摘要:

We studied isolated cat trabecula under conditions closely resembling those present for muscle fibers in the left ventricular wall. The purpose of the study was to see if muscle contraction under those circumstances could be described by a time-varying compliance as reported for intact canine left ventricle. We found the time of the end of systole to depend on the history of contraction. This time varied between 100 and 160 msec aa measured from the onset of contraction. Similar dependency, although less percentage-wise, was found by reanalysis for intact feline left ventricles. We conclude that the behavior of the canine left ventricle as a time-varying compliance may be related to the complex organization of the cardiac muscle fibers in the wall of the heart rather than to muscle properties.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Reducing blood oxygen affinity may enhance myoc-ardial oxygen delivery during ischemia. We evaluated this hypothesis in awake, previously instrumented dogs that received a 20 ml/kg infusion of a solution of dihydroxyacetone, phosphate, and pyruvate after acute occlusion of either the left anterior descending or circumflex coronary artery. This infusion reduced blood oxygen affinity (BOA) alter 2 hours; the PMincreased from 29.9 ± 0.7 torr (mean ± SD) to 32.1 ± 0.6 torr; P < 0.01 (↓BOA group). Four dogs received 20 ml/kg of phosphate and pyruvate solution to assess volume effects (V group), and five dogs were controls (C group). The 2-hour PMvalues in V and C were unchanged. Regional flow (15-fim spheres) reduction 2 hours postocclusion was compared to the percent tissue infarcted determined by histology 7–9 days after occlusion for multiple samples from the endocardial layer of the left ventricle. When flow was less than 40% of normal, V and C had 55% infarction while J, BOA had 37% (P < 0.05); at flow less than 20% of normal, V and C had 79% infarction while tBOA had 38% (P < 0.001); and at less than 10% of normal, V and C had 87% and 94% infarction, respectively, while I BOA had 58% (P < 0.001). Reducing blood oxygen affinity after coronary artery occlusion significantly decreased the extent of myocardial necrosis for the same degree of ischemia. Reducing BOA may increase oxygen delivery to ischemic myocardium when flow is restricted.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

To determine whether liposomes (microscopic phospholipid vesicles) may be useful In delivering drujfs to a region of myocardial igchemia, we studied the concentration of positively charged and neutral liposomes containing131I-albumin and horseradish peroiidase in ischemic myocardium of 20 dogs during the first 4 hours of experimental myocardial infarction. We also studied the interaction of liposomea containing fluorescent dyes and horseradish peroiidaae with isolated contracting cardiac myocytes. We found that positively charged and neutral liposomes accumulated in poorly perfused myocardium and that positively charged liposomes accumulated in the ischemic region to a greater extent than neutral liposomew [138 ± 21 vs. 81 ± 9% (mean ± SE) of the concentration of liposomes in uninvolved myocardium]. Electron microscopic examination of this myocardium showed liposome contents to be located in the vascular space, in endothelial cells, and in ischemic myocytes. We found that isolated cardiac myocytes avidly took up the liposomal contents when they were depolarized by a high potassium environment and that liposomal contents were scattered throughout the interior of the cells in electron micrographs of some of the isolated myocytefi. Anoxia alone for 20–30 minutes did not modify the liposome-isolated myoeyte interaction or cause depolarization of the cells. We conclude that liposomes may be useful as drug carriers to depolarized, ischemic myocardium, although significant uptake by normal myocardial cells cannot be expected with the lecithin, cholesterol, and octadecylamine liposomes we used.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

