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Biomedical subjects

T D Miller

Publications and source records attributed to T D Miller.

At least 73 records · Page 4Linked to original sources
PubMed1990

Risk stratification of single or double vessel coronary artery disease and impaired left ventricular function using exercise radionuclide angiography.

Patients with 3-vessel coronary artery disease (CAD) and normal left ventricular (LV) function have a worse prognosis if they manifest ischemia during exercise testing. The present study determines if exercise radionuclide angiography can aid in the risk stratification of patients with 1- or 2-vessel CAD and impaired LV function (ejection fraction less than 50%). Sixty-five consecutive patients with these findings were followed for a median duration of 24 months (range 12 to 49). Eleven of the 65 patients (17%) had severely ischemic exercise radionuclide angiograms, defined as: a decrease in ejection fraction with exercise; greater than or equal to 1.0 mm of ST-segment depression; and peak exercise workload less than or equal to 600 kg-m/min. During follow-up 11 patients had initial significant cardiac events: 4 cardiac deaths, 1 cardiac arrest, 4 myocardial infarctions and 2 bypass or angioplasty procedures for unstable angina greater than or equal to 3 months after the exercise study. Four of 11 patients (36%) with severely ischemic exercise radionuclide angiograms had events, compared to 7 of 54 patients (13%) without ischemic radionuclide angiograms. Event-free survival at 18 months was 73% for patients with severe exercise ischemia versus 92% for those without ischemia (p less than 0.05). Univariate analysis showed that severe ischemia on radionuclide angiography was the only variable of several tested that significantly predicted future cardiac events (chi-square = 8.16, p less than 0.005). Among patients with 1- or 2-vessel CAD and impaired resting LV function, severe ischemia on exercise radionuclide angiography identifies a subgroup at high risk for future cardiac events.

Coronary Disease↗
PubMed1990

Left ventricular systolic response to exercise in patients with systemic hypertension without left ventricular hypertrophy.

Supine exercise radionuclide angiography was performed in 367 men to assess left ventricular (LV) systolic response to exercise; 58 had systemic hypertension without LV hypertrophy on a resting electrocardiogram and 309 were normotensive. All patients met the following criteria defining a low pretest likelihood of coronary artery disease: age less than 50 years; normal electrocardiographic response to exercise; absence of typical or atypical chest pain; and exercise heart rate greater than 120 beats/min. Patients taking beta-receptor blockers were excluded. There were no significant differences between hypertensive and normotensive groups in peak exercise heart rate, workload or exercise duration. However, hypertensive patients had significantly higher peak exercise systolic blood pressures and peak exercise rate-pressure products. There were no differences between patients with and without hypertension in resting ejection fraction, peak exercise ejection fraction (hypertensive patients 0.71 +/- 0.01, normotensive patients 0.70 +/- 0.05) or change in ejection fraction at peak exercise (hypertensive patients 0.07 +/- 0.01, normotensive patients 0.07 +/- 0.04). Diastolic and systolic ventricular volumes tended to be smaller in the hypertensive patients, but the difference was not statistically significant. The change in systolic volume with exercise was similar in the 2 groups (hypertensive -10 +/- 3 ml/m2, normotensive -10 +/- 1 ml/m2). In the absence of electrocardiographic evidence of LV hypertrophy, systemic hypertension does not influence LV systolic response to exercise.

Adolescent↗
PubMed1990

Supine exercise electrocardiography compared with exercise radionuclide angiography in noninvasive identification of severe coronary artery disease.

STUDY OBJECTIVE: To determine the incremental value of exercise radionuclide angiography for identification of severe coronary artery disease. DESIGN: Retrospective analysis comparing logistic regression models. SETTING: A tertiary care referral center. PATIENTS: Three hundred and ninety-one consecutive patients who had normal resting electrocardiograms (ECGs) and no digoxin therapy within the previous week. MEASUREMENTS AND MAIN RESULTS: The exercise ECG model, consisting of magnitude of ST depression, exercise heart rate, and patient gender, was highly predictive of three vessel or left main coronary artery disease (chi 2 = 100, P less than 0.0001). The model correctly classified 60% of the study group which included 56 patients with and 179 without severe disease. The addition of radionuclide angiographic variables improved the predictive power of the model (chi 2 = 124, P less than 0.0001). However, the exercise radionuclide angiographic variables increased the number of patients who were correctly classified by only 11 and the percentage by 3% (to a total of 63% of the study group). CONCLUSIONS: The modest additional advantage provided by exercise radionuclide angiography for identification of three vessel or left main coronary artery disease in patients with normal resting ECGs would not appear to justify its routine use for this purpose. Before this conclusion is used as a guide for clinical practice, our results should be prospectively confirmed in a separate sample of patients in another institution.

