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Biomedical subjects

L Dumont

Publications and source records attributed to L Dumont.

At least 91 records · Page 5Linked to original sources
PubMed1988

Cardiac rejection following transplantation in dogs: transmural myocardial blood flow changes.

In cardiac allografts acute rejection produces deleterious effects on blood flow adjustments. In order to differentiate the role of rejection over that of denervation cardiac denervated and cardiac transplanted dogs were compared. A canine model of orthotopic cardiac transplantation was utilized. Electronic devices were implanted for chronic hemodynamic studies. Regional myocardial blood flow distribution was assessed by radioactive microspheres (15 micron in diameter). Studies were carried out when animals had fully recovered (two to three days postoperatively), then in the 'early rejection' stage (five to six days post transplant) and in the 'severe rejection' stage (24 h before death). No significant difference in hemodynamic data or blood flow values were observed between groups in the recovery stage. In the denervated group, adequate cardiac function and myocardial blood perfusion was maintained throughout the study. In the transplanted group, significant loss of function was observed at the severe rejection stage. This was combined with significant decrement in blood flow to all areas of the myocardium. No selective area of underperfusion nor an early reduction in total blood flow could be observed. This study indicates that within cardiac rejection there is a parallel impairment in function and transmural myocardial blood flow which is unrelated to denervation or interruption of lymphatics.

Animals↗
PubMed1986

Acute hypercalcemia and cardiac autotransplantation in dogs: long-term hemodynamic adaptability.

Cardiac autotransplantation (excision and reimplantation) is a unique model that isolates totally the cardiac afferent and efferent neural pathways and results in hemodynamic misadaptability to many provocative tests. Since the cardiovascular response to acute hypercalcemia is modulated by numerous factors among which the autonomic innervation plays a major role, the hemodynamic response to bolus administration of calcium gluconate was compared in normal and cardiac autotransplanted dogs. Twenty-two animals underwent an autotransplantation while a sham procedure was performed in 18 animals. Each dog was equipped with an electromagnetic flow probe positioned around the ascending aorta and with central venous and aortic catheters. Hemodynamic data were collected daily during 1 month, before and during rapid intravenous administration of calcium gluconate (0.90 mEq). Baseline hemodynamic studies indicate that for both groups myocardial failure is evident in the immediate postoperative period; despite progressive recovery, the autotransplants always show lower cardiovascular performance. Calcium administration elicits transient positive inotropism, which is more important in presence of myocardial failure; this is true for both control and autotransplanted dogs. In the early postoperative period, hemodynamic adaptability to this stress is impaired in the autotransplants. However, long-term results indicate that minimal differences subsist over time in response to calcium administration, and when they are observed, they result from interferences in baroreceptor regulation and reflexes.

Animals↗
PubMed1985

Profile of the oppositely acting enantiomers of the dihydropyridine 202-791 in cardiac preparations: receptor binding, electrophysiological, and pharmacological studies.

Receptor binding, electrophysiological, and inotropic effects of the pure dihydropyridine enantiomers (+)S202-791 and (-)R202-791 were studied in cardiac preparations. The KI for (+)S202-791 binding correlated with the ED50's for an increase in contractile force and an increase in calcium current, the latter effect occurring at depolarized as well as resting holding potentials. The KI for (-)R202-791 binding was much lower than the IC50's for inhibition of calcium current measured at holding potentials of -80 or -90 mV and a negative inotropic effect, but correlated closely with the IC50 for inhibition of calcium current measured at -30 mV. Thus, (+)S202-791, is a voltage independent calcium channel activator and (-)R202-791 is a voltage dependent calcium channel inhibitor.

Animals↗
PubMed1985

Peroperative myocardial ischemia and citrate administration: cardiovascular adaptability in conscious dogs.

Since the hemodynamic response elicited by the administration of citrate is sensitive to alterations in the baseline cardiovascular status, we have investigated the consequences of peroperative myocardial ischemia upon this hemodynamic response. 19 dogs equipped with an electromagnetic flow probe positioned around the ascending aorta served as control (group I). 16 dogs were equipped similarly and in addition submitted to 1 h of myocardial ischemia combined with topical cardiac hypothermia (group II). Hemodynamic studies were carried out 3 h postoperatively and then daily for 1 month, before and during rapid intravenous administration of citrate. From baseline hemodynamic data, cardiac failure was only evident 3 h postoperatively in group II. Transient hypotension and myocardial depression resulted from administration of citrate in both groups with no evidence of peripheral vasodilation. Hypotension and the negative inotropic response were more pronounced in the presence of cardiac failure following peroperative myocardial ischemia. Long-term studies indicate that global myocardial ischemia did not interfere with the cardiovascular adaptability to this pharmacologic interference.

Adaptation, Physiological↗
PubMed1985

Hemodynamic effects of hypertonic sodium bicarbonate on denervated canine hearts.

