Anorectal Manometry and the Rectoanal Inhibitory Reflex Johann Pfeifer and Lucia Oliveira

8 Anorectal Manometry and the Rectoanal Inhibitory Reflex Johann Pfeifer and Lucia Oliveira Anorectal sphincter assessment through physio- up investigations comparing results should logic testing has been in use for more than 120 be performed with the identical technique in years. The first studies of anorectal manometry the same anorectal manometry unit. General were done in 1877 by Gowers,1 who measured parameters evaluated by anal manometry anal canal resting tone and was reportedly the include (1) internal and external anal sphincter first to explore the rectoanal inhibitory reflex. A pressures, (2) anal and rectal pressure response comprehensive physiologic evaluation of the during straining, (3) anal sphincter length, (4) anorectal sphincter function includes assess- anal and rectal motility, (5) rectal sensation, (6) ment of the shape and function of the rectum, rectal capacity and compliance, and (7) anal the sphincter muscles, the pelvic floor, and the sphincter muscle reflexes. anal canal. Anorectal manometry is one way of evaluating the pressures in the rectum and anal canal as well as the compliance of the rectum Fluid-Filled and Air-Filled Balloon Systems and the basic reflex and sensory mechanisms. One of the most common methods of measuring anorectal pressure utilizes a closed balloon Methods of Performing system. The pressure result obtained with Anorectal Manometry balloon recording is an average of all pressures acting into the balloon; radial asymmetry cannot Anorectal manometry is an investigation used to be detected. However, larger balloons are assess the pressures in the rectum and anal unphysiologic as the probe itself may cause canal; in other words, it is a measurement of the reflex contractions but the results obtained are resistance of the anal sphincter complex invol- more representative of a greater area of the untary evacuation. This evaluation is performed sphincter. It is of tremendous importance to by placing a specially designed catheter or understand that a compliance hysteresis phe- balloon into the lower rectum and anal canal. nomenon exists in the anal canal, wherein both This pressure-sensitive device is connected to a pressure-radial curves (distention/deflation) are transducer, which converts mechanical into not superimposable, and the level of pressure is electronic signals that are then recorded and lower on return, for similar levels of distention displayed on a computer monitor. The aim is to due to compliance adaptation processes. Thus, record reproducible measurements and a quan- probes with a larger diameter generate greater titative assessment of the anal sphincter pressures in the same patient than do smaller complex. However, the procedure as well as the balloons.2 Furthermore, more rapid distention equipment used during anal manometry are not records higher pressures. Air is compressible; yet standardized; therefore, comparing results therefore the use of water for the balloon filling among various centers is difficult. Thus, follow- may be more reproducible.3 71 72 Constipation Air-Filled Balloon Technique (Schuster) In the 1960s, Schuster4 invented a simple method for measuring anorectal pressure changes. The device consisted of a metal cylinder around which double-molded latex balloons are tied forming two compartments (Fig. 8.1). These balloons were connected with separate catheters through a hole in the cylinder to either inflate air or to record pressure changes, when appropriate. The inner balloon has a doughnut shape when inflated with 7 to 10ml of air; the outer balloon has a pear-shaped structure. Through the metal cylinder, further balloons (rectal and/or colonic) can be inserted. Thus, rectal pressures can be measured or the rectoanal inhibitory reflex can be elicited. This device is inserted into the anus and posi- tioned where the inner balloon lies attached to the internal anal sphincter and the pear-shaped balloon to the outer bundle of the external anal sphincter. Thus, theoretically, the pressures of the internal and external sphincter can be inde- pendently measured; however, the overlap of these two portions is too wide to allow adequate differentiation. Normally, recording is performed with an aneroid manometer. The advantage is that recording is done from a larger surface reflecting overall pressures of a large area of the sphincters. Furthermore, the technique is simple and cost-effective, and the balloon stays fixed in place, thereby requiring only one operator. The disadvantage is that larger balloons create more artifacts during recording; therefore, this method is better for evaluating pressure changes than for evaluating actual pressures. Balloons and cylinders are available in three sizes: infant, pediatric, and adult. Although the device is not widely used for diagnostic evaluation, it may have a therapeutic 4,5 Figure 8.1. Air-filled balloon of Schuster. 