The microtip pressure transducer technique was introduced to provide a simplified method for performing anorectal manometry.7 As the name implies, the microtips are small electronic devices used to decrease artifacts; the 2-mm diameter of the microtip is mounted on a solidstate catheter (Fig. 8.3). The advantage of this technique is that, compared with balloons or larger catheters, the recordings are more physiologic due to diminished stretch artifacts of the sphincter complex.8 Furthermore, these devices

Figure 8.3. Microtransducer (3).

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 water perfused; pressures recorded are not "true 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 the sphincter muscles. If the amount of fluid increases, a limited capacity is reached. Overfilling does not increase the artificial capacity or increase pressures, but overflow runs into the distal rectum or out of the anus. This pressure is often referred to as "yield pressure."12 The yield pressure is reached faster with a faster perfusion rate. However, the artifacts created by the water-perfused fluid have been criticized.13

The advantages of the water-perfused system are its wide availability, the specific measurements, the longitudinal or radial positioning, and the relatively low costs.14,15 This system includes a water pump, pressure polygraph, computer, and water-perfused catheters (Fig. 8.4).

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