The after-contraction: a true detrusor contraction or a late dyssynergic urethral sphincter contraction?

Objective To evaluate the mechanism and significance of the after-contracti on, recorded in bladder pressure by urodynamics, at the end of micturition. Patients and methods The urodynamic recordings showing an after-contraction of the detrusor in 65 patients of all ages and with a variety of pathologi es were reexamined. Special attention was directed to the anal or urethral sphincter needle electromyographic activity and to the monitored urethral p ressure, to determine any relationships with the patterns of detrusor press ure. Results An after-contraction was noted in 61 patients with detrusor instabi lity and in 11 with urethral instability. In 59 patients it was evident tha t the aftercontraction, i.e. a renewed increase in detrusor pressure during the declining contraction, correlated with a sphincter contraction precedi ng it by a fraction of a second. Similar increases in detrusor pressure wer e apparent: in patients with detrusor-sphincter dyssynergia throughout void ing. In six patients the relationship was less clear mainly because there w ere artefacts in the curves. Conclusion The after-contraction arises by a sudden stopping of the outflow of urine, provoked by a sphincter contraction. This may occur by involunta ry dyssynergia or by an early voluntary interruption of the voiding stream. The 'milk back' of urine from the proximal urethra to the bladder and the inhibited detrusor contraction (if the perineal contraction is prolonged) m ay cause some postvoid residual urine. It occurs mainly in the presence of detrusor and/or urethral instability.