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Biomedical subjects

S Meerbaum

Publications and source records attributed to S Meerbaum.

35 records · Page 2Linked to original sources
PubMed1979

Cross-sectional echocardiography. I. Analysis of mathematic models for quantifying mass of the left ventricle in dogs.

Cross-sectional echocardiography was used to quantify left ventricular mass noninvasively in 21 dogs. Short- and long-axis cross-sectional images of the left ventricle were reproducibly traced at endocardial and epicardial borders during stop-motion video-tape replay. We used area, length and diameter measurements to calculate left ventricular mass by seven mathematic models, including the standard formulas used with M-mode echocardiography and cineangiography. Calculated mass was compared with excised weight of the left ventricle by regression and percent error analyses. Formulas using short-axis areas and long-axis length resulted in higher correlation coefficients (0.94--0.95) and lower mean errors (6--7%) than for standard formulas. Since short-axis areas account for regional left ventricular irregularities, noninvasive quantification of left ventricular mass by cross-sectional echocardiography in dogs is most accurate with formulas using short-axis areas.

Animals↗
PubMed1978

Synchronized retroperfusion of coronary veins for circulatory support of jeopardized ischemic myocardium.

A retroperfusion system was developed that augments retrograde delivery of arterial blood into an acutely ischemic myocardial region during diastole and facilitates coronary venous drainage in systole. An electrocardiogram-synchronized, gas-actuated bladder pump propels retroperfusate through an autoinflatable balloon catheter whose tip is placed within the regional coronary vein that drains the ischemic myocardium. Experiments were performed in 26 closed chest dogs with 4 hour intracoronary balloon occlusion of the proximal left anterior descending coronary artery. An untreated control series consisted of 13 dogs; the remaining 13 dogs were treated with retroperfusion, which was initiated after the first hour of acute coronary occlusion. Synchronized retroperfusion resulted in a significant 37 +/- 10 per cent (mean +/- standard error of the mean) decrease in left ventricular end-diastolic pressure from 11 +/- 2 to 5 +/- 21 mm Hg, a 20 +/- 4 percent decrease in peak systolic pressure (140 +/- 7 to 110 +/- 6 mm Hg) and a 25 +/- 6 percent reduction in systemic vascular resistance (3,880 +/- 340 to 2,380 +/- 300 dynes sec cm-5). Ischemic region intracoronary S-T segment elevation decreased 40 +/- 15 percent, and potassium loss was reduced 92 +/- 22 percent. Partial pressure of oxygen measured distal to the coronary occlusion decreased 36 +/- 2 percent, suggesting oxygen delivery to and extraction by the jeopardized ischemic myocardium. Ventriculography in four dogs revealed an increase in left ventricular ejection fraction and reversal of ischemic segment dyskinesia by synchronized retroperfusion. A nitro-blue tetrazolium study of 10 excised hearts indicated that 3 hours of synchronized retroperfusion significantly reduced the size of ischemic injury to 3.3 +/- 2 percent of the left ventricle (versus 16.2 +/- 5 percent in the untreated control group). In addition, retroperfusion appeared to correct ischemic arrhythmias. The experimental data suggest that this treatment is capable of improving cardiac function and salvaging jeopardized myocardium. Clinical application is envisioned as a prompt temporary emergency support for acute and profound ischemic dysfunction not readily treatable by other interventions.

Animals↗
PubMed1977

Derangements of myocardial metabolism preceding onset of ventricular fibrilliation after coronary occlusion.

To determine alterations in myocardial metabolism and and hemodynamics that occur within the first 30 minutes after coronary arterial occlusion, before the onset of ventricular fibrillation, measurements were compared in two series of dogs. Series A, 90 dogs that did not manifest ventricular fibrillation after coronary occlusion, were considered a control group. Series B consisted of 28 dogs that had ventricular fibrillation within 30 minutes after occlusion. All had similar comprehensive measurements completed preceding the onset of ventricular fibrillation. The animals in series B (subseuqnt fibrillation) had significantly higher heart rates before and after coronary occlusion. In this series cardiac metabolism of the occluded segment judged by transmyocardial lactate extraction, potassium balance, sodium/potassium ratio and blood pH because grossly more abnormal after coronary occlusion than in series A. In 5 animals whose measurements were obtained within 5 minutes of the onset of ventricular fibrillation, a sudden massive lactate production, potassium loss and increased acidosis of the occluded portion supervened minutes before the onset of the fatal arrhythmia. Animals with ventricular fibrillation had higher intracoronary S-T segment elevation that persisted until the onset of ventricular fibrillation. Measurements of abnormal hemodynamic function (left ventricular end-diastolic pressure, peak systolic pressure and first derivative of left ventricular pressure [DP/dt]) were not associated with an increased incidence of ventricular fibrillation. The study indicates that animals that manifest ventricular fibrillation within 30 minutes after coronary occlusion have higher preocclusion heart rates, a more severe metabolic disorder of the coronary occluded segment and more persistent intracoronary S-T segment elevation compared with animals that do not manifest ventricular fibrillation.

