The effect of rapid decreases of blood pressure by different mechanisms on coronary flow and flow reserve in normal coronary arteries

Background Changes in mean blood pressure (MBP) alter coronary blood flow (CBF). We evaluated the acute effects of three hypotensive medications on CBF parameters in angiographically normal coronary arteries. Methods We performed CBF measurements using the Doppler wire at rest and during hyperemia produced by intracoronary adenosine (18 μg) as follows: 1) in the normal left circumflex coronary artery in 20 patients with coronary artery disease (measurements were performed without drugs, and after intravenous infusion of nitroprusside [0.5 to 2 μg/kg/min] and nitroglycerin [10 to 90 μg/min]; drugs were titrated to decrease MBP 20% to 25% below the control values, and heart rate was held constant using right atrial pacing); and 2) in the normal left anterior descending coronary artery in 19 patients without coronary artery disease (measurements were performed before and after intravenous clonidine infusion [150 μg in 5 min]; time-averaged peak velocity [APV], CBF, and coronary flow reserve [CFR] were measured). Results Similar decreases in MBP were obtained in the two patient groups. Lumen diameter at the site of Doppler measurements increased after all medications (P< .005), whereas CBF did not change significantly. The CFR decreased after nitroprusside (1.79 ± 0.48 v 2.54 ± 0.45, P= .000), did not change significantly after nitroglycerin (2.74 ± 0.43 v 2.54 ± 0.45, P = .097), and increased after clonidine (3.12 ± 0.70 v 2.76 ± 0.75, P = .006). Conclusions In normal coronary arteries the infusion of three hypotensive medications to produce the same decreases in MBP is associated with different effects on CFR (increase with clonidine, decrease with nitroprusside, and no change with nitroglycerin).