Search PubMed⌕ Search

Biomedical subjects

B Lown

Publications and source records attributed to B Lown.

At least 19 recordsLinked to original sources
PubMed1997

Incremental bias in Finapres estimation of baseline blood pressure levels over time.

Finapres finger blood pressure monitoring appears to provide a reliable alternative to intra-arterial blood pressure measurement under many circumstances. However, few studies have focused on the limitations of Finapres assessment. In a previous pilot investigation, we observed that Finapres pressure following mental stressors failed to return to initial resting levels. Our objectives in the present study were to (1) replicate earlier findings, (2) examine whether local changes in the measured finger were responsible for the observed drift, and (3) test a method to facilitate the return of pressure to systemic baseline levels. We studied two groups of healthy subjects who underwent a protocol consisting of two mental stressors preceded and followed by baseline periods. In the control group, the Finapres continuously monitored pressure on a single finger for the entire protocol. The intervention group periodically had the Finapres cuff removed and the measured finger exercised to prevent local changes that might influence Finapres estimation of blood pressure. Comparisons indicated a group x baseline interaction effect for systolic and diastolic pressures (P < .0004 and P < .003, respectively). The group with the exercise intervention showed much greater recover during the final baseline than the control group. Recovery of pressures in the control group but not the intervention group was inversely related to the stress level of blood pressure (r = .86, P < .0002), indicating a relationship between blood pressure rise and the degree of distortion of subsequent baseline values. On the basis of our results, we propose that in prolonged protocols, the measurement finger be exercised to facilitate accurate measurements of finger pressure with the Finapres.

Adult↗
PubMed1993

Plasma norepinephrine changes after arousal and exercise were enhanced in conscious pigs with perinephritic hypertension.

This study found that pigs in the early stages of perinephritic hypertension had enhanced plasma norepinephrine (NE) and heart rate (HR) responses to behaviorally arousing stimuli (lifting in a canvas sling) and exercise. In the hypertensive animals, the increase in plasma NE in response to behavioral arousal caused by lifting was double that of the intact group, and the HR response was 50% greater. The increase in plasma NE in response to exercise was six times greater in hypertensive pigs. By contrast, mean arterial pressure changes were not enhanced in the hypertensive group. Exaggerated catecholamine responses in plasma to lifting and exercise stimulation were present when hemodynamic responses were not exaggerated.

Animals↗
PubMed1992

Results of a second-opinion trial among patients recommended for coronary angiography.

OBJECTIVE: To assess the feasibility of carrying out a second-opinion trial for patients urged to undergo coronary angiography and to assess the long-range outcome of such patients denied that procedure, and the criteria evolved for reaching such a conclusion. DESIGN: A case series of patients referred for a second opinion as to the need for coronary angiography. Patients were followed up by questionnaire, telephone call, and center visits. SETTING: Cardiovascular referral center and teaching hospital in Boston, Mass. PATIENTS: One hundred seventy-one patients with coronary artery disease (144 men, average age 60 years; range, 36 to 88 years). Three patients became unavailable for follow-up during a mean of 46.5 months. OUTCOME MEASURES: Concordant-discordant outcome as to the second opinion, cardiac events, invasive interventions, quality of life questionnaire, and level of symptoms. RESULTS: One hundred thirty-four (80%) of the 168 patients were judged not to require angiography; it was recommended in six. In 28 (16%) recommendation was deferred pending further studies. At a mean follow-up of 46.5 months among the 168 patients, there were seven cardiac deaths (annualized cardiac mortality of 1.1%); 19 patients experienced a new myocardial infarction (2.7% annualized rate), while 27 patients (4.3%) were judged to have developed unstable angina. Twenty-six patients (15.4%) ultimately underwent either coronary bypass or angioplasty. CONCLUSIONS: In a large fraction of medically stable patients with coronary disease who are urged to undergo coronary angiography, the procedure can be safely deferred. While there may be a limitation in terms of generalizing this experience to all patients with coronary disease, we reasonably conclude that an estimated 50% of coronary angiography currently being undertaken in the United States is unnecessary, or at least could be postponed.

Adult↗
PubMed1992

Transient coronary stenosis associated with arrhythmia and ischemia 24 hours after reperfusion.

