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Biomedical subjects

M V Cohen

Publications and source records attributed to M V Cohen.

At least 127 records · Page 7Linked to original sources
PubMed1986

Thallium-201 scintigraphic quantitation of regional flow disparity and subsequent redistribution in dogs.

Although quantitative analysis of postexercise thallium-201 (201Tl) scintigrams has been employed clinically for the diagnosis of coronary disease, the precise relationship of the quantitated defects to microsphere determined blood flow has not been determined. Accordingly, 201Tl was injected during exercise in 12 control dogs and seven with left circumflex (LCf) artery stenosis. Gamma camera scanning was started 10 min after 201Tl injection and continued for 3 hr. In the control animals, scintigraphic 201Tl activities in left anterior descending (LAD) and LCf perfusion territories were equal 10 min after 201Tl injection and the loss of 201Tl activity over 3 hr was 54.3 +/- 3.4% and 57.0 +/- 3.6% (mean +/- s.e.e.) of initial LAD and LCf activity, respectively (p = N.S.). In the experimental group, LCf activity 10-14 min after 201Tl injection averaged 67.4 +/- 5.9% of LAD activity in the same heart (p less than 0.001). Furthermore, LCf activity in the experimental animals was significantly lower than LCf activity in the control dogs (p less than 0.005), while LAD activities were not different in the two groups. The ratio of LCf/LAD scintigraphic 201Tl activity immediately after exercise was linearly related to, but higher than, the ratio of regional blood flows at peak exercise (r = 0.88, p less than 0.001) as determined by microsphere injection. Scintigraphic redistribution was also correlated with directly measured redistribution determined by well counter analysis (r = 0.83, p less than 0.025). Thus, in this exercise model, quantitative 201Tl scintigraphy accurately assessed the initial postexercise flow disparity and subsequent redistribution.

Animals↗
PubMed1985

Myocardial blood flow during cardiac tamponade in dogs with coronary occlusion: effects of isoproterenol.

To determine the effects of cardiac tamponade in dogs with ligation of the left anterior descending coronary artery, fluid was introduced into the pericardial space to raise right and left atrial and pericardial pressures, first to 7 to 9 mm Hg and then to 11 to 12 mm Hg. Normal and ischemic myocardial blood flow fell approximately 20% to 25% during mild tamponade (1.27 +/- 0.16 to 1.00 +/- 0.06 ml/min/gm and 0.52 +/- 0.12 to 0.39 +/- 0.08 ml/min/gm, respectively) and by 50% during moderate tamponade (0.66 +/- 0.08 and 0.23 +/- 0.05 ml/min/gm, respectively). The inner/outer left ventricular wall blood flow ratio decreased modestly from 1.16 to 1.08 (p less than 0.025) in normal areas but increased from 0.53 to 0.61 (p less than 0.05) in the ischemic regions, suggesting possible epicardial vessel compression. Isoproterenol resulted in prompt decreases in pericardial and filling pressures, 16% increase in aortic pressure, and 200% rise in cardiac output. Normal myocardial blood flow more than doubled (1.55 +/- 0.12 ml/min/gm, p less than 0.001). Although average ischemic blood flow rose slightly to 0.042 +/- 0.10 ml/min/gm, the increase was not significant. Furthermore, changes in ischemic blood flow were heterogeneous with frank decrease in one dog. Therefore, although isoproterenol has salutary hemodynamic effects, its unpredictable action on myocardial blood flow should cause one to use it cautiously in those with tamponade who are believed to have coronary occlusive disease.

Animals↗
PubMed1985

Exercise thallium-201 scintigraphy in dogs: effects of long-term coronary occlusion and collateral development on early and late scintigraphic images.

