3.2 Pressure-flow/volume analyses
In the cystometry, saline infusion into the pre-emptied bladder of patients provoked a voiding (Figure 2A). The pressure-volume analysis (PVA), which was established by plotting the detrusor pressure (Pdet) against the intra-vesical volume (Vive), demonstrated the trajectory of pressure-volume data moved counterclockwise and shaped an enclosed loop representing a voiding cycle (Figure 2B). Four phases were identified in the loop, namely (1) Filling (F; from the infusion began to the voiding contraction onset): an increasing Vive in accompanied by a slightly but progressively elevated baseline Pdet. (2) Iso-volumic contraction (IVC; from the voiding contraction onset to the emission began): the bladder contracted without fluid expulsion that resulted in an abruptly elevated Pdet with a nearly constant Vive. (3) Emission (E; from the beginning to the end of fluid emission): a plateau Pdet that slightly elevated at the end of this stage with a marked Vive decrease. (4) Iso-volumic relaxation (IVR; from the end of emission to the end of bladder relaxation): the bladder relaxed without fluid expulsion that resulted in a marked Pdet decline with an almost constant Vive.