Manovolumetry

In the manovolumetry system, the rectal volume is recorded as a dynamic response to a graded rectal distention at atmospheric pressure. This resembles the physiologic events in the intestine,

Barostat Measurement Rectal
Figure 10.1. Pressure-volume response range in normal subjects (n = 45, mean ± SD) measured with the manovolumetry method. Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88-91, ©1992, with permission from Elsevier.

Figure 10.2. Design of the manovolumetry system. Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88-91, ©1992, with permission from Elsevier.

Figure 10.2. Design of the manovolumetry system. Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88-91, ©1992, with permission from Elsevier.

which allow wide changes of volume with minimal corresponding changes in pressure. It differs from conventional systems where compliance is calculated by registration of pressure in response to distention with air or fluid.

The manovolumetry method was designed for investigation of reservoir organs.16'17 It was described and evaluated for studies of anorectal function by Akervall et al18 and Oresland et al.19 The design is shown in Figure 10.2 and the disposable part of the system in Figure 10.3. As depicted in Figure 10.2, a water-filled reservoir (a) is open to air and suspended on a weight transducer. This vessel is in continuity via a tube to a closed-air reservoir (b), which is connected to a large, noncompliant plastic bag. This plastic bag is placed in the rectum (c). When the water reservoir is raised, pressure is generated in the air reservoir and consequently in the plastic bag. This pressure is equal to the difference between the levels of water in the two reservoirs. The

Manovolumetry

Figure 10.3. The disposable part of the manovolumetry system.A polyethylene bag (length 12 cm, volume 600mL) hermetically tied to a tube, is placed in the rectum. An endotracheal tube (outer diameter 10 mm) is laced on the tube and used for anal canal pressure registration. Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88-91, ©1992, with permission from Elsevier.

Figure 10.3. The disposable part of the manovolumetry system.A polyethylene bag (length 12 cm, volume 600mL) hermetically tied to a tube, is placed in the rectum. An endotracheal tube (outer diameter 10 mm) is laced on the tube and used for anal canal pressure registration. Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88-91, ©1992, with permission from Elsevier.

amount of water flowing into the air reservoir is measured as weight reduction. This reduction is equal to the volume of the plastic bag, that is, the rectal volume. The water-filled reservoir is open to the air, meaning that the pressure in the rectum is kept constant despite variation in volume. An example of a manovolumetric recording is shown in Figure 10.4, which also shows a recording of the anal canal pressure made at the same time.

The manovolumetric method has the following properties:

1. Rectal distention with defined pressures allows dynamic registration of volume changes; thus compliance can be calculated in relation to defined pressure intervals.

2. The noncompliant plastic bag is sensitive to bowel wall contractions, making it suitable for motility studies.

3. Anal pressure is recorded simultaneously with rectal volume and motility, which allows assessment of the rectosphincteric reflexes.

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