Effects of atropine on diastolic time.

Atropine was given intravenously to 10 normal volunteers in increments of 0.01 mg/kg to a total dose of 0.04 mg/kg. This produced an increase in heart rate from 65 +/- 11 to 112 +/- 14 beats/min, a decrease in diastolic time from 534 +/- 131 to 180 +/- 65 msec, and a decrease in percent diastole from 55.6 +/- 5.3% to 32.4 +/- 7.2% (p < 0.001). Administration of isoproterenol in doses that increased heart rate from 69 +/- 9 to 99 +/- 12 beats/min produced a decrease in diastolic time from 485 +/- 98 to 312 +/- 47 msec and only a slight decrease in percent diastole, from 54.2 +/- 4.3% to 50.6 +/- 3.9%. Atropine, in doses commonly used clinically, may significantly reduce diastolic time and the percent diastole. Because diastolic time is an important determinant of coronary perfusion, administration of atropine to patients with coronary artery disease may increase myocardial ischemia.