There are three basic types of systems used for performing manometric examinations: air- or water-filled balloon systems, water perfusion systems, and solid-state microtransducer systems.

Our preference is to perform a station pull-through technique using a custom-built 4.8-mm diameter polypropylene flexible catheter with four radial ports located 8.5 cm from the tip (Arndorfer, Inc., Greendale, WI).^83,84 A further two ports are positioned 2 cm from the end of the catheter and are enclosed within a thin latex rubber balloon fashioned from the finger of an examination glove (Floor/exam latex glove no. 8857; Baxter Health Care Corporation, Valencia, CA). This balloon is secured at 3 cm from the tip of the catheter using a 2-0 silk ligature. An eight-channel hydraulic capillary infusion system (Arndorfer, Inc., Greendale, WI) is used with Medex transducers (M6677; Medex, Inc., Hilliard, OH). Mechanical pressures are transmitted to a PC Polygraf HR (Synectics Medical, Inc., Irving, TX). The resulting electrical impulses are displayed on a computer using Polygram V6.4 software (Synectics Medical, Inc., Irving, TX).

With the patient in the left lateral decubitus position, the catheter is inserted to 6 cm; 20 to 30 seconds are allowed for the sphincter to recover from this insult and for the pressures to equilibrate. It is important to permit adequate time for the small cavity between the rectal wall and the catheter to fill with perfusate so that the yield pressure is reached.

Following this period of equilibration, various wave patterns may emerge that demonstrate the presence of intrinsic cyclic activity attributable primarily to the internal
sphincter.¹⁷⁵ Three basic patterns are observed. Slow waves are the most frequently encountered. These vary in frequency from 10 to 20 cycles/minute with an amplitude from just above physiologic baseline noise to 15 mm Hg (Figure 7-9).¹⁴⁶ They can most often be observed in the region between the proximal border of the sphincter and the area of the maximal average resting pressure.^36,130 The clinical significance of these waves is unknown.

Ultraslow waves are the second most common waveforms recorded. They have a frequency of 0.5 to 1.5 cycles/minute and are of large amplitude (up to 100 mm Hg).¹⁴⁶ They are found more frequently in patients with high resting anal pressures,⁶⁹ such as in those individuals with an anal fissure,⁶⁶ hemorrhoids,⁶⁷ or primary anal sphincter hypertonia. They are seen most commonly in the region of maximal average resting pressure.

The intermediate wave is the least frequently observed type of oscillation (frequency, 4 to 8 cycles/minute). They are most often noted in patients with neurogenic fecal incontinence or following ileal pouch-anal anastomosis (Figure 7-10).¹⁶² When present, they make interpretation of resting and squeeze pressures more difficult. Resting pressure should be assumed to be the mean of the peak and trough pressures at rest.

Following equilibration of the pressures, the patient is asked to perform a single maximum squeeze effort followed by a period of rest, and then a maximal push effort (Figure 7-11). These measurements are repeated at a further five stations, separated by 1-cm intervals, as the catheter is progressively moved caudally. Thus, the rest and squeeze pressures over the entire length of the anal canal can be measured, and the mean resting and squeeze pressures over the high-pressure zone (HPZ) can be calculated. The HPZ is defined as that length of the anal canal through which pressures are greater than 50% of the average maximum pressure. This definition is similar to that used when a continuous pull-through technique is employed. Alternatively, the HPZ can be defined as that zone bounded caudally by a rise in pressure of 20 mm Hg and cephalad by a fall in pressure of 20 mm Hg in at least 50% of the channels. This latter definition may present a more accurate picture of the sphincters in incontinent patients because pressures are so low that there is no true HPZ. However, using the former definition, the HPZ will always be at least 1 cm, but this may be an inaccurate value in a patient with a patulous anus.

The catheter is then reinserted to a distance of 2 cm from the anal verge, and the latex balloon is insufflated with 40 mL of air over 2 to 3 seconds and kept inflated for 20 seconds in order to elicit the RAIR. In response to distension of the lower rectum and upper anal canal, external sphincter contraction is followed by internal sphincter relaxation (Figure 7-12). If the reflex is not present, it is important to repeat the test with increased insufflation. Some patients, especially those with neurogenic fecal incontinence, decreased anal sensation, or megarectum, may respond only at a higher volume. The air is removed and the balloon reinflated with 50 or 60 mL until a reflex is observed. If the reflex is still undetectable, the catheter is inserted to 3 cm and repeat insufflations are performed. In our laboratory, we record only the presence or absence of the reflex. Some software programs contain the algorithms for calculating various reflex parameters, including duration, percentage of excitation, and excitation latency. Although some authors suggest that delayed, diminutive or absent excitation, or excitation only in response to large volumes may be used as a crude indicator of pudendal neuropathy, the clinical implications of these values are problematic.¹⁴⁵ Some prefer a spiral catheter to detect the presence of the RAIR over the entire length of the anal canal. However, the use of a radial catheter at the two stations where the reflex is most likely to be detected avoids this requirement for each investigation. In rare instances in which a reflex cannot be elicited and there is no evidence of megarectum, the spiral catheter may be useful. The most common reasons for absence of the RAIR are megarectum and a prior ileoanal or coloanal anastomosis.

