The Mechanics of Ventricular Contraction

Linear and planimetric measurements have been made on tracings of the right and left ventricular chambers from successive motion picture frames, obtained by cinefluorographic angiocardiography in anesthetized dogs. At the end of systole, varying amounts of residual blood, some 35 per cent of the diastolic volume, remain in the chamber. Filling occurs more rapidly than ventricular ejection and is virtually completed in early diastole. The left ventricular chamber is reduced in size during systole primarily by a reduction in width rather than a shortening of the longitudinal axis. Increased stroke output was accomplished by three mechanisms: (1) increased emptying of the ventricle by progressive shortening of the ventricular chamber; (2) increased filling in early diastole; (3) increased filling in the presystolic period, persumably because the atrial contraction more effectively distended the ventricle. The mechanisms responsible for the systolic residual blood and the retardation of filling which occurs early in diastole are discussed in terms of the anatomy, geometry and functional characteristics of the ventricular myocardium. A comparison is made of the right and left ventricles with reference to their luminal pressure and fiber tension relationships.