1, aneroid manometer; 2, role as a biofeedback catheter. syringe for air insufflations; 3, pear-shaped balloon (for the external anal sphincter); 4, doughnut-shaped balloon (for the internal anal sphincter); 5, rectal balloon for eliciting the rectoanal inhibitory reflex. Small Balloon Tube Technique Another form of measuring anorectal pressures a three-balloon system is generally used. is with small tubes. The advantage of this tech- While the water-filled microballoons (diameter nique is that only minor changes and irritation 5–7mm) are placed in the upper and lower anal of the sphincters by the device itself are canal, the third balloon on top of the catheter is obtained.6 Standardization is very important in distended by air to elicit the rectoanal inhibitory order to obtain reliable and reproducible results; reflex in the distal rectum (Fig. 8.2). Anorectal Manometry and the Rectoanal Inhibitory Reflex 73 are easy to handle, stable against temperature changes, sensitive to pressure changes, and well tolerated by the patient. In the ambulatory setting, microtransducer catheters are more useful than plastic catheters.9 The disadvantages are that the recording area is very small, pressures are measured in only one direction and not circumferentially, and these catheters are more expensive.10 However,follow-up studies have shown no significant differences in the positioning of the microtip catheter.11 Electronic catheters are more fragile and expensive than catheters made from plastic. Microtip pressure transducers are connected directly to a computer for recording and displaying the results. Water-Perfused Systems The most widely used anal manometry system is Figure 8.2. Small balloon tube technique. 1, transducer; 2, syringe for water perfused; pressures recorded are not “true air insufflations; 3, microballoons (5–7mm); 4, rectal balloon. sphincter pressures” but resistance pressures to a flow of water out of the catheter. At the onset of water perfusion, an artificial cavity is created, filled with the perfused fluid surrounded by Microtransducer the sphincter muscles. If the amount of fluid increases, a limited capacity is reached. Over- The microtip pressure transducer technique was filling does not increase the artificial capacity or introduced to provide a simplified method for increase pressures, but overflow runs into the 7 performing anorectal manometry. As the name distal rectum or out of the anus. This pressure is implies, the microtips are small electronic often referred to as “yield pressure.”12 The yield devices used to decrease artifacts; the 2-mm pressure is reached faster with a faster perfusion diameter of the microtip is mounted on a solid- rate. However, the artifacts created by the water- state catheter (Fig. 8.3). The advantage of this perfused fluid have been criticized.13 technique is that, compared with balloons or The advantages of the water-perfused system larger catheters, the recordings are more physi- are its wide availability, the specific measure- ologic due to diminished stretch artifacts of the ments, the longitudinal or radial positioning, 8 sphincter complex. Furthermore, these devices and the relatively low costs.14,15 This system includes a water pump, pressure polygraph, computer, and water-perfused catheters (Fig. 8.4). Manometry Catheters Water-Perfused Catheters In principle, smaller catheters are superior to larger ones and flexible are preferred over rigid. The latter have the advantage of easy insertion but are associated with patient discomfort and are often refused. Flexible catheters are more comfortable for the patient but tend to twist in Figure 8.3. Microtransducer (3). the anal canal. The outside diameter should not 74 Constipation with two to eight lumina (Fig. 8.5). Arrangement of the lumina depends on the operator. Radial catheters are most useful in recording longitudinal pressures in the anal canal. Up to eight channels are used to give a precise pressure description of the different sections of the sphincter muscle during rest, squeeze, or push at a specific height. The catheters are normally marked in 1-cm intervals for vertical orientation (Fig. 8.6). Furthermore, for radial orientation into the anal canal, an additional mark should be made on the catheter. However, assessing sphinc- teric defects with anorectal manometry is limited.19,20 We use a water-perfused system with a four radial ports for routine evaluation and eight ports for scientific research studies. While the radial lumina are usually 5cm apart from the catheters end in adults, the radial ports are more proximal in children. If rectal pressures are measured, an open-end catheter is preferred. Spiral catheters are useful for investigating the rectoanal inhibitory reflex. In this catheter, eight ports are set at 45-degree intervals, 5 to 8mm apart on the longitudinal axis. A balloon at the very end of the catheter is used for rapid inflation to elicit the reflex. Sleeve catheters are rarely used in anal manometry, as with these catheters only global pressures can be recorded. b Solid-State Catheters Konigsberg catheters are solid-state/microtip catheters for pressure measurement. They require no water perfusion setup and are therefore easy to use and give reliable, accurate c Figure 8.4.

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