POWER SPECTRAL DENSITY IN​HIGH RESOLUTION ANORECTAL MANOMETRY

A Newly Developed Metric, PSDrest Predicts the Presence of Defecatory Disorders and Highly Correlates with the Balloon Expulsion Test

​Tengku Ahmad Iskandar Tengku Alang1,2, Lee Yeong Yeh1,2, Khairil Khuzaini Zulkifli3, Mung Seong Wong1,2, Nor Aslina Abd Samat1,2, Siti Norhasliza Muhamad1,2, Azliani Abd Aziz1,2, 

1 School of Medical Sciences, Universiti Sains Malaysia, Kota Bharu, Kelantan, Malaysia.
2 Hospital Universiti Sains Malaysia, Health Campus, Universiti Sains Malaysia, Kota Bharu, Malaysia.
3 Gastrenterology Unit, Faculty of Medicine, Universiti Teknologi MARA, Sungai Buloh, Selangor, Malaysia

Background: In defecatory disorder, there is poor correlation between conventional manometry parameters and balloon expulsion test (BET) and therefore new metric is needed. We aimed to develop a new metric from resting anal pressure based on the Fourier transform tool, to validate the new metric and to correlate the metric with BET. 
 
Methods: Consecutive healthy participants and patients with defecatory disorders (Rome IV) were recruited after informed consent. All underwent high resolution 6-channel solid state anorectal manometry (Laborie, Mississauga, Canada) and BET. Resting pressure profiles were converted into ASCII files and analyzed using MATLAB program (VR2010b, The MathWorks, Natick, USA). A new metric, Power Spectral Densityrest (PSDrest, unit V/√Hz) was developed using the Fourier transform tool. The ideal cut-off level of PSDrest was determined using ROC analysis, and its correlations with defecation index (DI) and BET were analyzed using Pearson correlation analysis, with P<0.05 as significant.
 
Results: 8 normal (mean age 22.8 years) and 16 constipated (mean age 51 years) females were analyzed. Of 16 constipated females, 8 had normal BET (< 1 min) and 8 with abnormal BET (≥ 5 min). Those with constipation vs. normal reported lower PSDrest (mean 0.58 vs. 0.88, P=0.05). Based on the ROC analysis, PSDrest cut-off value < 0.5 V/√Hz can accurately differentiate constipation from normal with an area under the curve (AUC) of 0.97 (95% CI 0.89-1.05, P=0.04), sensitivity 100%, specificity 88%, positive predictive value 89% and negative predictive value 100%. Among constipated individuals, PSDrest was correlated with BET (R=0.81, P<0.001) but not DI (P=0.14). No correlation was seen between BET and DI (P=0.3).
 
Conclusion: A PSDrest value < 0.5 V/√Hz predicts the presence of defecatory disorder and is highly correlated with abnormal BET. Further validation study in larger cohort is required.