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4. Physiologic Testing
A. Introduction
• Physiologic testing is used to assess pelvic fl oor and anorectal
disorders.
• These physiologic tests are performed in conjunction with a
history, diary of the disorder, physical examination, endoscopy, and imaging studies.
• Physiologic tests have provided or confi rmed a diagnosis in
75% of patients with constipation, 66% of patients with incontinence, and 42% of patients with chronic anorectal pain.
• Commercial equipment is available which produces reproducible
results.
• However, the lack of validated normal values for healthy
patients of both sexes and all ages remains a major problem.
• Physiologic testing includes several tests which complement
each other. No single test contributes the data necessary to analyze
disorders of the pelvic fl oor.
• Unfortunately, many patients have diseases or disorders that
are of multifactorial pathophysiologies which produce several
abnormal results, that are diffi cult to interpret.
B. Manometry
• Manometry is a technique for measuring pressures in the rectum
and anus, and pressures and refl exes elicited by voluntary actions
or by local stimuli.
• Interpretation of data, requires comparison to a range of normals
by sex and age (which is often lacking).
D.E. Beck et al. (eds.), The ASCRS Manual of Colon and Rectal Surgery, 49
DOI: 10.1007/978-0-387-73440-8_4, © Springer Science + Business Media, LLC 2009
50 The ASCRS Manual of Colon and Rectal Surgery
Indications
• First, manometry is used for evaluation of incontinence. A
sphincter defect can be located and quantifi ed.
• Second, constipation, mainly outlet obstruction type, is investigated to determine whether abnormal pressures exist. The loss
of the rectoanal inhibitory refl ex (RAIR) suggests Hirschsprung’s
disease.
• Third, some anorectal pain syndromes are associated with
abnormal pressures within the sphincter mechanism.
• Fourth, the study is conducted to establish a baseline when an
anorectal or pelvic fl oor procedure is contemplated. For example, if biofeedback or a surgical procedure is to be used for
incontinence or constipation, a pre- and postprocedure study
provides the means to quantify a change.
Equipment
• The equipment consists of several essential components: the
probe, the transducers, the recorder, and the hydraulic pump
for water infusion methods.
Probes
• The most popular type is the water-perfusion probe, which is
relatively inexpensive, durable, and easy to use.
• The solid-state catheter is expensive and fragile, but it gives the
most accurate, reproducible results.
Hydraulic Water-Perfusion Machines
• The water-perfusion machine is a key part of the waterperfusion method. The water is driven through each of the
individual channels in the tube at a chosen rate; the water
perfuses through the holes near the tip and thus is exposed to
pressure changes.
Transducers
• The mechanical water pressure is changed to electrical signals
in the transducer.
4. Physiologic Testing 51
Amplifi er/Recorder
• Many recording devices are available, but computerized systems with small amplifi ers and recorders are preferable.
• Software has been designed to give chart, table, and graph
printouts. An attached monitor is a useful way to observe the
tracings as the procedure progresses.
Technique of Manometry
Initial Considerations
• The study is performed with focus on the distal 5 cm, which is
the segment that contains the sphincter muscles.
• The internal sphincter and the external sphincter may be analyzed based on the portions of pressure represented by the resting tone and the squeeze pressure.
Preparation
• The preparation is a simple small, tap-water enema or commercially prepared enema to empty stool from the rectum and
anus before coming for the examination.
Calibration
• The calibration record should be saved with the actual procedure recording to validate the measurements.
Resting Pressure
• The probe is introduced higher than the 5-cm level and left
in place for 5 min to permit the temperature to equalize to
body temperature and the sphincter mechanism to relax to a
baseline.
• There is usually a stepwise increase in pressure as the sensors
progress distally (Fig. 4.1 ). As the sensor leaves the sphincter
mechanism, the pressure will drop to zero.
Squeeze Pressure
• The probe is reinserted to at least the 6-cm level and reoriented.
