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Biomedical subjects

C Y Choong

Publications and source records attributed to C Y Choong.

31 records · Page 2Linked to original sources
PubMed1986

Effects of nifedipine on arterial oxygenation at rest and during exercise in patients with stable angina.

The effects of nifedipine on arterial oxygenation and hemodynamics were studied at rest and during bicycle exercise in 12 men (mean age 55 years, range 41 to 67) with stable exertional angina. The study was conducted double-blind on 2 days, 1 week apart, using a placebo-controlled crossover design. On each day, measurements at rest were made before and 20 minutes after 20 mg sublingual nifedipine or placebo and were followed by measurements made during exercise. Compared with placebo, nifedipine reduced mean arterial pressure, systemic vascular resistance and pulmonary vascular resistance, and increased heart rate and cardiac output at rest and during exercise. It did not alter mean pulmonary artery or pulmonary artery wedge pressures at rest, but decreased them during exercise. Nifedipine decreased arterial oxygen tension (PaO2) from 96 +/- 10 to 90 +/- 13 mm Hg (p less than 0.05) at rest and from 99 +/- 11 to 92 +/- 12 mm Hg (p less than 0.005) at submaximal exercise (33 +/- 21 W), but did not alter it (100 +/- 12 versus 100 +/- 16 mm Hg, p = NS) at maximal exercise (68 +/- 30 W). The reduction in PaO2 was not due to alveolar hypoventilation, because nifedipine did not alter arterial carbon dioxide tension, or to changes in mixed venous oxygen tension, which nifedipine increased at rest (39 +/- 2 versus 43 +/- 3 mm Hg, p less than 0.001) and during submaximal exercise (31 +/- 4 versus 33 +/- 4 mm Hg, p less than 0.03) and maximal exercise (27 +/- 3 versus 31 +/- 3 mm Hg, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Left ventricular volume and ejection fraction response to exercise in chronic congestive heart failure: difference between dilated cardiomyopathy and previous myocardial infarction.

To determine if cause influences the left ventricular (LV) volume and ejection fraction (EF) response to exercise, 24 patients with chronic congestive heart failure (CHF) (13 dilated cardiomyopathy [DC], CHF-DC group; 11 previous myocardial infarction [MI], CHF-MI group) and 6 age-matched control subjects underwent simultaneous hemodynamic monitoring and radionuclide ventriculography during semiupright bicycle exercise. Both CHF groups had similar hemodynamic values, LV volumes and EF at rest. Exercise hemodynamics were also similar, but LV volume and EF responses to exercise were different. In the CHF-DC group LV end-diastolic volume increased by 15% during exercise, significantly less (p less than 0.01) than the 44% increase in CHF-MI group. During exercise, EF increased in CHF-DC group, but did not change in CHF-MI group because of a larger increase in end-systolic volume. The slope of mean pulmonary wedge pressure-LV end-diastolic volume relation was steeper in CHF-DC group than in CHF-MI group (p less than 0.01). The study suggests that LV volume and EF response to exercise in patients with CHF depends on the origin of the CHF.

Cardiac Output↗
PubMed1985

Effects of upright and supine position on cardiac rest and exercise response in aortic regurgitation.

The effects of upright and supine position on cardiac response to exercise were assessed by radionuclide ventriculography in 15 patients with moderate to severe aortic regurgitation (AR) and in 10 control subjects. In patients with AR, heart rate was higher during upright exercise, but systolic and diastolic blood pressure and left ventricular (LV) output were similar during both forms of exercise. LV stroke volume and end-diastolic volume were not altered during supine exercise. LV end-systolic volume increased and ejection fraction decreased during supine exercise, but both were unchanged during upright exercise. Of 15 patients, 5 in the upright and 12 in the supine position had an abnormal LV ejection fraction response to exercise (p less than 0.01). Right ventricular ejection fraction increased and regurgitant index decreased with both forms of exercise and was not significantly different between the 2 positions. Thus, posture is important in determining LV response to exercise in patients with moderate to severe AR.

Adult↗
PubMed1985

Improvement in exercise capacity and associated changes in hemodynamics and left ventricular function after the addition of metoprolol to nifedipine in patients with stable exertional angina.

