To firstly establish the initial (before pressure equilibrium) and initial resting intravesical and abdominal pressure of air-charged catheter (ACC) system urodynamic study (UDS) testing, to assess the correlation between these pressures and obesity-related measurements, and to estimate if obesity-related measurements can be a guide to interpret initial and initial resting pressures in the UDS testing.

This study was conducted in our UDS center from August 2022 to October 2022. Local ethics committee approval was obtained, and written informed consent was obtained. Patients with non-neurogenic lower urinary tract symptoms (LUTS) referred for UDS were prospectively enrolled. Conventional pressure flow studies were carried out in the sitting position with a Laborie Triton equipment using the ACC system (Laborie & Co, Canada) following Good Urodynamic Practice (GUP) guidelines published by the International Continence Society (ICS) [1,2]. All patients were asked to empty the bladder before UDS. Intravesical dual lumen catheter (T-DOC 7FD, Laborie) and single lumen rectal catheter (T-DOC 7FA, Laborie) were used to measure intravesical pressure (Pves) and abdominal pressure (Pabd). Catheters were inserted in the open position and the connector then switched to the “charge” position after the transducer exposed to the surrounding atmospheric pressure were set to zero [1,2]. We recorded the initial Pves and Pabd at this moment. Then we clicked Pabd = Pves for pressure equilibrium. The initial resting Pves, Pabd, and calculated detrusor pressure (Pdet = Pves − Pabd) were recorded after confirming the ‘‘live’’ signal tracing (the same pressure transmission while coughing) before filling. After the UDS procedure, BMI, weight, fat, muscle, and visceral fat grade were recorded using Direct Segmental Multi-Frequency Bioelectrical Impedance Analysis Method (InbodyH20B) (patients were asked to wear light clothing). The abdominal sebum thickness and waistline were also recorded. The initial and initial resting pressures were also expressed as 50% range (equivalent to the interquartile range). The correlation between initial and initial resting pressures and obesity-related measurements, including abdominal sebum thickness, waistline, BMI, weight, height, fat, and visceral fat grade, was studied using Pearson correlation coefficient. Then we used multiple linear regression analysis for further investigation (weight, height, and fat were not considered because of the effect of multicollinearity). Data was processed with the SPSS 24.0 and statistical significance was defined as P < 0.05.

Ninety-eight patients aged 56±16 were studied. The 50% range of the initial Pves ranged between 27.0 - 34.0 cmH2O and Pabd ranged between 35.0 - 46.0 cmH2O. While the initial resting Pves, Pabd, and Pdet ranged between 24.0 - 33.0, 24.0 - 32.0, and -1.0 - 1.0 cmH2O, respectively, which falls closely in line with the previous similar type of study [3]. Analysis of Pearson correlation coefficient revealed a significant correlation between initial pressures and obesity-related measurements. Initial Pves was positively correlated with abdominal sebum thickness, waistline, BMI, visceral fat grade, weight, and fat, with no significant correlation with height. The initial Pabd showed high correlation with abdominal sebum thickness, waistline, BMI, visceral fat grade, weight, and fat, while there was no correlation with height and muscle. Related factors were included in the multiple linear regression analysis. The results of the multiple linear regression analysis indicating a significant correlation between initial Pves and abdominal sebum thickness and BMI (r=0.651, p=0.041 and p=0.004, respectively), but no correlation with waistline and visceral fat grade. The results of the multiple analysis also show only visceral fat grade maintained a significant correlation with initial Pabd (r=0.679, p=0.021) (shown in Figure 1). For the initial resting pressures, we only analyzed the correlation between initial resting Pves and obesity-related measurements, because the value of initial resting Pabd was close to the initial resting Pves after the pressure equilibrium procedure. The results of Pearson’s correlation coefficient indicated a significant correlation between initial resting Pves and abdominal sebum thickness, waistline, BMI, visceral fat grade, weight, muscle, and fat, with no significant correlation with height. Regardless of weight, height, and fat, only BMI maintained a significant correlation with initial resting Pves over the multiple analysis (r = 0.608, P=0.007) (shown in Figure 1).

Our results firstly revealed that the obesity-related indexes were positively correlated with the corresponding bladder and rectal pressures in the ACC system. In the UDS procedure, if the initial value of Pabd is lower than the estimated value based on the obesity index of the patient, it should be considering whether the insertion depth of the rectal catheter is not enough. If it is higher than the estimated range, it should be considering whether the bowel preparation is inadequate or whether there is abnormal rectal contraction (e.g., neurogenic rectum, intestinal hyperperistalsis, etc.), or whether the balloon tip reaches the rectal wall. After adjusting the possible problems according to the situation, ensure that the initial or initial resting Pabd and Pves values are within the normal range estimated based on the obesity index, a good initial and initial resting pressure quality control can be better obtained. A good quality urodynamic trace can only be obtained when the procedure is started under a good quality control.

Our original study firstly carried out the values of both initial and initial resting pressures in the ACC system UDS testing. Our single center results were in accordance with the literature and reflected a good baseline quality control [3]. Though currently there is still a lack of the estimating model, our study showed the obesity-related measurements might be used as a guide to interpret the initial and initial resting pressures in urodynamic testing, and might provide a reference for the quality control of these pressures.

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