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.