Acute experiments were carried out on cats anesthetized with chloralose (50 mg/kg) and pentobarbital (20 mg/kg), with an open chest and artificially ventilated. SF of the left ventricular ejection was judged on the basis of measurements of volume velocity of blood flow in the ascending aorta (distally to the origin of the coronary arteries) by means of a vascular transducer (diameter 7 mm) of an RK~-2 electromagnetic flowmeter. CF was determined by measuring the outflow from the coronary sinus, multiplied by 3/2, by the method described previously [2, 3]. The intraaortie systolic pressure (AP I) was gradually raised by increasing the resistance in it with an occluder, located distally to the transducer of the electromagnetic flowmeter (Fig. i). The occluder consisted of a loop, wrapped around the ascending part of the aorta, and a micrometer system. The thread consisted of Kapron tape 0.8 mm in diameter. Successive adjustment of the micrometer system by 1 mm led to an increase of AP l by 1.5-60 mm Hg. The results were grouped on the basis of levels of all parameters corresponding to a rise of AP 1 by 30 mm Hg. The results of elevation of the intraaortic pressure were analyzed before andduring ~-adrenoreceptor blockade within the same pressure ranges. AP I was recorded proximally to the site of the occluder, through a catheter (diameter 0.6-1 mm), passed through the right carotid artery to the base of the aorta. The systemic blood pressure in the femoral artery (AP 2) was recorded simultaneously. Contractility of the heart was estimated by recording the first derivative of intraventricular pressure (dp/dt max), by means of an MN-7M analog computer, on the systolic pressure curve in the left ventricle, and the end-diastolic pressure (EDP) in the left ventricle also was recorded. The degree of filling of the ventricle also was judged from the measurements of the last parameter. Pressure in the left ventricle was measured by means of a catheter passed through the auricle of the left atrium. All pressures were recorded by means of a pressure transducer of the PDP-400p type. All parameters were recorded simultaneously on N-3021 and N-338 automatic writers. The results were subjected to statistical analysis by Student's t test. The $-adrenoreceptors of the heart and vessels were blocked by propranolo~ injected in a dose of 1 mg/kg into the animal's femoral vein.
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