Few studies have examined the effects of body position on urination efficiency morphologically. We aimed to dissect out the anatomical changes of pelvic organs during urination in the upright and supine positions by a real-time magnetic resonance imaging (rtMRI) system.

Thirteen healthy male volunteers aged 26-60 years were included in the study. The sagittal real-time 2D images were taken to evaluate urinary efficiency, along with change in five morphological indices at the time of storage and the beginning of voiding, in both upright ant supine positions.

Urination was more efficient in upright position than in supine position, as expressed by higher average rate of bladder emptying (9.9±4.2 vs. 6.8±2.9ml/sec, p<0.05), and also by fewer participants showing significant residual urine (1/13 vs. 7/13, p<0.05). At the onset of voiding in standing position, the levator ani muscle moves downward and backward followed by descent of the bladder neck and rotation of the prostate around the symphysis. Such changes were expressed by two morphological indices. One was posterior vesicourethral angle at the start of voiding, 152±7 vs. 140±1 in upright and supine position (p<0.05). The other index was the change in angle between levator ani line and pubo-coccygeal line in upright and supine position, 9.4±9.9 vs 1.6±7.9 before voiding (p<0.05), and 30.2±14.0 vs 17.3±12.9 after the start of voiding (p<0.05).

This is, to our knowledge, the first report to capture the anatomical changes of pelvic organs during urination in the upright position. In addition, we introduced a novel parameter to quantify the dynamic relaxation of the levator ani as the angle LA/PC, which seemed to be a key movement related to efficient urination.

Continence 2S2 (2022) 100402
DOI: 10.1016/j.cont.2022.100402