Aims of study
Whole animal and in vitro experiments with detrusor muscle have shown contractility to be dependent on changes in osmolality, pH (intracellular and extracellular), and potassium concentration of bladder infusate and muscle superfusate [1,2,3]. All these are relevant to physiological and pathophysiological situations in vivo which could lead to misinterpretation of urodynamic testing. We have studied the effect of variations in filling media on interpretation of the cystometrogram

Methods
88 women, (22-82 yrs) who were being investigated for lower urinary tract symptoms were consented to a repeat fill procedure (2 or 3 fills). The filling phase of standard urodynamics was performed then repeated immediately following drainage. Filling solutions were at 37 C and are listed: (1) NaCl 252 mM, NaHCO3 24 mM; (2) NaCl 46 mM, NaHCO3 96 mM, gas 5%CO2/ 95% O2 (mean infusate pH 8.3); (3) and (4) NaCl 118mM, NaHCO3 24 mM, with gas 5%CO2 / 95% O2 (mean infusate pH 7.6) and 20%CO2 / 80% O2 (mean infusate pH 7.1) respectively; (5) NaCl 76mM, NaHCO3 24mM, KCl 54 mM. Filling solutions and controls of normal saline (mean pH 5.5) were used in random order. The effect of order was analysed.

Results
There were no significant effects of filling solution composition on bladder capacity Intervention Median difference in bladder capacity

Similarly no significant differences were seen in other cystometric variables - volumes at first sensation of filling and first desire to void. Order of fill had no effect - the median differences between bladder capacities in first and second fills was 2 mls (interquartile range -13-61 mls)

Conclusions
The biochemical changes in bladder contents did not affect the microenvironment of detrusor muscle enough to produce changes to the urodynamic variables studied. References [1] J.Physiol. 432:1-21 (1991) [2] J.Urol. 154:1921-1924 (1995) [3] Eur.Urol. 11:127-130 (1985)