In accompanied by a cystometry, the current study analyzed workload of voiding using PVA because lasting overload on the bladder could lead to un-compensatory voiding dysfunctions [24]. Cystometry is well established and widely used in laboratory investigations [13] and clinical scenarios [14] to evaluate bladder physiology and identify deficits of bladder function. Nevertheless, when assessing thermodynamic processes/performance of the bladder, cystometry has hereditary limitations as it off-line analyzes voiding workload that needs waiting for processing after the laboratory investigation. Moreover, the thermodynamic work of a voiding cannot be comprehended immediately using cystometry, rather it needs adroit calculation by specialists. Particularly, because the duration of urine emission in a time-domain cystometry is a relatively short period in the whole voiding cycle that results in a miserable resolution in changes of the pressure and volume during emission, thereby requires careful data acquisition and analysis by experts in urodynamics.

Notably, results in this study demonstrated PVA provides continuous and graphic monitoring of voiding dynamics. In addition, the trajectory loop in PVA offers a conceptual illustration of voiding work that can be easily comprehended and calculated by scientists/physicians with minimal processing. Moreover, the trajectory of urine emission was about a quarter of a loop in the PVA, thereby it offers a satisfactory resolution in the pressure-volume relationship during emission that can be clearly visualized and analyzed with negligible training in data acquisition/analysis.

Nowadays, as the advancements in computer technology, to simultaneously display cystometry with PVA is no longer a challenge. Therefore, investigations comprise PVA and an ongoing cystometry would provide on-line, continuous, and clear assessment of voiding thermodynamics that can be immediately and easily acquired with minimal processing and calculation.

Because restoration of apical support is critical for the surgical reconstruction of symptomatic POP, a laparotomy abdominal sacrocolpopexy with mesh was first established [7]; and then laparoscopic sacrocolpopexy was described [29]. Though the laparoscopic procedure achieves comparable therapeutic outcomes to abdominal sacrocolpopexy but with diminished blood loss and shortened hospital stay [30], it entails surgeons with good laparoscopic skills and elevated surgeon’s ergonomic strain [30]. Remarkably, since the US Food and Drug Administration approved the robotic system in 2005 [6], robotic-assisted gynecological surgery has markedly shortened the learning curve [8] and reduced surgeon’s ergonomics [7] compared with the conventional laparoscopy. Therefore, RSCP has gained popularity for the POP repair [4].

Emerging publications support benefits of RSCP to POP patients by showing RSCP results in satisfactory structural restoration [10] and improves quality of life subjectively [9]. Because to objectively evaluate effects of RSCP on bladder functions is crucial for clinicians when making a therapeutic decision; and functional improvement is one of the goals of POP repair [9]; moreover, considering bladder function involves adequate urine storage and efficient disposal [12], and a previous study has demonstrated RSCP ameliorates storage dysfunction in POP patients [11], the current study investigated the potential impact of RSCP on the voiding function of patients with POP.

By specifically lying focus on the resistance and resistance-dependent voiding workload, results in the current study demonstrated RSCP diminished the voiding resistance; and we suggest this effect could be attributed to that RSCP relieved the kinking and/or compression of the bladder outlet by restoring the anatomical confines of prolapsed organs [26]. Furthermore, given the voiding resistance is defined by dividing the voiding pressure by voiding flow, we specified the impact of RSCP on voiding pressure and flow. Results in this study demonstrated that associated with the diminished voiding resistance, RSCP consistently and significantly decreased voiding pressure and increase flow rate of the voiding. Together with bivariate analyses revealed the RSCP-diminished resistance correlated with both the changes in voiding pressure and voiding flow, these findings collectively support that the RSCP-diminished voiding resistance brought about depressed voiding pressure associated with an enhanced flow rate during voiding. We thereby propose the RSCP-diminished voiding resistance on one hand reduced bladder pressure developed for driving flow thereby lessened the voiding work; and on the other hand, prompted urine emission hence increased voiding efficacy.

Our speculation is supported by lines of evidence. Firstly, analogously to the cystometry showing RSCP decreased voiding pressure without markedly affecting the voided volume, PVA demonstrated RSCP distinctly depressed the level of the top border (representing the voiding pressure) of the trajectory loop but negligibly affected the intercept between the right and the left borders (representing the voided volume) and the level of the bottom border (representing the baseline bladder pressure). Because the Apv is an integral of the pressure with respect to volume, these findings revealed the RSCP-decreased Apv was largely attributed to the decreased voiding pressure. This suggestion was supported by the finding that the RSCP-induced decrement in Apv was correlated with changes in voiding pressure. Given Apv is assumed to represent the thermodynamic work performed by the bladder in a voiding cycle [15,16,17], these results suggest the RSCP-diminished voiding resistance brought about decreased pressure developed for driving urine flow, and thereby lessened the voiding workload.

On the other hand, while the bladder post-operatively developed a decreased pressure, it drove urine flow with a higher emission rate that is evidenced by the cystometry showed the voiding flow was consistently and significantly increased after RSCP. Notably, though RSCP post-operatively displayed a trivial effect on the voided volume, it shortened the voiding time. Because the voiding flow is defined by dividing voided volume by voiding time; and the RSCP-induced flow increment correlated with the decrement in voiding time, these results not only support that RSCP post-operatively increased the emission rate but also reveal it enhanced voiding efficacy because bladder voided unmodified volume with a shortened time.

Together with above findings, these results collectively suggest RSCP diminished voiding resistance of the bladder that on one hand reduced the pressure gradient developed for driving urine flow that lessened the workload; and on the other hand, prompted urine emission that brings about an increased voiding efficacy.

Findings in this study have hereditary limitations in internal and external validity owing to a retrospective design. In addition, the patient number is not very large, thereby, the potential bias in the effects of measurement waits to be excluded using study with more patients. Moreover, post-operative effects were measured 107.31 ± 11.10 days after the RSCP in this study. Given benefits of a surgery need to be monitored for a long period, a lasting follow-up of therapeutic outcome is needed to confirm the advantage of RSCP to POP patients.