The relationship among flow index, uroflowmetry curve shape, and EMG lag time in children.

PURPOSE: To determine the relationship among flow index (FI), uroflowmetry curve shape, and electromyography (EMG) lag time in children. MATERIALS AND METHODS: A total of 294 children with lower urinary tract symptoms were included. The overall relationship between lag time and FI was investigated with curve estimation regression. Normal and primary bladder neck dysfunction was defined according to the previous classification, while patients with a lag time less than 2 seconds were grouped based on 2-second intervals. We also categorized cases into four groups (tower shaped, bell shaped, plateau shaped, and fractionated void) by FI and compared lag time. RESULTS: The overall distribution chart demonstrated that FI was the highest at lag time 0 second and decreased with the change in lag time both ways. The best fitting model for maximum FI and lag time was a cubic model (R2 = .282; P < .001). Children with lag times from 0 to less than 2 seconds showed the highest mean FI, while those with prolonged (>6 seconds) or delayed lag time (<-4 seconds) demonstrated lower mean FI values. EMG lag time of the tower-shaped curve was significantly close to 0 second, and plateau shaped and fractionated void had either prolonged or delayed. CONCLUSIONS: A lag time close to 0 second was associated with higher FI, representing hyperefficient voiding with a tower-shaped flow pattern. However, children with prolonged or delayed lag time showed a lower FI, implicating hypoefficient voiding and a plateau-shaped flow pattern. The relationship between FI and EMG lag time could be a cornerstone for a comprehensive understanding of voiding status.