Animals↗
PubMed1977

Is early revascularization following acute coronary occlusion a safe and effective surgical procedure?

Coronary bypass surgery performed after more than 3 or 4 hours of coronary occlusion may results in serious derangements of cardiac metabolic, contractile, and electrical functions, and lead to extensive myocardial infarction, as well as to an unacceptable mortality. If the operation can be performed within the first 1 to 2 hours of acute coronary occlusion, hospital mortality rate is acceptably low. Although the average infarct size was usually reduced by reperfusion after 3 hours of experimental occlusion, in about 30 percent of cases there appeared to be no salvage of jeopardized myocardium.

Acute Disease↗
PubMed1977

Do risk factor interventions prevent or reverse arteriosclerosis?

We have attempted to summarize the current controversies regarding risk factors and preventive measures for control of arteriosclerosis and coronary heart disease. Recognizing that the genesis and development of the disease process are extremely complex and the basic knowledge is limited, it is not likely that conclusive answers to questions will be forthcoming soon which will provide more effective preventive or therapeutic measures. It might be desirable to institute educational and control program aimed at curtailing, at a young age, known AS risk factors such as heavy smoking, particularly if the family history indicates severe risk. Few will question the normal approaches to the treatment of complications of coronary heart disease by control of hypertension, elevated cholesterol, and smoking. However, great caution must be exercised when trying to institute large scale modifications in prevailing life patterns, particularly when based on indefinite risk factor studies and in the face of potentially profound and frequently unknown consequences. The unknowns of atherosclerotic heart disease risk factors, coupled with uncertainties and even doubts about protracted and expensive population studies, lead us to propose an emphasis on alternate selective approaches. We strongly believe that fundamental to progress in the field of arteriosclerosis is an amplification of preventive research efforts with stronger attention focused upon influencing the atherosclerotic processes within the arterial wall. But, more immediately, we urge systematic gathering and careful evaluation of patient data in particular population subsets which exhibit and accelerated mode of arteriosclerosis. Comparative studies of patients, particularly twins, families, and ethnic populations with redilection to early or accelerated arteriosclerosis may be extremely rewarding. Our repeated review of the enormous literature suggests that worldwide collaboration is needed to perfect more meaningful protocols as well as to correlate and critically evaluate existing data provided by population studies of this insidious disease process which represents an evermounting burden to society.

Adult↗
PubMed1976

Significance of S-T segment elevations in acute myocardial ischemia. Evaluation with intracoronary electrode technique.

A method is described for measuring intracoronary S-T segment elevations in the closed chest, a technique that appears to provide more reliable measurements of myocardial ischemia. Electrodes were inserted through intracoronary balloon catheters that were placed within a coronary artery and its adjoining vein both proximal and at several points distal to a coronary occlusion. Intracoronary arterial and adjacent venous electrocardiograms produced equivalent tracings. The intracoronary S-T segment elevations after coronary occlusion resembled those recorded from the epicardial surface but were free of artifacts noted in open chest studies. Study of progressive alterations of the intracoronary S-T segment after proximal occlusion of the left anterior descending coronary artery in 18 closed chest dogs revealed a peak segment elevation of 3.2 +/- 0.6 mv within 5 minutes, followed within 2 to 3 hours by spontaneous reduction by more than 40% of the S-T elevation over the occluded zone. In 44% of these animals, the S-T elevation decreased spontaneously to less than 1 mv, and in 22% it decreased to the preocclusion control level within 2 hours of occlusion. This spontaneous decrease in S-T elevation was frequently followed by a secondary increase and then S-T segment fluctuations. Reperfusion of the left anterior descending coronary artery after 30 to 60 minutes of occlusion generally led to a prompt reduction in S-T elevation. In some cases S-T elevations persisted up to 14 hours of occlusion, were reduced after reperfusion and exhibited a renewed pronounced increase after subsequent reocclusion of the left anterior descending coronary artery. During the 1st hour after occlusion, the early S-T segment elevation followed by spontaneous reduction reduction generally corresponded temporally with the derangements in myocardial lactate extraction and potassium loss. However, after 1 hour of occlusion no clear-cut correlation could be established between S-T fluctuations and changes in hemodynamic or myocardial metabolic measurements. We conclude that the new closed chest intracoronary electrocardiographic S-T technique might be of use for monitoring the early ischemic myocardial derangements and to assess benefits or drawbacks of treatment in both the experimental animal and man. Correspondence of S-T segment elevation with lactate and potassium alterations in the coronary-occluded region in the 1st hour after occlusion indicates that S-T segment elevation might represent an index of early myocardial ischemia. The spontaneous S-T changes that follow coronary occlusion must be taken into consideration when investigators utilize S-T segment modification as a sign of effectiveness of treatment.