In 10 men with stable exertional angina, the changes in exercise capacity, hemodynamics, and left ventricular (LV) function were measured after 20 mg sublingual nifedipine (N) and again after adding 100 mg oral metoprolol (M). Nifedipine alone did not significantly improve exercise workloads (+18%) and duration (+21%), but the addition of metoprolol increased both parameters by a further 37 and 32%, respectively (both p less than 0.005 vs. N). After nifedipine the onset of angina was slightly delayed (5.14 +/- 2.41 min placebo (P), 6.00 +/- 2.31 min N, p less than 0.1) and occurred at higher workloads (36 +/- 17 W P, 43 +/- 8 W N, p less than 0.1). After the addition of metoprolol, the onset of angina was delayed substantially more (9.57 +/- 2.22 min, p less than 0.001 vs. P and N) and occurred at much higher workloads (62 +/- 20 W, p less than 0.001 vs. P and N). At rest (R) and during exercise (E), nifedipine decreased systemic vascular resistance (-36% R, -27% E, both p less than 0.001) and mean arterial pressure (-18% R, -21% E, both p less than 0.001), and increased heart rate (+15% R, +11% E, both p less than 0.001), Pulmonary artery wedge pressure on exercise increased less (22 +/- 7 mmHg P, 13 +/- 5 mmHg N, p less than 0.001). After adding metoprolol, the major change was a reduced heart rate (-25% vs. N at R and E, both p less than 0.001), and arterial pressure was unaltered. Pulmonary artery wedge pressure on exercise increased to 18 +/- 5 mmHg (p less than 0.05 vs. N). Exercise LV ejection fraction and volume did not change significantly after adding metoprolol despite marked improvement in angina. In this acute exercise study in patients with stable exertional angina, metoprolol added to nifedipine markedly improved exercise capacity by preventing the increase in heart rate seen with nifedipine. In our patients with relatively normal LV function at rest, the combination was safe and produced no deleterious effects on LV function.

Administration, Oral↗
PubMed1985

Radionuclide determination of right and left ventricular stroke volumes.

The relationship between radionuclide and thermodilution measurement of stroke volumes (SV) was investigated in 30 patients without valvular regurgitation or intracardiac shunt (group A) at rest and during exercise. Both attenuated radionuclide right ventricular (RV) and left ventricular (LV) SV measurements correlated well with the SV determined by the thermodilution method (r = 0.87 and r = 0.93, all P less than 0.001). The reliability of the radionuclide method to estimate SV was evaluated prospectively in two additional groups of patients. In 11 patients without valvular regurgitation or intracardiac shunt (group B) the radionuclide RVSV and LVSV closely approximated to thermodilution SV at rest and during exercise. In 15 patients with aortic regurgitation (group C) the radionuclide stroke volume ratio correlated well with the angiographic regurgitant fraction. Thus, both RVSV and LVSV and the severity of aortic regurgitation can be reliably measured with gated radionuclide ventriculography.

Cardiac Output↗
PubMed1985

The reproducibility of nongeometric analysis of cardiac output and left ventricular volume by radionuclide angiography.

This study examines the reproducibility of individual radionuclide attenuation factors used in the calculation of cardiac output and left ventricular volume by the nongeometric radionuclide method. Twenty male patients were studied at rest with thermodilution measurements of cardiac output on two separate days. Simultaneous equilibrium radionuclide angiograms were performed and left ventricular stroke volume and cardiac output were determined by the nongeometric method. Individual patient attenuation factors were calculated as the ratio of thermodilution and radionuclide cardiac output measurements at each study. There was a close linear relationship between radionuclide and thermodilution measurements of cardiac output in each study (r = 0.88 study 1, r = 0.97 study 2). A similar relationship was found for measurements of left ventricular stroke volume (r = 0.86, study 1, r = 0.97 study 2). Individual radionuclide attenuation factors ranged from 2.49 to 3.46 in study 1 and from 2.77 to 3.29 in study 2. The individual attenuation factors were reproducible to within 10% in 13 patients and to within 15% in 19 patients. When cardiac output was calculated from the radionuclide data of study 2, by means of individual attenuation factors previously determined in study 1, there was a good correlation with the simultaneous thermodilution measurements of cardiac output (r = 0.92, SEE = 0.38 L/min). Individual radionuclide attenuation factors show little variation in serial studies. Thus the nongeometric radionuclide technique can be used to make accurate serial measurements of cardiac output and left ventricular volume.

