Transcript Slide 1

K. Cattle, K. Telford, E. Kiff. University Hospital of South Manchester, UK.
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.
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 (cmH2O)
(minutes)
- fatigue rate (cmH2O/min)
The aim of this study was to compare manometry and
fatigability of the anal canal in nulliparous women before and
after childbirth.
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.
Figure 1 Myomed 932 system with
airfilled 8 mm balloon used for anal
manometry
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.
Pre delivery
Resting pressure 56 ± 12.76
(cm H2O)
Post delivery
p value
52.56 ± 11.49
0.144
Squeeze pressure 106.29 ± 41.37 77.77 ± 41.75
(cm H2O)
< 0.001 (paired ttest)
Fatigue rate
(cm H2O/min)
-126.22 ±
67.59
-80.84 ± 49.98 < 0.001 (paired ttest)
FRI
(minutes)
1.16 ± 1.3
1.32 ± 1.18
0.267 (Wilcoxon
signed rank sum)
Table 1 Mean ± standard deviation of stated measurements/calculations pre and post delivery
Anal canal pressure (cmH 2O)
Anal canal fatigue
250
y = -2.8139x + 225.22
200
Pre delivery
150
Post delivery
y = -1.445x + 167.53
100
Linear (Pre delivery)
Linear (Post delivery)
50
0
1
3
5
7
9 11 13 15 17 19 21
Time (seconds)
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 H2O /minute.
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.
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