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Biomedical subjects

J Lekven

Publications and source records attributed to J Lekven.

At least 73 records · Page 4Linked to original sources
PubMed1981

Unchanged myocardial tissue perfusion following pericardiotomy in acutely loaded cat hearts.

Myocardial tissue flow was measured by the distribution of labelled microspheres in cats which were volume-expanded by infusion of blood. Removal of the intact pericardium markedly reduced left ventricular diastolic pressure. However, despite the fact that diastolic ventricular pressure is a major determinant for myocardial tissue flow and its transmural distribution, no significant change in tissue flow occurred following pericardiotomy. Failure of tissue flow to increase in the face of lower diastolic intracavitary pressure can in this study be explained by concomitant ventricular dilatation and reduced systolic blood pressure.

Animals↗
PubMed1981

Effect of timolol on blood flow distribution in the myocardium during acute regional ischaemia in cats.

The beta-adrenergic blocking agent timolol was given to cats with acute coronary artery ligation. Regional myocardial tissue flow was measured by the distribution of 15 micrometers labelled microspheres. Timolol reduced heart rate, cardiac contractility and left ventricular systolic pressure, but end-diastolic pressure rose. Ischaemic tissue blood flow remained unchanged following timolol, thus improving the marked imbalance between oxygen demands and delivery. In normal areas of the myocardial tissue flow was reduced, indicating the beta 2-adrenergic blocking effect of timolol. This was also the case for the border area between ischaemic and non-ischaemic tissue, but significantly less flow reduction was found on the endocardial side than on the epicardial side in the border area. Except for this latter observation, timolol does not appear to improve coronary perfusion. The present study, therefore, indicates that beneficial effects of timolol on ischaemic myocardium are mainly related to a reduction of myocardial oxygen demand.

Animals↗
PubMed1981

Myocardial function of the interventricular septum. Effects of right and left ventricular pressure loading before and after pericardiotomy in dogs.

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 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 free left ventricular systolic pressure by about 60 mm Hg, end-diastolic MCL increased in the septum and free left ventricular wall, whereas end-diastolic 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.

Animals↗
PubMed1981

Mesenteric arterial vasopressin in cats: local and systemic effects.

The administration of intraaterial mesenteric vasopressin to induce small intestinal ischemia was evaluated in the cat. Small intestinal blood flow was measured by carbonized microsphere distribution and electromagnetic flowmetry. Injection of 99mTc labeled isotope into the superior mesenteric artery was monitored by gamma camera, and isotope kinetics were evaluated as indicators of small intestinal blood flow. Superior mesenteric arterial and small intestinal mucosal blood flow could maximally be reduced to 15%-20% of control by vasopressin administration. 99mTcO4 mesenteric-cardiac transit time was doubled in all animals when small intestinal mucosal blood flow was reduced to less than one-third of control. However, significant blood flow reductions were induced in other abdominal organs, most importantly in retroperitoneal lymph nodes and adipose tissue. Intraarterial mesenteric vasopressin administration does not induce sufficiently severe and specific intestinal ischemia to provide optimal conditions for selective small intestinal hypoxic radioprotection.

Animals↗
PubMed1981

Effects of vasopressin, noradrenalin and oxytocin on blood flow distribution in rat kidney with neoplasm.

The arterial blood flow distribution between tumour and intact renal tissue was investigated in rats with transplanted sarcomas. Changes in tissue flow were measured by the microsphere tracer technique, and the redistributing effects on blood flow of vasopressin, noradrenalin and oxytocin was recorded. Bolus injections of vasopressin gave a transient decrease of intact tissue flow, not found in tumours. At increasing doses of vasopressin and in early tumour growth phase, the flow discriminating effect tended to vanish. Constant intravenous infusion of vasopressin gave similar reduction of flow in tumour and intact tissue. Selective administration into the renal artery reduced flow in intact tissue but produced ambiguous effects in tumour tissue. Noradrenalin produced less reduction of tumour flow as compared with intact tissue flow. Oxytocin increased tumour blood flow while no flow change occurred in intact tissue. Oxytocin thus appeared to produce the most favourable redistribution of flow within tumour kidneys for the prospect of conveying cytotoxic agents selectively to the tumour.

Animals↗
PubMed1980

Migration of 15 micron microspheres from infarcted myocardium.

The fate of 15 micrometers microspheres in ischaemic myocardial tissue was investigated. The spheres were delivered to the left atrium before acute coronary artery ligation. 10 h later the myocardium was examined for its contents of preocclusion spheres, as well as spheres delivered immediately before sacrifice. The ischaemic tissue contained 11 to 60% less preocclusion spheres, compared with nonischaemic tissue in the same hearts. On average, 26% of preocclusion spheres were lost during the 10 h period. Negligible amounts of the lost spheres could be retrieved from cardiac lymph nodes in the mediastinum. Most likely, the spheres migrated through venous pathways; a substantial number of preocclusion spheres were present in the lungs after 10 h, the bulk of which had originated from other organs than the infarct. These results quantify an important limitation to the use of microsphere distribution as a method for tissue blood flow measurements in infarcted myocardium when the period of coronary artery occlusion exceeds a few hours.

