Estimation of Cardiac Performance and Efficiency During Aortic Occlusion and Induced Muscular Activity

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Abstract
1) Changes of oxygen uptake and energy output by the left ventricle were investigated during increased peripheral resistance (aortic occlusion) and increased cardiac output (induced muscular activity) in open-chest dogs under pentobarbital anaesthesia. 2) Evidence has been provided to show that energy expenditure during the isovolumic period (E1) participates significantly in the total oxygen consumption of the left ventricle (QO2). The correlation of E1 + E2 (compound energy expenditure during the whole cardiac cycle) to QO2 was closer than the correlation of the stroke work (E2) to QO2 under the experimental conditions studied. The increase of QO2 during increased peripheral resistance is due to a proportional increase of E1. 3) The determination of the total amount of compound energy released by the left ventricle, makes the estimation of the performance of the heart possible in a more specific way. Besides the classical mechanical efficiency, ηm = E2/QO2, an index of the chemomechanical turnover (compound index), ic = (E1 + E2)/QO2), and the so-called pumping index of the left ventricle, ip = E2/(E1 + E2), have been calculated. During increased peripheral resistance ic did not change while ip decreased, indicating that it is not the index of the chemomechanical turnover but the matching between the heart and the periphery which is impaired. On the other hand, during induced muscular activity, only ip increased, thus indicating an improvement of this matching.