MECHANISMS OF THE WARM-UP PHENOMENON

The warm-up phenomenon, described in patients with coronary artery dis ease, refers to the improved performance following a first exercise te st. The aim of this study was to investigate the causes of the warm-up phenomenon. Fifteen patients with coronary artery disease and positiv e exercise test were enrolled. Patients were off treatment throughout the study. They underwent two consecutive treadmill exercise tests acc ording to the Bruce protocol, with a recovery period of 10 min to re-e stablish baseline conditions. A third exercise test was then performed 2h later. Before the onset of ischaemia, the rate-pressure product fo r a similar degree of workload was similar during the first and second exercise test, while it was lower during the third test (P<0 . 05). T ime to 1 . 5 mm ST-segment depression during the second and third exer cise test was greater than during the first test (454+/-133 and 410+/- 161 vs 354+/-127 s, P<0 . 01, respectively). Similarly, the time to an ginal pain onset was increased during the second and third exercise te sts, compared to the first test (356+/-208 and 310+/-203 vs 257+/-204 s, P<0 . 01, respectively). In contrast, rate-pressure product at 1 . 5 mm ST-segment depression during the second test was higher than that during the first test (232+/-47 vs 210+/-39 beats.min(-1).mmHg.10(2), P<0 . 01), while in the third test it was similar to that during the first (209+/-43 beats.min(-1).mmHg.10(2), P=ns). The warm-up phenomeno n observed a few minutes after exercise is characterized by an increas e of both time to ischaemia and ischaemic threshold; this adaptation t o ischaemia may be due to an improvement of myocardial perfusion or to preconditioning. Conversely, the warm-up phenomenon observed a few ho urs after repeated exercise is characterized by an increase of time to ischaemia but not of ischaemic threshold and is caused by a slower in crease of cardiac workload. Thus, the mechanisms of the warm-up phenom enon may be different, time dependent and related to previous training .