Effect of nitroprusside-induced fall in systemic pressure on coronary stenoses

A fall in coronary pressure increases resistance across compliant coronary stenoses, probably because of passive collapse of the stenotic segment. The effects of a mechanically induced fall in coronary pressure were compared with the effects of a similar fall in pressure caused by intravenous sodium nitroprusside, a systemic and large coronary artery vasodilator. Seventeen dogs were studied in which a compliant circumflex coronary stenosis was produced by inflating an intracoronary balloon with saline. When coronary pressure was lowered from 105 +/- 3 to 78 +/- 3 mm Hg (P less than 0.001) by tightening a snare proximally on the circumflex coronary artery, the stenosis pressure gradient increased (9 +/- 1 to 17 +/- 3 mm Hg, P less than 0.005), flow fell (21 +/- 2 to 15 +/- 2 ml/mm, P less than 0.001) and stenosis resistance increased (0.67 +/- 0.15 to 2.06 +/- 0.68 units, P less than 0.05). When nitroprusside caused pressure to fall from 112 +/- 4 to 81 +/- 4 mm Hg (P less than 0.001), the stenosis pressure gradient did not change (16 +/- 1 to 16 +/- 1 mm Hg), flow increased (42 +/- 5 to 62 +/- 6 ml/min, P less than 0.001), and stenosis resistance decreased (0.46 +/- 0.07 to 0.32 +/- 0.06 units, P less than 0.01). These findings demonstrate that nitroprusside prevented passive collapse of the compliant stenoses as pressure fell, possibly by nitroprusside actively dilating the stenotic segment. Therefore a moderate fall in systemic pressure caused by a coronary vasodilator may not have deleterious effects on stenosis severity.