Application of the systolic stiffness concept to assess myocardial function in developing hypertension.

The concept of end-systolic myocardial stiffness permits the quantification of preload effects on fiber shortening and changes in the slope (max Eav) of the end-systolic stress-strain relation, which, if linear, reflect changes in the inotropic state. As an application of this new concept, the end-systolic stress-strain and shortening-afterload relations were evaluated on the basis of data from dogs studied during development of perinephritic hypertension. End-systolic stress-strain relations were linear before and 2 weeks after the induction of hypertension and the end-systolic pressure-diameter relations were not always linear. The shortening-afterload relations obtained directly from raw data points displayed enhanced contractility in the hypertensive state under beta-adrenergic receptor blockade. However, the preload-corrected shortening-afterload relations demonstrated that contractility was unchanged in hypertension. Hypertensive hearts operated at higher preload than normotensive hearts at any afterload levels. This discrepancy between the conventional method without preload-correction and the preload-corrected analysis indicates the importance of preload-correction on shortening-afterload relations in hypertension.