Paediatric Cardiology.316 For imaging of the carotid artery with the aim of measuring intima-media thickness, high-frequency linear array probes with frequencies of 7 MHz or above should be used Recently the use of ultrahighresolution ultrasound, with frequencies in the range of 25 to 55 MHz, has been shown to be feasible and probably more accurate for the measurement of carotid intimal-medial thickness in young children.329 To ensure optimal imaging of the arterial walls, the carotid artery should be imaged as perpendicular as possible to the plane of ultrasound Whereas combined assessment of both the near and far walls is common in adult studies, most of pediatric studies have focused on the assessment of the more clearly visualized far wall of the distal 10 mm of the common carotid artery (Fig 74.11) In several neonatal and pediatric studies, the intimal-medial thickness of the aorta was measured.330–332 Manual measurement using online calipers has increasingly been replaced by automatic analysis of acquired B-mode images (Fig 74.12) or real-time radiofrequency tracking technology.333 FIG 74.11 Measurement of intima-media thickness of the common carotid artery (CCA) with the target area positioned just proximal to the carotid bulb ECA, External carotid artery; ICA, internal carotid artery; US, ultrasound (From Dalla Pozza R, Ehringer-Schetitska D, Fritsch P, et al Intima media thickness measurement in children: a statement from the Association for European Paediatric Cardiology (AEPC) Working Group on Cardiovascular Prevention endorsed by the Association for European Paediatric Cardiology Atherosclerosis 2015;238:380–387.) FIG 74.12 Distal common carotid artery demonstrating automatic analysis and measurement of the intimal media thickness The thickness is measured from the border between the echolucent arterial lumen and the echogenic intima (upper blue line) to the border between the echolucent media and the echogenic adventitia (lower blue line) Systemic Arterial Dysfunction in Childhood Age-Related Evolution Aortic, upper limb, and lower limb pulse-wave velocities, as measured by the transcutaneous Doppler technique, increase progressively with age in a cohort of subjects aged 3 to 89 years.334 Age-dependent increase in brachioradial arterial pulse-wave velocity has similarly been demonstrated in a cohort of children and adolescents aged 6 to 18 years using the photoplethysmographic technique.335 Analysis of the area under the ascending aortic pressure-time curve using a twoelement Windkessel model further reveals a nonlinear increase in total arterial stiffness in children aged 6 months to 20 years.336 Previous findings did not, however, suggest that the change in pulse-wave velocity with age is due entirely to differences in systemic blood pressure.334,335 Rather, the gradual increase in arterial stiffness with age is probably related to progressive medial degeneration With cyclic mechanical stress, fragmentation of the elastin fibers and transfer of stress to the stiffer collagen fibers result in a progressive increase in vascular stiffness.337 Studies of developmental changes in arterial structure during childhood have further demonstrated a progressive increase in intimal and medial thickness after birth.338 Hence the observed agerelated increase in stiffness is likely related to progressive structural changes in the arterial wall during childhood In otherwise healthy adults, endothelial function has been shown to deteriorate with aging.339 Progressive endothelial dysfunction appears to occur earlier in men than in women Although puberty has been speculated to be a critical period for the vascular endothelium,340 a recent study showed that endothelial function as assessed by brachial artery flow-mediated dilation does not change significantly during the pubertal period.341 Cardiovascular Risk Factors Childhood obesity is a global epidemic Obese children have increased stiffness of the abdominal aorta342,343 and carotid artery,344 and endothelial dysfunction is evidenced by elevated serum biomarkers of endothelial activation345,346 and