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Biomedical subjects

J D Bristow

Publications and source records attributed to J D Bristow.

15 recordsLinked to original sources
PubMed1992

Prevalence and etiology of idiopathic dilated cardiomyopathy (summary of a National Heart, Lung, and Blood Institute workshop.

Idiopathic dilated cardiomyopathy (IDC) is the primary indication for cardiac transplantation, with associated costs of approximately $177 million per year. Recognizing the economic implications of IDC, the increasing incidence, and the limited information on pathogenesis and prognosis, the National Heart, Lung, and Blood Institute convened a workshop on the Prevalence and Etiology of Idiopathic Dilated Cardiomyopathy on June 13 to 14, 1991. The difficulties of studying the disease were reviewed, including its relatively low prevalence, its potentially pluricausal nature, and the fact that it is often a diagnosis of exclusion. Still, it presents significant challenges to the cardiovascular scientific community, since the mechanism of myocardial damage and related etiologic and prognostic factors are virtually unknown. The development of more reliable measures of immune-mediated damage and noninvasive measures of impaired cardiac function present new research opportunities in this disorder. Standardized diagnostic criteria for use in observational and interventional trials were developed, and priorities for future research were proposed. Population-based registries and nested case-control studies, where feasible, are appropriate study designs for tracking incidence and prevalence, and for identifying risk factors, respectively. Interventional studies should focus on secondary prevention, through modifying immune-mediated damage in clinically evident dilated cardiomyopathy, and through prevention of sudden death in patients with the disorder. Primary prevention trials must await the identification of modifiable risk factors and of appropriate and effective interventions.

Cardiomyopathy, Dilated↗
PubMed1992

Correlates of aortic distensibility in chronic aortic regurgitation and relation to progression to surgery.

Aortic distensibility decreases with increasing age. Patients with chronic aortic regurgitation eject a large stroke volume into the proximal aorta. A decrease in distensibility of the aorta may impose a higher afterload on the left ventricule and may contribute to deterioration of left ventricular function over time. Accordingly, aortic distensibility was measured in 33 patients aged 13 to 73 years who had chronic isolated aortic regurgitation with minimal or no symptoms. Ascending aortic diameter was measured 4 cm above the aortic valve by two-dimensional echocardiography and pulse pressure was measured simultaneously by sphygmomanometry. Aortic distensibility was calculated as (Change in aortic diameter between systole and diastole/End-diastolic diameter)/Pulse pressure. Left ventricular systolic wall stress and mass were derived from standard M-mode echocardiographic measurements. Left ventricular volumes and ejection fraction were measured by radionuclide ventriculography. Aortic distensibility decreased logarithmically with increasing age (r = -0.62, p less than 0.001) and also correlated inversely with systolic wall stress, left ventricular mass and end-diastolic volume. Patients who eventually underwent aortic valve replacement for symptoms of left ventricular dysfunction had significantly lower aortic distensibility than did those who did not yet require valve replacement: 0.09 +/- 0.08 vs. 0.22 +/- 0.19 x 1/100 (1/mm Hg) (p less than 0.05). Thus, the reduced aortic distensibility that occurs with increasing age may contribute to the gradual left ventricular dilation and dysfunction seen in patients with chronic aortic regurgitation.

Adult↗
PubMed1992

Energy metabolism and contractile function after 15 beats of moderate myocardial ischemia.

Difficulties in studying myocardial metabolism with adequate time resolution have led to contradictory conclusions regarding the mechanisms causing contractile abnormalities during the early stages of ischemia. In acutely instrumented swine, we investigated whether abnormalities in subendocardial ATP, phosphocreatine, or lactate content develop rapidly enough during the first few heart beats after onset of partial myocardial ischemia to contribute to contractile failure. Within the first 15 beats of a 40-50% reduction in left anterior descending coronary artery blood flow, regional myocardial function was significantly reduced but continuing to deteriorate. Rapidly frozen transmural left ventricular biopsies obtained on the 15th heart beat (+/- 1.5 beats) after the onset of ischemia revealed significant decrements in subendocardial phosphocreatine and ATP levels to 77% (p less than 0.05) and 84% (p less than 0.005) of control values, respectively, but minimal change in lactate content. Metabolic effects as assessed by transmural averages took longer to become detectable; thus, there was a tendency to underestimate the importance of subendocardial metabolic effects on myocardial function. When left ventricular preload was assessed during this early time period, left ventricular end-diastolic wall thickness only decreased by 3%, and left ventricular end-diastolic pressure did not change significantly despite a large fall in coronary perfusion pressure. Thus, in an in vivo pig model with techniques optimized to detect subendocardial metabolic changes within the period of very early moderate myocardial ischemia, abnormalities in high energy phosphate compounds occurred rapidly enough to contribute to developing myocardial dysfunction, whereas preload-mediated mechanisms related to vascular distending pressure could not explain the functional deterioration under these conditions.

