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Biomedical subjects

G S Uhl

Publications and source records attributed to G S Uhl.

At least 19 recordsLinked to original sources
PubMed1985

Segmental coronary artery disease: detection by rotating slant-hole collimator tomography and planar thallium 201 myocardial scintigraphy.

Normal quantitative circumferential profile limits were established for a 30 degrees bilateral rotating slant-hole (RSH) collimator tomographic system. This system's value in detecting segmental coronary artery disease was assessed in a study evaluating 196 patients by thallium 201 myocardial scintigraphy and coronary arteriography. Profile curves were calculated from images of 20 healthy patients and used to identify significant coronary artery disease (greater than or equal to 70% diameter narrowing) in the left anterior descending (LAD), the right, and the left circumflex (LCx) coronary arteries. In a group of 86 patients, an abnormality on the apical or middle plane optimally identified segmental coronary artery disease. When such abnormalities were prospectively evaluated in a test group of 110 patients, the sensitivity and specificity were 79% and 93% for LAD, 90% and 90% for right, and 83% and 83% for LCx coronary artery disease. Compared with qualitative interpretation of the planar and tomographic images, quantitative tomography significantly improved the sensitivity of T1-201 imaging in detecting LAD, right, and LCx coronary artery disease (P less than .001) in patients with or without previous myocardial infarction.

Adult↗
PubMed1984

Limitation of exercise-induced R wave amplitude changes in detecting coronary artery disease in asymptomatic men.

The exercise electrocardiograms of 255 asymptomatic men were analyzed for changes in R wave amplitude and ST segments. The results were correlated with findings at cardiac catheterization. There were 65 men with coronary artery disease and 190 normal subjects. R wave amplitude changes were evaluated in bipolar leads X, Y and Z. The predictive value of an abnormal ST segment response for detecting disease was only 29%. This value was improved to 42% using R wave amplitude changes with a sensitivity of 28% and specificity of 87%. Exercise-induced R wave amplitude changes enhance the specificity of detecting coronary disease in asymptomatic men over ST segment criteria alone but the sensitivity is poor and the predictive value is not enhanced. Thus, these criteria are limited in adding to the diagnostic accuracy of stress testing.

Adult↗
PubMed1984

Discriminant value of clinical and exercise variables in detecting significant coronary artery disease in asymptomatic men.

To determine whether clinical or exercise test variables could reliably detect coronary disease in asymptomatic men, several variables were compared with angiographic findings in 225 asymptomatic men. None of the individual clinical or rest electrocardiographic variables were able to detect coronary artery disease. The three individual exercise variables with a high likelihood ratio were: 1) at least 0.3 mV ST depression, 2) persistence of ST depression 6 minutes after exercise, and 3) total duration of exercise of less than 10 minutes. However, because of low sensitivity and predictive value, these single variables were not helpful in identifying individual patients with coronary disease. The combination of any single clinical risk factor and any two of these exercise risk predictors was highly predictive (89%) but relatively insensitive (37%) for detecting any coronary disease. These criteria have a sensitivity of 55% and a predictive value of 84% for the detection of two and three vessel coronary disease. The effectiveness of exercise testing for detecting asymptomatic coronary disease is improved when the group is first screened for the presence of risk factors and additional exercise variables other than ST segment criteria are evaluated.

Adult↗
PubMed1983

Screening for asymptomatic coronary artery disease.

Because it will be some time before the primary prevention of cardiovascular disease is a reality, it is advisable to evaluate screening methods for detecting latent cardiovascular disease. Because risk factor screening and techniques with the patient at rest have limited sensitivity, exercise testing that brings out abnormalities not present at rest deserves consideration. Numerous studies have shown the exercise electrocardiogram to have a sensitivity of approximately 50% and a specificity of 90%. The different reported predictive values are related to its use in populations with different prevalences of disease. Various techniques have been recommended to improve the sensitivity and specificity of exercise testing, including other exercise measurements, computerized probability estimates, nuclear cardiology, cardiokymography, cardiac fluoroscopy and risk factor analysis. There is promise that these techniques will improve attempts to screen asymptomatic subjects for coronary disease.

