The dynamic urethral sphincter function in healthy females assessed by rapid dilatations in the resting state: evaluation of reproducibility

Biomechanical properties of the anterior urethra of the male rabbitA study using impedance planimetry

OBJECTIVE

To evaluate the anterior urethra of the male rabbit regarding its luminal cross-sectional area (CSA), CSA distensibility, circumferential tension-strain relation, histology and the collagen content of the tissue. material and methods: Nineteen rabbits were examined with impedance planimetry by distending the urethra at the passage from the spongious to the bulbous part and 1 cm proximally in the bulbous part. Four weeks later, eight rabbits underwent a second examination. After the measurements the urethras were processed for either histology or determination of collagen content. The urethras from six additional rabbits served as controls for histology and collagen content.

RESULTS

The CSA and the CSA distensibility were smaller at the distal than the proximal distension site. At both sites the CSA distensibility was high at low luminal pressure loads and decreased with increasing pressure. The circumferential tension-strain plot displayed an exponential relation, with a steeper slope distally than proximally. Repeated biomechanical investigation revealed a significantly increased CSA and a decreased slope of the circumferential tension-strain relation at both distension sites. The biomechanical investigation induced abrasion of the epithelium, extravasation of erythrocytes and separation of the collagen fibres, suggesting oedema of the luminal part of the wall. After 4 weeks the epithelium had changed from transitional to stratified, squamous and often keratinized epithelium and the collagen beneath the epithelium formed a dense network instead of wavy lines as seen in the control urethras. The collagen content was larger at the distal than the proximal distension site. No change in collagen content could be demonstrated between the urethras investigated once or twice with impedance planimetry.

CONCLUSIONS

The non-linear pressure-CSA, pressure-CSA distensibility and circumferential tension-strain relations found at both distension sites demonstrate that the urethra yields readily at low pressures, thus facilitating flow. At higher pressure loads, the tissue becomes less distensible, a property that protects it against over-distension and damage. Impedance planimetry cannot be used to study before-and-after phenomena as the biomechanical investigation changed both the histology and the biomechanical properties of the rabbit urethra.

The urethral resistance to rapid dilation: an analysis of the effect of autonomic receptor stimulation and blockade and of pudendal nerve blockade in healthy females

The urethral closure function is based upon permanently as well as adjunctively acting closure forces during rest and stress episodes, respectively. During urine ingression intra- and peri-urethral structures are suddenly stretched resulting in a pressure response which strengthens the closure function by sustaining the resistance to dilatation of the urethra. A method for measurement of the resistance to rapid urethral dilatation was used to evaluate the influence of noradrenaline, prazosin, terbutaline, propranolol, carbachol, and atropine, as well as bilateral pudendal nerve blockades in 40 healthy women. The drugs caused no significant change in the urethral resistance to dilatation, whereas the pudendal blockade produced a significant (p < 0.05) reduction at the bladder neck and in the high pressure zone. Although a quantitative assessment of their contribution cannot be obtained from this study, it may be concluded that the striated muscles innervated by the pudendal nerve are of major importance for the urethral resistance to dilatation.

The effect of pharmacological stimulation and blockade of autonomic receptors and of pudendal blockade on urethral stress relaxation in healthy women

OBJECTIVE

To examine the influence of autonomic receptor stimulation and blockade (noradrenaline, prazosin, terbutaline, propranolol, carbachol and atropine), and of pudendal nerve blockade on urethral stress relaxation.

SUBJECTS AND METHODS

Forty healthy women were evaluated. The stress relaxation parameter was defined as the relative rate of pressure decrease during a fixed period of time following a rapid dilatation of the urethra. The dilatation was performed by water-infusion into a small rubber cylinder placed in the urethra.

RESULTS

The drugs did not affect stress relaxation significantly, whereas the pudendal blockade produced a significant change along the length of the urethra characterized by a faster pressure decay following dilatation.

CONCLUSION

In women, stress relaxation in the urethra relies significantly on the pudendal nerve-innervated striated muscles.