Adenosine Triphosphate↗
PubMed1992

Effects of stopping long-term vasodilator therapy in patients with chronic aortic insufficiency.

We studied the effects of stopping long-term vasodilator therapy in 17 patients with chronic stable aortic insufficiency. These patients received hydralazine for 37 +/- 15 months (mean +/- SD) and, as a result, had experienced a significant decrease in left ventricular volumes. All patients were followed clinically and ten of the patients underwent serial radionuclide evaluation at baseline, while receiving drug, and at 20 +/- 7 months after stopping drug therapy. No patient showed evidence of acute clinical deterioration when drug therapy was stopped. The rate of progression to valve replacement due to onset of symptoms or left ventricular dysfunction was not significantly different from that previously reported in a population with similar characteristics. Left ventricular size, however, returned to levels similar to baseline after drug therapy was stopped. We conclude that long-term vasodilator therapy may be discontinued in patients with chronic stable aortic insufficiency without causing clinical deterioration or significant alteration in rate of progression to valve replacement.

Adult↗
PubMed1991

Effects of long-term vasodilator therapy on electrocardiographic abnormalities in chronic aortic regurgitation.

Electrocardiographic abnormalities develop in patients with chronic aortic regurgitation (AR). Although vasodilator drugs may reduce left ventricular (LV) volume overload, the effects of such therapy on electrocardiographic abnormalities have not been previously evaluated. Accordingly, electrocardiograms were analyzed before and after double-blind, randomized administration of either hydralazine or placebo in 54 patients with chronic AR. These patients were without limiting symptoms and had preserved ejection fraction on entry in the study. The magnitude of ST-segment depression and Romhilt-Estes point score for LV hypertrophy were assessed. Baseline ST depression and LV hypertrophy scores in the placebo and hydralazine groups were not significantly different. At follow-up, after a mean of 19 +/- 6 months, there was a significant reduction in ST depression in patients taking hydralazine (n = 28) compared with patients given placebo (n = 26): -0.023 +/- 0.044 vs 0.029 +/- 0.055 mV, respectively (p = 0.0001); and in the LV hypertrophy score (-1.1 +/- 2.2 vs 0.9 +/- 2.3 points, respectively; p = 0.002). Hydralazine-treated patients also had significant decreases in LV end-diastolic and end-systolic volume indexes, and a significant increase in ejection fraction. These results suggest that such vasodilator therapy may be beneficial in patients with chronic AR.

Adult↗
PubMed1991

Active downregulation of myocardial energy requirements during prolonged moderate ischemia in swine.

We studied the effects of rapid atrial pacing during the final 10 minutes of a 70-minute, 31% reduction in coronary blood flow in anesthetized swine to understand the significance of apparent metabolic improvements during the initial 60 minutes of segmental ischemia. Within 5-10 minutes of ischemia, subendocardial phosphocreatine (PCr) and ATP were depleted to 47% and 63% of control, respectively; lactate accumulated within the subendocardium to 300% of control; and net arteriovenous lactate production occurred. Despite continued ischemia and no significant changes in the external determinants of myocardial oxygen consumption, by 60 minutes subendocardial PCr and lactate contents returned to near control levels and there was net arteriovenous lactate consumption. Ischemic left ventricular wall thickening and ATP levels remained depressed throughout the experiment. Atrial pacing during the final 10 minutes of ischemia again resulted in depletion of PCr and lactate production. Since the myocardium was capable of hydrolyzing PCr in response to atrial pacing at 60 minutes of ischemia, we conclude it was capable of hydrolyzing PCr during the period of constant ischemia when instead it was accumulating PCr. We propose the ischemic myocardium downregulates regional energy requirements below blood flow-limited rates of energy production during ischemia. This appears to be an active adaptation to ischemia and not a result of passive damage or cellular injury.

Adaptation, Physiological↗
PubMed1978

Physiological effects of lowered blood oxygen affinity in dogs.