Acute Disease↗
PubMed1976

Regional and global myocardial effects of intravenous and sublingual nitroglycerin treatment after experimental acute coronary occlusion.

The consequences of sublingual and intravenous nitroglycerin treatment after acute coronary occlusion were studied in 18 closed chest dogs. Intravenous (0.1 mg/min) or sublingual (0.4 mg/15 min) nitroglycerin therapy was instituted 1 hour after occlusion and the effects were observed over a period of 2 hours. Hemodynamics and global and regional cardiac function were measured in both the coronary occluded and nonoccluded segments of the left ventricle before and during coronary occlusion, and after administration of nitroglycerin. A similar nine dog control series was used to establish the significance of the measured effects of nitroglycerin. Intravenous nitroglycerin therapy after 1 hour of occlusion resulted in a marked increase in heart rate (37 +/- 12 [mean +/- standard error of the mean] percent), reduction of systolic blood pressure (9 +/- 3%), decrease in left ventricular end-diastolic and end-systolic volumes (32 +/- 5% and 34 +/- 5%), increase in coronary sinus flow (64 +/- 24%) and decrease in left ventricular stroke work (29 +/- 8%). Sublingually administered nitroglycerin produced similar trends but much less pronounced effects. However, intravenous or sublingual administration of nitroglycerin provided no improvement or caused further deterioration in ischemic region lactate extraction and potassium loss. The left ventricular ejection fraction, which was severly depressed after 1 hour of occlusion, changed minimally after administration of nitroglycerin, and there was no evidence of any correction of regional left ventricular akinesia or dyskinesia. Whereas mean systemic vascular resistance changed minimally as a result of nitroglycerin therapy, it increased 19 +/- 8% during a corresponding period of an untreated coronary occlusion series suggesting that nitroglycerin prevented an anticipated increase. Postocclusion S-T segment elevation in the electrocardiogram persisted after treatment. Our data corroborated that nitroglycerin reduced left ventricular volumes and increased coronary sinus flow; however, these improvements were accompanied by persisting metabolic and mechanical derangements in the ischemic region.

Animals↗
PubMed1976

Methylprednisolone treatment in acute myocardial infarction. Effect on regional and global myocardial function.

The effects of methylprednisolong treatment on acute myocardial ischemia were studied in nine closed chest dogs. After 1 hour of proximal occlusion of the left anterior descending coronary artery, an intravenous bolus injection (50 mg/kg body weight) of methylprednisolone was administered and its effects studied during an additional 2 hours of occlusion. After 2 hours of treatment the following significant mean alterations from levels after 1 hour of occlusion were noted: an increase of 16.7% in heart rate and decreases of 23% in left ventricular end-diastolic pressure, 32% in stroke volume, 14% in cardiac output and 37% in stroke work. Peak systolic pressure, maximal rate of rise of left ventricular pressure (dP/dt), left ventricular end-diastolic volume, systemic vascular resistance and coronary sinus blood flow changed less than 10%. Ejection fraction and regional cardiac wall motion were not improved. Metabolic dysfunction of the coronary-occluded myocardium, revealed by regional lactate as well as potassium derangements, persisted throughout the 2 hour treatment period. Comparison of these results with equivalent data from an untreated series of nine dogs with 3 hours of occlusion demonstrated no improvement in the treated series. Methylprednistone failed to restore regional cardiac metabolic and mechanical function, and treatment was associated with a further rise in S-T segment elevations. Administration of methylprednisolone after 1 hour of proximal left anterior descending coronary occlusion apparently does not reverse cardiac dysfunction in the first 2 hours of treatment.

