Rectodynamics--quantifying rectal evacuation.

A new technique is described which allows the graphic quantitation of voluntary rectal evacuation. The subject is asked to evacuate 100 ml of barium sulphate paste as rapidly and completely as possible. Using a weight transducer it is possible to determine the maximum emptying rate, time to achieve maximum emptying and proportion of barium evacuated. Normal subjects evacuate quickly and completely. Patients with severe constipation demonstrate a variable evacuation disturbance.