To examine the effects of coronary collateral development on thallium-201 (201Tl) distribution the left circumflex coronary artery was ligated in eight dogs. Three days later these animals ran on a treadmill, and 201-thallous chloride was injected into the right atrium at peak exercise. Scintigraphic scanning was begun within 10 min and continued for 3 hr. Scanning was repeated weekly for 6 weeks. In the last week radioactive microspheres were injected into the left atrium at peak exercise to measure regional myocardial blood flow. The scintigraphically determined disparity between perfusion of the ischemic and normal myocardium was most marked at 3 days after ligation. This difference gradually lessened over the first 4 weeks until there was no difference in 201Tl distribution to normally perfused myocardium and tissue distal to the ligation. Concomitant with the improvement in the scintigrams, exercise hemodynamics also improved over this 4 week period with significant increases in cardiac output and decreases in left atrial pressure. Serial coronary angiographic studies in two animals demonstrated the appearance of collaterals in the initial weeks after coronary occlusion, and by 4 weeks the left circumflex artery distal to the obstruction was completely opacified by collateral flow. The ratio of directly measured exercise blood flow to the left circumflex and normally perfused tissues was 0.89 +/- 0.08 at 6 weeks after ligation. Scintigraphic 201Tl redistribution after 3 hr also changed over the weeks after ligation. Three days after ligation washout from the ischemic area was significantly slower than that from the normal myocardium. By 6 weeks loss of 201Tl from the two regions occurred at nearly equal rates. Thus myocardial perfusion and function during exercise after coronary occlusion are dynamic events that change with time. It is likely that coronary collateral development is responsible for these phenomena. Therefore coronary collaterals do have salutary effects in the dog.

Animals↗
PubMed1984

Pulmonary arterial V waves in mitral regurgitation: clinical and experimental observations.

Pulmonary arterial early diastolic waves (V waves) were investigated in patients and experimental animals with mitral regurgitation. V waves exceeding systolic pressure in the pulmonary artery were recorded in the main pulmonary artery with micromanometer catheters both in patients and animals, eliminating the possibility of catheter artifact. In experimental animals, aortic closure preceded pulmonic closure by 33 +/- 12 msec at baseline. With the creation of acute mitral insufficiency, a pulmonary arterial V wave occurred in six of eight animals. Early pulmonic valve closure occurred only in the six animals with a pulmonary arterial V wave. In these animals, pulmonic closure preceded aortic closure by 28 +/- 7 msec during mitral insufficiency (p less than .05). Of 70 patients with severe mitral regurgitation at cardiac catheterization, 14 had a pulmonary arterial V wave. In five patients recordings with micromanometer catheters were made and early pulmonic closure was also observed in four of these patients who had pulmonary arterial V waves at rest or upon provocation. Patients with pulmonary arterial V waves had a more acute onset of symptoms, shorter duration of mitral regurgitation, higher pulmonary capillary wedge V waves, and lower pulmonary arterial resistances than patients without them and were more likely to have nonrheumatic mitral regurgitation.

Adult↗
PubMed1983

Production of free radicals and lipid peroxides in early experimental myocardial ischemia.

Free radicals and lipid peroxides have recently been identified by us [1, 2, 3] as metabolic intermediates during acute myocardial ischemia. The mechanisms by which evolving myocardial ischemia initiates free radical production are not clear. Based on studies in vitro, it is feasible to consider the following possibilities: (a) dissociation of intramitochondrial electron support system and altered phospholipid integrity with inactivation of cytochrome oxidase, which results in release of ubisemiquinone, flavoprotein and superoxide radicals; (b) accumulation and increased release of intra/extracellular metabolites like NADH, lactate flavoproteins and catecholamines which react either with themselves or with O2 and ascorbic acid; (c) interaction of the metabolic product hypoxanthine with O2 in the presence of xanthine oxidase and (d) activation of phospholipase by calcium influx with enhanced arachidonic acid metabolism and superoxide radical production. Detailed in vitro radiobiological studies [4] have demonstrated that free radical reactions occur even at very low O2 tensions (83% of maximum rate of PO2 approximately 6 mmHg and 50% at PO2 approximately 1 mmHg), and Smith [5] has demonstrated that free radical peroxidation takes place quite rapidly in rat brain homogenates incubated in gas mixtures containing only 5% O2. Thus, the low oxygen tensions in ischemic tissue are adequate to support free radical reactions. The free radicals thus produced may initiate and enhance lipid peroxidation by attacking polyunsaturated membrane lipids.

Animals↗
PubMed1983

Pulmonary valve gonococcal endocarditis. A forgotten disease.

