Glemain P, Cordonnier J P, Le Normand L, Karam G, Buzelin J M
Clinique Urologique, Centre Hospitalier Universitaire, Nantes.
Prog Urol. 1993 Aug-Sep;3(4):644-57.
The urethra is a collapsed tube in the absence of micturition. Consequently, the evaluation of instantaneous urethral resistance by the pressure/flow relation (R = P/Q2) derived from Bernoulli's equation has been criticised for not taking into account the opening pressure or at least the fact that flow must maintain patency of the urethra during voiding. The objective of this study was to determine whether such a criticism is justified in terms of fluid mechanics. A study of the pressure/flow relation was performed in a soft tube, collapsed by various peritubular pressures, which subsequently opened in response to flow. Experiments demonstrated that the pressure/flow relation, the instantaneous resistance to flow and the pressure drop were identical when the tube reached the same calibre, despite different peritubular pressures. The same pressure therefore propels the flow and maintains the patency of the tube. Consequently, it would be unreasonable to expect to improve the evaluation of instantaneous urethral resistance by subtracting an opening pressure from the maximal bladder pressure. The formula R = P/Q2 is valid, experimentally, and complies with the principles of fluid mechanics. In theory and in practice, it constitutes a good method of evaluation of instantaneous resistance.
在无排尿时，尿道是一根塌陷的管道。因此，根据伯努利方程推导的压力/流量关系（R = P/Q²）来评估瞬时尿道阻力受到了批评，因为它没有考虑开口压力，或者至少没有考虑到排尿时流量必须维持尿道通畅这一事实。本研究的目的是从流体力学角度确定这种批评是否合理。在一根软质管道中进行了压力/流量关系的研究，该管道在不同的管周压力作用下塌陷，随后因流量而张开。实验表明，尽管管周压力不同，但当管道达到相同管径时，压力/流量关系、瞬时流动阻力和压力降是相同的。因此，相同的压力推动流量并维持管道的通畅。所以，期望通过从最大膀胱压力中减去开口压力来改进瞬时尿道阻力的评估是不合理的。公式R = P/Q²在实验上是有效的，并且符合流体力学原理。在理论和实践中，它构成了一种评估瞬时阻力的良好方法。