Adult↗
PubMed1982

New criteria for computer interpretation of exercise electrocardiograms in a largely asymptomatic population.

We developed new discriminant functions for analyzing treadmill ECGs from a largely asymptomatic population. Treadmill ECG data were gathered from two patient groups: 70 patients with coronary artery disease with occlusions greater than or equal to 30% by angiography, and 138 patients without coronary artery disease. The group without coronary artery disease consisted of 76 false positive responders to treadmill testing using standard ST segment criteria, 22 supraventricular tachycardia patients (both groups free of coronary artery disease by angiography), and 40 patients at very low risk for having coronary artery disease. ECG leads CC5, CM5, V5, Yh and Z were recorded before, during and after exercise protocol conditions. Computer-averaged ECGs were processed to provide Q, R, S and T-wave amplitudes, ST amplitudes and slope, and QS and RT intervals. Each patient provided over 100 variables per lead for analysis. Stepwise statistical procedures yielded lead-specific linear discriminant functions containing four to six variables/lead. Application of these functions provided sensitivity and specificity in the range 70-84%. When compared with other standard interpretive criteria, these results provided improved diagnostic accuracy for the largely asymptomatic population.

Angiography↗
PubMed1982

Limitations of the exercise stress test in the detection of coronary artery disease in apparently healthy men.

During a 1-year period, the United States Air Force School of Aerospace Medicine reviewed routine exercise tests by 771 completely asymptomatic male flying personnel aged 35-54 years, who underwent the stress test as the sole screening procedure to detect latent coronary artery disease. All of the aviators had a normal baseline 12-lead electrocardiogram, which would not have required a stress test in accordance with current policies of the USAF Central Electrocardiographic Library. Of these 771 exercise tests, 153 were maximal treadmill tests without a previous Double Master's Step test, and 618 were Double Master's tests. Borderline abnormal or abnormal Double Master's tests were followed by treadmill testing. Airmen with abnormal treadmill tests were offered coronary angiography for clarification of the aeromedical significance of the test result. The predictive value of a routine abnormal treadmill test in a population of aircrew members with a borderline abnormal or abnormal Double Master's test ranged from 17-55%. Thus, mass screening for coronary artery disease with exercise stress tests in apparently asymptomatic individuals is hampered by a low yield of true positive test in an unacceptably high proportion of false positive results.

Adult↗
PubMed1981

Computer-enhanced thallium scintigrams in asymptomatic men with abnormal exercise tests.

The use of treadmill testing in asymptomatic patients and those with an atypical chest pain syndrome is increasing, yet the proportion of false positive stress electrocardiograms increases as the prevalence of disease decreases. To determine the diagnostic accuracy of computer-enhanced thallium perfusion scintigraphy in this subgroup of patients, multigated thallium scans were obtained after peak exercise and 3 or 4 hours after exercise and the raw images enhanced by a computer before interpretations were made. The patient group consisted of 191 asymptomatic U.S. Air force aircrewmen who had an abnormal exercise electrocardiogram. Of these, 135 had normal coronary angiographic findings, 15 had subcritical coronary stenosis (less than 50 percent diameter narrowing) and 41 had significant coronary artery disease. Use of computer enhancement resulted in only four false positive and two false negative scintigrams. The small subgroup with subcritical coronary disease had equivocal results on thallium scintigraphy, 10 men having abnormal scans and 5 showing no defects. The clinical significance of such subcritical disease in unclear, but it can be detected with thallium scintigraphy. Thallium scintigrams that have been enhanced by readily available computer techniques are an accurate diagnostic tool even in asymptomatic patients with an easily interpretable abnormal maximal stress electrocardiogram. Thallium scans can be effectively used in counseling asymptomatic patients on the likelihood of their having coronary artery disease.

Adult↗
PubMed1981

Relation between high density lipoprotein cholesterol and coronary artery disease in asymptomatic men.

