Effects of atropine on left ventricular volumes and ejection and filling rates at rest and during exercise

1. The influence of the parasympathetic nervous system on left ventricular function including ejection and filling rates was studied by radionuclide cardiography in eight healthy young men at rest and during upright exercise. 2. After parasympathetic blockade induced by atropine, the mean heart rate (HR) at upright rest increased from 67 to 114 beats min-1, cardiac output (CO) from 4.05 to 5.17 1 min-1 (both P less than 0.001), and the diastolic blood pressure by 13 mm Hg (P less than 0.01). 3. Stroke volume (SV), left ventricular end diastolic and end systolic volume all decreased significantly after atropine. The relative ejection time increased from 0.33 to 0.51 of the cardiac cycle length (P less than 0.001), and the appropriate ejection and filling rates increased by 13% (P less than 0.05) and 147% (P less than 0.001), respectively. Haemodynamic changes in the supine position were virtually the same. 4. During exercise atropine increased HR from 115 to 146 beats min-1 (P less than 0.001) and CO by 12% (P less than 0.05), whereas SV decreased by 12% (P less than 0.05) and the systolic blood pressure by 16 mm Hg (P less than 0.001). Changes in ejection and filling rate of the left ventricle were of the same nature as those found at rest. 5. Thus apart from its HR limiting properties, secondary effects of parasympathetic nervous tone are dilatation of the left ventricle and enhancement of ejection, effects that are counteracted by atropine.