Coronary Angiography↗
PubMed1990

Cardiovascular rehabilitation: status, 1990.

Cardiovascular rehabilitation is defined as the process of development and maintenance of a desirable level of physical, social, and psychologic functioning after the onset of a cardiovascular illness. Patient education, counseling, nutritional guidance, and exercise training play prominent roles in the process of rehabilitation. Benefits from cardiac rehabilitation include improved exercise capacity and decreased symptoms of angina pectoris, dyspnea, claudication, and fatigue. Recent pooled data regarding exercise training after myocardial infarction demonstrated a 20 to 25% reduction in mortality and major cardiac events. Exercise training may result in an improvement in systemic oxygen transport, a reduction in the myocardial oxygen requirement for a given amount of external work, and a decrease in the extent of myocardial ischemia during physical activity. The efficacy of modification of risk factors in reducing the progression of coronary artery disease and future morbidity and mortality has been established. Herein we review the history, current practice and results, and future challenges of cardiovascular rehabilitation.

Ambulatory Care↗
PubMed1990

What stimulates atrial natriuretic factor release during exercise?

Prior studies have shown that circulating atrial natriuretic factor (ANF) increases during short-term exercise, but the mechanism controlling ANF release, as well as the effect of exercise training on ANF release, remains unclear. Fifteen healthy mongrel dogs underwent short-term exercise testing before and after a 12-week period of exercise training (n = 8) or cage confinement (n = 7). ANF, norepinephrine, epinephrine, right atrial pressure, and heart rate were measured simultaneously at rest and during exercise at the time of each acute exercise study. Data were analyzed for all animals with normal baseline ANF values. Exercise training had no modulating effect on circulating ANF levels at rest or during exercise. Therefore, data before and after exercise training or cage confinement were grouped (n = 24) to determine the effects of short-term exercise. ANF levels increased from 49 +/- 2 pg/ml at rest to 60 +/- 4 pg/ml during exercise (p less than 0.05). Heart rate, norepinephrine, and epinephrine values also increased, but right atrial pressure actually decreased from 2.3 +/- 0.9 mm Hg at rest to -3.8 +/- 0.9 mm Hg during exercise (p less than 0.05). There was no correlation between ANF concentrations and levels of these other variables either at rest of during exercise. By demonstrating an increase in ANF with a simultaneous decrease in right atrial pressure, this study clearly shows that increased right atrial pressure is not the secretory stimulus for ANF release during exercise in the normal dog. The lack of correlation between ANF and right atrial pressure, heart rate, norepinephrine, and epinephrine levels suggests that factors other than these variables stimulate ANF release during short-term exercise.

Animals↗
PubMed1989

Plasma dopa and feeding.

Dopa is a normal constituent of plasma in man and experimental animals. Dopa concentrations in plasma have been used to reflect the activity of tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of catecholamines. However, it is not known to what extent plasma dopa is affected by feeding, since several foods contain dopa or tyrosine, the immediate precursor of dopa. In this study dopa and its major metabolites (3-O-methyldopa and free and conjugated catecholamines) were measured in plasma of dogs during 5 hr after feeding. Plasma dopa did not change significantly after feeding. This finding increases the value of plasma dopa as an index of tyrosine hydroxylase activity. Plasma norepinephrine decreased, and conjugated dopamine increased, after feeding; the other analytes did not change significantly.

Animal Feed↗
PubMed1989

Dopa in plasma increases during acute exercise and after exercise training.

