Development and Validation of the new metric, PSDrest, in Predicting Balloon Expulsion Time in Defecatory Disorders

Abstract Background/Aims: In defecatory disorders, the correlation between routine manometry readings, the balloon expulsion test (BET), and the defecation index (DI) is weak. In a retrospective cohort, the newly established measure (PSDrest) was found to have a good connection with BET. The purpose of the present investigation was to develop and validate the novel PSDrest measure with BET and DI in defecatory disorders. Methods: Using consecutive sampling, consenting healthy participants and patients with defecatory disorders were recruited prospectively. All of the participants received high resolution 12-channel solid state anorectal manometry (Laborie, Mississauga, Canada) and BET. Resting pressure profiles were converted to ASCII files and investigated using MATLAB (R2017a, The MathWorks, Natick, USA). Using the Fourier transform, a new metric, Power Spectral Densityrest (PSDrest, unit V/Hz), was devised. Using ROC analysis, the optimal cut-off level of PSDrest was found, and its relationships with the defecation index (DI) and BET were investigated using Pearson correlation, with P<0.05 indicating significance. Results: 123 retrospective data and 32 prospective subjects involving 16 normal and 138 patients with costipation were analyzed. Of 32 individuals, 8 had normal BET (< 1 min) and 24 with abnormal BET (> 1 min). Those with constipation vs. normal reported lower PSDrest (mean 0.80 vs. 1.04). Based on the ROC analysis of the retrospective data, PSDrest cut-off value > 0.93 V/√Hzm showed optimized validation parameters of specificity, sensitivity, positive predictive value, and negative predictive value of 71.43%, 46.67%, 60.87%, and 58.44%, respectively. During validation of the ROC analysis utilising prospective data, the results indicated that the selected PSDrest cutpoint could differentiate constipation from normal with, on average, an area under the curve (AUC) of 0.703 (95% CI 0.47-0.93, P=0.10), specificity of 93.75 %, sensitivity of 43.75 %, positive predictive value of 62.50 %, and a negative predictive value 87.5 %. Among constipated individuals, PSDrest was correlated with BET (P=0.443, p<0.005). Weak correlations observed between PSDrest and DI (P= 0.1601) and between BET and DI (P = 0.2774). Conclusion: A PSDrest value > 0.93 V/√Hz is predictive of defecatory dysfunction and is associated with abnormal BET.