Ex vivo perfusion of human coronary arteries demonstrates that coronary flow remains relatively constant until stenosis severity reaches 70-80%, after which flow decreases dramatically, especially under conditions of high demand.
Human coronary artery stenosis can have dramatic hemodynamic effects on coronary flow rate and perfusion. To quantitatively investigate these relationships, nineteen proximal coronary arteries with varying focal stenoses (2%-98%) were dissected from fresh post mortem adult hearts and perfused with isotonic glycerol saline (n = 2.7 centipoise) at constant pressures of 30, 50, 75, 100, 150 and 200 mm Hg, while varying the distal bed resistance (r b ) over the range 0.1 to 5 mm Hg/ml/min. Flow rate (Q) and arterial segment pressure drop (ΔP) were measured at each perfusion pressure and r b , and a permanent cast of silicone rubber was made under 100 mm Hg pressure following perfusion. Hydraulic resistance (R = ΔP/Q) tended to be constant at low Q (10-30 ml/min), with resistance increasing 2 or 3 times at higher Q (30-100 + ml/min). Curves of Q vs. % stenosis showed that Q was relatively constant with stenoses less than 70-80%. With a small further increase in stenosis, however, Q decreased dramatically. Furthermore, significant reductions occurred at lower % stenoses for greater demands (lower r b ), a contributing factor toward effort angina, as less severe stenoses became increasingly significant under flow demand. Elastic effects in eccentric lesions produced additional flow losses at lowered perfusion pressures. In addition, a critical relation was demonstrated between percent stenosis and the minimum coronary perfusion pressure necessary to maintain a given Q.
Samuel E. Logan (1975) studied this question.
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