Coronary response to diving in subjects with mild and severe left coronary artery disease

The cold pressor test (CPT) is commonly used to determine the vasospastic origin of angina and to investigate the factors modulating coronary vasomotor tone. However, coronary vasoconstriction associated with this manoeuvre is often limited, particularly in patients with mild coronary atherosclerosis. To identify stimuli that can more powerfully constrict the coronary arteries we compared the effects on coronary blood flow (thermodilution) and vascular resistance (mean aortic pressure divided by coronary blood flow) of CPT (2 min) and diving (D, 45 s) in subjects with angiographically documented mild (n = 11) or severe (n = 11) left anterior descending coronary artery stenosis. In subjects with severe coronary artery stenosis the rate-pressure product increased to a similar extent with CPT and D. The latter stimulus, however, caused a more marked fall in coronary blood flow and a much more pronounced increase in coronary resistance as compared to CPT (+44 +/- 3.1% vs +19 +/- 1.6%, P less than 0.01). In the face of a similar increase in rate-pressure product, D caused a significant increase in coronary vascular resistance also in patients with mild coronary artery stenosis (less than or equal to 50%) in which CPT failed to induce any coronary vasoconstriction (+16 +/- 1.8% vs +0.3 +/- 1.3%, P less than 0.01). Thus, diving is a much more powerful coronary vasoconstrictor stimulus than CPT. It can thus replace CPT when an increase in coronary resistance is needed for diagnostic purposes or for investigating abnormalities in coronary vascular regulation.