Viscoelastic properties of urinary bladder : a new method, rapid injection cystometry, for evaluation of physical properties of detrusor muscle, and biochemical analysis of collagen content
The stress relaxation phenomenon is a characteristic of viscoelastic properties involved in the urinary bladder. The analysis of this specifie characteristic has been attempted with Rapid Injection Cystometry (RICM), the practical modification of conventional intermittent cystometry. Rapid injection of saline solution into the bladder and the qualitative and quantitative analysis of the relaxation curve are the principles of the present technique. Furthermore, the collagen content in normal and pathological dog bladders vas determined through hydroxyproline analysis in order to confirm the results observed with RICM. A mechanical model was developed based upon the analysis of the stress relaxation curve of the in vivo dog bladder and was tentatively composed of three Maxwell elements and one Hooke element arranged in parallel. This relaxation curve could then be analyzed into three exponential components. Subsequently, four elastic constants, three time constants, and three viscous coefficients were calculated by mathematical treatment in 15 normal in vivo and 10 normal in vitro dog bladders. The animal studies in vivo and in vitro consisted of 25 normal dogs, six neurectomized, five with a eclerosing agent, and six with bladder neck obstruction. The clinical studies were performed with a random selection of 35 patients in vivo. Characteristic shapes of the stress relaxation curve of both animal and human bladders were discussed, where response of the muscle contraction to a quick stretch was observed. Modification of elasticity and viscosity was investigated in animal and clinical studies, presenting normal and pathological bladder conditions. The pathological bladder presenting fibrotic degeneration was characterized by augmented elasticity and increased viscosity of the bladder. In other words, this increased elasticity and viscosity was shown by the augmented elastic constants of E1+2+3 and E4, their steep increasing tendency with repeated injection, frequent appearance of muscle contraction of Type B and G, and prolonged half decay time. Collagen content was determined by biochemical analysis in animal specimens, which consisted of 20 normal dog bladders, eight neurectomized, five with sclerosing agent, seven with bladder neck obstruction, 11 rabbit bladders, and 10 dog ureters. Increased proportion of collagen content was consistent with bladders presenting pathological conditions and also significantly coincided with the enhanced ratio of bladder weight to body weight. Consequently, it was found that the pathological condition presenting neurogenic dysfunction, sclerotic degeneration, overdistension, and so forth had changed the viscoelastic properties of bladder elicited by the increased proportion of collagen. The present method, RICM, is promising to evaluate bladder function, a new diagnostic tool.