Urinary bladder volumetry by means of a single retrosymphysically implantable ultrasound unit.
AIMS: Optimal voiding is a crucial issue for patients with neurogenic bladder dysfunctions to prevent long-term damage to the urinary tract. In prior studies, implantable ultrasound (US) sensors have proved an appropriate method of measuring the urinary bladder volume. Their disadvantage is that they tend to dislocate in chronic applications as they are fixed directly onto the bladder wall. In the present study, we describe an implantable US volumetry unit that does not require fixing to the bladder wall and consists of a single receiver-transmitter unit. MATERIALS AND METHODS: Six Göttinger minipigs were anesthetized in ITN; a sensor was stitched behind the symphysis into the periosteum and aligned to the bladder so that an US measurement could take place in ventro-dorsal direction. In steps of 50 ml, the bladder was filled up to 250 ml via a transurethral catheter; after each filling step the volume was measured three times and compared to the instilled volume. RESULTS: On average the measurements with implanted US differed from the actual bladder filling by 77.4% at a bladder filling of 50 ml ("error" messages were included as 0 ml), 3.8% at 100 ml, 3.8% at 150 ml, and 0.3% at 200 ml, and 3.6% at 250 ml. When the empty bladder (= 0 ml) was measured, the US sensor detected no volume in 73% of the cases. CONCLUSIONS: In our animal model, the above-described US system proved tantamount with other external US measuring units and presented a precise and low-artefact system, allowing reliable measuring of the urinary volume with good chances of preserving these positive qualities over time. We expect that clinical application of this system may help to determine the optimal voiding time and thus to avoid bladder over-extension and damage to the urinary tract over time.