Animals↗
PubMed1980

Left ventricular asynergy during intracoronary isoproterenol infusion in dogs.

Myocardial contractions were examined in the left ventricle of anesthetized, open-chest dogs during infusion of a beta-adrenergic agent, isoproterenol (0.1-0.5 micrograms/min) into a shunt line to the left anterior descending coronary artery. Myocardial chord lengths were continuously monitored by pairs of ultrasonic elements inserted into the isoproterenol-infused and control regions. Heart rate remained constant, but isoproterenol altered contraction patterns in both control and infused regions. Contraction in the infused region started before ejection and stretched the control myocardium in early systole. Because of early relaxation, however, the infusion region was stretched at the end of ejection and in early diastole, while the control myocardium continued to shorten. Thus, isoproterenol infusion to a part of the left ventricle induces asynergic muscle contractions and despite localized inotropic stimulation stroke volume may not be significantly increased.

Animals↗
PubMed1980

Influence of left ventricular dimensions on endocardial and epicardial QRS amplitude and ST-segment elevations during acute myocardial ischemia.

The influence of acute myocardial ischemia and changes in ventricular dimensions on endocardial and epicardial electrograms were evaluated in 17 anesthetized open-chest dogs before and after left ventricular volume expansion and before and after coronary artery ligation. In eight dogs, regional myocardial blood flow was determined by the labeled microsphere technique. Endocardial QRS (endo-QRS) amplitude in ischemic and nonischemic zones, and epicardial QRS (epi-QRS) in nonischemic zones maintained a negative linear relation with left ventricular end-diastolic dimension before and after coronary artery ligation, although acute ischemia decreased endo-QRS independently. Epi-QRS amplitude in the ischemic zone decreased after coronary artery ligation but changed inconsistently during volume expansion. Ischemia-induced epicardial ST-segment elevation decreased during volume expansion and was associated with improved epicardial blood flow. Changes in epi-QRS in ischemic zones, however, were not related to epicardial blood flow during volume expansion. These findings indicate the potential problems of using changes in QRS amplitude for determining the extent of myocardial ischemic injury.

Acute Disease↗
PubMed1980

Transient intestinal ischaemia induced by degradable starch microspheres. Experiments in the cat.

Temporary ischaemia was induced in cat small intestine by degradable starch microspheres. Regional arterial and tissue blood flow immediately fell by 85 per cent with subsequent normalization within 26 min after microsphere injection. Degraded 99Tcm-labelled microspheres were exponentially removed from intestinal vessels and accumulated in the liver. Provided near-total arteriolar obstruction is induced, external isotope detection may permit assessment of the duration of the induced ischaemia, which implies a selection of the appropriate time for radiation therapy.

Animals↗
PubMed1979

Reduction in ventricular endocardial and epicardial potentials during acute increments in left ventricular dimensions.

Unipolar potentials were recorded from the endocardium (Endo-Pot) and the epicardium (Epi-Pot) of the left and right ventricles of anesthetized open-chested dogs during acute changes in left ventricular dimension by blood transfusion. A pair of implanted ultrasonic crystals were used to detail changes in left ventricular (LV) anteroposterior diameter. When the diameter increased by an average of 11 per cent, LV Endo-Pot decreased by 28 per cent and LV Epi-Pot decreased by 15 per cent. Right ventricular Endo-Pot and Epi-Pot concurrently decreased by similar magnitude (-36 per cent). The relationship between potentials and LV diameter showed negative linearity over the ranges examined, and was not influenced by changes in hematocrit. No inverse relation between changes in Endo-Pot and Epi-Pot was observed. It is suggested that potentials when recorded directly from the endocardium or epicardium mainly reflect the electrical activity of the tissues in the immediate vicinity of the electrode. It is postulated that an increase in ventricular volume by producing stretching and thinning of ventricular walls, reduces the effective tissue mass represented in the electrode signal, thereby accounting for a reduction in both endo and epicardial potentials. Although the precise mechanisms of changes in ventricular potentials remains unclear, such changes, nevertheless, may indicate, in clinical circumstances, an acute shift in left ventricular volume.

Action Potentials↗
PubMed1979

Resistance and volume changes caused by nitroprusside in the dog.

Changes in vascular volume caused by a pharmacologic agent are frequently inferred rather than directly measured. We investigated the effects of nitroprusside in 8 dogs divided into 2 groups: control and splenectomized. We anesthetized the dogs using pentobarbital, and surgically prepared a veno-right atrial bypass preparation whose controlled cardiac output and external reservoir allowed measurement of both changes in vascular resistance and changes in vascular volume. In both groups, blood pressure (mean +/- SD) decreased at each successive level of nitroprusside: 114 +/- 24 mmHg (base line), 101 +/- 19 mmHg (45 microgram/min), 90 +/- 16 mmHg (90 microgram/min), 81 +/- 17 mmHg (180 microgram/min), 68 +/- 18 mmHg (360 microgram/min). Nitroprusside caused a large and similar decrease in vascular resistance in both groups. In the control group, vascular volume increased above base line 5.5 +/- 2.7, 8.3 +/- 3.2, 11.6 +/- 2.9, and 14.7 +/- 3.5 ml/kg at each successive level of nitroprusside infusion, whereas in the splenectomized group vascular volume increased above base line 0.9 +/- 0.3, 2.5 +/- 1.0, 3.3 +/- 1.1, and 4.0 +/- 1.3 ml/kg at each successive level of nitroprusside infusion, but increased significantly less than the control group. We concluded that nitroprusside decreases vascular resistance and increases vascular volume and that the spleen is the major site of changes in vascular volume caused by nitroprusside.