Plasma dihydroxyphenylalanine (dopa) has been shown to originate in sympathetic neurons, and it has been suggested that plasma level reflects activity of tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of catecholamines. In this study, we measured the effects of acute exercise and exercise training on the levels of dopa and catecholamines in the plasma of healthy, older individuals. Venous blood was drawn from 19 men, from 52 to 75 years of age, at rest, at a standard submaximal work load, at peak exercise, and 3 minutes after exercise on a cycle ergometer. Ten of 12 men then completed 12 to 16 weeks of supervised training, and seven continued normal activity. All 17 men were then retested. The seven control subjects subsequently underwent exercise training as above and were retested again. Levels of dopa and catecholamines in plasma samples were measured by high-performance liquid chromatography with electrochemical detection. Dopa levels at rest were considerably higher than free dopamine, epinephrine, and norepinephrine. During short-term exercise, levels of dopa and catecholamines increased. The absolute increase in dopa was greater than the increase in epinephrine or dopamine but was not greater than that in norepinephrine. After the training period, basal dopa levels increased significantly and correlated with the increase in peak oxygen uptake. There was no change in basal conjugated norepinephrine or dopamine levels with exercise or training, but the level of conjugated epinephrine decreased slightly. No changes occurred in levels of dopa or catecholamines in the untrained group. Free dopamine, norepinephrine, and epinephrine levels at peak exercise were increased after exercise training.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Specimen Collection↗
PubMed1989

Does exercise training alter myocardial creatine kinase MB isoenzyme content?

Skeletal muscle biopsies from highly trained endurance athletes have been shown to contain an increased percentage of the creatine kinase MB (CK-MB) isoenzyme, which has been attributed to continuous regeneration of the skeletal muscle fibers in response to exercise-induced injury. The purpose of this study was to determine whether myocardium undergoes a similar degenerative-regenerative process as a result of exercise training. Fifteen mongrel dogs underwent a 12-wk period of training (N = 8) or cage confinement (N = 7). The animals were then sacrificed, and samples of left and right ventricular myocardium were analyzed for total CK activity and CK-MB isoenzyme content. Percentages of CK-MB were slightly but insignificantly higher from both ventricles of exercise-trained as compared with cage-confined dogs: left ventricle, 4.6 +/- 0.6% vs 3.3 +/- 0.6%, respectively (P = 0.15); right ventricle, 4.0 +/- 0.4% vs 3.0 +/- 0.8%, respectively (P = 0.29). We conclude that chronic exercise training does not induce physiologically important degenerative changes in myocardium.

Animals↗
PubMed1989

Exercise training produces changes in free and conjugated catecholamines.

In dogs the concentrations of conjugated dopamine in plasma have previously been shown to increase after exercise training. This study was done to determine whether conjugated norepinephrine and epinephrine also increase. Fifteen dogs were randomly divided into training (N = 8) or sedentary (N = 7) groups. All dogs were exercised acutely for 5 min at 4 mph with a 12% grade, following a 3-min warm-up, before and after either a 12-wk training or a 12-wk sedentary period. Free and conjugated catecholamines were determined in blood drawn at rest and during acute exercise using high-performance liquid chromatography (HPLC) with electrochemical detection. Before training, free norepinephrine, epinephrine, dopamine, and conjugated norepinephrine increased in plasma during acute exercise. Following the 12-wk training period, there were significant increases in free and conjugated dopamine and in conjugated norepinephrine in plasma taken at rest. There were no such increases in resting catecholamines after a 12-wk sedentary period. After either training or sedentary periods, dogs responded to acute exercise with an increase in free norepinephrine and a decrease in conjugated norepinephrine. Thus, after training both conjugated norepinephrine and dopamine, but not conjugated epinephrine, increased in plasma. The data suggest that sulfation of catecholamines increases as a result of exercise training.

Animals↗
PubMed1988

Prognosis in patients with an abnormal exercise radionuclide angiogram in the absence of significant coronary artery disease.

To investigate the prognostic importance of abnormal exercise left ventricular function on radionuclide angiography in the absence of significant angiographic coronary artery disease, 79 consecutive patients with these findings were followed up for a mean of 25 months (range 12 to 55). All patients had 1) an ejection fraction at rest greater than or equal to 0.40, 2) an ejection fraction that decreased with exercise or peak exercise ejection fraction less than 0.60, and 3) no significant coronary artery disease. The mean change in ejection fraction was a decrease of 0.07. In 63 patients (80%), the ejection fraction decreased during exercise; in 45 patients, it decreased by greater than or equal to 0.05. Twenty patients (25%) had a peak exercise ejection fraction less than 0.50. All patients were alive at follow-up study. One patient had a nonfatal myocardial infarction, and three patients were hospitalized for recurrent chest pain. No patient underwent coronary angioplasty or bypass surgery. The calculated infarction-free survival rate at 4 years by life table analysis was 97%. Patients with an abnormal exercise radionuclide angiogram in the absence of significant angiographic coronary artery disease have an excellent short-term prognosis.

