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Biomedical subjects

V F Froelicher

Publications and source records attributed to V F Froelicher.

At least 109 records · Page 6Linked to original sources
PubMed1987

Application of meta-analysis using an electronic spread sheet to exercise testing in patients after myocardial infarction.

Decision analysis is being applied to medical practice in order to achieve cost efficacy in health care delivery. Critical to this process is establishing the diagnostic and prognostic accuracy of medical tests and the effectiveness of interventions. Meta-analysis is an approach that applies statistical methods to groups of studies in order to extract consensus results. Electronic spreadsheets facilitate meta-analysis with their ability to store, sort, graph, and mathematically manipulate both the methodologic approaches and clinical findings of seemingly disparate studies. As an example, this application is demonstrated with an analysis of studies that were performed to evaluate the prognostic value of exercise testing in patients recovering from a myocardial infarction. The following conclusions were reached: (1) patients excluded from exercise testing have the highest mortality; (2) only subsets of patients have been tested resulting in highly selected patient samples that make findings difficult to generalize; (3) of the five exercise test responses, only an abnormal systolic blood pressure response and a poor exercise capacity predicted risk more frequently than by chance; (4) submaximal or predischarge testing has greater predictive power than postdischarge or maximal testing; and (5) exercise-induced ST segment depression only appears to be predictive of increased risk in patients with inferior-posterior myocardial infarctions. This approach to combining studies is important since even careful analysis of a single study cannot elucidate all of the complex interactions and selective biases that have occurred. However, comparison of many heterogeneous studies is at best an arduous and time-consuming task. This approach to using electronic spreadsheets to collate and analyze multiple studies facilitates recognition of the population characteristics, clinical factors, and methodologic considerations that affect outcome and allows the quick inclusion of additional studies for re-analysis and interpretation.

Blood Pressure↗
PubMed1987

Effect of beta-adrenergic blockade on exercise performance in patients with chronic atrial fibrillation.

Beta-adrenergic blocking agents are commonly used in combination with digitalis to control excessive heart rate during exercise in patients with chronic atrial fibrillation. However, little is known about the effect of beta-adrenergic blockade on exercise capacity in these patients. Accordingly, a randomized, double-blind, cross-over placebo-controlled study was performed to assess the efficacy of celiprolol, a new cardioselective beta-blocker with partial intrinsic sympathomimetic activity, on exercise performance in nine men with chronic atrial fibrillation. All but one patient was receiving maintenance digitalis during the study. Heart rate, blood pressure and gas exchange variables were measured at rest and during treadmill exercise testing while the patients were receiving maintenance celiprolol or placebo. Significant reductions in heart rate and systolic blood pressure compared with control values were observed at submaximal exercise, at the gas exchange anaerobic threshold and at maximal exertion while the patients were taking celiprolol. However, oxygen uptake at the gas exchange anaerobic threshold during celiprolol therapy was 12.3 versus 14.0 ml oxygen/kg per min during placebo administration (a 12% difference, p less than 0.01). Similarly, oxygen uptake at maximal exertion during celiprolol therapy was 17.6 versus 21.0 ml/kg per min during placebo administration (a 16% difference, p less than 0.01). Treadmill time was also reduced during the celiprolol phase compared with placebo (11.3 versus 10.3 minutes; a 19% difference, p less than 0.01). These results indicate that in patients with atrial fibrillation the major beneficial effects of beta-adrenergic blockade--reduced submaximal and maximal exercise heart rate and blood pressure--must be weighed against the decrease in exercise capacity.

Adrenergic beta-Antagonists↗
PubMed1987

Detection and measurement of the P-wave and T-wave during exercise testing using combined heuristic and statistical methods.