Adult↗
PubMed1985

Comparison of effects of isometric and supine bicycle exercise on left ventricular performance in patients with aortic regurgitation and normal ejection fraction at rest.

The effects of handgrip and supine bicycle exercise on hemodynamics and left ventricular (LV) performance were compared in 25 patients with moderate to severe aortic regurgitation (AR) and normal LV ejection fraction at rest (greater than or equal to 50%) and in 10 control subjects. In both groups, heart rate, systolic blood pressure, rate-pressure product, and LV output were higher during supine bicycle exercise. Compared with the controls, in patients with AR, stroke volume was unchanged during supine bicycle exercise. LV end-diastolic volume increased during handgrip exercise but was unchanged during supine bicycle exercise. LV end-systolic volume increased and ejection fraction decreased during both forms of exercise. Of 25 patients with AR, 15 (60%) during handgrip exercise and 19 (76%) during supine bicycle exercise had an abnormal ejection fraction response (p less than 0.05). In patients with moderate to severe AR and normal LV ejection fraction at rest, both handgrip and supine bicycle exercise induced LV dysfunction. An abnormal LV ejection fraction response occurred more often with supine bicycle exercise. Handgrip exercise may be a useful alternative method for detecting LV dysfunction in patients with AR in whom adequate bicycle exercise cannot be accomplished.

Adult↗
PubMed1985

Left ventricular response to exercise in coronary artery disease: relation to myocardial ischaemia and effects of nifedipine.

To assess the relationship between left ventricular (LV) response to exercise and myocardial ischaemia, 40 patients with coronary artery disease (CAD) and 17 control subjects underwent radionuclide ventriculography at rest and during semiupright exercise. In 14 of the 40 patients with CAD, radionuclide exercise studies were repeated 20 min after 20 mg of sublingual nifedipine. Patients with CAD had increases in both LV end-diastolic and end-systolic volumes and no change in ejection fraction during exercise. End-systolic volume increased and ejection fraction decreased significantly more in patients with multivessel disease, exercise-induced angina and/or ischaemic ST segment depression. Nifedipine reduced angina and ST-segment depression during exercise, attenuated exercise-induced increase in end-diastolic and end-systolic volumes and improved ejection fraction. This study suggests that in patients with CAD, the response of LV volumes and ejection fraction to exercise is related to the degree of exercise-induced myocardial ischaemia and nifedipine improves exercise LV performance.

Adult↗
PubMed1985

Evaluation of relationship between myocardial contractile state and left ventricular function in patients with aortic regurgitation.

We studied the relationship between myocardial contractile state and left ventricular functional response to exercise in 14 asymptomatic patients with isolated moderate-to-severe aortic regurgitation and six control subjects. The slope of the systolic blood pressure-left ventricular end-systolic volume (pressure-volume) relationship determined by radionuclide ventriculography during angiotensin infusion was used as an indirect measure of myocardial contractility and was compared with left ventricular ejection fraction at rest and during both isometric handgrip and dynamic bicycle exercise. The slope of the pressure-volume relationship was significantly lower in patients with aortic regurgitation than in the control subjects (1.75 +/- 0.57 vs 2.78 +/- 0.42, p less than 0.01). The slope correlated exponentially with resting ejection fraction and was linearly related to changes in left ventricular ejection fraction during both handgrip and bicycle exercise. In patients with aortic regurgitation, resting ejection fraction may overestimate myocardial function. The slope of the pressure-volume relationship measured during afterload stress and left ventricular ejection fraction response to exercise intervention more reliably reflect the degree of left ventricular dysfunction.

Adult↗
PubMed1985

Effects of nifedipine on systemic and regional oxygen transport and metabolism at rest and during exercise.

