Stiffness of Systemic Arteries in Appropriate- and Small-for-Gestational-Age Newborn Infants

OBJECTIVE. The purpose of this work was to study the stiffness of systemic arteries in appropriate and small for gestational age newborn infants. The distance between diametrically opposite points of the arterial lumen was measured with a phase locked loop echo tracking system coupled to a B-mode ultrasonic imager. PATIENTS AND METHODS. A cross-sectional study of 51 appropriate for gestation age infants including 22 preterm infants was done to obtain normal data. We also studied 47 small for gestational age infants, who were identified antenatally by an umbilical artery Doppler flow waveform pulsatility index >95th percentile. The stiffness index of the common carotid artery and abdominal aorta was calculated from the relationship between systemic blood pressure and arterial diameter during the cardiac cycle. RESULTS. In the appropriate for gestation age group, the systolic and diastolic diameters of the common carotid artery and abdominal aorta, as well as the stiffness index, increased with the gestational age at birth. In the small for gestational age group, the arterial diameters and blood pressure were also within the reference range. Using the arterial stiffness index values from the appropriate for gestation age group, the small for gestational age group was divided into 3 subgroups: 18 infants with normal stiffness index values for both arteries, 19 infants with a high stiffness index of the abdominal aorta, and 10 infants with a high stiffness index for both arteries. The clinical outcome was significantly worse in the latter 2 subgroups compared with the normal infants and was also worse in the infants with a high stiffness index for both arteries compared with the high abdominal aorta subgroup. CONCLUSION. The antenatal increase of afterload caused by a high placental vascular resistance was associated with a decrease of aortic distensibility in the compromised small for gestational age infants, suggesting that the structure of the aortic wall was altered. In the most profoundly compromised small for gestational age infants, the high stiffness index of both the common carotid artery and abdominal aorta may indicate more extensive arterial damage.