Objective: To introduce and evaluate a new implantable bladder volume monitor.
Design: Experimental study.
Setting: Animal laboratory.
Animals: Eight dogs.
Interventions: A coin-shaped permanent magnet was stitched onto the anterior bladder wall and a magnetic field sensor was fixed onto the lower abdominal external wall in 8 male dogs. The bladder was filled with sterile normal saline in consecutive steps of 25 mL each from 0 to 200 mL by a transurethral catheter.
Main outcome measure: Sensor readings were recorded after each step of bladder filling.
Results: The sensor baseline was set at 70 degrees when the bladder was empty. After filling the bladders with 25, 50, 75, 100, 125, 150, 175, and 200 mL saline water, the sensor readings were 74.6+/-0.9 degrees , 79.6+/-1.2 degrees , 84.5+/-0.9 degrees , 90.1+/-0.8 degrees , 95.5+/-1.1 degrees , 101.8+/-2.1 degrees , 110.5+/-2.9 degrees , and 121.9+/-3.5 degrees , respectively. Sensor readings were positively correlated with bladder volume (r=1; P<.01).
Conclusions: The design of a new bladder volume monitor that is made up of an external magnetic field sensor and an internal permanent magnet is reasonable and feasible. The new bladder volume monitor is simple in structure.