The importance of pressure-flow studies for the diagnostic work-up of patients suffering from benign prostatic hyperplasia (BPH) has recently been recognized more widely. For these studies, several different types and sizes of catheters have been used. According to our experience, the degree of obstruction seems to be dependent on the catheter size applied.
To evaluate the impact of catheter size on urodynamic results, 64 male patients underwent pressure-flow studies; 41 had the clinical diagnosis BPH; 23 were a nonobstructed control group. The 41 BPH-patients were randomized into two groups: group BPH 1 (n= 20) had a 5F catheter and group BPH 2 (n=21) had a 1OF filling catheter in addition to the 5F pressure transmission catheter in the urethra. All patients underwent three filling and pressure-flow studies. The filling catheter was removed for the third pressure-flow study. Peak flow rates (Qmax; ml/s), the corresponding detrusor pressure at maximum uroflow (pdetQmax; cm H20) and the degree of obstruction, rated according to the linear passive urethral resistance relation (linear-PURR), were assessed. The removal of the 5F (group BPH 1) or 10F (group BPH 2) filling catheter resulted in a 21.1% and 55.7% increase of maximum uroflow rate respectively. In parallel, we observed a 9.9% and 18.8% decrease of detrusor pressure at maximum flow. The degree of obstruction classified according to linear-PURR decreased by 14.6% and 21.1% respectively. Furthermore, it became evident that five patients (21.7%) of the unobstructed control group could have been wrongly interpreted as being obstructed if measured with the filling (10F) and the pressure measurement (5F) catheter in situ. In conclusion, the degree of obstruction is dependent on the cross-sectional diameter of the used catheters. Consequently, standardization with regard to catheter size is mandatory if data from different institutions are to be compared.