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Biomedical subjects

F R Cobb

Publications and source records attributed to F R Cobb.

At least 73 records · Page 4Linked to original sources
PubMed1984

Disproportionate effects of regional hypokinesis on radionuclide ejection fraction: compensation using attenuation-corrected ventricular volumes.

This study evaluates the potential effects of regional hypokinesis on measurements of global ejection fraction (EF) as determined by radionuclide angiographic techniques. Studies were performed in a two-compartment left-ventricular (LV) model that allowed stimulation of global, anterior-region, or posterior-region hypokinesis in a torso chamber with heart-to-background activity similar to that in clinical studies. Radionuclide techniques accurately measured changes in EF during global hypokinesis but progressively underestimated true EF during increasing anterior-region hypokinesis, and progressively overestimated true EF during increasing posterior hypokinesis. When EF (y-axis) was plotted against true EF (x-axis) for a 240-ml model, from linear regression equations, the slopes and intercepts were significantly different for anterior and posterior hypokinesis. The disproportionate effects of regional hypokinesis increased with LV size. Accurate EF was computed during regional hypokinesis by determining absolute LV volumes from count rates corrected for attenuation, depth, background activity and blood-pool activity. Thus, the disproportionate effects of regional hypokinesis on EF were corrected by considering differential count attenuation.

Cardiac Output↗
PubMed1983

Determinants of variable exercise performance among patients with severe left ventricular dysfunction.

The relation between bicycle exercise performance and determinants of central and peripheral cardiovascular function was assessed in 17 patients with class II to III heart failure and in 9 normal subjects. Proportional changes in oxygen consumption (VO2) from rest (R) to maximal exercise (Ex), or Mets, were used as an objective measure of the exercise capacity or functional reserve of the cardiovascular system. Left ventricular ejection fraction (EF) and proportional changes in end-diastolic volume, stroke volume, and cardiac output were determined from appropriate count data by equilibrium radionuclide angiography. Proportional changes in arteriovenous oxygen difference (A-VO2) were derived from the equation Ex/R A-VO2 = Ex/R VO2 divided by Ex/R CO, where CO = count output. Each subject exercised to an anaerobic endpoint. Maximal VO2 was significantly lower in patients than in normal subjects. Because Ex/R A-VO2 was comparable in normal subjects and patients, the lower exercise performance in patients resulted from a reduced count output response. The reduced CO response in patients resulted from failure of the ejection fraction to increase or from an attenuated heart rate response, or both. Exercise performance was variable in both groups. Multivariable analysis in the patient group identified changes in heart rate, count output, and A-VO2 with exercise as important predictors of Mets, but found no relation between Mets and changes in ejection fraction or stroke counts during exercise. Similarly, multiple regression analyses between Mets and determinants of cardiovascular function demonstrated significant correlations with Ex/R heart rate, Ex/R count output, and Ex/R A-VO2 in both groups. In patients, EF at rest ranged from 0.09 to 0.36, but it did not correlate with Mets, nor did changes in ejection fraction, stroke counts, or end-diastolic counts during exercise. The variable exercise performance among patients with severe left ventricular dysfunction was determined predominantly by a variable heart rate and A-VO2 response and not by rest or exercise indexes of left ventricular function.

Adult↗
PubMed1983

Comparison of high-dose and medium-dose propranolol in the relief of exercise-induced myocardial ischemia.

The effects of medium-dose (160 mg/day) and high-dose (480 mg/day) oral propranolol were compared in 22 patients who had typical angina pectoris and objective evidence of myocardial ischemia during exercise. Left ventricular (LV) ejection fraction (EF) and wall motion score (WMS) (an index of regional LV dysfunction) were assessed by radionuclide angiography both at rest and during exercise to the pretreatment maximum work load. Functional class improved in 11 of the 22 patients during medium-dose propranolol therapy. Medium-dose propranolol reduced mean resting heart rate from 71 to 55 beats/min, exercise heart rate from 122 to 93 beats/min, and exercise systolic blood pressure from 183 to 162 mm Hg (p less than 0.001 for each). The incidences of exercise-induced chest pain and S-T segment depression were reduced from 19 to 9 patients (p less than 0.001), and from 20 to 10 patients (p = 0.002), respectively. Medium-dose propranolol had no effect on mean EF or WMS at rest, but improved function in ischemic regions during exercise; WMS decreased (p = 0.001), and mean exercise EF increased from 0.51 to 0.56 (p = 0.025). Compared with the medium dose, high-dose propranolol improved functional class in 3 additional patients, and further reduced mean resting heart rate (from 55 to 52 beats/min, p = 0.001) and mean exercise heart rate (from 93 to 86 beats/min, p = 0.001). Exercise-induced chest pain and S-T segment depression were abolished in a further 7 and 6 patients, respectively. Exercise EF and WMS improved further in several patients, but the changes were not statistically significant for the group (p = 0.095 and 0.082, respectively). Thus, in patients with coronary artery disease and exercise-induced ischemia, propranolol reduced heart rate and blood pressure and the incidence of exercise-induced chest pain, electrocardiographic changes, and ischemic LV dysfunction. Although most of these effects were seen with medium-dose propranolol, higher doses provided additional relief of chest pain and S-T segment depression, and further improved global and regional LV function in several patients.