Accurate detection and measurement of the P-wave and T-wave components of the ECG complex have been difficult and often avoided in computerized ECG analysis. This is particularly so during exercise testing where T-P fusion occurs during higher heart-rates. By combining advanced pattern-recognition techniques, statistical measurements and empirically based heuristic decision-making logic, our ECG Analysis program has been able to reliably detect, measure and track these components during exercise testing to a degree surpassing visual detection by highly experienced readers. Complete analysis of each consecutive record gathered during the exercise test is performed and a data-base of measurements and parameters is created for reference comparison of previous results at each analysis step to current measurements. Thus, evaluation of each current record for appropriate and accurate analysis is based on an expert system approach which is constantly updated and can adjust itself to individual ECG morphology as the test progresses. Preliminary attempts are also being made to separate, extract and normalize the P-wave and T-wave during fusion for better understanding and comparison of changes which occur at high heart-rates. Theoretical and clinical reasons related to the detection and measurements of the P-wave and T-wave during exercise testing are also discussed.

Electrocardiography↗
PubMed1986

Myocardial perfusion changes following 1 year of exercise training assessed by thallium-201 circumferential count profiles.

The effect of exercise training on myocardial perfusion was assessed using initial and 1-year thallium-201 (Tl-201) exercise studies in 56 patients with stable coronary artery disease (CAD). Subjects had been randomized into a trained group participating in supervised exercise three times per week and a control group. Indices (non-dimensional units) based on computer-analyzed circumferential count profile from nine regions of the heart, assessed in three projections, were used to eliminate observer bias and more accurately quantitate Tl-201 distribution and 4-hour washout. There was serial improvement of the global distribution count profiles in 21 of 27 (77.8%) of the trained and in 9 of 29 (31.0%) of the control subjects (p less than 0.001). The mean interval change in global initial distribution over the year period was 5 +/- 13 (mean +/- SD) in the trained and -6 +/- 14 in the control groups (p less than 0.003). The mean initial distribution of the trained group had improvement in all nine regions (significant in three), while the control group showed mean improvement in only one of nine regions. Additionally, the trained group showed improvement in the mean washout in five of nine regions (significant in three), while no mean regional washout improvement occurred in the control group. Thus, in this group of patients with stable CAD, exercise training resulted in apparently improved cardiac perfusion evidenced by enhance Tl-201 uptake and washout.

Coronary Circulation↗
PubMed1985

The influence of exercise training on the ventilatory threshold of patients with coronary heart disease.

Out of 156 patients with stable coronary heart disease randomized to either an exercise intervention group or a control group, 41 had complete gas analysis data. Continuous gas exchange data, including the ventilatory threshold, and selected heart rates were determined initially and at 1 year. The mean attendance for the exercise group was 2.2 +/- 0.7 days a week at an intensity of 60 +/- 9% of estimated peak oxygen uptake for 1 year of the study. Statistically significant differences (p less than 0.05) were observed between the exercise group (n = 19) and the control group (n = 22) for peak oxygen uptake (L/min), total treadmill time, and supine rest and submaximal heart rates after 1 year. The most remarkable change was a 16% increase in treadmill time. There was no difference between groups for the ventilatory threshold expressed either as an absolute oxygen uptake or as a percentage of peak oxygen uptake at 1 year. However, there was a significant correlation (r = 0.45; p less than 0.05) between the absolute change in peak oxygen uptake and the absolute change in the ventilatory threshold. These results indicate that a moderate exercise program is inadequate to alter the ventilatory threshold in patients with coronary heart disease and that changes in ventilatory threshold do not explain the increase in treadmill time that usually occurs.

Coronary Disease↗
PubMed1985

Noninvasive testing in the evaluation of myocardial ischemia: agreement among tests.