In a placebo-controlled, randomized, cross-over, double-blind study of 12 patients with stable exertional angina, we measured at rest and during bicycle exercise the effects of 20 mg of nifedipine administered sublingually on hemodynamics and systemic and regional oxygen extraction and metabolism. Nifedipine decreased systemic vascular resistance by 38% at rest (p less than .001) and by 28% during exercise (p less than .001). Cardiac output increased from 4.6 +/- 0.6 to 6.0 +/- 0.9 liters/min (p less than .001) at rest after nifedipine and from 10.6 +/- 3.7 to 11.8 +/- 3.4 liters/min (p less than .005) during exercise. After nifedipine, the arterial-mixed venous O2 content difference decreased from 4.7 +/- 0.6 to 3.5 +/- 0.5 ml/100 ml (p less than .001) at rest and from 10.5 +/- 1.7 to 8.8 +/- 1.6 ml/100 ml (p less than .001) during exercise. After nifedipine the arterial-iliac venous O2 content difference also decreased at rest, from 5.9 +/- 1.5 to 4.8 +/- 1.7 ml/100 ml (p = .06) but increased during exercise from 13.1 +/- 1.5 to 14.0 +/- 1.8 ml/100 ml (p less than .05). Oxygen consumption was not significantly altered at rest or during exercise. Nifedipine decreased mixed venous carbon dioxide tension (PCO2) during exercise from 53 +/- 3.5 to 50 +/- 4.0 mm Hg (p less than .05) but increased iliac venous PCO2 slightly from 61 +/- 4.6 to 63 +/- 5.2 mm Hg (p less than .01). Exercise pH was not significantly altered, but arterial lactate increased more after nifedipine (2.65 +/- 1.95 mmol/liter placebo, 3.54 +/- 2.74 mmol/liter nifedipine; p less than .05). Thus nifedipine produces similar changes in O2 extraction in mixed venous and iliac venous blood at rest but directionally opposite changes during exercise. The data support the hypothesis that nifedipine does not alter the distribution of cardiac output to the legs at rest, but during dynamic leg exercise reduces the redistribution of cardiac output to the legs. This probably results from the shunting of blood flow away from exercising muscles by the generalized vasodilatation of nifedipine.

Angina Pectoris↗
PubMed1984

Beta-adrenergic stimulation of the failing ventricle: a double-blind, randomized trial of sustained oral therapy with prenalterol.

Eleven patients with severe left ventricular impairment (mean ejection fraction 24%) and moderate impairment of exercise tolerance underwent a double-blind, placebo-controlled, cross-over trial of the orally administered beta-agonist prenalterol. Exercise hemodynamics and tolerance were measured during bicycle and treadmill exercise after 2 weeks of therapy with placebo or prenalterol. Cardiac index, ejection fraction, and stroke work index were not improved and exercise duration and peak oxygen consumption were not significantly different during the two treatments. During prenalterol treatment heart rate during exercise was consistently reduced. These results show that prolonged therapy with prenalterol does not improve hemodynamics or exercise tolerance and is associated with a diminished heart rate response to exercise.

Administration, Oral↗
PubMedDate not supplied

A comparison of the effects of beta-blockers with and without intrinsic sympathomimetic activity on hemodynamics and left ventricular function at rest and during exercise in patients with coronary artery disease.

The effects on hemodynamics and left ventricular function of propranolol and pindolol, beta-blockers without and with intrinsic sympathomimetic activity (ISA), respectively, were compared in six men with stable exertional angina at rest and during symptom-limited bicycle exercise. The study was controlled and double blinded, and the order of drug administration was randomized. The dosage of each drug (propranolol 0.15 mg/kg i.v., pindolol 0.02 mg/kg i.v.) was chosen to reduce exercise tachycardia by approximately 18%. Exercise capacity and duration were similar after each drug, and both drugs similarly reduced ST depression during exercise. At rest, propranolol significantly reduced heart rate, systolic arterial pressure, rate-pressure product, stroke volume index, cardiac index, and left ventricular ejection fraction, and increased systemic vascular resistance. In contrast, pindolol significantly reduced only the rate-pressure product and cardiac index, and to a lesser extent than propranolol. During exercise on the other hand, both drugs reduced the heart rate, arterial pressure, rate-pressure product, and cardiac index to a similar degree. Neither drug altered pulmonary artery wedge pressure, systemic vascular resistance, stroke volume index, left ventricular ejection fraction, or left ventricular end-diastolic and end-systolic volume indices. At equipotent beta-blocking dosages, ISA in pindolol reduced the effects of beta-blockade on resting hemodynamics and left ventricular function compared to propranolol, but during exercise the influence of ISA was reduced; and both pindolol and propranolol exert similar effects on hemodynamics and left ventricular function.

Adult↗