Validation of a digital angiographic model to quantitate autoregulatory vasodilation of the coronary system

Compensatory vasodilation of the distal coronary vascular bed is the major autoregulatory mechanism in response to coronary stenosis. Using impulse response analysis (IRA) of digital angiographic time-density curves, myocardial contrast-transit was modelled as two-compartment system to obtain total coronary transit times (T) and microcirculation transit times (Tmicro) as parameters of flow (Q) divided by distribution volume (V) of the corresponding compartments. IRA parameters were compared with electromagnetic Q in eight dogs. At rest, Vmicro/V increased (P less than 0.02) from 0.69 +/- 0.08 in normal arteries (n = 25) to 0.86 +/- 0.06 in stenotic arteries (n = 24). With maximal vasodilation during hyperaemia, Vmicro/V was similar for normal (0.89 +/- 0.05; n = 19) and stenotic arteries (0.9 +/- 0.05; n = 18). There was a close linear (r = 0.88) correlation between 1/Tmicro and Q during hyperaemia. However, at rest with intact vasomotor tone, 1/Tmicro and Q were linearly related (r = 0.94; n = 12) only when Q was reduced below normal by tight stenosis; but the relationship became curvilinear in non-Q-limiting stenosed and normal arteries due to progressive decrease in Vmicro. Instead, resting 1/Tmicro demonstrated a very close linear correlation with coronary flow reserve (r = 0.95). We conclude that two-compartmental modelling of coronary contrast transit reflects stenosis-mediated autoregulatory vasodilation of the coronary microcirculation by a single measurement at rest.