Table 4.

Interpretation of the manometric data

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].