Total Versus Extra Oxygen Consumption in Muscle Activity in Relation to Fiber Length

It appeared to the author that it would be of considerable importance if the fundamental behavior of cardiac and skeletal muscle could be more closely correlated by the explanation of an apparent difference in their behavior following changes in initial fiber length.

Evans and Hill 1 showed that the heat produced during a short tetanus of the frog's sartorius increases as the muscle is extended rising to a maximum at about the in situ resting length, and then decreases upon further extension.

Starling and Visscher, 2 utilizing the isolated heart-lung preparation, showed that the oxygen consumption of the mammalian ventricle rises with increasing diastolic volume, but found no indication of a maximum with subsequent decline, although they explored a very wide range of alterations in ventricular volume. It is obvious that these experiments involved the measurement of the total oxygen requirement of the heart, while in the myothermic experiments quoted above only that excess metabolism due directly to activity was determined.

Feng 3 reported that the resting heat production and oxygen consumption of the frog's sartorius both rise with increase in the length of the muscle. These observations might have been anticipated in the light of the experiments of Clark and White, 4 who showed that the oxygen consumption of the quiescent, filled auricle of the cold blooded heart approached that of the beating, empty auricle.