Possible mechanism involved
Though the pathophysiology why compliance decrement occurs specifically at the late filling and the rationale how TVM ameliorates the impaired compliance are unclear, it worth notice that instead of a homogenous decrement in the entire filling stage, POP patients displayed decreased compliance at the late filling compared with the early stage, implying the compliance impairment is not resulted from a modified viscoelastic property of the bladder itself.
Moreover, considering pre- and post-operative C1/2 was statistically indistinctive; and both of them were above the level recognized as low bladder compliance, these results reveal the bladder of POP patients exhibits a relatively unaffected viscoelasticity property during the early filling stage before the surgical intervention. We thereby suggest, in POP patients, the compliance at low filling volume remains relatively unaffected because the bladder distension is not limited by the prolapsed organ at the initial stage. Nevertheless, as the filling volume increased, prolapsed organ restricts the normal expansion of the bladder that makes the bladder distends to un-restrained space in a manner failed to comply with its geometric conformation and/or anatomical location. An abnormal overstretch of part of the detrusor shifts the length-tension curve to a higher tension in response to elongation thereby results in a higher pressure to the filling volume26.
In the current study, patients received TVM to correct their anatomical abnormalities thereby relieved the restriction of bladder expansion caused by the prolapsed organ. As the restriction from the prolapse organ occurs mainly during the late filling, the benefit of TVM to the compliance is more significant in the late compared to the early filling. Though our proposal in part explains the involved pathophysiology of the heterogeneity of compliance in POP patients and the therapeutic rationale of TVM, a simultaneous compliance analysis in associated with real-time ultrasound images27 is need to validate this proposal.