Animals↗
PubMed1979

Myocardial ischemia. Relationship between local flow, function and ST-segment elevation.

The significance of reductions in local myocardial flow on mechanical function and intramural electrocardiograms (ECG) was studied in anesthetized open-chest dogs. Local dimensional changes in the anterior wall of the left ventricle were recorded by ultrasonic technique. By platinum electrodes in the same region, both intramural ECG and hydrogen tension were recorded. Local flow was calculated from hydrogen desaturation curves. At approx. 25% flow reduction (constriction of the left anterior descending coronary artery (LAD)) local enddiastolic dilation and reduced systolic shortening appeared. Significant ST-segment elevation first appeared with flow reduction of 50%. After complete LAD-occlusions, enddiastolic dilation appeared within 20 sec, ST-segment elevation 40 sec later. It is concluded that mechanical and electrical events can be dissociated during acute myocardial ischemia: enddiastolic dilation and reduced systolic shortening are more sensitive indicators of moderate reductions in myocardial tissue flow than ST-segment elevation.

Animals↗
PubMed1978

Pronounced dependence of ventricular endocardial QRS potentials on ventricular volume.

To evalulate the relation between ventricular endocardial potentials (QRS amplitude) and ventricular dimensions, left and right ventricular endocardial potentials were recorded with hook electrodes in anaesthetised open-chest dogs during transfusion and withdrawal of blood. Left ventricular end-diastolic diameter was measured by ultrasonic crystals, and end-diastolic volume was determined by thermodilution. In each dog, left ventricular endocardial potentials, whether recorded from anterior or posterolateral walls, decreased linearly as left ventricular end-diastolic diameter or volume increased, and vice versa. With an average increase in left ventricular end-diastolic diameter from 40.1 +/- 1.7 to 44.6 +/- 1.8 mm, left ventricular endocardial potentials decreased from 32.8 +/- 2.5 to 23.5 +/- 2.3 mV (P less than 0.001); and for an increase in left ventricular end-diastolic volume from 1.36 "/- 1.25 to 3.43 +/- 0.58 ml/kg left ventricular endocardial potentials decreased from 36.2 +/- 6.6 to 14.9 +/- 4.3 mV (P less than 0.001). Changes in right ventricular endocardial potentials paralleled the changes in left ventricular endocardial potentials. These findings indicate that acute changes in ventricular dimensions influence endocardial potentials considerably, and suggest a potential clinical application for detecting acute changes in ventricular volume.

Action Potentials↗
PubMed1978

Cardiac performance: independence of adrenergic inotropic and chronotropic effects.

During right atrial pacing in open-chest anesthetized dogs, the relationships between reduction in stroke volume and rise in heart rate were identical in control experiments, during intravenous infusion of isoproterenol, and after blockade of adrenergic beta-receptors by propranolol. To examine the mechanism of this constant relationship, left ventricular volume was estimated by continuous recordings of myocardial chord length (MCL) between ultrasonic elements inserted into the anterior ventricular wall. Diastolic filling curves were curtailed by raising heart rate and end-diastolic MCL was reduced. At constant heart rate, end-diastolic MCL was not altered by isoproterenol infusion, except for a slight rise at heart rates exceeding 220 beats/min. End-systolic MCL, however, was reduced, accounting for larger stroke volume during isoproterenol than during propranolol infusion. The reduction in end-systolic MCL was constant at all heart rates examined. Hence, chronotropic changes influence end-diastolic volume and inotropic changes influence end-systolic volume; their effects on stroke volume regulation are, therefore, virtually independent.

Animals↗
PubMed1978

Coronary sinus reflux. A source of error in the measurement of thermodilution coronary sinus flow.

In seven patients thermodilution coronary sinus flow (TD-CSF) was higher (164 +/- 21 ml/min) during ventricular pacing than during atrial pacing (119 +/- 21 ml/min, P less than 0.005) at identical heart rate, without an increase in the determinants of myocardial oxygen consumption. To assess the possibility of right atrial admixture in coronary sinus blood during ventricular pacing we compared electromagnetic coronary arterial blood flow (CBF) with TD-CSF in nine dogs during interventions that increased right atrial pressure. During ventricular pacing, rapid atrial pacing, pulmonary artery constriction and increased intrathoracic pressure, right atrial pressure increased and electromagnetic CBF was significantly less (41-166%) than TD-CSF. Marked reflux from the right atrium to the coronary sinus was also demonstrated by bolus injection of cold saline into the right atrium and continuous infusion of contrast material into coronary sinus. Caution needs to be exercised in interpreting TD-CSF in the presence of changing right atrial pressure.

Adult↗