Role of Oxygen and Exogenous Glucose and Lactic Acid in the Performance of the Heart

¹ From the Cardiovascular Department, Medical Research Institute, Michael Reese Hospital, Chicago, Illinois

The relationship (over the normal range) between work, the consumption of oxygen, glucose and lactic acid and the RQ have been studied on the heart in situ in controlled experiments. The following conclusions were reached: a) The correlation found between work and oxygen consumption was imperfect because the behavior of a heart when its work is increased is different as regards oxygen consumption when it is performing pressure-work than when it is performing an equal amount of volume-work. b) The heart rate is an important factor in determining the oxygen consumed by the heart in situ at a given work load. c) The RQ was found to be unrelated to the work level of the heart. It remained relatively constant over the normal range indicating that the nature of the metabolism is probably not altered. d) A low value of ‘efficiency’ was found in this preparation. It does not necessarily indicate an incompetent or insufficient heart. The biological significance of the term, ‘efficiency’ which actually represents merely the ratio of work done to the amount of oxygen consumed, is considered. e) The availability of glucose and lactic acid is not dependent upon the work of the heart; their availability is dependent upon the coronary flow and therefore varies with oxygen consumption. f) The consumption of exogenous glucose by the heart is related to the availability of glucose but not to its arterial blood level. The exogenous glucose consumption of the heart is not related to the cardiac oxygen consumption. g) The consumption of exogenous lactic acid by the heart shows a positive relation to its availability, to its arterial blood level and to the myocardial consumption of oxygen. It appears to be one of the substrates readily used for the work performance of the heart. h) The relative consumption of exogenous glucose and lactic acid by the heart varies with their relative availabilities. i) The significance of these findings is discussed.