10-sec vena caval occlusion at control and altered contractile states (either dopamine, 5 micrograms/kg/min, or propranolol, 0.2 mg/kg) and following arterial elastance variation (phenylephrine or nitroprusside), effecting an average 30% change in mean arterial pressure (MAP). Global contractility (dP/dt) was doubled (227% of control) by dopamine and halved (35% of control) by propranolol at constant preload (end-diastolic volume, end-diastolic pressure) and afterload (MAP). Regional contractility (RSW slope) was increased from 135 +/- 11 to 211 +/- 28, P less than 0.01, by dopamine, but unchanged with propranolol (106 +/- 10 vs 118 +/- 14, NS). Bidirectional changes in aortic elastance depressed the dopamine-augmented RSW slope (115 +/- 17, nitroprusside; 132 +/- 14, phenylephrine; P less than 0.01 vs dopamine). These differences were attenuated by propranolol infusion (98 +/- 7, nitroprusside; 132 +/- 9, phenylephrine; NS vs propranolol). Thus, optimizing ventriculoarterial coupling should supersede simple afterload manipulation in perioperative cardiac support.

Animals↗
PubMed1990

Technical considerations in aortocoronary bypass grafting.

Since the inception of aortocoronary bypass surgery, many technical advances have been rapidly achieved. Early experience was limited to reversed saphenous vein grafting of single vessel coronary artery disease. Multiple grafts to several vessels soon became commonplace and sequential grafting techniques were developed. Expanded use of the internal mammary artery resulted after analysis of superior patency rates achieved with this conduit. Use of alternative conduits such as upper extremity veins, allogenic veins, synthetic graft material (polytetrafluorethylene), radial artery, splenic artery, and gastroepiploic artery have been explored. Apart from the gastroepiploic vessel, none of these alternative conduits have been suitable. A grat deal of effort has been directed at the mechanisms of saphenous vein occlusion including technical considerations, early thrombosis, intimal hyperplasia and graft atherosclerosis. Platelet inhibition and lipid reduction have shown promise in improving patency rates. Further work in these areas should lead to even better results.

Coronary Artery Bypass↗
PubMed1990

Splenic septic emboli in endocarditis.

The significance of septic emboli to the spleen is inferred by the frequency of septic emboli in general seen in patients with left-sided infective endocarditis who are referred for valve replacement. To determine the proper management of splenic infarcts and abscess due to septic emboli, we retrospectively reviewed the records of 108 patients with left-sided endocarditis who underwent valvular surgery at the University of Illinois Hospital from 1980 through 1988. Intravenous drug abuse was the etiology in 68% (n = 73). The incidence of splenic infarcts and abscess was 19% (n = 20), but an incidental finding of splenic infarcts was found in 38% (n = 11) of 29 asymptomatic patients who had computed tomograms. Streptococci and staphylococci were the causative organisms in 85% (n = 17). Localized findings were absent in 90% of splenic infarcts and abscesses. Abdominal computed tomograms were diagnostic of the sequelae of splenic septic emboli in 100%. No patient had intra-abdominal bleeding complications associated with cardiopulmonary bypass. Splenectomy was performed in 50% (n = 10) of patients 3-24 days (mean, 11.2 days) after valve replacement. Indications for splenectomy included persistent sepsis in 60% (n = 6), large (greater than 2 cm) and peripheral lesions in 30% (n = 3), and splenic rupture in 10% (n = 1). Perioperative mortality of patients who underwent splenectomy was 30% (n = 3). The following conclusions can be drawn: 1) Splenic septic embolus is common in endocarditis. 2) Abdominal computed tomography should be performed for all patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Abscess↗
PubMed1989

Upgrading acellular to sanguineous cardioplegic efficacy.

To determine which biochemical entity of the red cell is responsible for preventing augmented postischemic myocardial oxygen consumption (MVO2), 28 canine hearts instrumented with ultrasonic dimension crystals underwent simultaneous determination of stroke work (SW) and MVO2 during incremental volume loading on right heart bypass before and 30 min after 2 hr of 10 degrees C cardioplegic arrest with unmodified oxygenated crystalloid cardioplegia (OC), OC with histidine of equal buffering capacity as 18% hematocrit blood (OC + H), or OC with 200 units/ml of superoxide dismutase and catalase (OC + SOD/C). In all groups, the slope of the linear SW vs end-diastolic volume relationship, Mw, and the slope of the linear SW vs MVO2 relationship, Me, were unchanged after cardioplegic arrest. The intercept of the SW vs MVO2 relationship, Eo, was augmented an average of 22.2% in the OC group, but both OC + H and OC + SOD/C prevented this subtle expression of ischemic injury. The characteristic of the red cell most likely responsible for the myoprotective efficacy of blood cardioplegia is buffering capacity; however, since the effects of tissue acidosis are partially mediated by free radicals, the use of free radical scavengers can also ameliorate ischemic damage incurred during cardioplegic arrest.

