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Biomedical subjects

H M Spotnitz

Publications and source records attributed to H M Spotnitz.

At least 127 records · Page 7Linked to original sources
PubMed1976

Comparative cardiovascular effects of propranolol and practolol in puppies.

The present results indicate that in 3-4-weeks-old puppies propranolol induces a significant depression of cardiovascular function expressed by a decrease in heart rate, myocardial contractility, and cardiac output, and an increase in systemic vascular resistance, in doses beyond beta-blocking levels. In contrast, practolol, in the same dose range, did not induce further cardio-circulatory depression, as shown by levels of heart rate, myocardial contractility, and cardiac output similar to the values obtained with beta-blocking doses of this agent. The cardio-depressant activity observed in puppies with doses of propranolol beyond blocking levels is thought to be due to direct negative inotropic and chronotropic effects of this agent, not related to influences on beta receptor sites. Such effect not observed with practolol at doses well beyond beta-blocking levels suggests that this drug exerts a more selective influence on cardiac sympathetic beta receptors.

Age Factors↗
PubMed1976

Cardiac output in infants and children after open-heart surgery.

Green dye measurements of cardiac index (in liters per minute per square meter) were compared in 32 infants and 58 children, 6 and 24 hours after normothermic cardiopulmonary bypass. Cardiac index was significantly lower in infants under one year of age, as compared to older infants and children. This parameter was also lower in patients with total anomalous pulmonary venous drainage, truncus arteriosus, and tetralogy of Fallot. Five infants who died had 6-hour cardiac index determinations of 2.0 L./min./sq. M. Only 2 of 27 survivors had cardiac indices below this level. Simultaneously recorded heart rate and central venous pressure did not correlate with cardiac index. Systolic blood pressure was significantly lower in infants in whom the cardiac index was less then 2.0 L./min./sq. M. (p less than 0.01). However, in individual situations, determination of systemic blood pressure lacked specificity in predicting outcome. Measurements of cardiac index are helpful in the management of infants and children following intracardiac repair by (1) assessing the hemodynamic status, (2) providing a useful indication of the cardiocirculatory effects of therapeutic interventions, and (3) predicting outcome.

Adolescent↗
PubMed1976

Effects of pulsatile and nonpulsatile coronary perfusion on performance of the canine left ventricle.

This study compares the effect of pulsatile (Group C, Fib/P) and nonpulsatile (Group B, Fib/NP) coronary perfusion on myocardial performance during 2 hours of normothermic ventricular fibrillation. Group A (BH/NP), used as a base-line observation, consisted of 2 hours of nonpulsatile coronary perfusion in beating hearts. The assessment of ventricular performance included diastolic ventricular compliance, myocardial oxygen consumption and lactate extraction, regional myocardial blood flow, and histology. After 120 minutes of ventricular fibrillation, Group C showed normal ventricular diastolic compliance as compared to a 50 per cent decrease in Group B (p less than 0.01). Myocardial oxygen consumption was not significantly different from that in Group B. Because of a 70 per cent increase in oxygen extraction above Group B (p less than 0.05), total left ventricular myocardial blood flow was reduced (103 +/- 23 versus 260 +/- 36 ml. per 100 Gm. per minute, p less than 0.05) and had near-constant resistance. Lactate extraction was significantly greater and more stable as compared to Group B (9.28 +/- 1.33 versus 1.8 +/- 1.08, p less than 0.05). Left ventricular endocardial/epicardial flow ratio was greater in Group C (1.21 +/- 0.08 versus 1.06 +/- 0.06, p less than 0.05). Minimal subendocardial histologic changes were present as compared to the marked patchy subendocardial ischemic changes seen in Group B. The results demonstrate that the addition of pulsatile flow to coronary perfusion minimized the deleterious effects of prolonged ventricular fibrillation on myocardial performance.

Animals↗
PubMed1970

Stress distribution in the canine left ventricle during diastole and systole.

A model is proposed for stress analysis of the left ventricular wall (LV wall) based on the realistic assumption that the myocardium is essentially composed of fiber elements which carry only axial tension and vary in orientation through the wall. Stress analysis based on such a model requires an extensive study of muscle fiber orientation and curvature through the myocardium. Accordingly, the principal curvatures were studied at a local site near the equator in ten dog hearts rapidly fixed in situ at end diastole and end systole; the fiber orientation for these hearts had already been established in a previous study. The principal radii of curvature were (a) measured by fitting templates to the endocardial and epicardial wall surfaces in the circumferential and longitudinal directions and (b) computed from measured lengths of semiaxes of ellipsoids of revolution representing the LV wall ("ellipsoid" data). The wall was regarded as a tethered set of nested shells, each having a unique fiber orientation. Results indicate the following. (a) Fiber curvature, k, is maximum at midwall at end systole; this peak shifts towards endocardium at end diastole. (b) The pressure or radial stress through the wall decreases more rapidly near the endocardium than near the epicardium at end diastole and at end systole when a constant tension is assumed for each fiber through the wall. (c) At end diastole the curve for the circumferential stress vs. wall thickness is convex with a maximum at midwall. In the longitudinal direction the stress distribution curve is concave with a minimum at midwall. Similar distributions are obtained at end systole when a constant tension is assumed for each fiber through the wall. (d) The curvature and stress distributions obtained by direct measurements at a selected local site agree well with those computed from "ellipsoid" data.

Animals↗