We examined the electrophysiologic sequelae of transient reductions in coronary blood flow (CBF) in conscious dogs. Animals were instrumented to measure arterial pressure, heart rate, repetitive extrasystole threshold (RET), and CBF before coronary stenosis, during 90 minutes of a 50% reduction in CBF, and at 1, 24, 48, and 72 hours after reperfusion. RET was decreased at 24 and 48 hours but returned to baseline by 72 hours after reperfusion. Frequent ventricular ectopic activity (VEA), absent during the control period, was noted during stenosis and at 1, 24, and 48 hours after reperfusion. beta-Adrenergic blockade (metoprolol) normalized the decreased RET at 24 hours. Addition of alpha 1-adrenergic blockade (prazosin) abolished VEA. Endocardial blood flow in the posterior papillary muscle of the left ventricle was reduced by 52 +/- 9% during stenosis, was similar to baseline levels by 1 hour after reperfusion, and decreased by 39 +/- 5% at 24 hours. We conclude that episodes of modest coronary artery stenosis may be followed by electrophysiologic changes indicative of increased vulnerability to malignant ventricular arrhythmias.

Animals↗
PubMed1992

The prevalence of proarrhythmic events during moricizine therapy and their relationship to ventricular function.

The prevalence of proarrhythmic events during moricizine therapy was studied in 144 patients who were treated for symptomatic ventricular tachycardia or ventricular fibrillation. The overall incidence of proarrhythmia was 15.3%. (Twenty-two patients exhibited 23 events.) Ventricular fibrillation occurred in six patients (which led to three deaths), incessant ventricular tachycardia occurred in seven, and new sustained ventricular tachycardia in four. Patients with proarrhythmia had significantly lower left ventricular ejection fraction (24% vs 39%; p less than 0.0001), higher prevalence of congestive heart failure (68% vs 36%; p less than 0.005), and higher incidence of previous proarrhythmia (45% vs 9%; p less than 0.0001). No significant difference between the two groups was found in respect to age, arrhythmia at presentation, underlying heart disease, moricizine dose, or concomitant drug therapy.

Drug Evaluation↗
PubMed1992

Catecholamines in cerebrospinal fluid are increased by behavioral arousal and myocardial ischemia.

To study the central neural mechanisms involved in malignant ventricular arrhythmia, concentrations of norepinephrine in the cerebrospinal fluid were measured during behavioral stimulation and during coronary artery occlusion. Pigs were instrumented via thoracotomy with catheters to measure mean arterial pressure and plasma catecholamines and with silk snares around the left anterior descending coronary artery for occlusion after recovery from surgery. Cannulas were placed in the lateral ventricle of the brain to sample cerebrospinal fluid. Behavioral arousal was induced by lifting the pig in a canvas sling for 5 min. Mean arterial pressure, heart rate, and both plasma and cerebrospinal fluid norepinephrine concentrations increased significantly after lifting stimulation. In a separate experiment, 5 min after coronary artery occlusion, both plasma catecholamines and norepinephrine in cerebrospinal fluid were significantly elevated. Furthermore, pigs in which ventricular fibrillation occurred after occlusion had significantly higher concentrations of norepinephrine in cerebrospinal fluid before coronary artery occlusion.

Animals↗
PubMed1992

Control of ventricular fibrillation after coronary artery occlusion via intracerebroventricular injections.

The central nervous system (CNS) may play a larger role than previously thought in the development of ventricular fibrillation after coronary artery occlusion. The probability of ventricular fibrillation after complete, permanent occlusion of the left anterior descending coronary artery was 52% in conscious control pigs. After the administration into the lateral cerebral ventricle of tyrosine, the amino acid precursor of the catecholamine neurotransmitters, 100% of the animals developed ventricular fibrillation. After tyrosine plus propranolol, a beta-adrenoceptor antagonist, only 9% of pigs developed ventricular fibrillation. Treatment with propranolol alone did not affect the outcome. Catecholamine synthesis in the CNS may be associated with the development of ventricular fibrillation after coronary artery occlusion.

Animals↗
PubMed1991

Changes in left atrial size in patients with lone atrial fibrillation.

A retrospective analysis was performed on 23 subjects with lone atrial fibrillation who were followed for an average of 6.2 years (1.1-12.8 years). In all patients, underlying organic heart disease was excluded based on history, physical exam, electrocardiogram, echocardiogram, and Doppler ultrasound interrogation. All patients had at least two echocardiographic studies during the period of observation. Atrial fibrillation was chronic in 11 subjects and paroxysmal in 12. All echocardiographic measurements were obtained by averaging the measurements of two blinded investigators. Left atrial size increased an average of 5.6 mm which translates into a 14.7% increase over the baseline measurement. This increase in size was not associated with a change in left ventricular mass or fractional shortening as determined by echocardiography. Subjects with chronic atrial fibrillation had a larger percent increase than subjects with paroxysmal atrial fibrillation (18.9 vs. 10.8%), although this relative change in size failed to reach statistical significance. The only variable which significantly contributed to the change in left atrial size was the duration of follow-up. We conclude that atrial fibrillation occurring in patients with lone atrial fibrillation may cause a slow and progressive increase in left atrial size independent of changes in left ventricular size or function.