The purpose of this study was to investigate the relations among four exercise-induced phenomena--angina, ST segment depression, decrease in ejection fraction and thallium perfusion defects--and to determine their impact on aerobic capacity. One hundred fifty-six men (mean age 52 +/- 8 years) with documented coronary heart disease were studied with radionuclide ventriculography during supine bicycle exercise, thallium scintigraphy and treadmill testing with computerized electrocardiography and maximal oxygen uptake. Of 624 administered tests, 243 results (39%) were considered to indicate ischemia. The average number of abnormal tests was 1.6 per patient and, when considered as continuous variables, their results correlated poorly. Correlations did not improve when adjusting for heart rate achieved or by eliminating patients with coronary artery bypass surgery or myocardial infarction. Statistical methods of comparing degree of interest agreement yielded surprisingly weak relations among the four tests of ischemia. Treadmill performance was markedly impaired by angina, but much less impaired by other indicators of ischemia. It is concluded that the usual test responses implying ischemia have weak agreement when uniformly applied to patients with known coronary artery disease.

Adult↗
PubMed1985

Use of clinical data in predicting improvement in exercise capacity after cardiac rehabilitation.

Fifty-nine men with coronary heart disease underwent 1 year of supervised aerobic exercise. They performed exercise tests for maximal oxygen uptake, ST segment analysis, thallium scintigraphy and radionuclide ventriculography before and after the year of exercise. A computerized data base that included clinical descriptors and exercise test results was retrospectively reviewed to determine whether initial features could predict the patient's response to the exercise intervention. Poor correlations were found between the initial measurements and change in maximal oxygen consumption and other indexes of training effect. Patients who initially were in the poorest state of fitness showed the most improvement with training. None of the initial features from the history and physical examination, treadmill study or radionuclide studies was a good predictor of a beneficial result from the exercise program. The usual measurements of work intensity during training were poor predictors of outcome. A significant decrease in the amount of ischemia measured by thallium perfusion scintigraphy was demonstrated after training.

Adult↗
PubMed1985

The physiologic sequelae of chronic dynamic exercise.

The physiologic results of acute dynamic exercise include complex neurologic, hormonal, pulmonary, and cardiovascular adjustments that provide an integrated response perfectly matching oxygen supply with oxygen demands. Long-term repeated bouts of dynamic exercise of sufficient intensity and duration yield predictable changes in anatomy and physiology. These changes affect active skeletal muscle and the heart. Changes in skeletal muscle include an increased capillary blood volume, increased mitochondrial density, increased oxidative pathway enzymes, and more efficient regulation of blood flow. These adaptations result in an increased oxidative capacity and more favorable fuel utilization. Oxygen extraction increases, accounting for up to 50 per cent of the increased maximal oxygen consumption, and endurance improves. Following chronic dynamic exercise the heart beats slower and has a larger stroke volume at rest and throughout a broad range of work intensities. The maximal cardiac output increases substantially, accounting for up to 50 per cent of the increased maximal oxygen consumption. The metabolic and biochemical changes found in skeletal muscle are not found in cardiac muscle. Changes found in isolated cardiac muscle do not always correlate with heart performance. The separation of central and peripheral factors in assessing heart performance is difficult because preload and afterload are major determinants of heart function and are altered by chronic dynamic exercise. Ischemia is a major stimulus for the development of coronary collateral vessel development in animals. Because dynamic exercise does not induce ischemia in normal humans, collateral vessel development may only occur in those with coronary heart disease. However, there is no convincing evidence that chronic dynamic exercise results in physiologically important coronary collateral vasculature in patients with angina. Improved work capacity is predictable following chronic dynamic exercise in patients with coronary heart disease. Although the rate pressure product that produces angina does not change following training, heart rates are lower at matched absolute workloads and the maximal consumption of oxygen increases. Changes in heart function are largely secondary to peripheral changes in these patients.

Animals↗
PubMed1984

Predicting oxygen uptake from treadmill testing in normal subjects and coronary artery disease patients.

