Variation in urinary flow according to voiding position in normal males

Our objective was to study whether the urinary flow rate would vary according to voiding position. Twenty-one normal healthy male volunteers aged 24 to 40 years (mean, 29 years) were studied. The bed used was designed so that a hole could be opened at its center for voiding, and the bed could be bent at two points so that the subject could void in various positions. Urinary flow was measured with a portable uroflowmeter (P-Flow), which permits measuring urinary flow rate. Each subject assumed five voiding positions (standing, sitting, lateral, supine, and prone) in random order. Urinary flow was measured at least twice in each position to record a stable voiding. For voiding in the lateral position, subjects were instructed to void while bending the upper leg to keep an open angle between the legs. All subjects were also instructed to void without increasing abdominal pressure. Maximum flow rate was 20.7 +/- 6.59 mL/sec with voided volume of 262 +/- 77.8 mL in the lateral, 22.1 +/- 7.05 mLl/sec with voided volume of 309 +/- 130 mL in the supine, 25.0 +/- 8.25 mL/sec with voided volume of 287 +/- 122 mL in sitting, 27.1 +/- 8.89 mL/sec with voided volume of 263 +/- 102 mL in the standing, and 28.7 +/- 10.6 mL/sec with voided volume of 303 +/- 98 mL (mean +/- SD) in the prone positions. The maximum and mean urinary flow rates were greatest in the prone position. With regard to these parameters, significant differences were noted between the prone and lateral positions and between the prone and supine positions. In conclusions, the maximum urinary flow rate was highest in the prone position, followed by the standing, sitting, supine, and finally the lateral positions in normal males. Neurourol. Urodynam. 18:553-557, 1999.