This experiment permit in general the detection of the ano-rectal inhibitory reflex [4], [5]. It's possible too, to detect the threshold of conscious perception of the rectum distension, the sphincterial pressures, the efficiency of the volunter contraction and the compliance of the rectal lining. This system is also used to trained subject in the case of biofeedback rehabilitation. In our case we will use this system as data set provider for the identification of our dynamical model.
The operation consist in inflating inside the rectum a balloon and mesuring in the same time the pressure inside the rectum (pressure sensor 1 in the picture 2) and a two different level in the anal channel. This two different level characterize normaly the activities of both internal (pressure sensor 2 in the picture 2) and external (pressure sensor 3 in the picture 2 ) sphincter. We are just using in our studie the response of the internal sphincter (pressure sensor 2) and the evolution of the pressure in the rectum (pressure sensor 1).
Figure 2: Schematic of the ano-rectal manometry experiment
The experiments used in this studie are made with various air volumen (typicaly 10, 20, 30, 40, 50 and 60 ml). The initial protocol implies to keep the choice volumen during 3 seconds. For one volumen the total duration of the record is currently 3 minutes. The data acquisition frequency is 5Hz and the inflation of the balloon would be considered as instantaneous. In fact the first experiment we use for the identification was ``hand-made'' so some of this data will be clearly improper for our purpose, we encountred a lot off error on volumen and time duration of the experiment. Now the procedure it's computer drived and the errors of this type are unusual.
Normaly a simple visual examen of the curve is sufficient for the physician to determine if the comportment is normal or pathological. So in this particular case (the diagnose of a disfunction) the relation with a parametrized model is not really useful. But on the other hand the gap between the main values and the current value of the model coefficients could give valuable informations to the physician in order to determine the type of pathology involved or, in the case of a rehabilitation process, to mesure the progress of the subject.
Figure 3: Typical curve of measure
We can see in figure (3) the normal shape of the experimental curves for a goodhealthy subject. It's obvious that this curve are very similar with the response of a controled system. This remark made by Dr. M. Bouchoucha was the begining of our collaboration and of this studie on the modelisation and identification.