Aged↗
PubMed1991

Diazepam administered prior to coronary artery occlusion increases latency to ventricular fibrillation.

Few studies have addressed the antiarrhythmic potential of pretreatment with diazepam in acute myocardial infarction. Thus, the effect of diazepam pretreatment prior to coronary artery occlusion was examined in conscious pigs. Animals were instrumented with aortic catheters to measure arterial pressure, a pulmonary artery catheter for drug administration, and a snare around the left anterior descending coronary artery for permanent occlusion one week later. Diazepam (1 mg/kg iv bolus) or vehicle was administered 10 minutes prior to occlusion. Eight of 14 animals receiving diazepam (57%) and 13 of 22 receiving vehicle animals (59%) developed ventricular fibrillation following coronary occlusion. However, the latency to ventricular fibrillation was significantly shorter (7 +/- 1 min) in animals receiving vehicle compared to animals receiving diazepam (11 +/- 1 min). Significant increases in heart rate were seen up to 5 hours after coronary occlusion only in animals receiving vehicle. The results indicate that diazepam pretreatment can increase ventricular fibrillation latency and prevent heart rate increases following acute myocardial infarction.

Animals↗
PubMed1991

Decreases in repetitive extrasystole threshold in the conscious pig with myocardial infarct were reversed by tyrosine.

Reports indicate that the administration of tyrosine, the precursor amino acid for catecholaminergic neurotransmitters, may be beneficial under conditions of physiologic stress. We studied the effects of tyrosine on vulnerability to ventricular arrhythmia in conscious pigs with healing myocardial infarcts, and sham operated (intact) pigs. Mean arterial pressure and heart rate were measured via chronically implanted aortic catheters. The repetitive extrasystole threshold (defined as the energy in milliamperes (ma) needed to cause a spontaneous ventricular beat following a premature beat induced by an electrical impulse), was measured via a bipolar pacing catheter placed during instrumentation surgery in the apex of the right ventricle. One week after infarct, the myocardial infarct group was studied before and ninety minutes after the administration of tyrosine (8 mg/kg iv). Before tyrosine, the myocardial infarct group had a significantly lower repetitive extrasystole threshold (12 +/- 1 ma) compared to the intact group (19 +/- 2 ma). Ninety minutes after tyrosine, the repetitive extrasystole threshold in the myocardial infarct group was 17 +/- 1 ma. The availability of tyrosine did not alter the repetitive extrasystole threshold in the intact group. Thus, vulnerability to ventricular arrhythmia was enhanced in pigs with recent myocardial infarction. Tyrosine, which can be nutritionally manipulated, may reduce myocardial vulnerability to arrhythmia after infarct.

Animals↗
PubMed1991

Decrease in repetitive extrasystole threshold during epinephrine infusion is enhanced in conscious dogs with perinephritic hypertension.

Hypertension is associated with myocardial hypertrophy as well as increased adrenergic responsiveness, both of which can predispose to malignant ventricular arrhythmias. This study was designed to test the effects of subpressor doses of epinephrine (0.15 and 0.3 micrograms/kg/min x 30 min) on vulnerability to ventricular arrhythmia in normotensive and perinephritic hypertensive dogs. Two groups of 6 dogs each were chronically instrumented with aortic catheters to measure mean arterial pressure and bipolar pacing catheters in the apex of the right ventricle to measure repetitive extrasystole threshold, an index of vulnerability to ventricular fibrillation. In the normotensive dogs, the low dose of epinephrine (0.15 micrograms/kg/min IV) had no significant effects on mean arterial pressure, heart rate of repetitive extrasystole threshold. However, in the hypertensive dogs, the same dose caused a significant 39% increase in heart rate (p less than 0.05) and 41% decrease in repetitive extrasystole threshold (p less than 0.05). These findings suggest that electrophysiological vulnerability of the myocardium caused by epinephrine infusion is enhanced in the hypertensive animal.

Animals↗