OBJECTIVE: To test the hypothesis that the administration of cimetidine will modify the chronotropic response to exercise testing through a random clinical trial. METHODS: The study selected 24 eligible healthy subjects, ages between 20 and 68 years, not athletes, who agreed to undergo cardiopulmonary exercise testing after the administration of placebo and 400 mg of cimetidine twice a day for one week. The tests were performed on a treadmill using a ramp protocol and direct analysis of the expired gases. Peak, resting and anaerobic threshold heart rate were recorded. RESULTS: The twenty subjects studied were equally distributed across sex with mean (± SD) age 43 ± 11 years. Tests on placebo and on cimetidine presented similar duration (578 ± 90 sec vs 603 ± 131 sec) and similar peak oxygen uptake (35 ± 8 ml/kg.min vs 35 ± 8 ml/kg.min). Cimetidine administration had no significant effect on resting heart rate (75 ± 10 bpm vs 74 ± 8 bpm), heart rate at peak exercise (176 ± 12 bpm vs 176 ± 11 bpm), and on the difference between the peak and the resting heart rates - delta HR (101 ± 14 bpm vs 101 ± 13 bpm). CONCLUSION: The administration of cimetidine for 7 days has no significant effect on the chronotropic response to exercise testing.
Chronotropic response; cardiopulmonary exercise testing; cimetidine; H1 and H2 receptors; histamine
