EFFECT OF HYPERVENTILATION AND MENTAL STRESS ON CORONARY BLOOD-FLOW IN SYNDROME-X

Objectives-To assess the effect of hyperventilation and mental stress on coronary blood flow and symptom production in patients with syndrom e X. Design-A prospective study. Hyperventilation and mental stress te sts were performed on the ward and were repeated in the cardiac cathet er laboratory where coronary blood flow velocity was also measured wit h an intracoronary Doppler catheter in the left anterior descending co ronary artery. Oesophageal manometry studies were also performed. Pati ents-29 patients with syndrome X (typical anginal chest pain, a positi ve exercise test, and normal coronary angiogram). Setting-A regional c ardiothoracic centre. Results-Hyperventilation produced typical chest pain in 16 patients on the ward. 13 patients experienced their typical chest pain with mental stress test 5. Ten patients experienced chest pain with both hyperventilation and mental stress tests. This pattern was reproduced exactly when the tests were repeated in the cardiac cat heter laboratory. Hyperventilation produced a significant increase in the rate-pressure product during ward and laboratory testing. There wa s, however, no significant change in the rate-pressure product on ment al stress tests. The mean (SEM) coronary flow velocity decreased signi ficantly on hyperventilation in the catheter laboratory from 10.0 (0.9 2) cm/s to 5.9 (0.72) cm/s (p<0.001). There was also a significant red uction in the mean (SEM) coronary blood flow velocity on mental stress tests from 9.8 (0.86) cm/s to 7.4 (0.6) cm/s (p<0.001). This reductio n in flow velocity occurred in the absence of any changes in diameter of the left anterior descending artery. Further analysis showed that t he coronary flow velocity was reduced significantly in only that group of patients in which hyperventilation and mental stress provoked ches t pain. There was a significant increase in the arterial concentration s of noradrenaline on both hyperventilation and mental stress testing. Oesophageal manometry showed abnormalities in 17% of patients. Conclu sions-Both hyperventilation and mental stress can produce chest pain i n patients with syndrome X and this is associated with a reduction in coronary blood flow velocity. The results of this study suggest that t his reduction in coronary flow occurs as a result of increased microva scular resistance.