Ventricular oxygen consumption as influenced by myocardial fiber length and tension in the rat.
Lentini, Eugene Alfred
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Experimental investigations were undertaken to determine the effects of fiber length, resting tension, isotonic contraction and isometric developed tension on the myocardial oxygen consumption. The tissue under study was a trabecula carneae from the left ventricle of rat heart. The metabolic studies were carried out in two different Warburg manometric systems. In a stationary manometric system, which permitted the simultaneous measurement of oxygen consumption, resting and developed tension, and also fiber length, the influence of both resting tension and fiber length was determined in respect to the oxygen consumption of non-stimulated preparations. Another experiment was performed in the same system on muscles stimulated to contract isometrically at a frequency of one per second. Developed tensions at various resting tensions were recorded and related to the respiratory activity of the muscles. In a standard oscillating Warburg system, muscles were placed under the same resting tensions as in the stationary manometric system. The resting tensions were imposed on the muscles by suspending weights from one end. The oxygen consumption of muscle columns was determined during non-stimulated and stimulated interval. During the period of stimulation, the muscles were stimulated to contract isotonically sixty times per minute. The lengths of the muscles with and without the attached weights were measured. It was found that stretching muscles to various lengths under the specified tensions did not uniformly influance the oxygen consumption. It was also found that the oxygen consumption of non-stimulated muscles was statistically identical to that of muscles stimulated to contract isotonically. However, non-stimulated muscles with known weights attached to one end and swaying in unison with the oscillations of the Warburg shaker, showed a relationship between magnitude of attached weight and respiratory activity. In this group of muscles, it was found that the respiration at a 1.0 gram resting tension was significantly higher than at a 0.5 gram resting tension. A statistical decrease in QO2 was noted from a resting tension of 1.0 gram to 2.0 grams. An explanation for this variation in respiratory aetivity is presented. Suggestive evidence was obtained to indicate that an inverse hyperbolic relationship existed between muscle QO2 and peak developed tension. It was concluded that: (1) Myocardial oxygen consumption is not a function of fiber tension, per se. (2) Myocardial oxygen consumption is not a function of fiber length, per se. (3) The oxygen consumptions of non-stimulated and stimulated heart muscles contracting isotonically at one per second do not differ statistically. (4) The myocardial oxygen consumption of isometrically contracting muscle is not a function of the resting tension or fiber length. Suggestive evidence was obtained to indicate that the myocardial oxygen consumption may be influenced by continual variations in fiber length and tension, and that the peak developed isometric muscle tension bears an inverse hyperbolic relationship to the muscle oxygen consumption.
Thesis (Ph.D.)--Boston University
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