Ten adult Labrador retrievers were studied under control conditions and while blood oxygen affinity was lowered by intravenous infusions of glycolytic intermediates. Blood P50 was increased from 32.4 +/- 1.3 mm Hg (mean +/- SD) to 34.3 +/- 1.2 mm Hg, a highly significant increase (P less than 0.001). Blood oxygen capacity, mixed venous oxygen tension and arterial PCO2 were not significantly different in the two conditions. Cardiac output (Q) was lower with the higher P50 (89 +/- 16 ml/kg/min) than in the control state (111 +/- 31 ml/kg/min) but the difference was not statistically significant. The arteriovenous oxygen concentration difference (CaO2 - C-V(O2)) was significantly increased (P less than 0.05) from 4.4 +/- 0.6 vol % to 4.9 +/- 0.8 vol %. Oxygen consumption, the product of Q and (CaO2 - C-V(O2)), was the same in the two conditions: 4.9 +/- 1.3 ml/kg/min (control) versus 4.4 +/- 0.9 ml/kg/min. The animals responded to lowered blood oxygen affinity with increased oxygen extraction by peripheral tissues and a concomitant, although not statistically significant, fall in cardiac output.

Animals↗
PubMed1978

Left ventricular stiffness.

Left ventricular stiffness is defined by the relationship between pressure and volume and can be altered by a variety of disorders. In disorders with high VLVED, such as mitral regurgitation, protection of pulmonary capillaries from high pressure is provided by a PV shift. In contrast, increased stiffness is produced by ventricular hypertrophy or ischemic heart disease, which puts the patient at increased risk for pulmonary capillary hypertension. Changing the ventricular PV relationship by therapy is an exciting prospect.

Animals↗
PubMed1976

Report of the Inter-Society Commission for Heart Disease Resources. Optimal resources for examination of the chest and cardiovascular system. A hospital planning and resource guideline. Radiologic facilities for conventional x-ray examination of the heart and lungs. Catheterization-angiographic Laboratories. Radiologic resources for cardiovascular surgical operating rooms and intensive care units.

This is an updated and expanded planning and oprimal resource guideline for diagnostic examinations of the cardiovascular system. Catheterization-angiographic laboratories are described and detailed specifications given for radiologic and physiologic equipment. Case loads for maintaining safe and effective performance are recommended and complication rates discussed. An optimal location for the laboratory is defined and the status of affiliated laboratories reviewed. Professional staff qualifications, relationships and requirements are enumerated and recommendations are made for organization and administration of the services. There is a protocol for electrical safety and radiation protection and a data base for assessing case loads in hospitals within a community or region. This statement also defines optimal facility and equipment criteria for conventional chest x-rays and radiologic equipment requirements for cardiovascular surgical operating rooms and intensive care units.

Angiocardiography↗
PubMed1975

Hemodynamic changes after valve replacement with Starr-Edwards prostheses.

A brief review of the pathophysiology of aortic and mitral valve disease and the hemodynamic results of valve replacement with caged ball prostheses are described. In most patients intracardiac pressures and restored to normal at rest, although there are small pressure gradients across mechanical valves. Severe pulmonary hypertension, if present, usually will regress. With exercise, abnormalities of left atrial pressure or left ventricular function may be found after valve replacement. The causes of failure to achieve hemodynamic improvement with surgery and the late return of congestive failure are discussed.

Aortic Valve Insufficiency↗
PubMed1975

Objective and subjective analysis of left ventricular angiograms.

In order to determine the reproducibility of analyses of left ventriculograms, 35 cineangiograms were evaluated by four observers, two using standard quantitative techniques to determine ventricular volumes and a newly devised quantitative system to evaluate wall motion and two others using only visual inspection of the angiograms. Objective analysis repeated by the same observer correlated well for end-diastolic and end-systolic volumes and ejection fraction (r = .98, .99, respectively) and only one of 105 (1%) wall segments were identified differently. Variability in assessments increased when comparisons were made with a second objective observer. Correlation coefficients for the three volumetric parameters were .93, .98, and .95 and there was disagreement in the assessment of 8% of wall segments. Wide variability was present between an objective and two subjective observers in analyses of end-diastolic volumes (r = .63, .64). Regional wall motion was assessed differently in 19% and 27% of segments, respectively. Though the correlation of objectively and subjectively determined ejection fractions was much better than the correlation for volume (r = .92, .84), it was not as good as the correlation between two objective observers. Occasional errors of clinical significance occurred. We conclude that subjective analysis has a significant error rate and that reproducibility and accuracy of analysis of left ventriculograms require objective analysis.

Angiocardiography↗