Table 4.
Test | Parameter evaluated | Interpretation |
Resting pressure | IAS (70% of resting pressure) and EAS (30% of resting pressure) | P increased: Hypertonic sphincters (IAS and/or EAS). Oral nitroglycerin can identify the sphincter involved because it relaxes IAS, but not EAS |
Squeeze pressure | EAS | The fatigue rate index can be calculated based on the pressure and duration of the contraction. However, the usefulness of the test in both constipated and incontinent patients is disputed[112,113] |
Rectoanal inhibitory reflex | IAS relaxation during rectal inflation | Absent: Possible hirschsprung; If present with elevated volume inflation: Megarectum[57] |
Rectal sensitivity | Rectal sensory function at different volumes | Elevated sensory thresholds may be linked to changes in rectal biomechanics (megarectum) or to afferent pathway dysfunction[114,115] |
Rectal compliance | Mechanical rectal function | Increased compliance: megarectum[57] |
Attempted defecation | Synchronisation between the increase in rectal pressure and the decrease in anal pressure during attempts to defecate | Three types of dysfunction may be detected[65]: Type 1: Adequate rectal P increase but associated with anal P increase; Type 2: Inadequate rectal P increase associated with anal P increase or inadequate anal P decrease; Type 3: Adequate rectal P increase but inadequate anal P decrease |
IAS: Internal anal sphincter; EAS: External anal sphincter; P: Pressure. Modified from Azpiroz et al[57].