When ring segments of artery free of external loads are cut longitudin
ally, they spring open. This property, which has been termed residual
strain, is a manifestation of an underlying residual stress and may be
quantified by measuring the degree to which the cut ring springs open
. Residual stress serves to redistribute the forces in the media and t
o minimize the stress gradient between its inner and outer margins. It
s magnitude and distribution are closely related to vascular growth an
d development. We have measured the degree of opening (in terms of an
opening angle, see below for its definition) in 168 rings removed from
six positions along aortae obtained at autopsy from 30 subjects aged
between 3 months and 87 years. At all ages, there was an overall incre
ase in opening angle along the aorta away from the heart. At all posit
ions, the opening angle increased with age and was higher in vessels w
ith visible atheroma. At all ages, the opening angle was significantly
greater in males than in females. This difference persisted when allo
wance was made for the greater incidence of atheroma in males. We have
found a similar age-related increase in rats, although there was no d
ifference between males and females. These observations are consistent
with a recently proposed 'stress-growth' law in which remodelling of
the arterial wall is driven by the non-uniform distribution of stress
across it and may be associated with known sex-related differences in
the aetiology of cardiovascular disease.