Digital angiographic impulse response analysis of regional myocardial perfusion. Estimation of coronary flow, flow reserve, and distribution volume by compartmental transit time measurement in a canine model.

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Abstract
A system impulse response function that describes the kinetics of radiographic contrast material transit through the coronary circulation was calculated from 175 selective digital angiograms of normal and stenotic arteries in 10 dogs during rest and hyperemia. The goal of the study was to determine if the flow and distribution volume characteristics of the epicardial coronary arteries and the myocardial microcirculation could be stimulated by specific mathematical compartments of a lagged normal density model impulse response function in which the flow/distribution volume ratio is the inverse of the mean transit time. The arterial compartment mean transit time correlated with flow (r = 0.75); however, the correlation was significantly improved in individual dogs (r = 0.83 +/- 0.13; p less than 0.005) and was highly dependent on the length of the conduit vessel. The microcirculation compartment mean transit time was distributed as two populations with respect to flow. There was a linear correlation during hyperemia (r = 0.87) and a nonlinear relation during rest, which was characteristic of an autoregulating system. Resting values of microcirculation compartment mean transit time correlated with coronary flow reserve (r = 0.84) and differed significantly between vessels that were normal and those with subcritical stenosis, critical stenosis, or total occlusion (p less than 0.01 for all comparisons). The estimated microcirculation compartment distribution volume increased from a minimum of 4.0 +/- 1.5 ml/100 g myocardium in normal vessels with resting flow to 11.2 +/- 3.5 ml/100 g during hyperemia. These data suggest that the model compartments functionally describe the physiological behavior of their anatomic analogues and permit the quantification of microcirculatory autoregulation from a single measurement at rest without provoking hyperemia.