The catheter is then inserted to a distance of 6 cm from the anal verge, positioning the balloon in the rectal ampulla. The balloon is then slowly filled with core temperature water at a
rate of approximately 1 mL/second. The first sensation perceived by the patient is noted as the minimal sensory volume, and the mean intraballoon pressure is noted. Thereafter, balloon filling is continued until the maximum tolerable volume is reached, and again the intraballoon pressure is noted. Using these values, rectal compliance can be calculated from the formula V/P.⁸⁴ Thus, with a large balloon volume and only a small increase in rectal pressure, the rectum is considered very compliant. In patients suffering from ulcerative colitis, Crohn’s proctitis, or radiation proctitis, the rectum may be poorly compliant in that a small increase in volume will result in a large increase in pressure. When one uses this technique, it is important to know the compliance of the balloon at various stages of insufflation so that it can be subtracted from the pressure measured via the intraballoon ports. Latex balloons may deform along the longitudinal axis with increased infusion of water. This may give a false impression of high rectal compliance.¹⁰⁹ As a consequence, some clinicians prefer to use barostat equipment to calculate this parameter, using a noncompliant balloon that does not deform with increasing pressure.

The measurement of compliance is not a diagnostic test but supplements other investigations for evaluating the pathophysiology of anorectal disease. It is of particular value in patients with proctitis and incontinence through ascertaining whether the incontinence is due to lack of rectal reservoir function or diminished anal sphincter tone. Similarly, in some constipated patients, compliance may be abnormally high. This finding can reflect overaccommodation and, therefore, a sensory contribution to the outlet obstruction.

Because most of our patients have several physiologic investigations performed on the same day, bowel preparation by means of a phosphate enema is usually performed before manometry. With the patient in the left lateral decubitus position, a digital rectal examination is performed to lubricate the anal canal, to ascertain the presence of any pathologic abnormality, and to ensure that the patient understands the instructions of how to squeeze and to push. Through an enema-tipped catheter, 50 mL of liquid barium (58% wt/wt barium sulfate suspension, Polybar) is introduced into the rectum followed by the insufflation of a small quantity of air to coat the mucosa of the sigmoid colon. Thickened barium paste is then introduced into the rectum until the patient experiences a feeling of fullness. A small quantity of paste is inserted into the anus in order to outline the anal canal, after which the vagina is opacified with Gastrografin. The patient is then turned to the right lateral side, and the table is slowly brought to the erect position. This enables one to slide down the table and to sit on the commode. The fluoroscopy tube is positioned so that the coccyx and the symphysis pubis are both visible on screening. Still pictures (proctograms) are taken at rest and at maximal squeeze prior to starting the video recording (Figure 7-14).
At the commencement of the video, the patients are asked to squeeze, to relax, and then to try to commence evacuation. As elimination starts, a further still picture is taken. Following evacuation, the recording is recommenced while the patient squeezes and pushes in order to check for the presence of an intussusception or nonemptying rectocele. A single still image of the evacuated rectum at rest is also obtained (Figure 7-15B).

With completion of the study, three lines of reference are drawn, so that the anorectal angle, puborectalis length, and extent of perineal descent can be assessed on the proctograms. First, a line is drawn between the tip of the coccyx and the anterosuperior surface of the symphysis pubis. Lines are also drawn along the axis of the mid-anal canal and along the posterior rectal wall (Figure 7-15A).⁸⁶ Whereas some have proposed using the dynamic images alone,¹⁵⁶ the authors prefer to rely on the combination of the dynamic and still images. This has been shown to produce reliable and reproducible measurements.³⁵

Much attention has been directed to the anorectal angle since Parks (see Biography, Chapter 29) first proposed its role in maintaining fecal continence.¹²⁹ The anorectal angle
is the angle formed by the axis of the posterior rectal wall and the axis formed by the anal canal; it is usually 70 to 140 degrees at rest.^59,110 This angle becomes more acute during the squeeze phase (75 to 90 degrees) and becomes more obtuse during evacuation (100 to 180 degrees at maximum strain).⁸⁶ Some investigators have reported greater anorectal angles in men,¹⁵³ but most clinicians believe that it is not affected by gender.⁴⁸ The wide variation in observed normal values is probably due to differences in interpretation.^49,59 It has even been suggested that a normal range is impossible to define.¹⁵³ Therefore, the change in angle seen during the squeeze and push phases is more important than the actual measurement.

The puborectalis length is measured as the minimal distance between the anterosuperior aspect of the symphysis pubis and the puborectalis notch. This ranges between 14 and 16 cm in the rest position, shortens to between 12 and 15 cm during the squeezing phase, and is elongated to 15 to 18 cm during the push phase.⁸⁸ As with the anorectal angle determination, the change in these parameters is more important than their definitive value.

Perineal descent is assessed as the length of a perpendicular line drawn from the pubococcygeal line to the anorectal junction. Perineal descent of either more than 3 cm in the rest phase or a further increase of 3 cm in the push phase is considered abnormal.

As with all of the studies performed in the physiology laboratory, interpretation of the results of defecography should be combined with a thorough assessment of the patient’s complaints through history and physical examination to ascertain the clinical significance of the findings. A normal defecogram should demonstrate relaxation of the puborectalis as indicated by (1) an increase in the anorectal angle, (2) lengthening of the puborectalis, and (3) a blunting of the puborectalis notch. These changes should be accompanied by symmetric opening of the anal canal to form a cone that is wider cephalad than it is caudad. This process takes ap- proximately 4 to 5 seconds. Contrast material in the upper rectum should subsequently be passed into the lower rectum and out the anus by rectal contraction, a process that may be facilitated by Valsalva’s maneuver, squeezing the rectum onto the levator plate.¹⁰⁸ Complete evacuation takes about 10 to 12 seconds when thickened contrast medium is used but is more rapid (8 to 9 seconds) when the mixture is more fluid.⁹⁷ Failure to relax the puborectalis is noted by the persistence of the puborectalis notch, failure of the anorectal angle to increase, and difficulty in emptying the rectum. Although these findings have been noted in normal individuals,⁸¹ patients with complaints of difficult evacuation who have these radiologic findings should be treated for paradoxical puborectalis contraction.