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Biomedical subjects

C M Oakley

Publications and source records attributed to C M Oakley.

At least 19 recordsLinked to original sources
PubMed1992

Angiotensin-converting enzyme inhibitors, left ventricular dysfunction, and early heart failure.

A study was undertaken to examine the effects of the angiotensin-converting enzyme inhibitor lisinopril on exercise performance in 18 patients with major impairment of left ventricular systolic function. The study was a randomized, double-blind, crossover design, and patients received treatment with either once-daily lisinopril (2.5-10 mg) or placebo for a period of 6 weeks. A total of 15 patients completed the study. Compared with placebo, lisinopril had no significant effect on supine or standing blood pressure or heart rate. Although lisinopril had no effect on exercise duration during a low-intensity exercise protocol, in patients undergoing a high-intensity exercise protocol, there was a trend toward improved exercise time and peak oxygen consumption improved significantly. In addition, treatment with lisinopril resulted in an increase in renal blood flow and a reduction in glomerular filtration rate. Moreover, administration of once-daily lisinopril 10 mg resulted in a decrease in plasma concentrations of angiotensin II, aldosterone, and atrial natriuretic peptide, and an increase in plasma concentrations of active renin.

Aldosterone↗
PubMed1992

Influence of left ventricular hypertrophy and function on the occurrence of ventricular tachycardia in hypertrophic cardiomyopathy.

Sixty-nine patients with hypertrophic cardiomyopathy were studied by 2-dimensional and Doppler echocardiography and 72-hour Holter monitoring to examine the relation between the degree of left ventricular (LV) hypertrophy and dysfunction and the occurrence of ventricular tachycardia (VT). Episodes of nonsustained VT were detected in 20 patients (29%). Maximal wall thickness was not different between patients with (22 +/- 5 mm) and without (21 +/- 5 mm) VT. Total hypertrophy score, calculated as the sum of 10 segmental wall thicknesses, was also similar in both groups (157 +/- 22 and 153 +/- 32 mm, respectively; p = not significant). Furthermore, no significant differences were found between the 2 groups in LV end-diastolic dimension (41 +/- 7 vs 40 +/- 6 mm), fractional shortening (33 +/- 7 vs 34 +/- 10%) and left atrial size (40 +/- 10 vs 41 +/- 11 mm). An LV outflow tract gradient was detected in 25% of patients with and 35% without VT (p = not significant). One or more Doppler indexes of diastolic function were abnormal in 70% of patients, but no difference in any of these indexes was found between those with and without VT. In summary, the occurrence of VT in hypertrophic cardiomyopathy is not related to the degree of LV hypertrophy, outflow tract gradient or dysfunction. This finding suggests a dissociation between the arrhythmogenic substrate and echocardiographic features of the disease.

Adolescent↗
PubMed1992

Effects of increased inspired oxygen concentrations on exercise performance in chronic heart failure.

Exercise capacity in patients with stable heart failure may be influenced by prolonged drug treatment or exercise training, but acute interventions are generally thought to have little effect. Cardiorespiratory responses to exercise were studied in 12 consecutive patients with chronic congestive heart failure who underwent serial submaximal and maximal exercise tests at inspired oxygen concentrations of 21% (room air), 30%, and 50%. Mean (SD) exercise duration during progressive testing to maximum exercise capacity was prolonged from 548 (276) s on room air to 632 (285) s on 50% oxygen (p = 0.012). During steady-state exercise at 45 W, oxygen enrichment to 50% was associated with significantly increased arterial oxygen saturation (94.6 [1.9]% to 97.5 [1.3]%), and significantly reduced minute ventilation (36.1 [8.6] l/min to 28.1 [5.9] l/min), cardiac output (7.5 [2.3] l/min to 6.5 [1.9] l/min), and subjective scores for fatigue and breathlessness (13.9 [3.1] to 11.5 [3.5]) compared with room air intermediate changes were observed with 30% inspired oxygen. Increased inspired oxygen concentrations can improve exercise performance acutely and modify the ventilatory response to exercise in patients with heart failure. Hyperoxia reduces ventilatory response and circulatory demand while maintaining oxygen delivery at a given workload. The potential benefits of increased inspired oxygen concentrations in the treatment of chronic heart failure merit further assessment.