Angina Pectoris↗
PubMed1983

Effect of rate-dependent left bundle branch block on global and regional left ventricular function.

Seven subjects with rate-dependent left bundle branch block (RDLBBB) and 13 subjects with normal conduction (control group) underwent upright bicycle exercise radionuclide angiography to determine the effects of the development of RDLBBB on global and regional left ventricular function. Six of the seven subjects with RDLBBB had atypical chest pain syndromes; none had evidence of cardiac disease based on clinical examination and either normal cardiac catheterization or exercise thallium-201 scintigraphy. Radionuclide angiograms were recorded at rest and immediately before and after RDLBBB in the test group, and at rest and during intermediate and maximal exercise in the control group. The development of RDLBBB was associated with an abrupt decrease in left ventricular ejection fraction (LVEF) in six of seven patients (mean decrease 6 +/- 5%) and no overall increase in LVEF between rest and maximal exercise (65 +/- 9% and 65 +/- 12%, respectively). In contrast, LVEF in the control group was 62 +/- 8% at rest and increased to 72 +/- 8% at intermediate and 78 +/- 7% at maximal exercise. The onset of RDLBBB was associated with the development of asynchronous left ventricular contraction in each patient and hypokinesis in four of seven patients. All patients in the control group had normal wall motion at rest and exercise. These data indicate that the development of RDLBBB is associated with changes in global and regional ventricular function that may be confused with development of left ventricular ischemia during exercise.

Adult↗
PubMed1983

The use of radionuclide angiography in the diagnosis of coronary artery disease--a logistic regression analysis.

We applied logistic regression analysis to a group of 736 patients with chest pain to determine which radionuclide angiographic (RNA) parameters were most useful in the diagnosis of significant coronary artery disease. The most useful parameters were exercise ejection fraction, exercise heart rate, "ischemia score," and the presence of a regional wall motion abnormality at exercise. Ten clinical variables were used in one logistic regression model to estimate each patient's pretest probability of disease. A second logistic regression model considered these clinical variables and the four important RNA parameters to estimate each patient's posttest probability. These models were applied prospectively to a group of 76 patients with chest pain who did not have a high pretest probability of disease. Twenty-four patients (32%) could be diagnosed with 90% probability; 32 patients (42%) could be diagnosed with 85% probability. RNA testing is therefore helpful in the noninvasive diagnosis of coronary artery disease. However, a majority of patients who do have a low or intermediate pretest probability of disease will require additional testing for a definitive diagnosis.

Cardiac Catheterization↗
PubMed1983

Transitional blood flow zones between ischemic and nonischemic myocardium in the awake dog. Analysis based on distribution of the intramural vasculature.