The probe is again removed at 1-cm increments. The patient is
52 The ASCRS Manual of Colon and Rectal Surgery
4
Fig. 4.1. Normal tracing of resting tone in one quadrant on the manometry
probe. The scale is 100 mm Hg. The pressure progressively increases from the
4-cm level to 2-cm level with a small decrease in pressure at the 1-cm level, and
then to zero as the probe exits.
3
2
1
Fig. 4.2 . Normal tracing of voluntary squeeze in one quadrant on the manometry
probe. The scale is 100 mm Hg. The squeeze essentially doubles the resting
pressure.
instructed to squeeze the sphincter muscles as if to stop a bowel
movement and hold the squeeze for 3 s (Fig. 4.2 ). The patient
is also instructed to avoid using accessory muscles, especially
the gluteals.
Squeeze-Duration Study
• The probe is positioned in the site of the highest pressure in
the anal canal. The high pressure zone is the length of the
anal canal with resting pressures at least 30% higher than rectal
pressure. The patient is instructed to squeeze and hold the
4. Physiologic Testing 53
squeeze for 45 s as the recording is made. Some investigators
perform this maneuver once and others do two or three runs
and average the results.
• This study is also termed sphincter endurance.
Refl exes
• The probe is again positioned in the high pressure zone in the
anal canal to observe for the RAIR. Then 10 cc of air is injected
into the balloon and the pressures are observed for 10 s. Then
air is infl ated into the balloon at 20-, 30-, 40-, 50-, and 60-cc
increments (Fig. 4.3 ).
• The recording normally shows a relaxation from the baseline,
which verifi es the intact refl ex from the stimulated rectal wall
to the internal sphincter.
Strain Maneuver
• The probe is positioned in the high pressure zone. The patient
is instructed to bear down as if to defecate for at least 5 s.
• The pressure is normally reduced for a few seconds similar to
the RAIR (Fig. 4.4 ). This maneuver is repeated after a 30-s rest.
The result is obtained by averaging the total runs. To appreciate what is happening to the sphincter, the rectal pressure is
measured at the same time with the rectal balloon, which corresponds to the increased abdominal pressure.
Rectal Sensation
• The balloon is infl ated in 10-cc increments until the patient
senses the balloon. The fi rst sensation is normally at or before
20-cc infl ation.
Compliance
• Having recorded the fi rst rectal sensation, the balloon is infl ated
slowly in 50-cc increments. The patient will feel a point at
which there is a strong urge to defecate. This is recorded. At a
further point, the patient will experience a discomfort, which is
recorded as the maximal tolerated volume.
• In the normal-sized rectum, this will be 200–250 cc (Fig. 4.5 ).
54 The ASCRS Manual of Colon and Rectal Surgery
Pos
Pos
Pos
Pos
Pos
1st Sens 15cc
Stim 15cc
Stim 20cc
Stim 30cc
Stim 40cc
100
Stim 50cc
mmHg
U
100
mmHg
U
Fig. 4.3. Normal RAIR in one quadrant on the manometry probe. The scale is 100 mm Hg.
4. Physiologic Testing 55
Fig. 4.4. Normal strain maneuver. A relaxation occurs.
Stim 50cc
Stim 100cc
Stim 150cc
Stim 200cc
Stim 250cc
Fig. 4.5. Normal compliance in one quadrant on the manometry probe. The
patient reports the insuffl ation causing the fi rst sensation, the fi rst urge, and the
last tolerable volume.
Interpretation
Normals
• In the anal canal there are subtle differences in the upper, middle, and distal segments.
• Overall, men and young patients have higher pressures. However, there is overlap of normal measurements by sex and age.
• The resting pressure has contributions from both the internal
and external sphincters, with the internal sphincter providing
75–80% of the total.
• The squeeze pressure is derived dominantly from the voluntary
external sphincter.
Interpretation of Resting Pressure
• The resting pressure is the pressure in the high pressure zone at
rest after a period of stabilization. Seventy-fi ve to eighty percent of the resting pressure is a measure of the internal sphincter tone.
