Does the cystometric filling rate affect the afferent bladder response pattern? A study on single fibre pelvic nerve afferents in the rat urinary bladder.

Aims: To study the effect of physiological and supraphysiological filling rates on the response pattern of single fibre pelvic nerve afferents of the rat urinary bladder.

Materials And Methods: A total of 37 single afferent bladder units were identified electrophysiologically and their mechanosensitive properties studied. Afferent activity of 13 units was studied at filling rates of 40 and 200 microl/min. Afferent activity of the other units was studied at 200 and 400 microl/min.

Results: At the physiological filling rate of 40 microl/min two clearly different types of response pattern were noted. However, at higher supraphysiological filling rates, all units exhibited nearly the same pattern. The difference in mechanosensitive properties of the units that showed a change in response pattern at the supraphysiological filling rate, was characterized by a decrease in pressure at which afferent firing rate peaked. For all units it was found that an increase in filling rate induced an increase in the activation pressure threshold for afferent units, whereas the afferent firing rate at all pressures decreased.

Conclusions: In rats supraphysiological filling rates delay afferent activation, lower afferent firing activity and even change the characteristics of some afferents completely. These data may elucidate some of the differences between ambulatory and conventional urodynamics observed in man.