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Anorectal Manometry and the Balloon Expulsion Test: An Instrument Guide

UROGYNECOLOGY Anorectal Manometry and the Balloon Expulsion Test: An Instrument Guide CincyMed Clinical Resource  ·  4 min read Anorectal manometry instruments form the diagnostic backbone of the GI motility laboratory, enabling precise measurement of anorectal sphincter pressures, rectal compliance, and the neuromuscular coordination required for normal defecation. When combined with the balloon expulsion test (BET), anorectal manometry provides the functional data that guides diagnosis and management of fecal incontinence, constipation, and defecatory disorders. This guide covers the instruments used in both tests and helps clinicians choose the right catheter system for their motility lab. What Anorectal Manometry Measures Anorectal manometry measures pressure profiles along the anal canal and rectum using a pressure-sensing catheter inserted transanally. Key measurements include: Resting anal sphincter pressure — reflects internal anal sphincter (IAS) tone; reduced in passive fecal incontinence Squeeze pressure — reflects external anal sphincter (EAS) voluntary contraction; reduced in urgency incontinence Rectoanal inhibitory reflex (RAIR) — transient IAS relaxation on rectal balloon inflation; absent in Hirschsprung disease Rectal sensation thresholds — first sensation, urge, and maximum tolerable volume; elevated in constipation syndromes Rectal compliance — distensibility of the rectal wall; reduced in radiation proctitis and IBD Defecatory dynamics — pusher vs. non-relaxer pattern; diagnostic for dyssynergic defecation Anorectal Manometry Catheter Types Manometry catheters are the primary instrument variable in anorectal testing. The three catheter categories in common clinical use differ by sensing mechanism, single vs. dual balloon configuration, and reusability. Catheter Type Configuration Sensing Method Reusable / Disposable Primary Application SR1B (Single Rectal Balloon) Multi-channel pressure sensors + 1 rectal balloon Air-charged solid-state or water-perfused Reusable Standard anorectal manometry; RAIR testing; rectal compliance SR2B (Single Rectal, 2-Balloon) Multi-channel pressure sensors + separate rectal and anal balloons Air-charged Reusable Advanced manometry; combined BET; rectal sensation profiling CR1B (Combined Rectal/Balloon) Integrated rectal balloon + pressure sensors in single device Air-charged Disposable (single-use) High-resolution manometry; single-use infection control protocols; outreach labs Water-perfused multi-channel 8–16 radially oriented water perfusion ports Water-perfused; requires external pneumohydraulic pump Reusable with sterilization Traditional HRM; established reference database compatibility High-resolution solid-state (HRM) 36+ closely spaced solid-state sensors Solid-state pressure transducers Reusable; require HLD between patients HRM anorectal topography; research; tertiary motility centers The Balloon Expulsion Test (BET) The balloon expulsion test is the single most useful screening tool for dyssynergic defecation — a condition in which patients paradoxically contract the puborectalis and EAS during attempted defecation rather than relaxing them. The test is performed by inserting a water- or air-filled balloon (50 mL) into the rectum and asking the patient to expel it within a defined time limit (typically 1–2 minutes) in a private bathroom setting. Normal expulsion time is less than 60 seconds for most patients; failure to expel in 2 minutes has a sensitivity of approximately 85% and specificity of 87% for dyssynergic defecation when used in conjunction with anorectal manometry findings. The BET balloon catheter is typically a thin, pliable latex or silicone balloon mounted on a rigid or semi-rigid catheter shaft; balloon capacity and compliance must be standardized across your lab to ensure reproducible results. Instrument Setup for a Complete Anorectal Testing Protocol A complete anorectal manometry and BET testing protocol requires: a motility workstation with dedicated anorectal manometry software, an air-infusion system or pneumohydraulic pump (depending on catheter type), the manometry catheter, BET balloon kit, rectal balloons in standard 50 mL capacity, and calibration standards. Position the patient in the left lateral decubitus position with knees flexed to 90° for reproducible pressure profiles. Browse CincyMed's complete range of anorectal manometry and balloon expulsion test instruments and our GI motility instrument page for full product details. Clinical Applications and Referral Criteria Anorectal manometry is indicated in the workup of fecal incontinence, chronic constipation (particularly when biofeedback therapy is being considered), evacuation disorders, and pre-surgical assessment before sphincter repair. The combination of anorectal manometry and BET provides the physiological substrate for biofeedback program design. The American Neurogastroenterology and Motility Society (ANMS) consensus position documents define clinical indications and technical standards for anorectal manometry that should guide motility lab protocol development. Conclusion Anorectal manometry and balloon expulsion testing provide complementary data on anorectal sphincter function, rectal compliance, and defecatory mechanics. Catheter selection — air-charged reusable vs. disposable single-use designs — should be based on lab volume, infection control protocols, and reference database compatibility. A well-equipped anorectal testing program with standardized instruments and interpretation protocols is the foundation of evidence-based pelvic floor disorder management. Need instruments for this procedure? CincyMed supplies surgical and endoscopy instruments for hospitals and ASCs. Browse Our Catalog