Study on the relation of the shape of the uroflowmetrogram and the urethral loss coefficient calculated from the uroflowmetrogram.

The shape of the uroflowmetrogram reflects voiding conditions. Using a voiding simulation, we examined whether the urethral loss coefficient (LC) calculated from the approximated uroflowmetrogram correlates with parameters that regulate the shape of the uroflowmetrogram. A total of 161 normal and abnormal uroflowmetrograms were used. Normal female subjects and patients before and after transurethral resection of the prostate (TURP) were also studied. The ratio of maximum flow rate (Q(max)) to flow time (T), a parameter expressing the shape of the uroflowmetrogram, was calculated. The uroflowmetrograms were approximated using a voiding model, and the urethral LC was calculated. As a result, a strong negative correlation was observed between the Q(max)-flow time ratio, Q(max)/ T, and LC. Q(max)/T is the vertical to horizontal ratio of the uroflowmetrogram and indicates the average degree of acceleration of flow rate during voiding. On the other hand, urethral LC, which can be estimated from the shape of the uroflowmetrogram, is considered a kind of urethral resistance. We concluded that when urethral resistance is high, the degree of acceleration of flow rate is low on average. Our study also indicated that Qmax/T was less affected by voided volume (VV) compared to Q(max). As Q(max)/T is not as dependent on VV, it is useful for comparing cases with different VV.