Reflex decline in internal sphincter pressure. Hirschsprung's disease ---> Pressure fails to drop, Paradoxical rise in pressure with rectal distention. o Radiography (Barium enema) It demonstrates the presence of transition zone between normal dilated proximal colon and a smaller caliber obstructed distal colon caused by non relaxation of aganglionic bowel. Delayed passage of stool (meconium) and abdominal distension suggests low intestinal obstruction.">