Influence of cardiac sympathetic and vagal nerve stimulation on the relation between left ventricular diastolic pressure and myocardial segment length.

THAT THE catechol amines or cardiac sympathetic nerve stimulation will increase the vigor of ventricular contraction has been established." Further, it is now known that the ventricle will contract more forcefully from any given filling pressure under these influences." The early studies of Anrep and other more recent studies" indicate that a changed myocardial extensibility cannot, of itself, account for the increased ventricular contraction. However, whether or not the augmented stroke work is produced solely by a more forceful contraction from a given diastolic ventricular fiber length, or whether changes in the relation between ventricular diastolic pressure and fiber length contribute to the observed augmentation, has not been established. The development of a technic which makes it possible to examine the relation between left ventricular diastolic pressure and the length of a selected segment of ventricular myocardium facilitated a study of this problem. Also the effect of vagal efferent stimulation on the relation between left ventricular diastolic pressure and segment length was investigated. A preliminary report of this work has appeared. Methods The changes in length of a segment of left ventricular myocardium were measured simultaneously with ventricular pressure during diastole. The measurements were made over a wide l'ange of pressures so that curves relating left ventricular diastolie pressure and myocardial segment length could be plotted (pressure-length curves). This relation was examined before and during sympathetic or parasympathetic stimulation, both at a