Animals↗
PubMed1989

The efficacy of blood cardioplegia is not due to oxygen delivery.

Twenty-seven canine hearts instrumented with ultrasonic dimension crystals underwent simultaneous determination of stroke work and myocardial oxygen consumption during incremental volume loading on right heart bypass before and 30 minutes after 2 hours of cardioplegic arrest at 10 degrees C. Three cardioplegic solutions were used: Hematocrit values were 17.0% (group I), 8.2% (group II), and 0% (group III). In all groups the slope of the linear stroke work versus end-diastolic volume relationship, a measure of contractility, was unchanged after ischemic arrest. However, the myocardial oxygen consumption for basal metabolism was increased an average of 25.5% after arrest with plasma (group III). Since the plasma concentration in all three groups was identical, and the oxygen available to the hearts during ischemia was the same in groups II and III, the efficacy of blood-based cardioplegic solutions cannot be attributed to a plasma component or to the greater oxygen-carrying capacity of the red blood cell. Future studies should attempt to identify the salutory entity of the red cell responsible for preservation of myocardial oxygen consumption efficiency.

Animals↗
PubMed1989

Compartmentalizing chemomechanical transduction in the ejecting heart.

The efficiency of transferring the total energy generated by ventricular contraction (pressure-volume area, PVA) to external work (EW) and internal work (IW) and the myocardial oxygen consumption (MVO2) at zero PVA were determined during volume loading on right heart bypass before and after a 50% augmentation (CaCl2, 0.03 mEq/kg/min, n = 7) or depression (20 minutes of 37 degrees C ischemia with 30 minutes of reperfusion, n = 7) of the contractile state. An increased EW efficiency (64% +/- 7% vs. 81% +/- 6%, p less than 0.01) with reciprocally decreased IW efficiency (36% +/- 7% vs. 19% +/- 6%, p less than 0.01) occurs with calcium chloride-augmented contractility. A reversible ischemia and reperfusion insult has the converse effect on these relative efficiencies (EW, 73% +/- 4% vs. 49% +/- 4%; IW, 27% +/- 4% vs. 51% +/- 4%; each p less than 0.01). Calcium chloride increases the oxygen requirements of both basal metabolism (28 +/- 2 vs. 67 +/- 9 ml O2/beat/100 gm LV, p less than 0.01) and fiber shortening (11 +/- 5 vs. 62 +/- 11 ml O2/beat/100 gm LV, p less than 0.01). The postischemic heart has a decreased oxygen need for shortening (20 +/- 2 vs. 3 +/- 4 ml O2/beat/100 gm LV, p less than 0.01), paralleling the depressed inotropic state. This new model of compartmentalized chemomechanical transduction may allow specific modulation of the energetic derangements attendant to the surgically treated heart.

Animals↗
PubMed1989

Assessment of the intrinsic contractile state within an area of myocardium.

Afterload independent, inotropic state sensitive indices of regional function were sought in 31 canine hearts instrumented with piezoelectric crystals to depict trapezoidal areas in the left anterior descending and circumflex arterial beds. Control and postinterventional end-systolic pressure versus regional length and area relationships and regional stroke work versus end-diastolic length and area relationships were inscribed during incremental volume loading on right heart bypass. Hearts were randomized to undergo afterload variation with phenylephrine infusion, contractility augmentation by calcium chloride, or 20 minutes of ischemia in the region of the left anterior descending artery with 30 minutes of reperfusion. All relationships were linear before and after each intervention (mean r = 0.726 to 0.974). The slopes of each correlation were interpreted to quantify intrinsic regional contractility, and all were afterload insensitive (unaffected by phenylephrine). Regional stroke work versus end-diastolic area and length relationships were depressed 55% and 62%, respectively, after ischemia (p less than 0.001 each), whereas neither end-systolic pressure versus regional area nor regional length was significantly altered. Calcium chloride increased regional stroke work versus area 45% in both arterial beds, but significantly increased the other indices only in the left anterior descending and not the left circumflex region. Unlike previous studies of global contractility, correlation of end-systolic events alone did not reliably discriminate perturbations in regional function. The superiority of regional stroke work versus end-diastolic area may be due to incorporating pressure-area changes during the entire cardiac cycle and obviating variability owing to crystal orientation inexactly parallel to fiber shortening.

