Age-related changes in microvascular permeability: a significant factor in the susceptibility of children to shock?

During studies of the pathogenesis of dengue shock syndrome, a condition largely confined to childhood and characterized by a systemic increase in vascular permeability, we observed that healthy controls, age-matched to children with dengue shock syndrome, gave high values of filtration capacity (K_f), a factor describing vascular permeability. We hypothesized that K_f might be age dependent. Calf K_f was studied in 89 healthy Vietnamese subjects aged 5 to 77 years. The K_f was highest in the youngest children [7.53 (1.96–15.46) K_fU; median (range); where the units of K_f, K_fU = ml·min^-1·100 ml^-1·mmHg^-1]. Values were 3- to 4-fold lower towards the end of the second decade [4.69 (1.91–7.06) K_fU]. Young mammals are known to have a larger microvascular surface area per unit volume of skeletal muscle than adults. During development the proportion of developing vessels is greater. Moreover, the novel microvessels are known to be more permeable to water and plasma proteins than when mature. These factors may explain why children more readily develop hypovolaemic shock than adults in dengue haemorrhagic fever and other conditions characterized by increased microvascular permeability.