Quantifying the need for cardiac support in human shock by a functional model of cardiopulmonary vascular dynamics: with special reference to myocardial infarction

Abstract

A quantitative method of analyzing cardiac and pulmonary vascular dynamics has been developed on the basis of a functional model of central indicator dilution. Using this model it has been possible to demonstrate a segregation of patients with various clinical states by virtue of the quality of their dynamic cardiac mixing. Patients with hyperdynamic states secondary to sepsis or cirrhotic liver disease show rapid cardiac mixing times ( t m ), unless there is evidence of myocardial failure when a prolongation of mixing time occurs, even at high cardiac outputs. Patients with myocardial infarction (MI) shock have very prolonged cardiac mixing times. A critical level of t m has been established for MI shock patients, at which some form of mechanical cardiac support seems mandatory if patient salvage is to be possible. A group of MI shock patients has been identified who also show evidence for a significant cardiac nonmixing volume which appears associated with the magnitude of the akinetic area of infarcted myocardium. The appearance of such a cardiac nonmixing volume appears to be an important prognostic sign which suggests the need for cardiac support and may also have implications regarding the necessity for definitive surgery. The dvnamic aspects of pulmonary volume shifts with changing myocardial contractile states can also be inferred from the quantitative model. A technique of estimating the important model parameters at the bedside is described which can be applied as a guide to assist the surgeon in patient management.