Although gonococcal infections of the pulmonary valve were common before the introduction of antibiotics, such infections have rarely been reported since penicillin became available. In an elderly man with gonococcal endocarditis of the pulmonary valve the non-specific signs and symptoms, the late appearance of a pulmonary murmur, and the sterility of early blood cultures made the diagnosis unclear until three weeks after admission. Endocarditis was localised to the pulmonary valve by M-mode and cross-sectional echocardiography. Echocardiography may be useful for diagnosing endocarditis in patients with fever of unknown origin. Gonococcal infection should be suspected in patients with pulmonary vegetations and sterile blood cultures.

Aged↗
PubMed1982

Coronary collateral stimulation by exercise in dogs with stenotic coronary arteries.

To determine the effects of an exercise-training program on coronary collateral development, we instrumented 13 1-yr-old beagles with left circumflex (LCf) coronary artery flow probes and balloon occluders and left atrial and aortic catheters. The LCf artery was constricted resulting in a 58 +/- 4% reduction of the peak reactive hyperemia response following release of a 154-s LCf occlusion. All dogs were studied during the first week of the study protocol. Resting heart rate, cardiac output, and left atrial and aortic pressures were evaluated before and during a 1-min LCf occlusion. Myocardial blood flow was also measured with radioactively-labeled microspheres injected into the left atrium during the LCf occlusion. Subsequently the dogs were exercised at 6.4 km/h and 12% grade, and all hemodynamic and blood flow measurements were repeated. The animals were then randomized to either a sedentary or exercising group. The six sedentary animals were confined to their cages, while the seven training beagles did sprint and endurance running for 75 min/day, 5 days/wk. After 12 wk the hemodynamic and blood flow studies were repeated at rest and during treadmill running. There were no statistically significant differences in resting or exercise hemodynamics, response to LCf occlusion, or myocardial blood flow in the two groups in wk 1. Hemodynamics and blood flow data were virtually unchanged in the sedentary animals after 12 wk. However, the trained dogs demonstrated less evidence of left ventricular failure following LCf occlusion while running and had significantly higher myocardial blood flows. Their resting collateral flow increased from 0.52 +/- 0.16 ml . min-1 . g-1 at wk 1 to 0.90 +/- 0.28 ml . min-1 . g-1 at wk 12 (P less than 0.05), while the ratio of collateral to normal myocardial blood flow increased from 0.46 +/- 0.12 to 0.64 +/- 0.16 (P less than 0.05). Thus chronic exercise can stimulate coronary collateral development, and the enhanced collateral flow has a salutary functional effect.

Animals↗
PubMed1982

Left ventricular volume and function during relief of cardiac tamponade in man.

To determine the causes of cardiac failure during cardiac tamponade in man, we studied left ventricular volume and function in eight patients during pericardiocentesis using gated equilibrium radionuclide ventriculography. In the seven patients with clinical and hemodynamic evidence of cardiac tamponade, end-diastolic and end-systolic volumes increased progressively as the initial 500 ml of fluid were removed; the most marked increase occurred during the removal of the first 200 ml of pericardial fluid. After removal of 500 ml of pericardial fluid, end-diastolic volume increased from 52 +/- 8 ml to 111 +/- 13 ml (p less than 0.05) and end-systolic volume from 17 +/- 5 ml to 34 +/- 7 ml (p less than 0.05). Additional aspiration of fluid resulted in no further changes in left ventricular volume. The ejection fraction averaged 70% before removal of fluid and was unchanged by pericardiocentesis. In the one patient who did not have hemodynamic evidence of tamponade, there were only minor changes in left ventricular volumes and ejection fraction. These data suggest that pump function of the left ventricle is well preserved in cardiac tamponade, and that the diminution in stroke volume and consequent cardiovascular collapse seen in tamponade are due to marked underfilling of the ventricle.

Cardiac Output↗
PubMed1981

Effects of thyroid hormone on left ventricular function in patients treated for thyrotoxicosis.

