No abstract

In order to assess the role of the autonomic system in the age differences in heart rate, propranolol 0-2 mg./kg. and atropine 30 Fxg./kg. were given to I03 infants and children during the course of heart catheterization. Mean control minute heart rate varied from II8 at age I year to 8i at age I6 years. Heart rate after drugs was termed intrinsic heart rate after Jose, and the mean variedfrom I39 at age I to I02 at age I6 years. After propranolol alone, mean heart rate was 120 at age I,7I at age I6, and after atropine corresponding rates were I62 and I28. The scatter in predicting heart rate from age was not lessened by autonomic blockade, suggesting that interindividual variations in heart rate are not entirely dependent on different levels of autonomic function. The inverse relation between heart rate and age persisted after autonomic blockade, indicating that different levels of autonomic function are not responsible for the age differences in heart rate. The most important determinant of the heart rate after blockade was the initial control heart rate. Increases in cardiac indexfollowed autonomic blockade in patients over 4 years of age and in patients without intracardiac shunts, while stroke index decreased, and femoral artery pressure increased 2/7 mm. Hg.Heart rate in the intact animal is determined by the basic rate of impulse formation at the pacemaker centre, and modifying factors such as neurohumoral control, body temperature, and thyroid function. In children, the average resting heart rate declines from I30 beats a minute or higher at i month of age to 8o beats a minute at i6 years of age (Keith, Rowe, and Vlad, I958). A difference in autonomic control may contribute to the variation in heart rate with age. Autonomic blockade of the heart can now be effectively and safely produced with atropine and propranolol, partially isolating the heart from the chronotropic effects of vagal and sympathetic stimulation (Jose, I966). In order to assess the influence of autonomic control on the heart rate of children of different ages, atropine and propranolol have been given to 103 infants and children at the time of diagnostic heart catheterization studies. The alterations in heart rate, systemic and pulmonary arterial pressures, and cardiac output after autonomic blockade, form the basis of this report.

In order to assess the role of the autonomic system in the age differences in heart rate, propranolol 0-2 mg./kg. and atropine 30 Fxg./kg. were given to I03 infants and children during the course of heart catheterization. Mean control minute heart rate varied from II8 at age I year to 8i at age I6 years. Heart rate after drugs was termed intrinsic heart rate after Jose, and the mean variedfrom I39 at age I to I02 at age I6 years. After propranolol alone, mean heart rate was 120 at age I,7I at age I6, and after atropine corresponding rates were I62 and I28. The scatter in predicting heart rate from age was not lessened by autonomic blockade, suggesting that interindividual variations in heart rate are not entirely dependent on different levels of autonomic function. The inverse relation between heart rate and age persisted after autonomic blockade, indicating that different levels of autonomic function are not responsible for the age differences in heart rate. The most important determinant of the heart rate after blockade was the initial control heart rate. Increases in cardiac indexfollowed autonomic blockade in patients over 4 years of age and in patients without intracardiac shunts, while stroke index decreased, and femoral artery pressure increased 2/7 mm. Hg.Heart rate in the intact animal is determined by the basic rate of impulse formation at the pacemaker centre, and modifying factors such as neurohumoral control, body temperature, and thyroid function. In children, the average resting heart rate declines from I30 beats a minute or higher at i month of age to 8o beats a minute at i6 years of age (Keith, Rowe, and Vlad, I958). A difference in autonomic control may contribute to the variation in heart rate with age. Autonomic blockade of the heart can now be effectively and safely produced with atropine and propranolol, partially isolating the heart from the chronotropic effects of vagal and sympathetic stimulation (Jose, I966). In order to assess the influence of autonomic control on the heart rate of children of different ages, atropine and propranolol have been given to 103 infants and children at the time of diagnostic heart catheterization studies. The alterations in heart rate, systemic and pulmonary arterial pressures, and cardiac output after autonomic blockade, form the basis of this report.

Eight patients with aortic coarctation were studied at rest and during supine bicycle exercise before and after intravenous propranolol O0r7 mg./kg. The accentuated pressor response to exercise in patients with coarctation may be due to the mechanical effect of an increase in the rate of left ventricular ejection into an aorta with a limited run-off capacity. As the rate of left ventricular ejection may be reduced by beta-adrenergic inhibition (Cumming and Carr, I967), the exercise haemodynamics of coarctation of the aorta were restudied after the intravenous administration of propranolol. PatientsData on the patients are given in Table I. Case 7 was a woman, the others were men or boys. The mean age was 14 years and the mean work load on