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Biomedical subjects

Y L Lim

Publications and source records attributed to Y L Lim.

49 records · Page 3Linked to original sources
PubMed1982

Radionuclide angiographic assessment of global and segmental left ventricular function at rest and during exercise after coronary artery bypass graft surgery.

Left ventricular ejection fraction (LVEF) was measured by radionuclide angiography at rest and during supine bicycle exercise before and 3 months after coronary artery bypass graft surgery (CABG) in 20 patients with chronic stable angina. The right anterior oblique gated first-pass technique was used to assess LVEF response to maximal exercise (Wmax), while the left anterior oblique equilibrium-gated technique was used to assess LVEF and relative LV volume changes during graded submaximal exercise. Mean LVEF was unchanged at rest after CABG by both the first-pass (60 +/- 12% vs 60 +/- 12%) and equilibrium-gated (61 +/- 13% vs 62 +/- 13%) measurements. At Wmax, mean first-pass LVEF was significantly higher postoperatively than preoperatively (63 +/- 17% vs 53 +/- 17%; p less than 0.01) with a higher Wmax (750 +/- 182 vs 590 +/- 202 kpm/min; p less than 0.001) and higher rate-pressure product (302 +/- 59 vs 222 +/- 57 units; p less than 0.001). Similarly, equilibrium-gated LVEF levels during graded exercise, using stepwise regression analysis, were significantly higher postoperatively than preoperatively (p less than 0.001); at the highest graded work load, they averaged 63 +/- 19% postoperatively and 53 +/- 17% preoperatively, with higher work loads (500 +/- 190 vs 417 +/- 155; p less than 0.05) and higher rate-pressure products (271 +/- 55 vs 207 +/- 53; p less than 0.001). The increase in exercise LVEF after surgery was due to a marked decrease in the ratio, relative to resting values, of counts-based end-systolic volumes during submaximal exercise (preoperatively 1.91 +/- 1.04; postoperatively 1.14 +/- 0.46; p less than 0.01). The five subjects in whom LVEF decreased significantly during exercise postoperatively all had one or more blocked or stenosed grafts. This study documents, by two independent radionuclide techniques, an improved LVEF during exercise at an increased maximal work capacity and rate-pressure product 3 months after successful CABG.

Adult↗
PubMed1980

Isotope angiocardiography of the left ventricle.

Radionuclide imaging of the left ventricle is a recent innovative procedure requiring a gamma-camera interfaced to a computer. It has the advantages of being non-invasive and of allowing studies at rest and exercise. Left ventricular function may be assessed by viewing the images as an endless loop cine-display, or by quantitating the over-all and segmental functions. Validation studies comparing the technique with standard contrast angiograms have confirmed its reliability. Clinical studies have been undertaken in normal volunteers, and in patients. The technique will have increasing application in assessing the aetiology of chest pain, in selection of patients for cardiac surgery, and in determining the effects of interventions, such as drug therapy or coronary artery bypass surgery, on ventricular performance.

Adult↗
PubMed1980

The radionuclide assessment of left ventricular function using graded exercise in normal subjects.

In 20 normal volunteers, two minute equilibrium gated blood pool scanning (GBPS) was used to assess left ventricular function during rest and three stages of graded supine exercise on a bicycle ergometer. The three work loads were individualised for each subject from a previously performed exercise test and corresponded to mild, moderate and severe stress. The short imaging time was validated against standard GBPS. With exercise all subjects increased their left ventricular ejection fraction and in the majority, most of this rise occurred with the lowest work load. This change was predominantly due to a marked fall in end-systolic volume. The end-diastolic volume initially fell, then at peak exercise returned to baseline values. The major change in stroke volume occurred at peak exercise.

Adult↗
PubMed1979

Haemodynamics of mild hypertension in pregnancy.

One hundred and sixty-three haemodynamic studies were done serially in 23 normotensive and 25 mildly hypertensive women during pregnancy. With all subjects resting in the left lateral position, heart rate, cardiac output, stroke volume, left ventricular work index, total peripheral vascular resistance and haematocrit were all significantly higher while plasma volume per unit body weight was significantly lower in the hypertensive than in the normotensive pregnant women. It is postulated that this hyperkinetic circulatory state is due to hyperactivity of the sympathetic adrenergic component of the autonomic nervous system in hypertensive pregnancy.

Adolescent↗
PubMed1976

Systolic time intervals in normotensive and hypertensive human pregnancy.

Systolic time intervals were measured in 10 nonpregnant, 37 normotensive, and 18 hypertensive pregnant women in both supine and lateral positions. With all the subjects in the supine position, left ventricular ejection time (LVET) was shortened; the pre-ejection period (PEP) lengthened, and the PEP/LVET ratio increased in normotensive late pregnancy compared with the nonpregnant state. Similar alterations in systolic time intervals were observed in hypertensive women in both early and late pregnancy in the supine position. In normotensive women in early pregnancy, alterations in systolic time intervals were inconclusive. When normotensive women in late pregnancy were turned from the supine into the left lateral position, a prolongation of LVET and a decrease in the PEP/LVET ratio were observed. When hypertensive women in late pregnancy adopted the left lateral position, no significant alterations in systolic time intervals occurred. Isovolumetric contraction time (ICT) was prolonged only in the hypertensive pregnant women in the supine position. The study suggests that left ventricular performance is diminished in normotensive women in late pregnancy when supine but improves when they adopt the lateral position. In addition, hypertensive pregnant women show evidence of diminished left ventricular performance which is not improved in late pregnancy by assumption of the left lateral position.

Adult↗
PubMedDate not supplied

Skeletal myoblast transplant in heart failure.

Despite recent advances in the prevention and treatment of ischemic heart disease (IHD), treatment of patients with heart failure secondary to myocardial infarction remains a therapeutic challenge. Heart transplantation has emerged as a viable option but is fraught with problems of supply. Mechanical assist devices are extremely expensive and dynamic cardiomyoplasty has shown only limited success in the clinical setting. Recent insights into the pathogenesis of myocardial diseases and the progress made in the field of molecular biology have resulted in the development of new strategies at molecular as well as cellular levels for cardiac muscle repair. One such strategy is to augment ventricular function by means of cellular cardiomyoplasty through intracardiac cell grafting using adult and fetal cardiomyocytes, stem cells, and autologous skeletal myoblasts.

Animals↗
PubMedDate not supplied

Therapeutic angiogenesis for coronary artery disease.

Therapeutic angiogenesis may be a realistic approach in treating ischemic heart disease. VEGF is a major angiogenic factor involved in physiological as well as pathological angiogenesis. The ability of VEGF to promote angiogenesis in animal and clinical studies has been studied extensively. However, it is becoming clear that VEGF alone may not be sufficient to effectively complete the angiogenesis process. The use of more than one growth factor may be more pertinent in creating a sustainable angiogenic effect with clinically significant outcome. The challenge is to find complementary partners in angiogenesis to better affect the outcome of the process. To this end, we have been studying the effects of other angiogenic factors such as angiopoietin-1 (Ang-1) in a chronic ischemic porcine model. Single intramyocardial introduction of adenovirus-mediated gene transfer of Ang-1 into the left ventricle free wall has been found to enhance angiogenesis by augmenting the formation of new capillaries that manifested in improved total blood flow in the myocardium. A combined therapeutic angiogenesis study involving VEGF and Ang-1 is currently underway. Due to their unique complementary properties, it is expected that the combination will not merely enhance angiogenesis but will also lead to healthy and mature vascular network in the ischemic myocardium.

Angiogenesis Inducing Agents↗