Submitted on October 12, 2005
Accepted on January 23, 2006
Comparison of Rectoanal Axial Forces in Health and Functional Defecatory Disorders
Adil E. Bharucha1*, Andrew J. Croak2, John B. Gebhart2, Lawrence J. Berglund3, Barbara M. Seide1, Alan R. Zinsmeister4, and Kai-Nan An3
1 Clinical Enteric Neuroscience Translational and Epidemiological Research Program (C.E.N.T.E.R.), Division of Gastroenterology and Hepatology, Department of Medicine, Mayo Clinic College of Medicine, Rochester, MN, USA
2 Division of Gynecologic Surgery, Mayo Clinic College of Medicine, Rochester, MN, USA
3 Orthopedics Biomechanics Laboratory, Mayo Clinic College of Medicine, Rochester, MN, USA
4 Division of Biostatistics, Mayo Clinic College of Medicine, Rochester, MN, USA
* To whom correspondence should be addressed. E-mail: bharucha.adil{at}mayo.edu.
Anal manometry measures circumferential pressures, but not axial forces, which are responsible for defecation and contribute to fecal continence. Our aims were to investigate these mechanisms by measuring axial rectoanal forces with an intra-rectal sphere or a latex balloon, fixed at 8, 6, or 4 cm from the anal verge, and connected to axial force and displacement transducers. Rectoanal forces and rectal pressures within a latex balloon were measured at baseline (i.e., at rest) and during maneuvers (i.e., squeeze, simulated evacuation, and a Valsalva maneuver) in 12 asymptomatic women and 12 women with symptoms of difficult defecation. Anal resting and squeeze pressures were also assessed by manometry and were similar in controls and patients. At rest, axial rectoanal forces were directed inward and increased as the device approached the anal verge. Controls augmented this inward force when they squeezed and exerted an outward force during simulated expulsion and a Valsalva maneuver. The force change during maneuvers was also affected by device location and was highest at 4 cm from the verge. In patients, the force at rest and the change in force during all maneuvers was lower than in controls. The rectal pressure during a Valsalva maneuver was also lower in patients than in controls, suggestive of impaired propulsion. In conclusion, a subset of women with defecatory symptoms had weaker axial forces not only during expulsion but also during a Valsalva maneuver and when they squeezed (i.e., contracted) their pelvic floor muscles, suggestive of generalized pelvic floor weakness.