Acute Disease↗
PubMed1976

Diastolic retroperfusion of acutely ischemic myocardium.

The effectiveness of coronary venous retroperfusion treatment of an ischemic myocardial segment was assessed by measurements of regional and global myocardial function in 16 dogs. The left anterior descending coronary artery was acutely occluded for 75 minutes. After the first 30 minutes of occlusion, diastolic retroperfusion was instituted for 45 minutes by synchronized pumping of arterial blood from the brachial artery into the anterior interventricular coronary vein. Data collected in the preocclusion control period, during occlusion and the subsequent retroperfusion period included simultaneous measurement os ischemic and border zone myocardial forces, epicardial electrocardiographic S-T segments, intracoronary pressure, coronary blood flow and oxygen pressure (PO2) sampled distal to the site of occlusion. Retroperfusion resulted in significant improvement from the level of regional dysfunction observed after 30 minutes of occlusion: Ischemic zone myocardial force increased 106%, epicardial S-T elevation decreased 46%, normalized peripheral left anterior descending coronary arterial flow increased 50% and distal left anterior descending PO2 decreased 44%. These regional improvements were significant when compared with findings in an untreated series of 12 dogs with 75 minutes occlusion of the left anterior descending coronary artery. Diastolic-augmented coronary venous retroperfusion with arterial blood provided significant but not complete restoration of function in the ischemic segment. Therefore, in the earliest phase of acute myocardial infarction, retroperfusion might represent a useful temporary support to an otherwise inaccessible jeopardized zone of the heart. Regional retroperfusion may constitute an effective emergency procedure, particularly when the occlusive lesions are diffuse and other medical or surgical emergency procedures are inadvisable, unavailable or ineffective.

Animals↗
PubMed1975

Revascularization after 3 hours of coronary arterial occlusion: effects on regional cardiac metabolic function and infarct size.

Two experimental series of closed chest dogs were compared: Group A (five dogs with 7 days of continuous occlusion of the proximal left anterior descending coronary artery); and Group B (six dogs with 7 days of reperfusion after 3 hours of acute occlusion of the same artery). Hemodynamic measurements, ventricular wall motion, coronary sinus blood flow and regional metabolism in both coronary occluded and nonoccluded segments of the left ventricle were measured sequentially. The infarct size was characterized by detailed histopathologic analysis. In the control dogs (Group A), mechanical and metabolic function remained severely depressed after 7 days of occlusion, and mean infarct size was 31.6 percent. In Group B, significant mechanical and metabolic dysfunction developed during 3 hours of occlusion and did not improve during the 1st hour of reperfusion. However, after 7 days of reperfusion, function returned to near preocclusion level. Mean infarct size was 14.2 percent, but in two of the six dogs infarct size was 43 percent and 23 percent, respectively. The study confirmed the unstable character of the early phase of reperfusion, attributed to cell swelling, edema and hemorrhages that resulted in inadequate coronary reflow, arrhythmias and functional derangements. Prolonged reperfusion for 7 days reduced mean infarct size and improved cardiac function.

Animals↗
PubMed1975

Consequences of coronary arterial occlusion on remote myocardium: effects of occlusion and reperfusion.

Focal necrosis (microinfarcts) and regional lactate derangements were observed in closed chest dogs in the nonoccluded (remote) posterior segments of the left and right ventricles after acute occlusion of the proximal left anterior descending coronary artery. Focal infarcts in the remote areas were observed in five of the six dogs with 7 days of occlusion of the left anterior descending artery and in six of seven dogs with 7 days of reperfusion after 3 hours of occlusion. There was a good correlation between the finding of microinfarcts and myocardial lactate derangements in the corresponding remote myocardium. No significant lactate derangements or microinfarcts were found in sham experiments. These findings suggest that ischemia of the remote myocardium frequently accompanies an acute coronary occlusion and may result in irreversible focal lesions.

Animals↗
PubMed1975

Regional myocardial metabolism following acute coronary artery occlusion.

