摘要:

Removal of premigratory neural crest over somites 1 through 3 in chick embryos has been shown previously to result in a significant incidence of persistent truncus arteriosus. In the present study, single somite-length pieces of premigratory neural crest were removed unilaterally at slightly different embryonic ages. These lesions resulted in a number of different heart defects. Two defects, ventricular septal defect and double outlet right ventricle, were significantly correlated with the location of neural crest removed. The stage at which the ablation was performed was important in determining the incidence but not the type of defects.

ISSN:0009-7322    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Tachycardia produces subendocardial ischemia and ST segment abnormalities after coronary obstruction. To determine whether a quantitative relationship exists between these ST shifts and transmural blood flow, 19 dogs were studied. Coronary obstruction was produced by ameroid constriction of the left circumflex artery, and tachycardia was generated by atrial pacing at 90 to 210 beats/min. ST shifts were studied by body surface isopotential mapping with an 84-electrode torso grid, and blood flow was quantitated by serial radiolabeled microsphere injections. Isopotential maps at each paced rate, 40 msec into the ST segment, were classified as normal or ischemic based on spatial patterns of voltages. Pacing after 3 weeks of ameroid constriction reduced endocardial/epicardial flow ratios in 11 dogs from 1.16 ± 0.22 at rest to 0.41 ± 0.18 at 210 beats/min. Abnormal ST depression developed in these dogs at a rate of 184.0 + 16.5 beats/min. Endocardial/epicardial ratios with ST depression (0.45 + 0.15) were lower than at those without ST depression (1.05 + 0.19; p < .01). Logistic regression analysis demonstrated that ST depression corresponded to an endocardial/epicardial ratio of 0.67 or less (p < .01). With this model, 95.5% of data sets were correctly classified. Neither heart rate nor perfusion bed size were significant independent predictors of an ischemic electrocardiographic response. The magnitude of abnormal ST segment shift was significantly correlated (r = .87) with the transmural flow ratio. Thus (1) development of electrocardiographic changes indicative of ischemia corresponds to a predictable degree of flow redistribution and (2) the magnitude of the ST shift is correlated with the intensity of the flow abnormality.

ISSN:0009-7322    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

The day-to-day variations in epicardial defibrillation threshold (DFT) were examined in closed-chest, unanesthetized dogs. In 11 animals, DFT decreased from 15.8 ± 2.1 J (mean SE) at the beginning of the study (day 1), to 7.4 + 1.7 J on day 2 (p < .0001). DFT measured daily for 5 consecutive days in seven dogs decreased from 22.1 + 3.1 J on day 1 to 9.3 + 2.3 J on day 2 (p < .01) and remained stable from day 2 to day 5. Transcardiac impedance, measured in six dogs, decreased from 112 + 6 Q on day 1 to 100 + 6 Q on day 2 (p = NS). Propranolol given on day 2 in 14 dogs increased DFT from 12.0 + 2.2 to 18.0 ± 3.1 J (p < .05). The effects on DFT of sequential administration of isoproterenol and propranolol were examined in 10 dogs. Isoproterenol decreased DFT from 10. O + 1. 9 to 5.5 + 1. 5 J when given before propranolol (p < .001, n = 10), and from 1 1. 7 ± 3.0 to 9.7 + 3.1 J when given after propranolol (p < .05, n = 9). Propranolol increased DFT from 10.6 + 3.0 to 14.6 + 3.9 J when given before isoproterenol (p < .02, n = 9), and from 10.7 + 1.4to 14.4 + 1.5 J when given after isoproterenol (p < .01, n = 10). These experiments demonstrate a sustained cardiac effect of epicardial defibrillation reflected by a decrease in DFT that is partially reversible by propranolol. A similar decrease was produced by /3-adrenergic stimulation, an effect that was partially blocked by propranolol. Thus, variations in the autonomic state of the heart may be an important modulator of cardiac DFT. These findings, however, are experimental, and do not support the use of isoproterenol alone in traditional clinical defibrillation.

ISSN:0009-7322    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

On May 20, 1984, the Surgeon General challenged the health community to work toward attainment of a smoke-free society by the year 2000. The leadership of the nation's three major voluntary organizations joined numerous associations of health professionals in accepting the challenge. The Subcommittee on Smoking of the American Heart Association (AHA) has concluded that attaining this objective requires the development and implementation of public policies designed to facilitate the transition from a smoking to a nonsmoking society. To study the relevant issues and recommend appropriate policies, the subcommittee commissioned a working group of distinguished experts in the field of smoking and health to prepare a policy statement. The statement, published here, has received the enthusiastic endorsement of the Subcommittee on Smoking and the leadership of the AHA. The working group discusses and recommends four policies: 1. Increase the federal cigarette excise tax. 2. Eliminate or restrict tobacco advertising and other forms of promotion. 3. Assure the rights of nonsmokers to clean air through legislative means. 4. Identify mechanisms to ease and assist the transition of tobacco farmers to other crops or careers.

ISSN:0009-7322    

出版商:OVID    

年代:1986

数据来源: OVID