1. Introduction Anal manometry is used for the assessment of patients with faecal incontinence. The fatigue rate index (FRI) has been shown to discriminate between symptomatic patients and controls, 1 and is calculated as follows: Fatigue rate index = Squeeze pressure (cmH 2 O) (minutes) - fatigue rate (cmH 2 O/min) The aim of this study was to compare manometry and fatigability of the anal canal in nulliparous women before and after childbirth. 1. Marcello P, Barrett R, Coller J, et al. Fatigue rate index as a new measurement of external sphincter function. Diseases of the Colon and Rectum 1998; 41 (3): 336-343 2. Snooks S, Swash M, Mathers S, Henry M. Effect of vaginal delivery on the pelvic floor: a 5-year follow up. British Journal of Surgery 1990; 77 (12): 1358-1360 3. Parks A, Swash M. Denervation of the anal sphincter causing idiopathic anorectal incontinence. Journal of the Royal College of Surgeons of Edinburgh 1979; 24 (2): 94-96 Method Anal manometry and fatigue rate were measured in nulliparous women during the last trimester and by 20 weeks postpartum. An 8 mm air-filled balloon, connected to the Myomed 932 system (see figure 1), was used to measure maximum resting pressure, maximum squeeze pressure, and fatigue rate over a 20 second squeeze. Fatigue rate index was calculated as described. Results Manometry data is available for 23 women both pre and post delivery. Four delivered by Caesarean section, 2 electively and 2 underwent emergency Caesarean section after trial of labour. Table 1 shows the results. Figure 2 shows a typical fatigue curve pre and post delivery. Table 1 Mean ± standard deviation of stated measurements/calculations pre and post delivery Pre deliveryPost deliveryp value Resting pressure (cm H 2 O) 56 ± 12.7652.56 ± 11.490.144 Squeeze pressure (cm H 2 O) 106.29 ± 41.3777.77 ± 41.75< 0.001 (paired t- test) Fatigue rate (cm H 2 O/min) -126.22 ± 67.59 -80.84 ± 49.98< 0.001 (paired t- test) FRI (minutes) 1.16 ± 1.31.32 ± 1.180.267 (Wilcoxon signed rank sum) Figure 2 Example of graph of anal canal pressure during a maximal voluntary contraction, sustained over 20 seconds, pre and post delivery. The linear best fit lines are applied and adjacent equation indicates the slope and intersection of the line. The fatigue rate is obtained by multiplying the slope by 60 to give a rate in cm H 2 O /minute. K. Cattle, K. Telford, E. Kiff. University Hospital of South Manchester, UK. Discussion Our findings of reduced voluntary squeeze pressure and preserved resting pressure after childbirth are consistent with other published data. 2 The effect of vaginal delivery on fatigability of the anal sphincters has not been studied. Biopsies of the external anal sphincter of patients with faecal incontinence showed muscle fibre type grouping, 3 consistent with denervation and subsequent reinnervation. The changes in fatigability that are seen post partum may reflect a selective loss of fatigue-sensitive type II muscle fibres, with preservation of type I fibres. A loss of type II fibres would result in reduced power generation (i.e. reduced squeeze pressure) but increased ability to resist fatigue (reduced fatigue rate). The reasons for this alteration in muscle fibre proportion is unknown. Further work, especially histological studies, is required to substantiate this theory. Figure 1 Myomed 932 system with airfilled 8 mm balloon used for anal manometry Abstract Anal manometry is an established assessment tool for patients with faecal incontinence (FI). Fatigue rate index (FRI) has been shown to discriminate between symptomatic patients and controls. The aim of this study was to compare manometry and fatigability of the anal canal in nulliparous women before and after childbirth. An air-filled manometry device was used to record maximum resting and squeeze pressures, fatigue rate (recorded over 20 seconds) and FRI. Recordings were made before and after childbirth. 23 women were studied. Maximal squeeze pressure and fatigue rate of the anal canal are significantly reduced after childbirth. Resting anal canal pressure and fatigue rate index are not significantly different. This may reflect preferential loss of type II (and preservation of type I) muscle fibres.