Lower skin capillary density, normal endothelial function and higher blood pressure in children born preterm

Preterm birth is a risk factor for blood pressure (BP) elevation already at young age. The mechanisms are unknown. Low skin capillary density and impaired endothelial function characterize adults with hypertension.

To investigate the early relationships between BP, capillary density and endothelial function after very preterm birth. Design and subjects. Clinical follow-up study of 60 healthy school children aged 7-12 years; 39 born very preterm (mean gestational age 29 weeks) and 21 control subjects born at term with normal birth weights.

Using intravital video-microscopy, the dermal capillary densities in the fingers were measured before and during venous occlusion. Endothelial function was assessed using a Laser-Doppler technique to determine skin perfusion before and after transdermal delivery of acetylcholine, an endothelium-dependent vasodilator. Brachial BP and heart rate (HR) were also recorded.

Children born very preterm had lower functional capillary density than term controls (89.9 capillaries mm(-2) vs. 96.6 capillaries mm(-2), P = 0.04). During venous occlusion--measuring structural differences--this difference diminished (91.4 capillaries mm(-2) vs. 96.8 capillaries mm(-2), P = 0.12). In multivariate analysis, systolic BP (SBP) was higher in children born preterm, but SBP and capillary density did not correlate. HR was also higher in children born preterm, but did not correlate to BP or capillary density. Endothelial function did not differ between groups and did not correlate to capillary density.

Children born very preterm have lower functional skin capillary density, higher BP and higher HR. Longitudinal studies are needed to fully understand the long-term significance of these findings.