The present study evaluates the transitional or border zone of intermediate blood flow reduction between nonischemic and ischemic regions after acute coronary artery occlusion in chronically instrumented dogs, using methods that minimize an admixture of ischemic and nonischemic myocardium in the tissue analyzed. The regions perfused by occluded and nonoccluded vessels were identified by tracing the extra and intramural distribution of the coronary vasculature from postmortem angiograms. Regional blood flow was evaluated in serial 3-mm-wide epicardial and endocardial zones from outside and inside the interface between occluded and nonoccluded vessels. The zone of intermediate reduction in blood flow between nonischemic and ischemic regions occurred in the first 3-mm section immediately inside the region supplied by the occluded vasculature. Mean blood flow in this region was reduced to 58 +/- 6% and 61 +/- 5% (+/- SEM) of nonischemic region blood flow at the lateral and medial epicardial margins, respectively, and 47 +/- 5% and 45 +/- 6% at the lateral and medial endocardial margins, respectively. In the remaining ischemic zone, significant differences in blood flow existed between epicardial and endocardial layers; these differences were highly variable between animals. The data indicate that when the analysis of regional blood flow following acute ischemia is based on the anatomic distribution of the coronary vasculature, the transitional or border zone of intermediate reduction in blood flow is limited to a narrow zone immediately inside the occluded vasculature. Studies performed in acutely anesthetized dogs in which the occluded region was perfused via a two-chamber blood reservoir that allowed maintenance of perfusion and exclusion of microspheres from the circumflex region indicate that intermediate reductions in blood flow at the border of the ischemic zone resulted from an admixture of normal myocardium and, thus, do not represent a border zone of intermediate ischemia.

Animals↗
PubMed1982

A QRS scoring system for assessing left ventricular function after myocardial infarction.

A QRS scoring system for estimating the size of a myocardial infarct was evaluated in 55 patients who did not have left ventricular hypertrophy or conduction abnormalities. Serial 12-lead surface electrocardiograms were scored according to a 29-point system based on the duration of Q and R waves and on the ratios of R-to-Q amplitude and R-to-S amplitude. The scores were proportional to the severity of wall-motion abnormalities, which was determined by radionuclide blood-pool scanning and which correlated inversely with the radionuclide-determined left ventricular ejection fraction (LVEF). A score less than 3 was 93 per cent sensitive and 88 per cent specific for both severe regional dyssynergy and major depression of the global LVEF. The following equation was used to estimate the LVEF from the QRS score: LVEF (%) = 60 - (3 x QRS score). After acute myocardial infarction, an electrocardiogram can provide important indirect quantitative information about left ventricular function.

Electrocardiography↗
PubMed1982

Assessment of left ventricular function by resting and exercise radionuclide angiocardiography following acute myocardial infarction.

Left ventricular function was evaluated by first-pass radionuclide angiocardiography in 42 patients at 3 and 8 weeks following acute myocardial infarction. Left ventricular ejection fraction, diastolic volume, and wall motion were measured at rest and submaximal exercise at 3 weeks and at rest, submaximal and maximal exercise at 8 weeks. The mean ejection fraction, end-diastolic volume, and wall motion index did not change between 3 and 8 weeks in any group either at rest or during submaximal exercise. Ventricular function was decreased at rest in patients with previous and anterior myocardial infarctions, but not in patients with inferior and subendocardial myocardial infarctions. During maximal exercise at 8 weeks, nine patients (21%) had ST segment depression, whereas 25 patients (60%) had a decrease in ejection fraction or a deterioration in wall motion. These abnormalities of ventricular function during exercise occurred equally among the infarct groups. Radionuclide angiography in patients with recent myocardial infarction demonstrated highly variable ventricular function at rest and/or during exercise in each infarct subgroup.

Adult↗
PubMed1982

Relation between regional distribution of thallium-201 and myocardial blood flow in normal, acutely ischemic, and infarcted myocardium.

Myocardial localization of thallium-201 was compared with direct measurements of myocardial perfusion in normal, acutely ischemic, and recently infarcted myocardium. Studies were performed in 6 chronically instrumented dogs that were subjected to myocardial infarction by occlusion of the proximal left circumflex coronary artery. Four days after myocardial infarction, thallium-201 and 9 +/- 1 micrometer niobium-95-labelled microspheres were injected simultaneously after acute left anterior descending coronary arterial occlusion; the animals were killed 5 minutes later and the entire left ventricle was sectioned into 1 to 2 g samples. Regression analyses between thallium-201 activity and regional myocardial blood flow using all myocardial samples demonstrated a very close linear relation in each dog; r values were 0.98 or greater, indicating that the initial localization of thallium-201 in acutely ischemic and recently infarcted myocardium as a function of regional blood flow was essentially identical. Consequently, in each dog the regional distribution of thallium-201 closely approximated myocardial perfusion over a wide range of blood flow and potentially different local metabolic conditions that may be encountered in the clinical use of the isotope.

Animals↗
PubMed1982

Prospective evaluation of radionuclide angiocardiography for the diagnosis of coronary artery disease.

