Effect of beta-blockade on exercise core temperature in coronary artery disease patients

The effect of pharmacologic blockade of beta-adrenoceptors on the relationship between rectal (Tre) and pulmonary artery (Tpa) temperatures was studied in six coronary artery disease patients during 30 min of exercise. Exercise was performed at a set work rate (120 W) on a cycle ergometer before and 2 h after the ingestion of 80 mg propranolol. The heart rate on completion of exercise was reduced (P less than 0.001) from 140 +/- 5 to 108 +/- 3 beats.min-1 by propranolol demonstrating a considerable degree of beta-adrenoceptor blockade. At rest, neither Tre nor Tpa were modified by propranolol. Likewise, propranolol failed to modify the Tre response to exercise. However, propranolol induced an alteration of the normal relationship between Tre and Tpa during exercise. In particular, although Tre was essentially unchanged, propranolol accentuated both the initial fall (by 0.28 degrees C, P less than 0.001) and the subsequent rise (by 0.46 degrees C, P less than 0.01) in Tpa during exercise. The present data therefore demonstrate a considerable limitation to the use of Tre when assessing thermal homeostasis during acute beta-adrenoceptor blockade. Furthermore, although research with more chronic therapy is warranted, our study suggests an accentuated risk of hyperthermia and, by implication, its adverse physiologic consequences during prolonged exercise performed by coronary artery disease patients treated with propranolol.