The hemodynamic consequences of an intravenous bolus of hypertonic sodium bicarbonate were studied in normal dogs and in dogs that had undergone heart autotransplantation. Twenty-one autotransplanted dogs and seventeen sham-operated dogs were instrumented with an electromagnetic flow probe positioned around the ascending aorta. Hemodynamic data were collected three hours after the operation and then at daily intervals for one month, before and during sodium bicarbonate administration. The data indicates that hemodynamic base-line parameters remain lower in autotransplanted dogs than in the control animals during the whole length of the study. At the peak of the hypotensive response that follows the sodium bicarbonate injection the left ventricular performance is decreased to the same extent in both the autotransplanted and the control dogs. This negative inotropic response is enhanced in the presence of myocardial failure. In the autotransplanted group, reflex tachycardia was absent, resulting in a greater reduction in the cardiac index. These two effects explain the greater reduction of arterial pressure in the autotransplanted dogs.

Animals↗
PubMed1985

[Cardiovascular adaptability to acute hypercalcemia in the dog. The role of peroperative myocardial ischemia].

Since the hemodynamic consequences of acute hypercalcemia are altered by numerous interferences we have evaluated the role of peroperative myocardial ischemia on the adaptability to rapid calcium increment. Twenty-two dogs served as control and 16 were submitted to 1 hour of myocardial ischemia along with topical myocardial cooling. Each animal was equipped with blood flow transducer positioned around the ascending aorta and with central venous and aortic catheters. During each study 0.90 mEq of calcium was rapidly injected and hemodynamic data were recorded until base-line resetting. This experimental protocol was carried out 3 hours postoperatively and then daily during one month. Base-line hemodynamic data indicated the presence of myocardial failure in the experimental group in the immediate postoperative period only. Rapid calcium administration elicited transient positive inotropic response, widening of the arterial pulse pressure, reflex bradycardia and no evidence of peripheral vasoconstriction. In the early postoperative period (3 hours after surgery) the failing myocardium is more sensitive to the inotropic effect of hypercalcemia. Twenty-four hours after surgery both groups of animals have the same hemodynamic response to this stress; thereafter for both groups this response gradually decreased and finally stabilized by the 6th to 10th day after surgery. Acute hypercalcemia bears hemodynamic consequences that are amplified early after peroperative myocardial ischemia. However in long term this surgical component widely used clinically does not interfered with the cardiovascular adaptability to this pharmacological stress.

Acid-Base Equilibrium↗
PubMed1984

Effects of propranolol and exercise on cardiac dynamics and organ blood flow distribution in dogs.

The additive effects of propranolol and exercise on peripheral blood flow distribution were studied in conscious dogs. During treadmill exercise (8-10 km/h and 0% grade for 15 min.) cardiac performance increased significantly in parallel with myocardial and muscular blood flow (greater than 100%). Blood perfusion to liver and spleen decreased significantly (30% and 34%) while blood flow to other organs was unaltered. Under resting conditions propranolol only modified blood flow to liver and spleen (-50% and -38%). During exercise after propranolol a limited augmentation in cardiac performance and in myocardial and muscular blood flow was observed; splanchnic blood flow which was most affected by propranolol at rest did not further decrease during exercise after propranolol. The present observations demonstrate that propranolol, despite minor haemodynamic modifications, induces significant alterations in blood flow to splanchnic organs. The influence of beta-adrenoreceptor blockade was even more evident under conditions of augmented sympathetic activity as reflected by a significant limitation of increase in cardiac performance, myocardial and muscular blood flow and by a sustained redistribution of splanchnic blood flow during exercise after propranolol.

Animals↗
PubMed1984

The cardiovascular effects of hypertonic sodium bicarbonate in conscious dogs: underlying mechanisms of action.

Mechanisms underlying the transient hypotensive effect (central or peripheral) of rapid bolus administration of hypertonic sodium bicarbonate (NaHCO3) were studied in conscious dogs. Thirteen animals equipped with an electromagnetic flow probe positioned around the ascending aorta were utilized. NaHCO3 (18.5 mequiv. of 1786 mosmol/L), hypertonic saline solution having the same sodium concentration as NaHCO3, and mannitol solution with the same osmolarity as NaHCO3, were injected in the right and in the left atrium. Intra-arterial NaHCO3 was tested to assess its direct peripheral vascular effects. Blood ionic as well as acid-base modifications following NaHCO3 were also studied. Our results indicate that right atrial injection of NaHCO3 elicited transient hypotension (-10 to -15 mmHg (1 mmHg = 133.322 Pa)) and myocardial depression as revealed by a significant decrease of stroke volume (-8%), stroke power (-18%), stroke work (-12%), maximum systolic flow (-13%), peak velocity (-13%), and maximum acceleration (-24%). When the solution is injected in the left atrium, myocardial depression is more pronounced suggesting that the coronary bed is the site of action. Hypertonic saline injections indicate that the sodium load plays a role in this decrement of myocardial function while hyperosmolarity per se, as exemplified with mannitol injections, elicits no negative effect. Transient ionic as well as acid-base disturbances are other mechanisms that have to be considered along with coronary vasoconstriction. Decrement in peripheral resistance appears only with right intra-atrial NaHCO3 suggesting that the pulmonary vascular bed is the origin of this reflex.

