[Thesis]. Manchester, UK: The University of Manchester; 2018.
Anal Acoustic Reflectometry (AAR) is a technique for assessing the physiology of the
anal canal. It involves placing an ultra-thin polyurethane bag in the anal canal,
into which sound waves are transmitted and reflected back to a recording device. At
the same time, a pressure pump inflates and deflates the bag with air to simulate
anal canal opening and closing. Using the reflected sound waves, cross-sectional area
is measured as pressure changes, generating a profile of the opening and closing characteristics
of the anal canal at rest and during voluntary squeeze. A particular advantage of
AAR is that unlike catheter techniques, there is negligible distortion of the anal
canal. The noise of the pressure pump, however, interferes with sound recording and
therefore has to be used in a time consuming, stepwise manner which prevents the measurement
of rectal reflexes. The aim of this thesis was to compare a new faster technique of
performing AAR with the existing stepwise technique, to determine if it can be used
to measure the recto-anal inhibitory reflex (RAIR), and to identify a possible relationship
of AAR parameters with severity of rectal prolapse.
A prospective analysis of 32 patients found that the first of ten cycles of fast-fill
AAR performed at rest were significantly higher than the subsequent cycles, a finding
not replicated in squeeze parameters. Therefore the mean of nine cycles were used
in the subsequent studies.
A comparative analysis of 32 patients undergoing both the stepwise and fast-fill techniques
found a small difference in Opening Pressure between the two techniques with superior
repeatability between cycles of fast-fill. Opening and Closing Elastance are significantly
higher and represent an increased resistance to opening and closing at an increased
rate of stretch. There was no difference in Squeeze Opening Pressure; however fast-fill
correlates more strongly with symptom severity. The fast-fill technique is a valid
method, but cannot be directly compared with stepwise.
The measurement of rectal reflexes requires a rectal balloon catheter to be placed
alongside the AAR catheter. In a prospective study of 35 patients with pelvic floor
dysfunction, the placement of this catheter was found to have no effect on measured
AAR parameters allowing the measurement of rectal reflexes to be explored in future
Inflation of a balloon in the rectum triggers the Recto-anal Inhibitory Reflex (RAIR),
the reduction in anal canal pressure in response to rectal distension. A novel method
for measuring this reflex was developed by placing the rectal balloon catheter alongside
the AAR catheter. Measurement of AAR parameters before and after inflation of the
rectal balloon found the RAIR to be present in 30/32 patients; defined by a fall in
Opening Pressure by greater than 20% in response to this rectal distension. In two
patients, the Opening Pressure increased. In three patients, complete inhibition of
the anal sphincter complex occurred; however, the extent of RAIR does not appear to
correlate with symptom severity scores in this cohort.
Finally, the relationship between the grade of rectal intussusception (intra-rectal,
intra-anal and overt prolapse) and AAR parameters was explored. Interim analysis of
the recruited 32 patients (99 patients required for this study), investigating this
relationship found a significant decrease in Opening and Closing Pressure, and Opening
and Closing Elastance across all three groups. This suggests a relationship between
worsening sphincter function and increasing severity, with preservation of anal sphincter
squeeze function in intussusception, and loss in overt prolapse.
Introduction of the fast-fill technique provides a more physiological measurement
of anal sphincter function, taking less time, and has expanded the clinical application
of AAR to include the measurement of rectal reflexes. Interim results of AAR parameters
in patients with rectal intussusception are promising and may suggest a role in discriminating
between different grades. Further recruitment to this study should provide further
information about this relationship.