Background--Cardiovagal autonomic control declines with age in adult subjects, which is related in part to increasing stiffness of the barosensory vessel wall. It is not known, however, whether autonomic function changes with age in children.

Methods and Results--We studied 137 healthy subjects divided into 4 age groups: group 1, 7 to 14 years; group 2, 11 to 14 years; group 3, 15 to 18 years; and group 4, 19 to 22 years. Brachial artery pressure was measured by sphygmomanometry and continuous radial artery pressure and carotid artery pulse pressure (P) by applanation tonometry. The R-R interval was derived from the ECG. Autonomic function was assessed by spontaneous sequence and frequency-domain indices, which indicate the extent of coupling between fluctuations in heart rate and systolic pressure. Carotid artery diastolic diameter (DD) and pulsatile distension (D) were measured by echo wall tracking; carotid compliance coefficient (CC) was defined as D/P and distensibility coefficient as 2D/DD · P. From group 1 to group 3, spontaneous indices increased significantly (18.1±1.7 versus 33.3±4.0; 14.4±1.1 versus 25.5±22; 12.9±1.1 versus 20.8±2.0; and 6.4±0.6 versus 16.2±1.4 ms/mm Hg [mean±SEM] for Seq+, Seq-, LF, and LF_gain, respectively), with no significant changes afterward. CC and DC were inversely proportional to age (r=-0.49 and -0.62, respectively, P<0.001). The efficiency of neural integrative mechanisms, estimated as the ratio of spontaneous indices and CC, more than doubled from group 1 to group 3. Spontaneous indices were linearly related to measures of cardiac vagal activity.

Conclusions--The increase in spontaneous indices from early childhood to adolescence, despite gradual stiffening of the carotid artery, may indicate improved cardiovagal autonomic function, which is most likely a result of maturation of neural mechanisms, attaining peak level at adolescence.