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Left ventricular dynamics was studied in the unanesthetized dog by an analysis of simultaneous recordings of left ventricular transverse dimension, pressure, and ascending aortic flow in 16 experiments while the dogs were reclining, standing, and during graded treadmill exercise. Statistical analysis of the dimension data revealed typical patterns of isovolumetric changes which suggest asynchronous contraction and relaxation. The fact that maximum and minimum dimension levels did not coincide with levels at onset and end of ejection led to the concept of the "effective" stroke shortening in the left ventricular transverse dimension. An ellipsoid of revolution was the best approximation of left ventricular shape while reclining and standing, but during exercise the shape constant decreased toward a paraboloid of revolution. Analysis of the data from correlation coefficients and by using the principle of the compression ratio, which is independent of shape, indicated that stroke shortening and stroke volume may be a function of initial length or volume for the resting states but that during exercise their increase was due primarily to extrinsic influences which acted to change the magnitude of the contractile response.
Ninomiya et al. (Mon,) studied this question.