EFFECT OF AGE AND OUTLET RESISTANCE ON RABBIT URINARY-BLADDER EMPTYING

Purpose: To investigate the influence of age and effect of increased o utlet resistance on the ability of rabbit bladders to empty in respons e to various methods of stimulation. Materials and Methods: Bladders f rom six-month-old (young) and three-year-old rabbits (aged) were mount ed in an in vitro whole organ bath system and filled with 15 mi. salin e. The ability of the bladders to empty against low outlet resistance (LOR) and high outlet resistance (HOR) in response to field stimulatio n, bethanechol, and KCl was measured. The following parameters were me asured: intravesical pressure and volume emptied. From these, flow rat e, power, and external mechanical work were calculated. Results: Maxim um isometric pressure did not change with age. All bladders emptied wi th increased pressure and decreased flow rate at HOR. The young bladde rs generated a greater maximum power in response to bethanechol and KC L than the aged bladders at both outlet resistances, and maximum power did not change with increased resistance. The aged bladders did less work and emptied significantly less than the young bladders at the HOR . Conclusions: The aged rabbit bladders were unable to maintain the bl adder contraction long enough to empty completely through an increased outlet resistance. Because maximum power remained constant when the o utlet resistance was increased, it might be useful clinically to deter mine the emptying ability of the urinary bladder, independent of chang es in outlet resistance. In addition, bladder work could be used to ev aluate bladder function if the volume emptied is also taken into consi deration.