Neurourology and Urodynamics 25:162^167 (2006) Does the Cystometric Filling Rate A¡ect the A¡erent Bladder Response Pattern? A Study on Single Fibre Pelvic Nerve A¡erents in the Rat Urinary Bladder Stefan De Wachter,* Kevin De Laet, and Jean-Jacques Wyndaele Department of Urology, University of Antwerpen, Antwerp, Belgium Aims: To study the e¡ect of physiological and supraphysiological ¢lling rates on the response pat- tern of single ¢bre pelvic nerve a¡erents of the rat urinary bladder. Materials and Methods: A total of 37 single a¡erent bladder units were identi¢ed electrophysiologically and their mechanosensitive properties studied. A¡erent activity of 13 units was studied at ¢lling rates of 40 and 200 ml/min. A¡erent activity of the other units was studied at 200 and 400 ml/min. Results: At the physiological ¢lling rate of 40 ml/min two clearly di¡erent types of response pattern were noted. However, at higher supraphysiological ¢lling rates, all units exhibited nearly the same pattern. The di¡erence in mechanosensitive properties of the units that showed a change in response pattern at the supra- physiological ¢lling rate, was characterized by a decrease in pressure at which a¡erent ¢ring rate peaked. For all units it was found that an increase in ¢lling rate induced an increase in the activation pressure threshold for a¡erent units, whereas the a¡erent ¢ring rate at all pressures decreased. Conclusions: In rats supraphysiological ¢lling rates delay a¡erent activation, lower a¡erent ¢ring activity and even change the characteristics of some a¡erents completely. These data may elucidate some of the di¡erences between ambulatory and conventional urodynamics observed in man. Neu- rourol. Urodynam. 25:162 ^167, 2006. ß 2005 Wiley-Liss, Inc. Key words: a¡erent;cystometry;¢llingrate;nervoussystem INTRODUCTION Urodynamic tests are the mainstay in the diagnosis of sev- eral lower urinary tract (LUT) dysfunctions. They are widely used to reproduce patient’s symptoms while making precise measurements in order to identify the underlying cause for the symptoms, and to quantify the related pathophysiological processes [Schafer et al., 2002]. In man, normal diuresis is esti- mated at 1 ml/kg/hr and can increase to 15 ml/kg/hr after large £uid intake [Klevmark, 2002]. In conventional urody- namics the bladder is ¢lled at a rate usually between 30 and 100 ml/min, which is clearly higher than the maximal physio- logical diuresis. Despite the widespread use of conventional urodynamics, it is largely unknown how these unphysiological ¢lling rates in£uence lower urinary tract function during investigation. One study systematically compared sensory and motor func- tion in healthy volunteers using natural bladder ¢lling during ambulatory urodynamics, and arti¢cial bladder ¢lling at 50 and 100 ml/min during conventional urodynamics. Although signi¢cant di¡erences were found between physiological and supraphysiological ¢lling rates, the authors did not provide an explanation for their ¢ndings [Robertson et al., 1994]. In order to clarify possible neurophysiologic changes induced by high bladder ¢lling rates during urodynamics, we studied in a rat model the response of single unit bladder a¡erent nerve ¢bres to cystometrical bladder ¢lling at both physiological and supraphysiological ¢lling rates. MATERIALS AND METHODS Adult female Sprague^Dawley rats weighing 250^350 g were used for the experiments. The protocol was approved and performed in accordance with institutional ethics com- mittee guidelines for animal research. The animals were anesthetized with urethane (1.5 g/kg IP). The trachea was can- nulated and the animals were allowed to respire sponta- neously. Body temperature was maintained by heated support. The pelvic structures were exposed by a laterally incision at the left £ank.The ureters were ligated close to the bladder.The left pelvic nerve was identi¢ed proximal to the major pelvic ganglion and cleared from surrounding tissue. A pair of Te£on-coated silver electrodes, stripped at the tips, was placed around the pelvic nerve and sealed withWacker Silgel. *Correspondence to: Stefan DeWachter, Department of Urology,University Hospital Antwerp,Wilrijkstraat 10, 2650 Edegem, Belgium. E-mail: Stefan.dewachter@ua.ac.be Received 1 February 2005; Accepted 25 May 2005 Published online 21 December 2005 inWiley InterScience (www.interscience.wiley.com) DOI 10.1002/nau.20157 ß 2005Wiley-Liss,Inc.