ADAPTATION OF THE RECTAL WALL TO DISTENSION IN CHILDREN WITH CONSTIPATION

To determine whether there is significant change in the tension-length relationship of the digestive smooth-muscle mechanical function in co nstipation in children and to examine a new method of analysis of the mechanical properties of the rectal wall. Design: Case-control study. Participants: Thirty children with constipation and 30 control childre n who did not have constipation. Intervention: Rapid distension of the rectal wall by inflation of a rectal balloon with air. Main outcome m easures: The in vivo rectal pressure-volume P[t,V] curve was determine d according to the quasilinear viscoelasticity law. The recorded press ure was defined as the product, of 2 functions: the elastic response P -0[V] and the reduced relaxation function G[t], a normalized function of time such that P[t,V] = P-0[V] x G[t]. Analysis of variance with re peated measures and modelling (linear for P-0[V] and exponential plus constant term for G[t]) were used for data analysis. Results: The quas ilinear viscoelastic law can be applied to the in vivo determination o f the mechanical properties of the rectal wall in controls and in chil dren with constipation. The elastic response was similar in the 2 grou ps. The reduced relaxation function was significantly different betwee n the 2 groups, with the absence of an asymptotic value in the group w ith constipation (p < 0.01). Conclusion: Distension of the rectal wall with the use of an air-inflated balloon, with this type of interpreta tion according to the viscoelastic law, is useful in the analysis of c hronic constipation.