THE CONCEPT OF AFTERLOAD MISMATCH AND ITS IMPLICATIONS IN THE CLINICAL ASSESSMENT OF CARDIAC CONTRACTILITY
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概要
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The characteristics of left ventricular ejection (velocity and extent of wall shortening) can be analyzed in relation to the appropriateness of the matching between afterload and the level of inotropic state ( contractility), as modified by the preload (Frank-Starling) reserve. In the normal left ventricle if the preload is not allowed to compensate for and acute increase in afterload, or if the limit of preload reserve is reached, velocity (V_<CF>) and stroke volume will diminish; that is, an afterload mismatch occurs. This acute mismatch can be corrected by administration of a positive inotropic agent. In normal conscious animals and in man the ejection phase measures in the basal state (such as ejection fraction, and V_<CF> corrected for heart size) encompass a relatively narrow range, and when the normal heart adapts successfully to a chronic pressure or volume overload such measures remain normal per unit of muscle. These findings provide the basis for their use in detecting a depressed basal level of inotropic state, even in the presence of certain valvular lesions. When there is mild depression of the basal inotropic state, enhanced preload and dilatation can allow full compensation of V_<CF>, but acute pressure loading can allow detection of the reduced preload reserve by inducing a substantial fall in stroke volume and V_<CF>. When the basal inotropic state is greatly reduced, a mismatch between afterload and contractility, expressed as reduced V_<CF> or ejection function, will become evident in the basal state even if the afterload is normal. Any increase in aortic pressure will then cause a sharp reduction in stroke volume or V_<CF>. Also, under these circumstances therapeutic afterload reduction with agents such as nitroprusside can increase velocity and extent of wall shortening, and the cardiac output, providing the preload is maintained. The concept of afterload mismatch with limited preload reserve provides a framework for understanding the behavior of the normal or depressed ventricle and how it can operate on a "descending limb" of function. It helps to explain why measures of the ejecting phase (which are sensitive to afterload) appear to be more reliable than isovolumic phase indices (which are relatively insensitive to afterload) for detecting depressed basal inotropic state. Finally, the concept allows for interpretation of the responses observed in the clinical setting to acute and chronic increases and decreases in loading conditions on the left ventricle.
- 社団法人日本循環器学会の論文
- 1976-09-20
著者
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Ross John.jr.
The Cardiovascular Division Department Of Medicine Schcol Of Medicine University Of California
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Ross John
The Cardiovascular Division, Department of Medicine, Schcol of Medicine, University of California