The effect of a week's beta‐adrenoceptor antagonism on daytime heart‐ rates, subjective responses to exercise, and physical activity in normal subjects.

Abstract

The effects on heart rate (HR) and physical activity of 1 week's treatment with three different beta‐adrenoceptor antagonists (20 mg betaxolol (Lorex); 160 mg propranolol LA; or 100 mg atenolol daily) have been compared with placebo in a double‐blind study of 12 normal men. On the fifth day of each treatment a body‐borne tape‐recorder was worn during waking hours for recording of ECG and footfall signals. Each record was calibrated in terms of the subject's response to laboratory ergometer exercise, and a computer analysis provided objective indices of physical activity. While on beta‐adrenoceptor antagonists the subjects perceived standard exercise as significantly harder than on placebo and reported more side‐effects (albeit mild and transient). Ambulatory monitoring of HR showed that subjects spent 13% of their waking day at heart rates below 50 beats min‐1 while on propranolol, compared with 1% on placebo and 20% on atenolol and betaxolol. On these latter drugs, the group spent as much as 10% of their waking time with HR below 45 beats min‐1. The lowest individual heart‐rates recorded were below 35 beats min‐1. Objective indices of physical activity, such as the duration of periods spent with heart rates above the HR found at 100 W in the ergometer test, showed no differences between the treatments. This negative finding was confirmed by pedometer step counts over the whole week.