Acid-Base Equilibrium↗
PubMed1984

Hypotension and arteriovenous shunting: effects of intravenous infusion of nitroprusside, nitroglycerin and phentolamine.

The effects of nitroprusside, nitroglycerin and phentolamine on cardiac dynamics and on the fraction of cardiac output shunted through systemic arteriovenous communications, which may explain disparate responses elicited by these systemic vasodilators upon venous return, have been studied in 15 nonanesthetized dogs. Cardiac dynamic parameters were measured by electromagnetic flow probe placed at the root of the aorta. Quantitative measurements of total systemic arteriovenous shunting were determined from the fraction of 9 mu radioactively labeled microspheres, injected into the left atrium, recovered in the pulmonary artery. To provide a common basis for comparison, the mean arterial pressure was lowered by 15-20% either with an intravenous infusion of nitroprusside, nitroglycerin or phentolamine. At the fifteenth minute of infusion, nitroprusside produced significant decrease in stroke volume index (23%) and left ventricular power and work (28% and 40%). Nitroglycerin decreased significantly stroke volume index (12%), cardiac index (9%) and left ventricular work (22%). Phentolamine significantly increased heart rate (72%) and left ventricular maximum acceleration (30%) while it decreased stroke volume index (41%), left ventricular power and work (19% and 55%). Total peripheral resistance was significantly affected only by infusion of phentolamine (-18%). Left ventricular maximum velocity, mean systolic ejection rate and maximum systolic flow did not change significantly under infusion of these systemic vasodilators. Under control conditions, total systemic shunting of cardiac output averaged 8.9-10% and was not modified by any of the vasodilators used. Arteriovenous O2 difference and oxygen consumption, corroborated these findings since they remained within normal limits before and after infusion of nitroprusside, nitroglycerin or phentolamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Effect of nitroglycerin on regional myocardial blood flow following an experimental coronary spasm.

This study was designed to evaluate the effect of nitroglycerin (30 micrograms given as an i.v. bolus) on regional distribution of myocardial blood flow in conscious dogs, following an acute coronary occlusion similar to a coronary spasm. The left anterior descending (LAD) coronary artery was acutely occluded with a balloon cuff occluder. The distribution of blood flow between the endocardium and the epicardium of both the normal and ischemic area of the left ventricle was determined by means of the radioactive microsphere technique. Acute occlusion of the left anterior descending coronary artery produced a significant decrease of blood flow reaching the area irrigated by this artery; this decrease was of a lesser magnitude after administration of nitroglycerin. In addition, ischemia produced a disproportionate decrease in endocardial blood flow. This decrement was also of a lesser magnitude following administration of nitroglycerin. Blood perfusion to the non-ischemic myocardium was not altered. These results indicate that an intravenous bolus of nitroglycerin, given after a brief coronary occlusion simulating a coronary spasm, increases blood flow to the ischemic myocardium, induces a favorable redistribution of blood flow toward the ischemic endocardium and does not produce any decrement of blood perfusion to the non-ischemic myocardium.

Animals↗
PubMed1984

Effects of peroperative myocardial ischemia on early and late hemodynamic response to hypertonic sodium bicarbonate in dogs.

Because hypotension induced by the administration of hypertonic sodium bicarbonate is more severe when cardiac performance is impaired, the authors evaluated the hemodynamic consequences of peroperative myocardial ischemia upon the response of conscious dogs to an intravenous bolus of sodium bicarbonate. Twenty-two control dogs (group 1) were equipped with an electromagnetic flow probe positioned around the ascending aorta. Seventeen dogs (group 2), equipped in the same manner, were subjected to 1 hour of myocardial ischemia combined with topical cardiac hypothermia. Hemodynamic studies were performed daily for 1 month before and during the administration of sodium bicarbonate. Baseline hemodynamic values in group 1 were always within normal limits. In group 2, cardiac failure was evident in the immediate postoperative period but hemodynamic values reached normal limits 24 hours postoperatively. For both groups, the peak hypotensive response to sodium bicarbonate was combined with a substantial reduction in all hemodynamic values reflecting the left ventricular performance. However, this response is significantly (p less than 0.01) more pronounced in group 2 during the first 4 postoperative days, being maximal 3 and 24 hours after operation. Afterwards, the hemodynamic response to sodium bicarbonate was similar in both groups. These results indicated that an intravenous bolus of sodium bicarbonate decreases left ventricular performance and that this decrement is greater when cardiac performance is impaired following peroperative myocardial ischemia. Long-term hemodynamic studies show that this temporary myocardial ischemia is not deleterious to cardiovascular adaptability to hypertonic sodium bicarbonate administration.

Animals↗