Adult↗
PubMed1992

Response of the pulmonary circulation to acetylcholine, calcitonin gene-related peptide, substance P and oral nicardipine in patients with primary pulmonary hypertension.

Endothelium-dependent vasodilation of the pulmonary vascular bed was investigated in five patients with primary pulmonary hypertension. Three endothelium-dependent vasodilators (acetylcholine, calcitonin gene-related peptide and substance P [in two patients]) were infused sequentially into the right atrium, followed by nicardipine given orally during full hemodynamic monitoring. Acetylcholine, calcitonin gene-related peptide and substance P had no effect on pulmonary artery pressure, total pulmonary vascular resistance or cardiac output, although calcitonin gene-related peptide significantly decreased systemic arterial systolic pressure from 132 +/- 34 to 113 +/- 33 mm Hg. In contrast, oral nicardipine decreased total pulmonary vascular resistance from 23 +/- 12 to 13 +/- 8 U, with a concomitant increase in cardiac output from 3.1 +/- 1 to 4.7 +/- 2 liters.min-1 and decrease in systemic vascular resistance from 30 +/- 9 to 13 +/- 4 U. Thus, despite the presence of a reversible component in these five patients with primary pulmonary hypertension, pulmonary vascular resistance did not decrease in response to the infused endothelium-dependent vasodilator agents, indicating that endothelium-dependent vasodilation is impaired in these patients.

Acetylcholine↗
PubMed1992

Diastolic function in hypertrophic cardiomyopathy: relation to exercise capacity.

Doppler echocardiography was used to assess diastolic function in 40 patients with hypertrophic cardiomyopathy and to relate it to the patients' symptoms, anaerobic threshold and maximal oxygen consumption during cardiopulmonary exercise testing. The patients had a smaller early (E wave) (p less than 0.01), higher late (A wave) (p less than 0.05) mitral diastolic flow velocity, larger A/E ratio (p less than 0.01), longer isovolumetric relaxation time and E wave duration (p less than 0.001) and slower deceleration rate of the E wave (p less than 0.001) than 40 age- and gender-matched normal subjects. In the patients with hypertrophic cardiomyopathy, maximal oxygen consumption and anaerobic threshold were, respectively, 26.3 +/- 9.2 and 21.1 +/- 6.1 ml/kg per min compared with 47 (range 39 to 68) (p less than 0.01) and 41 (range 27 to 58) ml/kg per min (p less than 0.01) in normal subjects. There was no relation between Doppler indexes and symptoms but symptomatic patients had lower maximal oxygen consumption and anaerobic threshold compared with asymptomatic patients (21.4 +/- 7 vs. 30.7 +/- 10, p less than 0.001 and 18.6 +/- 4.7 vs. 23.1 +/- 5.7, respectively, p less than 0.001). In conclusion, Doppler echocardiography can identify abnormalities of left ventricular filling in patients with hypertrophic cardiomyopathy. However, these indexes measured at rest do not correspond to the patient's professed symptomatic status or exercise capacity measured objectively. Conversely, cardiopulmonary exercise testing reveals a depressed maximal oxygen consumption and anaerobic threshold even in the least symptomatic patients.

Adolescent↗
PubMed1992

QT-interval abnormalities in hypertrophic cardiomyopathy.

To examine whether QTc and QTc dispersion across the leads of a surface electrocardiogram (ECG) are different in patients with hypertrophic cardiomyopathy (HCM) compared with normal subjects, we measured QT and calculated QTc in all 12 leads of a surface ECG in 24 patients with HCM and in 20 age- and sex-matched normal control subjects. Maximal QTc was prolonged in HCM patients (465 +/- 24 ms) compared with controls (410 +/- 20 ms) (p < 0.001). QTc dispersion defined as the difference of maximum-minimum QTc was also greater in HCM patients (71 +/- 21 ms) compared with normals (35 +/- 11 ms) (p < 0.001). A correlation was found between the degree of left ventricular hypertrophy expressed by the maximal wall thickness and maximal QTc (r = 0.48, p < 0.02). However, QTc dispersion did not correlate with maximal wall thickness. Thus, patients with HCM show a prolonged QTc (> 440 ms) and increased QTc dispersion compared with normal subjects. In addition, the degree of left ventricular hypertrophy correlates with maximal QTc. The presence of a prolonged QT with increased regional dispersion may be associated with the occurrence of serious ventricular arrhythmia and sudden death in HCM.