The well established inverse relation of high density lipoprotein cholesterol (HDL) and the risk of coronary artery disease was tested in a cross-sectional group of 572 asymptomatic aircrew members who were being screened for risk of coronary artery disease. A battery of tests was performed, including determinations of fasting serum cholesterol, HDL cholesterol and triglycerides and performance of a maximal symptom-limited exercise tolerance test. Of the 572 patients, 132 also had an abnormal S-T segment response to exercise testing or were otherwise believed to have an increased risk of organic heart disease and subsequently underwent coronary angiography. Significant coronary artery disease was found in 16 men and minimal or subcritical coronary disease in 14; coronary angiograms were normal in the remaining 102 men. The remaining 440 men, who were believed to have a 1 percent chance of having coronary artery disease by sequential testing of risk factors and treadmill testing, had a mean cholesterol level of 213 mg/100 ml, a mean HDL cholesterol of 51 mg/100 ml and a mean cholesterol/HDL ratio of 4.4. The mean values of cholesterol, HDL cholesterol and cholesterol/HDL cholesterol did not differ significantly in men with normal angiographic finding and those with subcritical coronary disease. However, 14 of 16 men with coronary artery disease had a cholesterol/HDL ratio of 6.0 or more whereas only 4 men with normal coronary arteries had a ratio of 6.0 or more. Of the classical coronary risk factors evaluated, the cholesterol/HDL ratio of 6.0 or more had the highest odds ratio (172:1). It appears that determination of HDL cholesterol level helps to identify asymptomatic persons with a greater risk of having coronary artery disease.

Adult↗
PubMed1981

Exercise-induced myocardial oxygen supply-demand imbalance in asymptomatic or mildly symptomatic aortic regurgitation.

Left ventricular (LV) performance may remain normal in patients with LV volume overload from aortic regurgitation, but this entity results in progressive LV dysfunction. Impairment of myocardial reserve may remain undetected by current methods of assessing ventricular performance at rest, but the stress of exercise may demonstrate a reduction of myocardial reserve. To analyze the relationship between the myocardial supply and demand for oxygen in patients with aortic regurgitation, the ratio of the diastolic pressure-time index (DPTI) over the systolic pressure-time index (SPTI) was derived from recordings of pressure tracings during cardiac catheterizations in 14 patients with aortic regurgitation, and this ratio was compared with that of 24 normal subjects. The patients with aortic regurgitation had a DPTI/SPTI that fell with exercise (0.91 +/- 0.2 to 0.55 +/- 0.2) to lower values than did the ratio in the normal subjects (1.3 +/- 0.2 to 0.8 +/- 0.1) with stress. Among the patients with aortic regurgitation, a DPTI/SPTI ratio less than 0.50 with exercise identified two groups of patients that were not well separated by more common indices of severity of aortic regurgitation. The only other parameter that separated these two groups was the end-systolic volume, which is an index that reflects myocardial contractile function independent of preload. The DPTI/SPTI ratio that falls to abnormal levels with exercise may accurately reflect a failure of myocardial reserve in aortic regurgitation.

Adult↗
PubMed1980

Detection of coronary artery disease in asymptomatic aircrew members with thallium-201 scintigraphy.

Thallium-201 exercise myocardial perfusion scintigraphy was accomplished in 130 aircrew members prior to their undergoing coronary angiography. Most were undergoing cardiac catheterization for an abnormal exercise response to treadmill testing. Of these, 22 men had arteriographic evidence of obstructive coronary disease of at least 50% narrowing in a single vessel. All had abnormal myocardial scintigrams. There were 12 other aviators who had minimal degrees of coronary artery disease with lesions less than 50% as the maximum degree of obstruction. Of these, 8 had abnormal thallium scans showing a perfusion defect in the area of the myocardium, presumably supplied by the diseased coronary artery. Of the 96 men with normal angiograms, only 4 had abnormal myocardial scintigraphy. An abnormal myocardial scintigram was often associated with significant obstructive disease. A normal scan accurately ruled out the presence of high-grade obstructive lesions and missed only four cases of minimal coronary disease. The application of gated thallium myocardial perfusion scans in the practice of aerospace cardiology has important significant applications for followup of therapeutic modalities as well as screening for evidence of myocardial ischemia in apparently healthy aircrew members.