This investigation assesses prospectively the accuracy of rest and exercise radionuclide angiocardiography (RNA) in detecting coronary artery disease (CAD). By retrospective analysis of 496 patients, optimal RNA criteria were determined for the presence or absence of CAD. Multivariate analysis of patients with normal coronary arteries on catheterization provided a formula to predict normal exercise ejection fraction (EF) in a given patient. The presence of CAD was indicated by 1 or more of the following RNA measurements: (1) rest EF less than 0.50, (2) exercise EF at least 0.06 less than the predicted value, (3) exercise increase in end-systolic volume greater than 20 ml, (4) exercise-induced wall motion abnormality. The absence of CAD was indicated by the absence of all 4 criteria. After applying these criteria to 221 consecutive patients, the RNA determinations were compared with the catheterization, determinations. Significant CAD was present in 71% of the patients studied. The sensitivity of the test was 0.87 and the specificity 0.54. Thus, because of its high sensitivity, RNA is of value in screening patients under consideration for cardiac catheterization. No patient with significant left main coronary narrowing and only 4 of 65 patients with 3-vessel disease were misdiagnosed. The poor specificity of the test, however, limits its overall accuracy.

Adult↗
PubMed1982

Myocardial infarct extension: incidence and relationship to survival.

Myocardial infarct extension, defined as reelevation or reappearance of creatine phosphokinase-MB (CK-MB) 48 hours after the onset of symptoms, was evaluated prospectively in 56 consecutive patients with acute myocardial infarction. Myocardial infarct extension occurred in eight patients (14%). The sensitivity, specificity and predictive accuracy in the diagnosis of myocardial infarct extension were 63%, 85% and 42%, respectively, for recurrent chest pain requiring morphine; 50%, 65% and 19% for recurrent ST-segment elevation on routine 12-lead ECGs; and 88%, 63% and 28% for reelevation of total CK. Three of the eight episodes of extension were clinically silent. Four of eight patients (50%) with extension died, compared with one of 46 patients (2%) without extension (p = 0.0009). CK-MB persisted for 72 hours or longer in 16 patients and identified seven of eight patients who subsequently had infarct extension. We conclude that myocardial infarct extension is an infrequent complication of acute myocardial infarction and is associated with a very high mortality rate. Persistence of CK-MB for 72 hours or more identifies a subgroup of patients at high risk for subsequent infarct extension and death.

Creatine Kinase↗
PubMed1982

Effects of exercise training on ventricular function in patients with recent myocardial infarction.

We evaluated the effects of 6 months of exercise training (bicycle ergometry, walking and jogging) on exercise performance and ventricular function in patients with recent myocardial infarction. Fifteen patients were selected on the basis of myocardial infarction at least 6 weeks but not more than 6 months before the study and age younger than 65 years. The patients were evaluated by maximal treadmill exercise testing and radionuclide angiography at rest and exercise before and after training. Before exercise training, maximal treadmill exercise time ranged from 1.5 to 11 minutes, ejection fraction at rest from 18% and 67% and end-diastolic volume from 108 to 208 ml. The mean EF was 48 +/- 5% (+/- SD) at rest and did not change at maximal exercise (48.5 +/- 5%). All 11 patients who completed the exercise training program achieved a significant training effect, as defined by a reduction in heart rate at 50% maximal pretraining effort or an increase in maximal treadmill time. The mean ejection fraction and end-diastolic volume and wall motion abnormalities at rest and at comparable pretraining exercise work loads and heart rates were not significantly different after training. Despite a wide range of rest and exercise ventricular function, patients with recent uncomplicated myocardial infarcts significantly increased their exercise performance. Because rest and exercise ventricular function were comparable before and after training, improvement in exercise performance probably resulted from training effects on the peripheral vasculature.

Adult↗
PubMed1982

Ejection fraction response to exercise in patients with chest pain, coronary artery disease and normal resting ventricular function.

We studied the ejection fraction (EF) response to upright exercise using first-pass radionuclide angiography (RNA) in 281 patients with chest pain, significant coronary artery disease and normal resting ventricular function. A wide range of resting function (heart rate and EF) and exercise function (heart rate, EF and peak work load) was measured in this population. The EF response to exercise (delta EF) varied widely, ranging from a decrease of 36% to an increase of 26%. Twenty-eight clinical, catheterization and RNA variables were examined to determine their relationship to delta EF. Considered individually, the variables showing the strongest relationship were resting pulse pressure, positive exercise ECG changes and adequate exercise. Multivariable analysis identified resting pulse pressure, adequate exercise, resting EF, the change in end-diastolic volume index with exercise, positive exercise ECG changes and, to a lesser degree, the number of diseased vessels as variables that were significant independent predictors of delta EF. These observations indicate that delta EF is a complex response that is influenced by many pathophysiologic variables in the presence of coronary artery disease. Several of these variables are not related to the extent of coronary artery disease.