To test the hypothesis that the rise in arterial pressure occurring with maturation is due to an increase in the vascular responsiveness to angiotensin II, sequential cumulative doses of angiotenmn II were infused intravenously into chronically catheterized newborn lambs maintained on a constant, weight-adjusted sodium intake from birth to 8 weeks of age. Basal mean arterial pressure correlated with both age and weight, but age was a stronger determinant of mean arterial pressure than was weight. No change in the mean arterial pressure response to angiotensin II occurred with maturation. Basal plasma renin activity and plasma aldosterone concentrations were low and did not change significantly with age. Therefore, in the newborn lamb in the sodium replete state, age is a better determinant of arterial pressure than is weight. However, an age-related change in vasoconstrictor responsiveness to angiotensin II does not occur and, therefore, cannot account for the rise in arterial pressure that is observed with maturation.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Myocardial oxygen consumption (MVO2) increases in proportion to the cumulative product of active tension and time throughout the normal isometric contraction. However, rapid shortening at any time during a contraction prevents further tension generation and oxygen consumption during the remainder of that contraction. My hypothesis is that, under physiological conditions, shortening produces this effect by reducing the extent and duration of the energy-dependent events subserving contraction. I tested this hypothesis by minimizing the potential reduction of metabolism via muscle shortening during contraction; this was done by lowering temperature (23°C), reducing shortening rate (0.8 muscle length/sec) and increasing myoplasmic calcium (7.5 mM Ca2++ 10 mM caffeine). Twelve right ventricular cat papillary muscles were released from that length at which maximum active force is developed to a slack length at increasing intervals after stimulation. Under these conditions, absolute MVOj increased significantly, but the relative increase with progressively longer stimulus-release intervals was greatly attenuated. At a 0-miec stimulus-release interval under the present conditions, MVO2was 8.26 nl/mg dry wt per contraction; for a full contraction MVOa was only 27% greater. Under the more physiological conditions employed in a prior study, this increase, from 0.41 to 2.97 nl/mg dry wt per contraction, was 824%. The addition of 10−7M norepinephrine under otherwise physiological conditions increased MVO2at all times during contraction, but the relationship between MVO2and length was not altered. These data suggest that, both under normal conditions and after inotropic augmentation, shortening of cardiac muscle during contraction decreases the level of the energydependent events supporting contraction; this may be the mechanism by which MVO, is regulated by length-dependent changes in metabolism throughout contraction.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We have quantified the ultrastructure of myocardial cells in tissue samples obtained from six adult normal Yucatan swine, tissue samples were obtained from 20 different sites in the left ventricle, right ventricle, and interventricular septum. The samples were processed for electron microscopy and quantitative morphometric analysis. The percent relative volumes of myoflbrils, mitochondria, transverse tubular system, sarcoplasmic reticulum, and clear intracellular space were determined using stereologic&l morphometric methods. Overall, the data were distributed homogenously among the 20 individual sites. However, when certain eubcellular components were examined regionally, some differences appeared. The mitochondrial:myofibril volume ratios were significantly increased in the left ventricle and interventricular septum compared to the right ventricle. They also were greater in the endocardial region compared to the epicardium, which is consistent with higher metabolic activity of these zones. Similarly, the sarcoplasmic reticulum: myofibril ratio was greater in the endocardial region vs. the epicardial region and the basal layer compared to the mid-layer, suggesting the greater need for provision of calcium ions in these particular cones. Since the swine is a convenient large animal fur physiological studies, these results indicate that swine can also be used for quantitative morphometric measurements of myocardial changes in normal and pathologic hearts, and for the study of regional changes in various layers and regions of heart walls.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

