Aspects and Equipment

HRAM and HDAM

Non-HRM

Number of sensors

Closely spaced more sensors

Fewer sensors at wider intervals

Display

Color contour and line plot

Line plot

Techniques

Stationary examination

Pull-through examination

Preparation

Easy

More time consuming

Spatiotemporal resolution

Good

Limited

Cost

High

Low

Catheter durability

Limited

Excellent

Lifespan

Limited

Excellent

6.1 Conventional Anorectal Manometry

Water-perfused manometry requires more preparation, technical skills, and training [4]. The dynamic performance of water-perfused systems is several orders of magnitude less than that of solid-state systems, limiting their accuracy where rapidly changing pressures must be measured (e.g., in the pharynx/upper esophageal sphincter) [4]. However, this is not a limitation in the anorectum where rapidly changing pressures are not observed.

The conventional anorectal manometry water-perfused system consists of (Fig.6.1) the following:

1.

Polygraph.
2.

Dedicated software.
3.

Water perfusion pump.
4.

Single-use or multipurpose water-perfused catheter with four or eight channels.
5.

Pressure transducers.

../images/475577_1_En_6_Chapter/475577_1_En_6_Fig1_HTML.png — Fig. 6.1

(a) Polygraph dedicated software, (b) Water perfusion pump, (c) Single-use or multipurpose water-perfused catheter with four channels

The catheter capillaries are filled with water and constantly perfused through the pump (0.5–1 mL/min); it is necessary to do a periodical check of the perfusion flow counting the numbers of the water drops per minute (20 drops = 1 mL). At the exit of each capillary a constant quantity of water flows at a constant speed. The capillaries are connected to the pressure transducers and these are connected to the polygraph [2, 3].

The pressure exerted at the exit point of the capillaries is transmitted to the whole water column inside the capillary and is transformed into an electrical signal by the pressure transducer. The electrical signal is transmitted to the polygraph which, through the software, represents it on the computer screen. The pressure measurement performed through the catheter is carried out at a constant frequency, so that the resulting graphic representation is a wave with time on the X axis and pressure values on the Y axis (Fig. 6.2) [2, 3].

../images/475577_1_En_6_Chapter/475577_1_En_6_Fig2_HTML.jpg — Fig. 6.2

The graphic representation of conventional anorectal manometry. Time on the X axis and pressure values on the Y axis (Laborie-Software)

The catheter configuration can be different regarding the number of channels (four, six, or eight) and their spatial arrangement which can be as follows:

1.

Fully radial.
2.

Fully helicoidal.
3.

Mix between the two previous provisions.

A disposable catheter of a latex free material is generally used.

Although the procedure does not present any particular difficulties, it is important to take into account some technical aspects that could affect the quality of the manometric exam:

Regardless of the type of the configuration of the catheter, the pressure measurements take place in a unidirectional manner: the pressure is evaluated only at the point where the water exits out of the capillary; no information about the pressure from other areas is available.
The water perfusion, produced by the pneumatic pump, has to be constant and equal for all the channels.
It is mandatory to calibrate the catheter at two different levels holding the horizontal catheter at the level of the couch before, low level, and then at high level, 50 cm above low level.
To avoid false pressure values, it is extremely important to maintain the catheter at the same level during all procedure (low calibration level: 0 mmHg).
During the different phases of the manometric test, it is necessary to move the catheter inside the anal canal manually or by using a mechanical extractor controlled by the software.

6.2 High-Resolution Water-Perfused Manometry (HRWPM)

The way HRAM perfused system works is similar to the conventional system seen above, except for the increased number of catheter channels (up to 24) [1, 8, 9].

Obviously the polygraph and the software have to be able to manage this increased number of channels and, hence, this increased amount of information.

The catheter, made of bio-compatible plastic material, can be single-use or multipurpose (50 uses are generally permitted after autoclaving).

The increased number of channels provides a greater detail of the rectal and anal pressures allowing to obtain a more accurate examination.

One critical point is maintaining a constant perfusion of all the channels. This is even more necessary than conventional ARM and before starting the examination the operator has often to spend some time to perform the setup (e.g., to verify that all transducers are correctly connected and all channels are really working). Also HRWPM requires that the catheter and the acquisition system are placed at the same level.

In comparison with conventional water-perfused ARM the increased number of channels allows to maintain the catheter in place during the examination without needing to change its position. This aspect speeds up the execution of the exam itself.

The software can display pressures via linear track and as contour plot (Fig. 6.3). This last type of visualization is typical of high resolution manometric examinations and allows to have a continuous representation of pressure through an isobaric colored representation of immediate comprehension [1, 8, 9].