| Why
the sleeve was developed
Difficulties with reliable monitoring of maximal sphincter
pressure with perfused side holes led to development of the
sleeve. (1)
Perfused side holes can be used to give an accurate sample
of maximal sphincter pressure when pulled through a sphincter.
(2)
Reliable monitoring of sphincter pressure is not possible
with a side hole positioned within the sphincter (1,3), even
from second to second, because of three main factors
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the focal pressure sensing properties
of side holes
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the narrowness of the region of maximal
sphincter pressure
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the mobility of sphincters relative
to a luminal recording assembly (4).
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The sleeve overcomes the effect of these
factors by being a sensor which can be made long enough to
span the normal range of sphincter movement.
The sensing function of the sleeve ensures that it records
maximal sphincter pressure, regardless of where the sphincter
is positioned along the sleeve length.
These unique recording properties make the sleeve the only
sensor that can monitor sphincter pressure reliably. |
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Focal pressure sensing
properties of side holes
Side holes are very focal pressure sensors, recording only
the pressure that prevails over approximately the diameter
of the side hole when the gut wall is contracted over the
side hole.
This recording property allows excellent spatial resolution
of luminal pressures, but is a disadvantage for monitoring
of sphincter pressure.
The different recording properties of sleeves and side holes
make them complementary types of sensors.
Narrowness of the region
of maximal sphincter pressure
Pullthrough of a perfused side hole across a sphincter shows
that the region of maximal sphincter pressure is very narrow,
usually occupying less than 25% of the length of the high
pressure zone (2).
All measurements of sphincter pressure are intended to reflect
maximal sphincter pressure, as this is considered to be the
value that best reflects mechanical function of the sphincter.
It follows that the target zone for sphincter manometry is
very narrow - in the case of adults it is less than
5 mm wide in the upper and lower oesophageal sphincters and
probably about 2 mm wide in the pylorus (5).
Mobility of sphincters
There has been inadequate appreciation of the mobility of
sphincteric regions and how this impacts on sphincter manometry.
The mobility of the upper and lower oesophageal sphincter
with swallowing has been well documented, and amounts to an
excursion of 1.5-2.0 cm in adults (4, 6).
This mobility of the oesophageal sphincters, coupled with
the focal recording properties of side holes and the narrow
zone of maximal sphincter pressure, makes it impossible to
record sphincter responses to swallowing with a side hole
stationed within either oesophageal sphincter. |
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Despite this
well established fact, many manometric laboratories evaluate
lo220wer oesophageal sphincter relaxation with stationed side
holes.
This practice will inevitably lead to failure of recognition
of incomplete sphincter relaxation in some patients.
Major undermeasurement of sphincter pressure also results
from displacement of a stationed side hole from the region
of maximal pressure as a result of:
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respiration-induced sphincter movement
(4)
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changes of manometric assembly position
due to changes of head posture or body position
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movement of the manometric assembly
relative to the sphincter by variations in the degree
of bowing of an assembly between the point of assembly
fixation and the sphincter. |
The tolerance of sphincter/manometric assembly
movement by the sleeve allows a continuous recording with
an anchored manometric assembly, and removes the need for
repeated pullthrough or manometric assembly repositioning,
thereby greatly improving tolerance of manometry by patients.
Design of the sleeve
The sleeve sensor is a perfused channel made of silicone rubber.
(1)
Perfusate enters the channel at one end and vents freely from
the other end.
The channel consists of a concave moulded bed on one side,
and a very thin silicone rubber membrane on the other side.
The sleeve sensor channel has identical dimensions along its
length, which is chosen to suit particular recording applications.
Sleeve sensor length is tailored to exceed the normal range
of axial movement of the particular sphincter relative to
the manometric assembly.
This length varies according to body size and sphincter type.
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How the sleeve
signals sphincter pressure
When there is no squeeze acting on the sleeve sensor, there
is minimal resistance to the passage of perfusate down it.
