Quantitative assessment of coronary vasoreactivity in humans in vivo.  Importance of baseline vasomotor tone in atherosclerosis. 
Disturbances in vasomotor tone are closely linked to the development of atherosclerosis and play an integral part in the pathophysiology of myocardial ischemia in patients with coronary artery disease.  Currently, evaluation of coronary vasomotor tone relies on assessment of luminal changes in response to vasoactive stimuli by quantitative angiography.  Assessment of luminal changes, however, may be misleading because of the effects of geometric magnification induced by atherosclerotic wall thickening and differences in basal tone, which may obscure potential effects of vasoactive stimuli.  Combining angiographic measurements of luminal changes with measurements of coronary wall architecture determined by intracoronary ultrasound, we calculated absolute coronary arterial vasomotor tone in 34 patients with angiographically normal or "minimally diseased" coronary arteries.  Epicardial artery vasodilator capacity in response to intracoronary nitroglycerin decreased significantly with increasing atherosclerotic wall thickening.  An inverse relation existed between local atherosclerotic plaque load and nitroglycerin-induced changes in vasomotor tone (r = -.65, P < .0001) regardless of potential systematically operative factors.  At the same time, basal vasomotor tone significantly decreased with increasing local atherosclerotic wall thickening (r = -.38, P = .004).  The vasomotor effects of acetylcholine, an endothelium-dependent vasodilator, were inversely related to wall thickening only in segments with very minor degrees of atherosclerosis, whereas no such relation was observed for epicardial artery segments with more advanced atherosclerotic wall thickening.  In these segments, however, vasoreactivity to acetylcholine was closely correlated with basal vasomotor tone (r = -.62, P = .0002).  Atherosclerosis is associated with impairment of the vasodilator response to both nitroglycerin and acetylcholine in epicardial arteries in vivo.  Basal vasomotor tone appears to be the primary determinant of the altered coronary vasoreactivity in response to vasoactive stimuli.