Haemodynamics during repeated exercise tests with special reference to the 'warm-up' phenomenon in patients with angina pectoris.

The haemodynamic effect of two successive supine exercise tests 20 min apart was examined in 12 patients with angina pectoris. All the patients had coronary artery disease verified by angiography and were accepted for coronary bypass surgery. They exercised 20-40 W and all of them had angina during the first exercise test. Half the patients did not experience angina during the second of the two exercise tests ('warm-up' responders). In these patients left ventricular filling pressure (LVFP) was reduced by 40% (P less than 0.01) in the second compared to the first exercise test. The non-responders showed no significant change in LVFP. The heart rate pressure product (RPP) and thus myocardial oxygen demand were unchanged in responders and non-responders. In another 10 patients with angina and coronary artery disease, also accepted for coronary bypass surgery, atropine (1.5-2.0 mg) was given intravenously. Ten minutes after administration of atropine, these patients followed exactly the same investigation programme including two successive supine exercise tests as in the group not given atropine. In the group given atropine, four 'warm-up' responders and six non-responders showed the same pattern of response in LVFP as in the group not given atropine. In the 'warm-up' responders a smaller increase in RPP was observed during the second exercise test compared to the first. The present study indicates that cholinergic mechanisms are probably not involved in the 'warm-up' phenomenon. Due to the difference in haemodynamic response, the 'warm-up' phenomenon has to be taken into account when evaluating results from haemodynamic studies of cardiovascular drugs.