Suprapubic track pressure and force-deformation measurements in a (live) human subject and in animal models post-mortem

Tests have been performed on animal models shortly post-mortem and on a hea lthy human subject in order to obtain estimates of the forces which act on suprapubic urinary catheters and similar devices and to develop an abdomina l wall simulator. Such data and test methods are required for the systemati c design of suprapubic devices because of the dual need to maintain the fun ctionality of devices and to avoid excessive pressure on soft body tissue w hich could lead to ischaemia and in turn necrosis. In the post-mortem anima l models, electrical excitation was applied to the abdominal wall in order to stimulate muscle activity. Two types of transducers were used: a soft me mbrane transducer (SMT) for pressure measurement and novel instrumented 'to ngs' to determine indentation stiffness characteristics in the suprapubic t rack or artificial pathway created for a device. The SMT has been extensive ly used in the urethras and bladders of human subjects while the tongs were built specifically for these tests. Only the well-established SMT was used with the human subject; a peak pressure of 22 kPa was obtained. In the ani mal models the pressure profile given by the SMT had a peak whose position corresponded well with the estimated location of the rectus muscle measured on the fixed tissue section. The peak value was 5.5 kPa, comparable with v alues likely to cause necrosis if maintained for more than 1 day. Remarkabl y consistent indentation stiffness values were obtained with the instrument ed tongs; all values were close to 0.45 N/mm (33 kPa/mm).