Adult↗
PubMed1982

Comparison of 180 degrees and 360 degrees data collection in thallium-20 1 imaging using single-photon emission computerized tomography (SPECT): concise communication.

Thallium-201 imaging using SPECT is being done with 180 degrees (RAO to LPO) data collection in some centers with single-gamma camera systems. Using our SPECT system with two gamma cameras, we have compared the effects of 180 degrees data collection without attenuation correction against 360 degrees collection with attenuation correction, using phantoms and patients. With a heart phantom in a chest phantom, TI-201 activities simulating "normal myocardium," "ischemia," "infarction," and "background" were placed in object contrast ratios (with respect to background) of 5.0, 2.0, and -1.0, respectively. The 180 degrees data gave image contrast ratios of 1.6, 0.2, and -0.8, and the 260 degrees data gave ratios of 1.5, 0.8, and -0.3, respectively. Uniform activity throughout the heart gave similar image contrast with both data-collection methods, but there was more variability with the 180 degrees collection than with 360 degrees collection. Since attenuation correction is available with the 260 degrees collection, the effects of attenuation are seen only on the 180 degrees collection images. In eight patients the image contrasts from the 180 degrees and 260 degrees collections are similar. For our two-camera SPECT system, the 360 degrees collection permits attenuation correction, has less variability in counting statistics, and gives contrast ratios like those of 180 degrees collection.

Coronary Circulation↗
PubMed1981

Influence of resting left ventricular function on the left ventricular response to exercise in patients with coronary artery disease.

First-pass radionuclide angiocardiography was used to access the left ventricular response to submaximal exercise in 150 patients with coronary artery disease (CAD). To test the hypothesis that resting systolic left ventricular function as determined by left ventricular ejection fraction (LVEF) was a predictor of the hemodynamic response to exercise, the study group included patients with a wide range of resting LVEF (0.12-0.82). The influences of resting LVEF, resting end-diastolic volume, the number of diseased vessels, exercise end point and exercise double product on the change in LVEF (delta LVEF) during exercise were tested using multiple linear regression analyses. Resting LVEF was a highly significant predictor of the delta LVEF (p = 0.0001). Exercise duration was not related to either the resting LVEF or the delta LVEF. For the 112 patients in whom coronary anatomy was known, resting LVEF retained its significance as a predictor of delta LVEF (p = 0.002) even after adjustment for the significance of the extent of CAD (p = 0.0007) and the exercise end point (p = 0.06). Patients with normal resting LVEF showed the most profound decreases in LVEF, the highest frequency of new regional dysfunction and the largest relative increase in end-diastolic volume during exercise. As rest LVEF decreased, the magnitude of the delta LVEF and the frequency of new regional dysfunction decreased. Therefore, left ventricular function at rest is an important determinant of the direction and magnitude of change in left ventricular function during exercise.

Adult↗
PubMed1981

Accuracy of diagnosis of coronary artery disease by radionuclide management of left ventricular function during rest and exercise.

Rest and exercise radionuclide angiocardiographic measurements of left ventricular function were obtained in 496 patients who underwent cardiac catheterization for chest pain. Two hundred forty-eight of these patients also had an exercise treadmill test. An ejection fraction less than 50% was the abnormality of resting left ventricular function that provided the greatest diagnostic information. In patients with normal resting left ventricular function, exercise abnormalities that were optimal for diagnosis of coronary artery disease were an injection fraction at least 6% less than predicted, an increase greater than 20 ml in end-systolic volume and the appearance of an exercise-induced wall motion abnormality. The sensitivity and specificity of the test were lower in patients who were taking propranolol at the time of study and in patients who failed to achieve an adequate exercise end point. In the 387 patients with an optimal study, the test had a sensitivity of 90% and a specificity of 58%. Radionuclide angiocardiography was more sensitive and less specific than the exercise treadmill test. The high degree of sensitivity of the radionuclide test suggests that it is most appropriately applied to patient groups with a high prevalence of disease, including those considered for cardiac catheterization.

Adult↗