Changes in urethral resistance in the presence of detrusor activity.

This was a prospective study performed at two tertiary referral teaching hospitals. The aim of our study was to investigate changes in urethral resistance with the bladder full compared to empty in women with different urodynamic diagnoses. Consecutive women attending the urodynamic clinics were asked to undergo urethral retro-resistance pressure (URP) measurement with the bladder empty and then full. 106 women were recruited - 25 had normal urodynamic studies, 17 had detrusor overactivity, 57 had urodynamic stress incontinence and 7 had mixed incontinence. Women with urodynamic stress incontinence have lower URP values than women with normal urodynamic studies or those with detrusor overactivity with the bladder empty (p = 0.01). Women with normal urodynamic studies and urodynamic stress incontinence showed a statistically significant rise in URP with the bladder full (p = 0.013 and p = 0.003, respectively). In women with detrusor overactivity, the converse was seen - URP was significantly lower with the bladder full compared to empty (p = 0.004). Our study has shown that bladder filling alters URP measurement and bladder volume should be standardised for reporting URP.