Urethral instability: related to stress and/or urge incontinence?

Urethral instability (pressure variations of more than 15 cm. water during bladder filling) was noted in 12 of 34 women with bladder instability and 13 of 139 with a stable bladder. Of the patients 10 had urge, 5 mixed and 8 genuine stress incontinence, while 1 had enuresis and 1 had recurrent cystitis. A clear correlation between urethral pressure variations and electromyographic fluctuations in the anal and/or urethral sphincter was found in 14 of 17 patients. Only urethral pressure variations of more than 35 cm. water are reported as provoking urgency. Different types of pressure fluctuations are described but no fundamental differences or causative factors were found. A nervous rather than a vascular factor is designated as the main cause for urethral instability.