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 studies. 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.