OBJECTIVES--To assess the effect of hyperventilation and mental stress on coronary blood flow and symptom production in patients with syndrome X. DESIGN--A prospective study. Hyperventilation and mental stress tests were performed on the ward and were repeated in the cardiac catheter laboratory where coronary blood flow velocity was also measured with an intracoronary Doppler catheter in the left anterior descending coronary artery. Oesophageal manometry studies were also performed. PATIENTS--29 patients with syndrome X (typical anginal chest pain, a positive exercise test, and normal coronary angiogram). SETTING--A regional cardiothoracic 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 catheter laboratory. Hyperventilation produced a significant increase in the rate-pressure product during ward and laboratory testing. There was, however, no significant change in the rate-pressure product on mental stress tests. The mean (SEM) coronary flow velocity decreased significantly on hyperventilation in the catheter laboratory from 10.0 (0.92) cm/s to 5.9 (0.72) cm/s (p < 0.001). There was also a significant reduction 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 reduction in flow velocity occurred in the absence of any changes in diameter of the left anterior descending artery. Further analysis showed that the coronary flow velocity was reduced significantly in only that group of patients in which hyperventilation and mental stress provoked chest pain. There was a significant increase in the arterial concentrations of noradrenaline on both hyperventilation and mental stress testing. Oesophageal manometry showed abnormalities in 17% of patients. CONCLUSIONS--Both hyperventilation and mental stress can produce chest pain in patients with syndrome X and this is associated with a reduction in coronary blood flow velocity. The results of this study suggests that this reduction in coronary flow occurs as a result of increased microvascular resistance.
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