Analysis of heart rate variability demonstrates effects of development on vagal modulation of heart rate in healthy children.

OBJECTIVES: Analysis of heart rate variability (HRV) has been found to be a useful method of assessing cardiovascular autonomic control, but normal values for standard HRV measures in children have not been established. We analyzed HRV in 60 healthy children aged 3 to 15 years to determine normal values and to assess the effects of development on cardiac autonomic control with the use of ambulatory electrocardiographic monitoring. RESULTS: The high-frequency (HF) component, an index of cardiac autonomic tone, increased significantly with age from 3 to 6 years (p < 0.01) and decreased with age from 6 to 15 years (p < 0.01), and the magnitude of HF correlated significantly with the R-R intervals. Thus the changes in cardiac autonomic tone could be described as a simple equation using age and heart rate. CONCLUSIONS: We present normal values and changes in the cardiac autonomic system during childhood after HRV analysis, which could lead to a better understanding and treatment of cardiac disease in children.

Comparison of casual blood pressure and twenty-four-hour ambulatory blood pressure in high school students.

OBJECTIVE: To perform ambulatory blood pressure monitoring (ABPM) in high school students and to compare the 24-hour values with casual blood pressure (BP). METHODS: Ambulatory BP monitoring was carried out in 190 high school students, 15 or 16 years of age, with elevated casual BP during the first examination at school for hypertension; 66 had elevated casual BP at both the first and the second examinations (group H1), and 124 students were normotensive at the second examination (group H2). Sixty-two students who were consistently normotensive served as control subjects (group N). Average BPs for the 24-hour period, the awake period (10 AM to 10 PM), and the sleeping period (1 AM to 6 AM) were calculated. RESULTS: Average BP for each period was significantly higher in group H1 than in group N. Average BP in group H2 for these periods was intermediate between those of group H1 and of group N. The casual BP had a significant positive correlation with the average BP during the awake period (r = 0.55, p < 0.01 for systolic BP; r = 0.37, p < 0.01 for diastolic BP). In most subjects the casual BP readings were higher than BP during ABPM. CONCLUSIONS: Casual BP measurements correlated with 24-hour BP, but they tended to be higher than the measurements obtained during 24-hour ABPM.