News from the American Heart Association

A variety of factors have been considered to be of importance in influencing the oxygen consumption of the heart.Among these have been the amount of work done by the heart, 1 ' 2 the end diastolic volume or fiber length, 3 " 5 the heart rate, 6 " 10 the developed myocardial tension, 11 and the heart rate times the mean arterial pressure. 12More recently, it has been suggested that coronary blood flow may influence myocardial oxygen consumption independently of changes in the activity of the heart. 13" 17 The objective of the investigation described below was to ascertain whether or not this occurs in the isolated, metabolically supported heart preparation and, if so, under which experimental circumstances. MethodsExperiments were performed on mongrel dogs of both sexes ranging in weight from 20.0 to 27.0 kg.The animals were anesthetized with a warmed mixture of ehloralose (60 mg/kg) and urethane (600 nig/kg) given intravenously.The experimental preparation employed was a modification of the isolated supported heart. 18This is shown in figure 1.A large-bore eannula was inserted into the left atrium through the appendage and then connected to a blood reservoir (RES) by way of an electrically operated inflow resistance (IR).Atrial inflow was continuously recorded using a Potter eleetroturbinometer (PET). 19The lower thoracic aorta was ligated and a eannula inserted proxirnally.Outflow from the aorta was led to the blood reservoir (RES) through a second, electrically operated, outflow resistance (OR).A eannula previously placed in the left main pulmonary artery was connected through a recording rotameter (TR) to a reservoir (TCR) supplying blood to the support dog's (SD) jugular veins.Previously placed ligatures around the subclavian and brachiocephalic arteries, superior and inferior venae cavae, the azygos vein, the hilum of the