The mechanical properties of the large bowel have been largely neglected
to date. A method was established using the rat colon to mechanically
test colonic tissue. The method involved 10 mm rings of colon being
tested mechanically at right angles to the long axis of the colon. Tests
chosen to measure "strength" were burst strength and tensile strength.
"Stretch" was measured by percentage elongation and width of the colon
at burst. The internal diameter of the colon at zero stress and the thickness of the colon wall, at rest were taken as reference dimensions.
Viscoelastic properties were measured by stress relaxation and hysteresis
in the rat and stress -relaxation in the human.Post-mortem material was the only practical source of non -diseased colonic
tissue across the spectrum of age. The tests used were not affected
significantly by death or time after death. Because colons required to be
transported from Uganda to be tested in Edinburgh, a method of preserving mechanical properties during storage had to be devised. The method of
choice was salt, mechanical properties as tested being well preserved for at
least 35 days.Twenty -tw adult Edinburgh colons (age range 19 to 81) and 17 adult
Kampala colons (age range 14 to 62) were studied. In addition, 10
Edinburgh children's colons (age range 28 weeks gestation to 4 years) and
3 Kampala children's colons (age range 36 to 40 weeks gestation) were
tested. Segments from an ascending, transverse, descending and sigmoid
colons were tested in each case.The tensile strength of the human colon declined with age (P < 0,05).
Once adult life was reached its capacity to stretch remained fairly
constant, except in the sigmoid colon, where there was a fall in stretch
capacity with age (P <0,001. ). The diameter of the colon fell with
increasing age in adult life (P <0,05), this was most pronounced in the
Edinburgh colon. Viscoelastic properties were unaffected by age. There
were no consistent sex differences in mechanical properties.The Kampalan colon had a significantly greater tensile strength than its
Edinburgh counterpart (P <0,05). The distal but not the proximal colon
had a greater stretch capacity in the Kampala group (P <0,001). The
viscoelastic property of stress relaxation was similar in both groups.
Children's colons were similar in the two race groups.Comparing those colons with and without diverticular disease in the
Edinburgh over 50 group, no differences were found in mechanical properties.The results are discussed in the light of the few mechanical or structural
studies previously reported for the colon and also mechanical studies of
other tissues. Their relevance to the high incidence of diverticular disease
in Edinburgh compared with Kampala is discussed, together with theories for
the aetiology of diverticular disease
