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Anal manometry
Anal
manometry is distinct from defecography or EMG in that
it specifically measures the function of the anal sphincter, not
of the pelvic floor muscles. The resting anal pressure is a measure
of internal sphincter function, and the squeeze pressure is indicative
of the function of the external sphincter. The pressures exerted
by the sphincters can be measured by a water-filled balloon or
by a transducer-tipped catheter, with a variety of techniques
being used. However, unless the technique is carefully controlled,
it is not possible to compare the results of different studies
(Miller
et al., 1988). Anatomical sphincter abnormalities can be assessed
directly by anal endosonography, but the correlation of the findings
with function is not necessarily strong (Schafer
et al., 1997).
The
integrity of the distal colonic myenteric
nervous system can be demonstrated by
a reflex fall in resting pressure in
response to inflation of a balloon in
the rectum; this reflex is absent in
Hirschprung's Disease.
Rectal
compliance
Rectal
compliance is measured according to the volume to which
a rectal balloon can be inflated before either the patient detects
it or the desire to defecate is triggered. It is apparent that
some chronically constipated people have significantly impaired
rectal sensation (Bannister
et al., 1986) and that sensation may also decline with age,
putting the elderly at increased risk of fecal impaction (Read
et al., 1985).
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