Animals↗
PubMed1989

Amelioration of postischemic stunning by deferoxamine-blood cardioplegia.

Limitation of oxygen free-radical injury was assessed in canine hearts by sonomicrometrically quantifying regional stroke work (RSW) in areas of myocardium perfused by the left anterior descending (LAD) and left circumflex (LCX) arteries. Volume loading of the left ventricle was performed on modified right-heart bypass before and 30 minutes after 20 minutes of LAD occlusion followed by 60 minutes of global cardioplegic arrest with either blood cardioplegia (group 1), blood cardioplegia with adjuvant deferoxamine (500 mg/l) plus 100 mg infused into the aortic root for 5 minutes after unclamping (group 2), or blood cardioplegia with adjuvant deferoxamine (600 mg/l) with unmodified reperfusion (group 3). Surgical revascularization was modeled by reopening the LAD with the first cardioplegia reinfusion. The slope of the RSW versus preload relation (a load-independent index of contractility) was decreased by a mean amount of 44% in the LAD region of group 1 hearts but was preserved in group 2 and 3 hearts. The slope of the LCX region was preserved in all groups. The use of adjuvant deferoxamine in this model of early surgical reperfusion eliminates measurable postischemic stunning.

Animals↗
PubMed1988

Developmental changes in reperfusion injury. Comparison of intracellular ion accumulation in ischemic and cardioplegic arrest.

Developmental differences in ischemic and potassium cardioplegic arrest were evaluated in newborn (birth to 7 day old) and adult (6 to 12 month old) New Zealand white rabbit hearts isolated and perfused by Langendorff's method. An extracellular space washout technique was used to measure intracellular sodium and calcium in the two age groups after ischemia alone, after normothermic and hypothermic cardioplegia, and after cardioplegia with reperfusion. Although the intracellular ionic contents of nonreperfused adult hearts after 30 and 40 minutes of ischemia were identical, there was a twofold elevation in intracellular sodium level after 40 minutes of ischemia in the newborn hearts. Adult hearts arrested by normothermic potassium cardioplegia demonstrated no alteration in the intracellular ionic content, whereas in the newborn hearts, potassium cardioplegia produced excess intracellular calcium loading before reperfusion, which was greater than that occurring with ischemia alone. When hypothermia (12 degrees C) was combined with cardioplegic arrest, a prereperfusion influx of sodium and calcium was not observed in the newborn hearts, and ionic reperfusion injury was blunted in both newborn and adult hearts. These studies demonstrate that the newborn heart is more susceptible than the adult to both ischemia and cardioplegia. This may be due to age-dependent differences in transmembrane passive diffusion, sodium/calcium exchange, or calcium slow channel properties and suggests alternative myocardial protective strategies for the newborn infant.

Aging↗
PubMed1987

Developmental changes in reperfusion injury. A comparison of intracellular cation accumulation in the newborn, neonatal, and adult heart.

Intracellular sodium and calcium accumulation were measured after 30 and 40 minutes of ischemia and 30 minutes of reperfusion in newborn (0 to 7 day), neonatal, (14 to 21 day), and adult (4 to 6 month) New Zealand white rabbit heart preparations. Newborn hearts showed twofold and threefold elevations of calcium when exposed to 30 and 40 minutes of ischemia and reperfusion, respectively, whereas sodium increase was noted only in the 40 minute group. Conversely, adult hearts exhibited sodium elevation if exposed to ischemia for 30 minutes and calcium accumulation occurred only after 40 minutes of ischemia. There was no significant alteration in intracellular sodium and calcium levels after ischemic intervals of 30 and 40 minutes in the neonate. These studies demonstrate that the immature newborn heart is the most susceptible and the neonatal heart is the least susceptible to injury sustained by ischemia followed by reperfusion. These differences in susceptibility to ischemia may be due to age-dependent alterations of intramembrane ionic pumps and channels.

Age Factors↗