STUDIES ON STARLING'S LAW OF THE HEART. III. OBSERVATIONS IN PATIENTS WITH MITRAL STENOSIS AND ATRIAL FIBRILLATION ON THE RELATIONSHIPS BETWEEN LEFT VENTRICULAR END-DIASTOLIC SEGMENT LENGTH, FILLING PRESSURE, AND THE CHARACTERISTICS OF VENTRICULAR CONTRACTION *

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Abstract
The present investigation was designed to determine whether left ventricular end-diastolic segment length and end-diastolic pressure are important determinants of ventricular contraction. Systemic arterial pressure and effective end-diastolic pressure were measured at operation in 26 adult patients with rheumatic mitral valve disease and atrial fibrillation. Continuous alterations of the length of a segment of left ventricular muscle were recorded simultaneously in 13 of these patients by means of a mercury-filled resistance gauge sutured to the surface of the left ventricle. The variability of the duration of diastole resulted in beat-to-beat alterations of ventricular filling which resulted in variations of end-diastolic segment length and pressure. For each individual beat the peak systolic ventricular pressure was utilized as an index of maximum tension developed; the area beneath the left ventricular pressure curve (tension-time index) was employed as a measure of the total tension developed. The systolic period indicated the duration of the tension state, and the systemic arterial pulse pressure was utilized to indicate relative changes in stroke volume. In every patient alterations in end-diastolic segment length correlated closely with all 4 parameters utilized to characterize ventricular function. In order to determine whether these relationships also exist in intact unanesthetized subjects, left ventricular end-diastolic pressure was determined by means of transseptal feft heart catheterization in 4 pationts. The correlations of end-diastolic pressure with systolic pressure, tension-time index, duration of systole, and arterial pulse pressure were similar to those obtained in the patients studied at operation. These results are consistent with the view that Starling''s law of the heart operates in patients with mitral stenosis and atrial fibrillation on a beat-to-beat basis, and that end-diastolic segment length and end-diastolic pressure are important determinants of the characteristics of the subsequent ventricular contraction.