This report evaluates pulse wave propagation with respect to contributions by vascular wall elastic and geometric properties, vessel wall and blood viscosity, and noniinearities in system parameters and in the equations of motion. Discrepancies in results obtained with different experimental methods and theory are discussed and resolved. A three-point pressure technique was used to obtain measurements from the abdominal aorta, carotid, iliac, and femoral arteries of dogs. Computations involved linear, as well as nonlinear methods. Results are presented along a continuous path of transmission (abdominal aorta, iliac, femoral), and it is shown that variations in phase velocity can be explained entirely by the geometric variation of these vessels. Phase velocities are shown to be frequency independent at 54 Hz whereas attenuation increases progressively for higher frequencies. Determination of propagation coefficients using maximal, compounded values of reported viscoelastic and geometric properties just manages to span the range of phase velocities, determined in different laboratories, but does not do so for attenuation. Also, differences in experimental techniques cannot explain these discrepancies. Consideration of geometric taper, nonlinear compliance, all the terms in the equation of motion, and the effect of wall and blood viscosity resolves discrepancies betweeen theoretical models and experimentally derived phenomena.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We studied the effect of aspirin and sulfinpyrazone on changes in platelet count, thromboxune Bi production, and pulmonary vascular resistance following the onset of veno-venous membrane oxygenator pcrfusion in sheep. Perfusion under identical circumstances was performed in three groups of animals, with one group serving as controls, one group receiving pretreatment with 1.5 grams of sulfinpyrazone iv, and one group receiving pretreatment with aspirin 50 mg/kg, iv. Both aspirin and sulfinpyrazone eliminated the rise in thromboiane B, and the increase in pulmonary vascular resistance seen in control animals. Platelet preservation was improved significantly with sulfinpyrazone pretreatment, but not affected by aspirin. We conclude that sulfinpyrazone and aspirin have different mechanisms of action as far as platelet preservation during extracorporeal perfusion is concerned. The major difference may be sulfrapvrazone's ability to reduce platelet adhesion to the membrane surface. Since both aspirin and gulfinpyrazone eliminated the pulmonary vascular response, but only sulfinpyrazone preserved platelets, it is apparent that the pulmonary vascular response is more closely related to thromboxane synthesis than to platelet disappearance.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

The radioactive microaphere technique was used to trace regional blood flow and total cardiac output diatribution in rate in heart failure Becondary to biventricular volume overload during acute intravenous infusion of nitroglycerin. Data from rats with heart failure (chronic arteriovenous shunt) were compared to data obtained from rats subjected to sham surgical procedures. In both groups, data were obtained at rest and during treadmill exercise during alternate infusions of nitroglycerin and normal saline (control). In heart failure, nitroglycerin slightly increased cardiac output at rest and during exercise, increased stroke volume, and reduced systemic vascular resistance at rest but not during exercise. In the heart failure group, exercise reduced flow to the renal, gastrointestinal, and cutaneous circulations but had little or no effect in the sham group. Nitroglycerin dramatically increased renal, gastrointestinal, and cutaneous blood flow during exercise in the heart failure group but had minimal effects on active hyperemia in the skeletal muscle bed. In the sham group, nitroglycerin decreased blood flow in the renal, gastrointestinal, and cutaneous beds and had no effect on skeletal muscle blood flow. Thus, in the renal, gastrointestinal, and cutaneous circulations during exercise, nitroglycerin increased flow in the heart failure group and decreased flow in the sham group to the extent that the respective values in the two groups were equal.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

To determine whether chronic bradycardial pacing could change myoeardial capillary density and heart performance, we used transvenous right atrial pacing to reduce the heart rate of rabbits to about 66% of normal for up to 52 days. We compared control animals, animals which had been chronically paced, and sham-operated animals. The chronically paced animals showed no cardiac hypertrophy [heart;body weight ratio (H:BR) was unchanged]. All animals paced for longer than 10 days showed increased myoeardial capillary density (CD) when compared with controls of similar heart weight. The increase in CD was correlated with the duration of pacing (r = 0.830) and reached levels up to 70% greater than those of controls. The increase In stroke volume seen during acute bradycardial pacing was more than twice as great in animals which had been chronically paced as in the controls, which had not previously been paced (84% vs. 38%). Resting minute work and stroke work were similar in all groups, but maximum values achieved after norepinephrine administration were much greater in animals that had been chronically paced. Minute work increased by 59.1 ± 9.6% in controls, by 82.1 ± 18.3% in sham-operated animals, and by 107.1 ± 8% (means ± SE) in paced animals. Stroke work increased by 84.9 ± 9.8% in controls, by 75.4 ± 19.5% in sham-operated animals, and by 121.8 ± 7.8% in paced animals. Although the greater CD of most of the chronically paced hearts may be partly responsible for their improved performance, this cannot be the only factor, since animals paced for short periods showed improved performance but normal CD.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID