ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Lysophosphatidylcholine (LPC) accumulates in ischemic but not normal myocardium and has electrophyriological actions. We studied the effects of LPC on passive and active membrane properties and on repolarization in the Purkinje fibers of sheep using multiple microelectrodes: one for intracellular current injection and the other for transmembrane voltage (Vmax) recording. Synthetic 1- palmitoyl LPC (10–50 /IM) was used in normal Tyrode's solution. These concentrations are presumably equivalent to those of free LPC in ischemic myocardium. At a low [LPC]Oof 10–20 jtM, cable analysis showed increased membrane (R«) and longitudinal (Ri) resistances (P< 0.010 and <0.013, respectively); LPC increased the length (K*) and time (Tm) constants (P < 0.018 and <0.010, respectively) with the balance between R. and Ri determining input resistance. The increased R», without a change in threshold or resting Vmax, enhanced excitability as manifested by a decrease in rheobasic current (P < 0.009) or charge threshold (P < 0.005), or a downward shift in the nonnormalized strength-duration (SDC) (P < 0.048) and charge-duration curves (CDC). Normalized SDC and CDC suggested that altered passive properties were primarily responsible for the phase of increased excitability. [LPC]oat 10–20 fiM decreased the maximal rate of rise of phase 0 (V J (P < 0.001), even during the phase of increased excitability, and depressed and flattened the V− vs. charge relationships. This depression of the sodium system resulted in a phase of decreased excitability and often inexcitability despite Rm being maintained near or somewhat above the values observed during the control period or the phase of increased excitability. Abnormalities of repolarization included a marked increase or decrease in action potential duration, two stable steady states at resting and plateau Vmax, or one steady state at a low Vmax. Abnormal sustained rhythmic activity was observed commonly both at high and low Vmax. High [LPC]oof over 40 μM usually produced only the phase of decreased excitability, although occasionally a biphasic response was noted.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

This study examined the relationships between left ventricular (LV) regional function, regional myocardial blood flow (RMBF), and myocellular necrosis after sudden proximal occlusion of the left anterior descending coronary artery (LAD) in 36 awake, unsedated dogs. Net wall thickening during systole (NET) was used to assess regional LV function, was expressed as percent control, and was measured with chronically implanted ultrasonic crystals. RMBF was measured with 8- to 10-jun radioactive microspheres. In regions with a moderate degree of functional loss, NET fell to 35.3 ± 2.2% of control at 5 minutes when RMBF fell from 1.19 ± 0.08 to 0.86 ± 0.09 ml/g per min (P < 0.05). No significant change occurred in midwall or epicardial RMBF. The relationship between endocardial flow and NET was non-linear (r - 0.89, P < 0.0001). In these segments, subsequent changes in RMBF were unrelated to corresponding functional alterations through 24 hours. In segments with paradoxic systolic wall thinning RMBF fell in endocardial, midwall, and epicardial layers; endocardial ischemia was most severe (0.30 ± 0.0S ml/g per min). Segmental myocellular necrosis was most severe in the endocardial layer and correlated significantly with both RMBF and segmental function. Myocellular necrosis increased in severity as flow was reduced below 70–76% of normal. Thus, in this model of LV ischemia, (1) regional LV functional loss is most sensitive to reductions in endocardial RMBF; (2) subsequent increases in RMBF are largely unassociated with functional recovery; (3) transmural ischemia results in paradoxical systolic wall thinning.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Xenon-133 washout curves were recorded from the anterior wall of the left ventricle down to at least 1% of the peak following bolus injection into the bypassed left anterior descending coronary artery of dogs. Washout curves were obtained for awide range of independently measured flows (0-36-9.67 ml/min per g). Thirty-six curves were analyzed in order to evaluate the effect of tracer recirculation and flow inhomogeneity (assessed by simultaneous microsphere injection) on the flow values derived from monoexponential fitting of the curve and from stochastic analysis. The results were compared to those obtained by computer model simulation. Although minimized in this study, recirculation significantly affected the evaluation of flow by both methods of analysis (monoexponential fitting down to 30% of the peak underestimated actual flow by an average of 15%, stochastic analysis by 45%). Correction for recirculation by the dual injection method led to correct estimation of flow by monoexponential fitting, whereas stochastic analysis produced an average underestimation of 24%. The failure of stochastic analysis to estimate flow correctly was explained mainly by a lower observed peak activity caused by noninstantaneous input. As predicted on the basis of a multicompartimental model, tranamural flow inhomogeneity as great as that explored in this study (a 3-fold difference in flow between the best and worst perfused thirds of the wall) did not significantly affect the computation of flow by monoexponential analysis. Flow-limited, xenon blood-tissue diffusion cannot be supported by the results of this study, as the underestimation of actual flow observed at high flow rates can be ascribed to the effect of tracer recirculation.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We examined the function of the interventricular septum in six open-chest dogs by inserting piezoelectric crystals into the interventricular septum. Continuous ultrasonic recordings showed that the changes in myocardial chord length (MCL) in the septum and free walls of the right and left ventricle were similar during saline infusion and during pericardiotomy. End-diastolic MCL and myocardial shortening during ejection (MS) rose in the septum and free walls of both ventricles during saline infusion as end-diastolic pressures rose by an average of 6 mm Hg to 12–13 nun Hg. Subsequent pericardiotomy increased end-diastolic MCL and MS in the septum and free walls of the ventricles, and reduced end-diastolic pressures by 1–2 mm Hg. The responses to aortic and pulmonary artery constrictions were similar before and after pericardiotomy. When aortic constriction had raised left ventricular systolic pressure by about 60 mm Hg, end-diastolic MCL increased in the septum and free left ventricular wall, whereas end-diaetolic MCL and MS of the free right ventricular wall fell. Pulmonary artery constriction increased end-diastolic MCL in the free right ventricular wall and reduced end-diastolic MCL and MS in the septum and free left ventricular wall. Thus, the myocardium, including the interventricular septum, is uniformly expanded during saline infusion and pericardiotomy. The interventricular septum behaves as part of the left ventricle during aortic and pulmonary artery constriction. The pericardium imposes a restraint on the interventricular septum and free walls of the ventricles during volume loading, but not during pressure loadings, because dilation of one ventricle is associated with shrinkage of the other.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

The applicability of the 2-deoxyglucose tracer method to study tranamural distribution of glucose uptake in the left ventricle isolated, Langendorff-perfused rat heart was validated for the myocardium. The total 2-deoxy[2H]glucose trapped in the myocardium was proportional to the glucose uptake which was varied by the mechanical work load and availability of other oxidizable substrates. When the mechanical work of the heart was eliminated by K+-induced arrest, the glucose uptake of 2.0 junol/min per g protein was evenly distributed across the left ventricular wall. In the beating heart, glucose uptake averaged 4.7 mol/min per g protein, and was about 40% higher in the subendocardial layer than eubepicardium {P < 0.001). Measurement of the transmural distribution of coronary flow by the microsphere method indicated that there were no areas of underperfusion in the left ventricle. The transmural gradient glucose uptake probably is caused by uneven distribution of the mechanical work load.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We examined regional mechanics of the left ventricular free wall in naturally pumping dog hearts during β-blockade. Local systolic wall force (F) and segment length (L) were obtained with an auxotonic force gauge and an ultrasonic dimension gauge, both inserted at the equatorial level of the wall to measure F and L in the circumferential direction. Shortening velocity (−dL/dt) was obtained by differentiation of L, Preload and afterload were changed by acute caval and/or aortic occlusion so that a wide variation in F, L, -dL/dt, and dF/dt during shortening was obtained. In all experiments, F vs. L at identical time (t) after end-diastole (ED) fell on well-defined lines, Irrespective of the -dL/dt values. Control F (at t = 200 ma) over the 0.5-cm wide gauge was 85.5 ± 11.5 g, and slope of the F vs. L line (t = 200 msec) was equivalent to a drop of approximately 50% in F at 10% reduction in L. No defined relationship was observed between F, L, and -dL/dt. However, by superimposing F, L, and -dL/dt curves from contractions of high EDL and high -dL/dt on those from contractions of low EDL and low -dL/dt, and comparing F and -dL/dt at identical L and t, a slightly lower F (difference 2.23 ± 1.09 g, P ≈ 0.08) could be associated with the higher -dL/dt (difference 0.6 ± 0.1 muscle length/sec, P < 0.001). These data suggest that the F-L-t relationship is a valid descriptor of auxotonic contractions in the ventricular wall, and that the direct effect of shortening velocity on the wall force is modest.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Regional dilation (expansion) of newly infarcted myocardium has been associated with increased mortality. To study this entity further, and to define the relationship of expansion to infarct morphology, infarcts were created in 44 open-chest dogs by a coronary ligation and coronary embolization method. Twenty-one transmural and 18 nontrangmural infarcta of 1 to 11 days of age were studied. Infarct expansion was quantified by comparison of lengths of infarct and noninfarct containing segments of transversely sliced hearts. Five dogs died less than 6 hours after infarction and showed no evidence of expansion. Of those surviving more than 24 hours, 17 had infarct expansion and 22 did not. In the latter group, four infarcts were transmural and 18 were nontansmural; in the former, all 17 infarcts with expansion were transmuraL Infarct thinning for the 17 infarcts with expansion was significantly greater than that observed in the nontransmura) infarcta or the nonexpanded transmural infarcts (P < 0.001). Of the 21 transmural infarcts, the largest infarct without expansion was 10.8%, and the smallest infarct with expansion was 11.3% of left ventricular weight. Among infarcts with expansion, there was a poor correlation between the extent of expansion and infarct size (r = 0.19). A significant inverse relationship (P<0.02) was observed, however, between the extent of expansion and postinfarct survival for the transmural infarcts. Although infarct expansion occurred only in transmural infarcts exceeding a critical but relatively small threshold of injury, the absence of a further relationship between transmural infarct size and extent of expansion suggests that other anatomic, metabolic, or hemodynamic factors affect the development of acute infarct expansion. Circ Res 49: 80–88, 19S1

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Quantitative characterization of myocardial properties represents a rapidly emerging area of echocardiographic investigation. Because measurement of the ultrasonic integrated backscatter is theoretically applicable to analysis in vivo with reflected ultrasound, this study was performed to develop and evaluate a suitable method for measurement of quantitative backscatter in vivo. In view of the desirability of characterizing ischemic myocardium noninvasively, the study was performed with animal preparations simulating myocardial ischemia in humans. In one series of open-chest dogs, integrated backscatter among 22 ischemic regions was increased by 200% (P< 0.01) compared to values in control rgions within 1 hour after coronary occlusion and by 400% (−45.1 ± 0.7 dB compared to −50.9 ± 0.4 dB) (P < 0.001) within 6 hours. In a second series of open-chest dogs, ischemia was quantified with141Ce microspheres, and mean integrated backscatter was found to increase (280% of control) {P < 0.01) in regions with flow less than 20% of control 2 hours following coronary occlusion. Additional studies -with perfused hearts revealed two determinants of the increased ultrasonic backscatter observed: (1) an increase in cardiac fluid content reflected by the wet-to-dry weight ratio, and(2) the contributions of formed elements in whole blood. The results indicate that ultrasonic integrated backscatter distinguishes severely ischemic from nonischernic myocardium in vivo in open-chest animnlK. Because it was possible to obtain these results in the reflection mode, potential extension of the approach to clinical applications is promising.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We studied the importance of collateral blood flow in the genesis of epicardial conduction delay and ventricular arrhythmias by creating a model of myocardial ischemia in which coronary collateral channels were embolized with a rapidly hardening vinyl latex. In 33 open-chest anesthetized dogs, heart rate was held constant (18O-200/min) and the proximal left anterior descending coronary artery (LAD) was occluded for 10 minutes, followed by 30 minutes of reperfusion. The LAD then was ligated and latex was injected just below the ligature. The latex filled coronary vessels branching from the LAD down to a diameter of 20–30 jun and produced transmural infarcts averaging 42% of the left ventricular mass (range 35–58%). The amount of epicardial conduction delay was measured during atrial rhythm at multiple electrode sites within the ischemic zone. The maximal delay following coronary occlusion was 97 ± 48 msec (mean ± SD), whereas latex embolization increased the delay to 203 ± 51 msec (P < 0.001). In response to coronary occlusion, 8% of the electrograme demonstrated Wenckebach-like alternation, whereas 58% showed alternation following latex embolization (P < 0.001). Compared to coronary occlusion, coronary embolization with latex significantly increased the number of dogs that developed ectopic beats during the first 10 minutes of ischemia (66% vs. 94%; P = 0.02). However, coronary occlusion evoked ventricular fibrillation in 21% of the dogs, whereas no animal developed fibrillation at any time following coronary embolization (P = 0.002). Ventricular fibrillation also was absent in an additional 18 animals in which the LAD was embolized without an earlier period of occlusion. The results indicate that embolization of the LAD with vinyl latex increases the severity of local conduction abnormalities while reducing the incidence of lethal arrhythmias. The interruption of collateral blood flow to the ischemic myocardium may depress conduction in a homogeneous manner such that the ischemic zone may be unable to support a sufficient number of reentrant circuits to initiate fibrillation.

ISSN:0009-7330    

出版商:OVID    

年代:1981

数据来源: OVID