Systolic time intervals, echocardiographic indexes of left ventricular contractile function and serum triiodothyronine and thyroxine levels were measured before treatment in nine patients with hyperthyroidism, and again every 2 weeks for the first 2 months after therapy and then every 4 weeks until the subjects were clinically and chemically euthyroid. Six of the nine became transiently hypothyroid. Although the preejection period corrected for heart rate (preejection period index) increased as the patients became euthyroid, the change was not significant. Preejection period index increased dramatically in the patients becoming hypothyroid (p less than 0.005). Corrected left ventricular ejection time (left ventricular ejection time index) also increased as the patients became euthyroid (p less than 0.001), and increased again with the appearance of hypothyroidism (p less than 0.05). There was a linear correlation between velocity of circumferential fiber shortening and serum triiodothyronine level (r - 0.77) and between velocity of circumferential fiber shortening and serum thyroxine level (r = 0.70) at all stages of thyroid function. Thus thyroid hormone definitely enhances left ventricular function in human beings, and both excess and deficiency cause predictable reversible changes in myocardial contractile function. Thus thyroid hormone definitely enhances left ventricular function in human beings, and both excess and deficiency cause predictable reversible changes in myocardial contractile function. Furthermore echocardiographic measurements of velocity of circumferential fiber shortening provide rapid estimates of the chemical status of thyrotoxic patients before and after treatment.

Adult↗
PubMed1981

Clinical presentation and non-invasive diagnosis of right heart masses.

Right-sided cardiac masses do not have a uniform clinical presentation. Successful diagnosis is dependent on a high index of suspicion and appropriate echocardiographic examination. Five cases of right sided intracardiac masses have been detected during the period that echocardiography has been routinely available to us--two of right atrial myxoma, one of right atrial thrombus, and two of right ventricular tumour. M-mode echocardiography identified four of the five cases. Two-dimensional echocardiography was necessary to establish the non-invasive diagnosis in the fifth case. Echocardiography should be used in any patient in whom a right sided mass is suspected, or in those patients presenting with signs of tricuspid regurgitation, tricuspid stenosis, pulmonary stenosis, cyanotic heart disease, progressive right heart failure, constrictive pericarditis, or pulmonary emboli without obvious source.

Adult↗
PubMed1981

Restoration of cardiac function and myocardial flow by collateral development in dogs.

Hemodynamics of instrumented beagles with 75-85% stenoses of the left circumflex (LCf) coronary artery were evaluated before and during transient LCf balloon occlusion at rest and during treadmill running. Studies were done after surgery and 3 mo later. Myocardial blood flow was measured with radioactive microspheres during the LCf occlusions. Nine dogs (group I) had patent LCf arteries at the second study, and six (group II) had occluded vessels. Transient LCf occlusion during running in group I at weeks 1 and 12 and in group II at week 1 caused significant left ventricular failure, whereas the same protocol in group II dogs at week 12 produced minimal hemodynamic changes. Left ventricular failure precipitated by coronary occlusion during exercise diminished from week 1-12 in those animals with increasing LCf collateral flow, but actually increased in the animals with diminishing collateral flow. In group II dogs after chronic LCf occlusion total flow to LCf myocardium as well as inner-to-outer layer ratios were normal both at rest and during exercise. Thus coronary collaterals do preserve myocardial function, limit adverse hemodynamic responses to myocardial ischemia, and restore postocclusion tissue flows to normal even during the stress of exercise.

Animals↗
PubMed1979

Abnormal mitral valve motion associated with ventricular septal defect following acute myocardial infarction.

It is often difficult to make the clinical distinction between acute mitral regurgitation caused by papillary muscle dysfunction or rupture and ventricular septal defect complicating an acute myocardial infarction. A case of a patient with rapidly progressive congestive heart failure and a loud murmur is presented. Echocardiography strongly suggested the presence of a flail posterior mitral leaflet. However, the patient was subsequently found to have rupture of the interventricular septum. This diagnosis was made with bedside right heart catheterization and was later confirmed by left ventriculography and direct inspection at the time of surgery. The mitral valve apparatus was completely normal. Thus this case demonstrates the apparent lack of specificity of the accepted echocardiographic criteria for flail mitral leaflet and acutely ruptured interventricular septum, and the potential necessity of cardiac catheterization to distinguish between these entities.

Aged↗