Adult↗
PubMed1980

Coincident loss of consciousness and ventricular tachycardia during +GZ stress.

The environment of the advanced fighter aircraft represents a unique combination of stressful factors. Each of the individual stresses is hazardous, with the summation of these factors possibly resulting in an additional risk for sudden in-flight incapacitation. Advanced fighter aircraft are capabble of producing both rapid onset and high sustained +GZ forces which, on occasion, can exceed the tolerance limits of the pilot. The +GZ forces encountered during aerial combat maneuvering are physiologically stressful and have a profound effect on the regulatory mechanisms of the body. The influence of these stresses, including +GZ stress, on the autonomic nervous system is complex. The overall normal regulation of the cardiovascular system depends on a balance between both branches of the autonomic nervous system. An imbalance between sympathetic and parasympathetic tone can result in cardiac dysrhythmias and symptoms not conducive to safe and effective flight. An episode of ventricular tachycardia, coincident with an episode of loss of consciousness, was observed in an apparently healthy aircrewman during +GZ stress on the USAF School of Aerospace Medicine human centrifuge. The implications of autonomic imbalance in the production of similar potentially hazardous dysrhythmias and symptoms in the multistress environment deserve more in-depth investigation.

Adult↗
PubMed1979

Analysis of exercise-induced R wave amplitude changes in detection of coronary artery disease in asymptomatic men with left bundle branch block.

The exercise electrocardiograms of 44 asymptomatic men with acquired left bundle branch block were analyzed for changes in R wave amplitude. Results were correlated with findings on selective coronary angiography. There were two subgroups: 7 men with significant angiographic coronary artery disease (Group I) and 37 with normal coronary angiograms (Group II). Exercise induced an increase in R wave amplitude in all seven men with coronary artery disease but in only 10 of the 37 men without significant coronary artery disease. This criterion thus had a sensitivity of 100 percent but a poor specificity of 73 percent, a predictive value of 41 percent and an accuracy rate of 77 percent for the diagnosis of coronary artery disease. The greater the increase in R wave amplitude the greater was the likelihood of some degree of left ventricular dysfunction as measured by wall motion abnormalities and elevated left ventricular end-diastolic pressure. The increase in R wave amplitude with exercise appears to be a sensitive test in identifying coronary artery disease in asymptomatic men with acquired left bundle branch block.

Adult↗
PubMed1979

Pericardial tamponade in systemic sclerosis (scleroderma).

The frequency of pericardial disease in scleroderma found at necropsy in high. The clinical recognition of pericarditis with or without effusion is rare and tamponade with haemodynamic impairment is exceptional. Three patients with scleroderma presented with an acute syndrome of dyspnoea, chest pain, and cardiomegaly requiring pericardiocentesis for relief of pericardial tamponade. One patient died. The mechanism of the pericardial effusion remains unknown. The haemodynamic data recorded from one patient suggested that pericardial fibrosis in scleroderma may predispose to pericardial tamponade.

Adolescent↗
PubMed1979

Myocardial supply-demand ratio in aortic regurgitation.

To analyze the relationship between the myocardial supply and demand for oxygen in patients with aortic regurgitation, the ratio of the diastolic pressure-time index (DPTI) over the systolic pressure-time index (SPTI) was derived from recordings of pressure during cardiac catheterization in 24 patients with aortic regurgitation, and this ratio was compared with that in 14 normal subjects and in ten patients with congestive cardiomyopathy (an ejection fraction less than 0.30). Patients with aortic regurgitation had a DPTI/SPTI of 0.75 +/- 0.06 (mean +/- SE), which was lower than in the normal subjects (1.24 +/- 0.06) and patients with cardiomyopathy (1.06 +/- 0.03) (P less than 0.001). Among the patients with aortic regurgitation, the 13 with a DPTI/SPTI below 0.70 had more severe aortic regurgitation than the 11 with a DPTI/SPTI above 0.70. Aortic regurgitation results in a reduced myocardial supply-demand ratio, as measured by the DPTI/SPTI, which is related to the severity of the valvular regurgitation and is not present in patients with left ventricular dysfunction secondary to congestive cardiomyopathy.

Adult↗