A standardized isoproterenol sensitivity test. The effects of sinus arrhythmia, atropine, and propranolol

Isoproterenol hydrochloride sensitivity was measured from dose/response curves to rapid intravenous injections as the dose required to increase the heart rate by 25 beats per minute (chronotropic dose25or CD25). The most accurate assessment of CD25was achieved by using the three shortest R-R intervals of the electrocardiogram to calculate heart rate before and after administration of isoproterenol to eliminate the effect of sinus arrhythmia. In ten subjects the CD25appeared to increase with age between 21 and 35. Neither the chronotropic nor hypotensive effects of the CD25for isoproterenol were affected by atropine sulfate, suggesting that vagal withdrawal does not contribute to the chronotropic effect of this dose. Propranolol hydrochloride increased the CD25by acting as a competitive antagonist. The test procedure was safe, accurate, reproducible, and convenient for measuring both β-receptor responsiveness and β-adrenergic blockade in man.