Straining urethral reflex: description of a reflex and its clinical significance. Preliminary report.

The present communication describes a reflex, which I call 'straining urethral reflex', and discusses its clinical significance. The study was performed on 17 healthy volunteers with a mean age of 39.6 years. The intrarectal pressure (representative of the intra-abdominal pressure) was measured by means of a balloon-tipped catheter introduced into the rectum and connected to a pressure transducer. A concentric needle electrode was introduced into the external urethral sphincter. The subject was asked to strain, and the urethral sphincter electromyographic activity and the intrarectal pressure were recorded. Two types of straining were investigated: sudden and slow. The procedure was repeated in 10 subjects after urethral sphincter infiltration with xylocaine or saline. On sudden straining, the external urethral sphincter contracted. The anesthetized sphincter did not respond, while the saline-infiltrated sphincter responded to sudden straining. Slow sustained straining did not evoke the reflex response. The latency of the reflex was calculated. The external urethral sphincter contraction on sudden straining guards against the involuntary opening of the vesical neck and urinary leak under stress conditions of a sudden increase in the intra-abdominal pressure. The reflex may prove significant in the diagnosis of micturition control disorders. It can thus be included as an investigative tool in urologic practice.