Adult↗
PubMed1988

Impaired exercise tolerance after inferior vena caval interruption.

Four patients were evaluated for persistent dyspnea eight months to four years after inferior vena caval interruption for treatment of pulmonary emboli. Maximal exercise testing with gas-exchange analysis was performed. All patients attained less than 64 percent of predicted maximal oxygen uptake. Peak exercise heart rates were 85 percent or greater of predicted values. Arterial hypoxemia was not observed. The ratio of dead space to tidal volume (VD/VT) decreased with exercise, and the ratios of maximal exercise ventilation to maximal voluntary ventilation (VE/MVV) were less than 67 percent. These results suggest a cardiac rather than a ventilatory limitation to exercise. Inadequate venous blood return to the heart is the likely mechanism for the impaired exercise performances.

Adult↗
PubMed1988

Paradoxic heart rate deceleration during exercise. Relationship to a mid-right coronary artery stenosis.

A patient developed paradoxic deceleration of his heart rate at a high exercise level. Angioplasty of a right coronary artery stenosis distal to the sinoatrial branch and institution of diltiazem therapy resulted in normal cardioacceleration during repeated exercise testing. This unique pathophysiologic response appears to be due to direct or indirect effects of ischemia.

Coronary Disease↗
PubMed1987

How many electrocardiographic leads are required for exercise treadmill tests?

Forty-four consecutive patients who had perfusion defects on thallium-201 scanning and positive exercise treadmill tests were prospectively studied. Thirty-eight (86%) subjects had diagnostic ST segment changes in lead V5, 37 (84%) in lead V4, and 44 (100%) in either lead V4, V5 or both. Thirty patients had ST segment changes in the inferior leads, 20 in lead aVR, and only four in lead I and/or aVL. All of these latter subjects had diagnostic ST segments in lead V4 and/or V5. It is concluded that: combined electrocardiographic leads V4 and V5 detect the vast majority of ischemic changes during exercise treadmill testing, regardless of the site of perfusion defects detected by thallium-201 scanning; and monitoring the inferior and lateral leads rarely provides more diagnostic information.

Coronary Disease↗
PubMed1987

Graded exercise testing and training after renal transplantation: a preliminary study.

Aerobic exercise training has been used as part of the treatment for a variety of chronic disorders, most notably cardiovascular disease. In order to determine the feasibility and utility of regular exercise after renal transplantation, the responses of 10 patients to graded exercise testing were compared before training (T1), immediately after a program of supervised exercise training (T2), and a mean of 2.2 years after completion of the supervised program (T3). Supervised exercise sessions began a mean of 17 days postoperatively and continued for a mean of 5.5 weeks. Patients were encouraged to continue regular unsupervised exercise thereafter. All patients easily tolerated the supervised exercise sessions, which consisted of treadmill walking and cycle ergometry. Exercise capacity improved 90% between T1 and T2 and an additional 12% between T2 and T3. On the average, patients achieved a normal exercise capacity by 8 weeks after transplantation. Of the 10 patients, 7 had continued regular exercise training at T3. The observed increase in aerobic exercise capacity was probably related to improved renal function, an increased hemoglobin concentration, and the surgical healing process as well as the exercise training. We conclude that supervised exercise training for selected patients after renal transplantation is feasible and worthwhile.

Adolescent↗
PubMed1984

Alterations in the rat kidney associated with sodium saccharin feeding: a scanning electron microscopic study.

Sodium saccharin has previously been demonstrated to induce hyperplasia of the urothelium of the rat kidney pelvis. It was fed as 5% of the diet to male F344 rats for 18 weeks. In the present experiment, scanning electron microscopy (SEM) was utilized to detect early morphologic changes. Pleomorphic microvilli (PMV) were observed in all four sodium saccharin-fed rats, located on cells at the junction of the papilla and pelvis. PMV also occurred at the papilla-pelvic junction in three of the ten control rats, but the affected area was smaller and the PMV exhibited less severe atypia.

Animals↗