Adult↗
PubMed1992

Xamoterol in hypertrophic cardiomyopathy: effects on diastolic function and heart rate.

The aims of this study were to determine the effects of the partial beta 1-adrenergic agonist, xamoterol, on diastolic function and ambulatory heart rate in hypertrophic cardiomyopathy. Eleven patients with non-obstructive hypertrophic cardiomyopathy were studied with cross-sectional and Doppler echocardiography and 24-h Holter monitoring before and after a single intravenous dose of xamoterol. Resting heart rate (mean +/- SD) increased from 76 +/- 16 before, to 83 +/- 15 beats/min 15 min after xamoterol, p = 0.03. In the 4-h period after xamoterol, maximum heart rate was reduced (127 +/- 21 to 112 +/- 19, p = 0.01) and minimum heart increased (60 +/- 16 to 67 +/- 17, p = 0.04) compared to the same 4-h period of the previous day. There were no significant changes in cross-sectional or Doppler echocardiographic measurements of left ventricular function following xamoterol. Xamoterol stabilises the heart rate in hypertrophic cardiomyopathy. The absence of a significant effect on Doppler measurements does not preclude a beneficial effect on diastolic function. This initial study suggests that xamoterol should be further investigated as a new medical therapy for hypertrophic cardiomyopathy.

Adolescent↗
PubMed1992

Amiodarone reduces QT dispersion in patients with hypertrophic cardiomyopathy.

To compare QT interlead variability (dispersion) in patients who receive a class III antiarrhythmic with those not on antiarrhythmic therapy, we measured QT in all 12 leads of a standard ECG in 24 patients with hypertrophic cardiomyopathy, 12 (50%) of whom were on amiodarone monotherapy and 12 (50%) who were not on amiodarone or other cardioactive medication which could affect QT. Age, functional class, chamber dimension or the degree of left ventricular hypertrophy expressed by maximal wall thickness (21 +/- 5 vs 20 +/- 4 mm; p = NS) was not different between the amiodarone and the non-amiodarone group. Maximal corrected QT (QTc) was greater in patients receiving (488 +/- 25 ms) compared to those not receiving amiodarone (451 +/- 23 ms) (p less than 0.001). However, QTc dispersion defined as the difference of maximum minus minimum QTc was decreased in the amiodarone (48 +/- 10 ms) compared to the non-amiodarone group (78 +/- 17 ms) (p less than 0.001). We conclude that in patients with hypertrophic cardiomyopathy, amiodarone prolongs QTc but reduces QTc dispersion. These results agree with expected changes in ventricular recovery time in patients who receive Class III antiarrhythmic agents and provide further support to the theory that QTc dispersion reflects regional differences in ventricular recovery time.

Adolescent↗
PubMed1992

Dobutamine stress echocardiography for detection and assessment of coronary artery disease.

Stress echocardiography with dobutamine infusion for detection of coronary artery disease is a potential alternative to exercise stress testing with some theoretic advantages. Fifty patients who were not receiving cardioactive medication were prospectively studied with two-dimensional echocardiography and 12-lead electrocardiography (ECG) during incremental dobutamine infusion (5, 10, 15 and 20 micrograms/kg body weight per min, each dose for 8 min). Images were analyzed by using an 11-segment left ventricular model. All patients underwent correlative exercise ECG and coronary angiography, which revealed normal coronary arteries in 14 and significant disease (greater than or equal to 70% diameter stenosis) in 36. Peak rate-pressure product during dobutamine infusion was 18,845 +/- 4,156 versus 23,740 +/- 6,158 mm Hg/min on exercise (p less than 0.01). Interobserver concordance for wall motion analysis was good (kappa coefficient = 0.77). The use of baseline (n = 14) or reversible (n = 24) regional asynergy to define an abnormal dobutamine echocardiogram resulted in a sensitivity for detecting coronary artery disease of 78% and a specificity of 93%. Corresponding data for the dobutamine ECG were 47% and 71% and for the exercise ECG were 72% and 71%, respectively. The development of new mitral regurgitation on Doppler color flow imaging (n = 4) improved sensitivity to 81% without loss of specificity. Inducible asynergy or new mitral regurgitation was observed in 6 (50%) of 12 patients with single-, 6 (60%) of 10 with double- and 12 (86%) of 14 with triple-vessel disease. The site of transient asynergy provided additional localizing information. Exercise duration and time to diagnostic ST segment shift were shorter in patients with coronary artery disease with versus those without echocardiographic evidence of ischemia (both p less than 0.05). Side effects during dobutamine infusion were mild and short-lived. Dobutamine stress echocardiography is well tolerated, is useful for detection and assessment of coronary artery disease and is applicable to patients unable to exercise.

