Hyperventilation reduces coronary blood flow in syndrome X patients

Abstract

The mechanism of chest pain in syndrom X patients is not clear. The authors investigated the effect of hyperventilation in a group of 18 syndrome X patients. All patients first underwent hyperventilation tests on the ward twenty-four hours prior to cardiac catheterization A 3.6F intracoronary Doppler catheter was positioned in the proximal left anterior descending coronary artery. The resting coronary blood flow velocity was measured with the patient in the supine position and breathing normally and after hyperventilation. during the tests performed on the ward, 10 patients experienced their usual chest pain on hyperventilation, but none of these episodes produced significant ischemic ECG changes. This exact pattern was repeated during the cardiac catheterization with hyperventilation. Hyperventilation on the ward produced a significant increase in heart rate (66±12 beats/minute before to 82±18 after, p=0.001), but there was no significant change in the systolic blood pressure. The rate pressure product increased significantly from 9,050±1,663 to 11,156±2,872 (p=0.009). Hyperventilation in the catheterization laboratory again produced a significant increase in heart rate (77±17 beats/minute before, to 85±16 after, p=0.001) but there was no significant change in the systolic blood pressure. The rate-pressure product increased significantly from 9,267±2,216 to 10,528±3,045 (p=0.009). Coronary blood flow velocity, however, decreased significantly from 7.6 cm/sec ±4.9 to 6.6±5.0 (p=0.02, paired t-test). The authors conclude that in syndrome X patients hyperventilation can reduce coronary blood flow significantly in those who experienced chest pain during the test.