Effects of bilateral common carotid arteries occlusion on cardiac inotropism in anesthetized dogs. Role of the autonomic nervous system on the reflex response

A C Cicogna, J Spadaro, P J Tucci
1976 Arquivos Brasileiros de Cardiologia  
Inotropic variations induced by bilateral carotid occlusion (BCO) under different conditions of the autonomic nervous system were studied in dogs anesthetized with morphine and sodium pentobarbital and submitted to cardiac pacing. Maximal velocity of contraction (V max TP) was utilized for evaluation of the myocardial contractile state. The animals were divided into four groups: eight control dogs, ten dogs submitted to vagal blockade with atropine, ten animals submitted to beta-adrenergic
more » ... eta-adrenergic blockade with propranolol and ten dogs with double autonomic blockade. They presented significant elevations of the systolic and the diastolic aortic pressures and left ventricular and diastolic pressure during BCO. Following carotid occlusion, the V max TP rose in control (2.95 ± 0.16 to 3.27 ± 0.23 L/s; P < 0.01) and in vagal blocked (3.12 ± 0.15 to 3.61 ± 0.26 L/s; p < 0.01) animals. In beta blocked animals, the values of the index decreased during BCO (2.38 ± 0.10 to 2.09 ± 0.11 L/s; p < 0.001) and in the dogs submitted to double autonomic block there was no modification of the V max TP (2.59 ± 0.07 to 2.61 ± 0.08 L/s). It is concluded that the variations of V max TP in control and vagal blocked animals reflect the inotropic improvement due to sympathelic hyperactivity. It was supposed that the impairment of the contractile state found in animals treated with propranolol was caused by myocardial hypoxia secondary to alpha-adrenergic coronary vasoconstriction while the administration of atropine permitted adequate accommodation of the coronary circulation in dogs submitted to double autonomic blockade. Hence, in the last group of animals, there was no variation of the V max TP. max Carotid sinus baroreceptors exert considerable influence on the control of the cardiocirculatory system. It has been found that carotid sinus hypotension that occurs during carotid occlusion, through reflex alterations of autonomic activity, promotes changes of the heart rate 1-3 , cardiac output 4,5 , peripheral vascular resistance 4,5, arterial pressure 2,5,6 and cardiac inotropism 2,3,5,6 . During bilateral carotid occlusion (BCO), there are important modifications of the left ventricular end diastolic pressure (preload) and the aortic diastolic pressure (afterload). Nevertheless, the indices of myocardial contractility utilized in investigations relating BCO and inotropic state, are influenced by alterations of these variables. Previous studies indicate that maximal velocity of contraction (V max TP) is insensitive to changes in afterload 7-10 and is not affected by variations of the preload, when there are no important changes in myocardial fiber length 9-12 . Accordingly, the present investigation was conducted in order to evaluate the behavior of the inotropic state during BCO in anesthetized dogs submitted to cardiac pacing. The study was undertaken in dogs with no previus treatment and animals submitted to autonomic blockade using atropine and/or propranolol. METHODS Experiments were performed in 28 healthy, male, mongrel dogs, weighing from 10 to 15 kg, anesthetized with intramuscular morphine (2 mg/kg) followed by intravenous sodium pentobarbital (20 mg/kg). The animals were heparinized with 500 i.u/kg. Through a midline incision in the neck, both common carotid arteries were dissected and freed in the mid cervical region. The heart was paced by an atrial electrode inserted through the right
pmid:1008716 fatcat:ywdmjefbqfcenazvovf2vkns4i