Regional measurements of the consequences of coronary artery occlusions indicate myocardial derangements in both the coronary occluded and nonoccluded myocardium. The proximal left anterior descending coronary artery (LAD) was acutely occluded in 34 closed-chest anesthetized dogs through inflation of an intracoronary balloon. Temporary seperation of venous compartments was achieved by means of a balloon catheter placed within the great cardiac vein, and simultaneous blood sampling from both occluded and nonoccluded segments was carried out. Acute coronary occlusion resulted in early cardiac dysfunction which persisted during the subsequent 3 hours of LAD occlusion. Oxygen extraction increased 6-8% in both occluded and nonoccluded zones. Lactate extraction in the nonoccluded segment decreased significantly from 34.4 to 23.7% (P less than 0.05). In the occluded zone, lactate extraction dropped from 35.0 to 7.8% (P less than 0.05). Of the 34 dogs studied, 17 exhibited lactate production in the occluded segment, while 7 dogs also had lactate production in the nonoccluded region. Significant postocclusion myocardial potassium efflux was noted in both zones.

Acute Disease↗
PubMed1975

Consequences of reperfusion following acute coronary occlusion.

The sequential effects of reperfusion following acute intracoronary balloon occlusion were investigated in closed-chest anesthetized dogs by simultaneous measurement of hemodynamics and regional metabolism and histopathologic study. Simultaneous regional determinations of myocardial metabolic function were carried out in coronary-occluded and nonoccluded segments of the left ventricle. A 3-hour occlusion of the proximal left anterior descending coronary artery (LAD) resulted in significant decrease in cardiac function. Intitial reperfusion was marked by major washout of metabolites and development of frequently serious arrhythmias. Reperfusion following 3 hours of LAD occlusion led to futher deterioration in hemodynamics and metabolism: 30% of the dogs developed shock. Lactate extraction decreased further in the nonoccluded region and reached production levels in the occluded zone. Potassium loss increased in both zones. Oxygen extraction remained unchanged. Pathophysiologic examination of tissue specimens from the reperfused zone revealed microthrombi, patchy necrosis, fragmentation of myofibrils, vascular congestions, and hemorrhages.

Acute Disease↗
PubMedDate not supplied

Factors affecting penetration of retrograde coronary venous injections into normal and ischemic canine myocardium: assessment by contrast echocardiography and digital angiography.

Ths experimental study described myocardial echo contrast enhancement through coronary venous injections. Retrograde administration of renografin was performed in 15 closed-chest dogs. Two-dimensional echocardiography was used to study myocardial echo contrast enhancement before and after coronary artery occlusion. Digital subtraction venography was used to assess delivery, drainage and shunting of the retrograde injectate. Systolic/diastolic blood pressure in the great cardiac vein measured 7 +/- 3/1 +/- 0.6 mm Hg and increased to 29 +/- 11/5 +/- 3 after coronary sinus occlusion and to 55 +/- 2.3/15 +/- 12 mm Hg during coronary sinus contrast injection. Myocardial contrast echo appearance in a midpapillary left ventricular short axis cross-section was limited to the anteroseptal region, extending to 28.4 +/- 11.3% of the section circumference after great cardiac vein injections and 35.3 +/- 17% after coronary sinus injections (difference NS). After occlusion of the left anterior descending coronary artery, great cardiac vein contrast injections resulted in opacification of 36.6 +/- 9.7% of the section circumference (N.S. vs preocclusion control) and opacified most, but not all asynergic segments. After occlusion of the circumflex coronary artery, myocardial echo contrast uptake was restricted to the septum and the anterior wall. The ischemic and asynergic posterolateral myocardial segments were not opacified. Digital subtraction coronary venography revealed rapid drainage of retrogradely injected contrast to the right atrium, in spite of coronary sinus balloon occlusion via venovenous anastomoses. Retrograde coronary venous contrast injections may help define myocardial regions which are accessible with retrograde coronary venous interventions.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Experimental evaluation of a new transducer tipped catheter.

The accuracy and fidelity of a new transducer-tipped catheter (Camino Laboratories) was compared in 10 closed chest anesthetized dogs with standard Millar catheters. Simultaneous Camino and Millar measurements of left ventricular pressures and its first derivative (dp/dt) were recorded in control, after Isoprenaline infusion and during left anterior descending coronary artery balloon occlusion, to vary the pressures for comparison. Linear regression analysis comparing the Camino and Millar systems yielded a good correlation, and one way analysis of variance showed no difference between the two catheter readings, thus revealing that the recently developed Camino disposable transducer-tipped catheter provides accurate measurements of left ventricular pressure and its first derivative.

Animals↗