56 The ASCRS Manual of Colon and Rectal Surgery
• For women, the resting pressure is approximately 52 mm Hg
(range, 39–65). For men, the resting pressure is approximately
59 mm Hg (range, 47–71).
• Sometimes a normal patient may have low pressures, but does not
have a complaint if the stool is well formed. However, a patient
may have “normal” pressures, but yet complains of incontinence.
These measurements cannot be interpreted alone, but must be
analyzed in the context of the history and other measurements.
• Low resting pressures are usually seen in patients who have the
chief complaint of incontinence (Fig. 4.6 ).
• Patients who have low pressures may not be good candidates
for a surgery that will leave them with a poorly formed or liquid
stool, such as total colectomy with ileorectal anastomosis or
proctocolectomy with ileal pouch to anal anastomosis; these
patients might be better served with a permanent ileostomy.
• High basal pressures may be associated with anorectal pain.
• Some patients have spastic sphincters, which may be associated with outlet obstruction.
• Patients with anal fi ssure have a spastic internal sphincter with
high pressure measurements as part of the pathophysiology.
These patients may be candidates for lateral internal sphincterotomy. Pharmacologic relaxation may be achieved in lieu of
surgery. Relaxation of internal sphincter spasm can be achieved
by 10 mg of sublingual nitroglycerine. Topical 0.2% nifedipine
or 0.2% nitroglycerine applied to the anoderm relaxes the
underlying muscle.
Interpretation of Squeeze Pressure
• The maximum voluntary pressure is the highest pressure recorded
above the zero baseline at any level of the anal canal during
maximum squeeze effort by the patient.
• The squeeze pressure is the pressure increment above resting
pressure after voluntary squeeze contraction and is a calculated
value that is the difference between the maximum voluntary pressure and the resting pressure at the same level of the anal canal.
• The squeeze pressure is mainly a measure of the external sphincter.
For women, the squeeze pressure is approximately 128 mm Hg
(range, 83–173). For men, the squeeze pressure is approximately
228 mm Hg (range, 190–266).
4. Physiologic Testing 57
1
2
3
4
5
1
3
2
3
4
1m
mmHg
U
Fig. 4.6. Low resting and voluntary squeeze pressures in an incontinent patient.
58 The ASCRS Manual of Colon and Rectal Surgery
• The squeeze pressure is examined as a total squeeze pressure,
which includes the resting pressure plus the squeeze, and as
a maximum squeeze pressure, which is the squeeze pressure
minus the resting pressure.
• A low squeeze pressure may be associated with sphincter injury
or nerve damage from surgery, especially anal fi stula surgery,
obstetric trauma, or other anorectal trauma (Fig. 4.6 ).
• High squeeze pressure is found in those patients who have
pelvic fl oor spasm (anismus), often associated with anorectal pain. These same patients are unable to relax the sphincter
when asked to bear down as if to defecate.
Interpretation of Squeeze Duration
• The sphincter duration is the length of time the patient can
maintain a squeeze pressure above the resting pressure.
• The duration of squeeze should be >30 s at >50% of maximum squeeze pressure. When patients are unable to maintain a
squeeze, they may be incontinent.
Interpretation of Refl ex Studies
• The RAIR is the transient decrease in resting anal pressure by
>25% of basal pressure in response to rapid infl ation of a rectal
balloon, with subsequent return to baseline.
• The decrease in pressure during the RAIR test is a measure of
the internal sphincter relaxation.
• This refl ex may be present even with central nervous system
disorders; however, disease that interferes with the peripheral
nerves or ganglion cells of the myenteric plexus or fi brosis of
the internal anal sphincter may interfere with a measurable
refl ex relaxation.
• The presence of a normal RAIR rules out Hirschsprung’s disease (Fig. 4.7 ).
• The cough refl ex is the pressure increment above resting pressure after a cough, and is a calculated value that is the difference between the maximum pressure recorded during cough
and the resting pressure at the same level in the anal canal.
• The cough refl ex, also equated with a Valsalva refl ex, is a rectal
refl ex to counter a sudden abdominal pressure increase.
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