Adult↗
PubMed1992

Doppler haemodynamic profiles of clinically and echocardiographically normal mitral and aortic valve prostheses.

Doppler echocardiographic studies were performed in 380 consecutive patients with 415 normally functioning artificial valves to establish normal Doppler characteristics for each type of prostheses used in our institution, with particular reference to Starr-Edwards valves, and to serve as control studies for future assessment. None of the patients were in heart failure at the time of the study. Peak transaortic velocities (m.s-1) were higher and effective orifice areas (cm2) smaller in mechanical valves as a whole, when compared with bioprostheses (P less than 0.01); 2.7 +/- 0.7 and 1.4 +/- 0.55 for Starr-Edwards, 2.7 +/- 0.6 and 1.5 +/- 0.6 for Bjork-Shiley, 1.8 +/- 0.1 and 1.5 +/- 0.6 for Duromedics and 1.5 +/- 0.06 and 2 +/- 0.12 for bioprostheses, respectively. In the mitral position, the average peak diastolic velocities (m. s-1) and pressure half-times (ms) were higher in mechanical valves, but there was a large overlap between the various types and sizes of prostheses (P = NS); 1.6 +/- 0.3 and 98 +/- 25 for Starr-Edwards, 1.4 +/- 0.3 and 88 +/- 26 for Bjork-Shiley, 1.8 +/- 0.1 and 75 +/- 5 for Duromedics and 1.5 +/- 0.3 and 90 +/- 20 for bioprostheses, respectively. There was an inverse relation between valve size and pressure halftime for Starr-Edwards prostheses (P less than 0.01). Doppler flow characteristics in mechanical valves where similar in patients with normal and dysfunctioning prostheses. Valvular or myocardial dysfunction could best be ascertained when early postoperative studies were available for comparison.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Stress Doppler echocardiography using dobutamine in coronary patients with and without ischaemia induction.

To examine the effects of dobutamine on pulsed-Doppler left ventricular ejection dynamics and its utility for evaluation of coronary disease (CAD) we studied 10 patients with normal coronaries (Group 1) and 24 patients with significant CAD (greater than or equal to 70% diameter stenosis) using a graded stress infusion (5 to 20 micrograms.kg-1.min-1). Two-dimensional echocardiography was performed to detect regional asynergy and analysed using an 11-segment model. Patients with CAD were divided into those with (Group 3, n = 14) and without (Group 2, n = 10) inducible ischaemia; six patients had reversible involvement of greater than or equal to three segments (subset 3A). Groups were well matched for baseline left ventricular function and all studies were carried out while the patients were not taking cardioactive therapy. Hyperkinetic wall motion was typical and exaggerated hyperkinesis of normal segments was commonly seen in those with baseline (n = 9) or reversible asynergy (n = 14). Normals and CAD patients showed comparable changes in heart rate and blood pressure (P = NS between groups).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Aspirin to prevent growth of vegetations and cerebral emboli in infective endocarditis.

The incidence of stroke on cranial computed tomography (CT) and change in echocardiographic vegetation area was prospectively compared in a preliminary observational study involving nine patients with infective endocarditis randomized to either low-dose aspirin (75 mg d-1, Group I, n = 4) or no aspirin (Group II, n = 5). Two symptomatic cerebral infarcts and one myocardial infarct occurred in the controls, compared to no events in patients on aspirin during a total observation period of 343 d (range 28-49 d). The mean vegetation area decreased in the aspirin group (mean change = -0.24 cm2), compared to an increase in controls (mean change = +0.35 cm2). The platelet half-life (normal range 5-6 d), which was measured using Indium-111 radiolabelling, tended to be lower in Group II (4.6 +/- 0.2 vs. 3.9 +/- 0.5 d). No side-effects or complications attributable to aspirin were observed. A possible role for adjunctive aspirin therapy in the prevention of embolic complications in infective endocarditis is suggested, and warrants further study.

Adult↗