In order to evaluate the clinical practice of estimating oxygen uptake from treadmill time, patients with coronary heart disease and normal subjects had their oxygen uptake measured during treadmill testing. Continuous expired gas analysis was performed in order to see if the gas exchange anaerobic threshold could explain the difference between measured and estimated oxygen uptake. Below the gas exchange anaerobic threshold, normal subjects and patients had similar oxygen uptakes for a given workload. However, at workloads above this threshold, patients had approximately 1 MET lower oxygen uptake than normal subjects. Regression equations relating treadmill time to oxygen uptake are specific to groups of patients or individuals due to differences in anaerobic threshold. In addition, the use of standard workloads to predict aerobic capacity depends on the rate at which oxygen uptake obtains a steady state value. These findings must be considered in clinical practice when attempting to estimate aerobic capacity from treadmill testing.

Coronary Disease↗
PubMed1984

Treadmill performance and cardiac function in selected patients with coronary heart disease.

To investigate the cardiac determinants of treadmill performance in patients able to exercise to volitional fatigue, 88 patients with coronary heart disease free of angina pectoris were tested. The exercise tests included supine bicycle radionuclide ventriculography, thallium scintigraphy and treadmill testing with expired gas analysis. The number of abnormal Q wave locations, ejection fraction, end-diastolic volume, cardiac output, exercise-induced ST segment depression and thallium scar and ischemia scores were the cardiac variables considered. Rest and exercise ejection fractions were highly correlated to thallium scar score (r = -0.72 to -0.75, p less than 0.001), but not to maximal oxygen consumption (r = 0.19 to 0.25, p less than 0.05). Fifty-five percent of the variability in predicting treadmill time or estimated maximal oxygen consumption was explained by treadmill test-induced change in heart rate (39%), thallium ischemia score (12%) and cardiac output at rest (4%). The change in heart rate induced by the treadmill test explained only 27% of the variability in measured maximal oxygen consumption. Myocardial damage predicted ejection fraction at rest and the ability to increase heart rate with treadmill exercise appeared as an essential component of exercise capacity. Exercise capacity was only minimally affected by asymptomatic ischemia and was relatively independent of ventricular function.

Adult↗
PubMed1984

Individual variability of radionuclide ventriculography in stable coronary artery disease patients over one year.

To determine the individual reproducibility of radionuclide ventriculography over an extended period of time, 33 patients with stable coronary artery disease were studied at rest and during three stages of exercise on two occasions separated by 1 year. The individual interstudy variability of ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume, and cardiac output was determined by calculating the mean and standard deviation of the difference between the individual studies (initial - 1 year). Despite high correlations between an EF measured at study 1 and study 2 of 0.96 at rest and 0.87 during maximal exercise, the individual interstudy difference was 0.01 +/- 0.04 and -0.02 +/- 0.09, respectively. The correlation of percent change in EF from rest to maximal exercise was 0.49 and the individual interstudy differences was -1.2 +/- 19%. Correlations of the EDV were 0.81 at rest and 0.72 during maximal exercise while the individual difference was 0.7 +/- 38 and -0.8 +/- 49 ml, respectively. Considering two standard deviations as the confidence limits for a true change, an EF change of 8 EF units (0.08) at rest and 18 (0.18) during exercise, and EDV changes of approximately 100 ml are needed in an individual to state with confidence that the observed difference between the two studies are true changes and not the result of technologic variability. Because of the large individual interstudy variability in EF and volume measurement, caution must be taken in assuming that any change over a year is due to more than technique variability.

Adult↗
PubMed1983

Exercise testing and training: clinical applications.

The application of exercise in clinical cardiology continues to progress because of research findings. Advances have occurred in the applications, methodology and interpretation of exercise testing. Exercise training has been documented to have a place in the primary prevention of coronary heart disease. In regard to cardiac rehabilitation, both early ambulation and early discharge are safe and beneficial in patients with uncomplicated infarction, and a subsequent exercise program is at least as effective as other interventions. High intensity exercise training in the patient with heart disease may be necessary to cause changes in myocardial perfusion and performance, but it carries an increased risk.

Adult↗