When the sleeve is positioned within a sphincter, the squeeze
of the sphincter compresses the silicone rubber membrane against
the sleeve bed, increasing the resistance of the sleeve to
passage of perfusate down it.
This increased resistance to water flow down the sleeve causes
an increase in the perfusion line pressure to the sleeve,
in the same way as an increase of pressure at a perfused side
hole causes an increase of perfusion line pressure.
The increase in the sleeve perfusion line pressure is detected
by an external pressure transducer exactly as for side holes.
Validation studies have shown that the sleeve sensor perfusion
line pressure is a faithful indication of maximal sphincter
pressure (1).
It has also been proven that the sleeve signals the maximal
sphincter pressure, regardless of where the sphincter is positioned
along the length of the sleeve.
Thus the sleeve can be regarded as an hydraulic resistor whose
resistance is varied precisely in proportion to the highest
degree of sphincter squeeze acting on it.
Factors that determine sleeve fidelity
Several factors determine how exactly the sleeve reflects
sphincter squeeze.
These factors have been researched in detail only by Dentsleeve;
knowledge of them ensures that all of our sleeve designs provide
optimal fidelity.
Careful definition of details of sleeve design is not a guarantee
of satisfactory fidelity, as minor mismatch of the sleeve
membrane to its bed during sleeve manufacture can result in
a sleeve sensor that looks satisfactory but has poor fidelity.
Because of this possibility, the performance of all of our
sleeves is validated by testing in a sphincter model, and
only those that satisfy stringent standards are incorporated
into assemblies supplied to customers. |
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Dimensions of sleeves
Sleeve sensors vary both in their length and width.
They are also built onto different types of manometric extrusion.
There has been a progressive miniaturisation of sleeves over
the years (7, 8, 9).
The width of the channel of different sleeve sensors varies
from 1.2 to 3.4 mm.
Sleeve pressure rise rates
The silicone rubber sleeve membrane makes the sleeve a relatively
compliant sensor.
Sleeve compliance increases in proportion to the length of
membrane between the point of entry of perfusate into the
sleeve, and the point along the sleeve at which the sphincter
squeeze is applied (1).
Accordingly, sleeve pressure rise rate decreases substantially
along the length of the sleeve.
For most sphincter recordings however, a pressure rise rate
of 5-10 mmHg/sec at the distal sleeve end is sufficient
for reliable monitoring of sphincter pressure.
These pressure rise rates are acceptable because rises of
basal sphincter pressure are relatively slow.
Rapid decreases of sphincter pressure are tracked as quickly
by the sleeve as they are by side holes, as this function
is not determined by compliance. This is relevant to recording
of sphincter relaxations.
The rapid increase of sphincter pressure that follows swallow-induced
sphincter relaxation cannot usually be recorded accurately
with the sleeve; this is a relatively minor limitation, as
it is not a measure of sphincter function that is believed
to be of any major clinical diagnostic or physiological relevance.
The above comments indicate that the needs for rates of pressure
rise differ between sphincters and non-sphincteric regions.
These different needs have not been well understood. |
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Adjustment of
sleeve perfusion rate to sleeve sensor width
The narrower the sleeve sensor, the lower the perfusion rate
required to achieve adequate pressure rise rates.
If a sleeve is perfused at a rate more than double that recommended
for routine use, the segment of the sleeve closest to the
sleeve perfusion point may under-record sphincter pressure
by 2 to 3 mmHg.
This may be an acceptable trade-off for some recording situations,
but for routine use, recommended sleeve perfusion rates should
be observed.
In most designs, the dimensions of sleeves, and so their recommended
perfusion rates are matched to the diameter of manometric
infusion channels, so that the sleeve can be perfused at the
same rate as that needed to give adequate pressure rise rates
on the side hole channels.
Stiffening of sleeves
The resistance of the sleeve to perfusion can be increased
if it is bent too acutely.
This resistance due to bending will be evident as a basal
pressure, and this pressure will not reflect sphincter squeeze.
The sleeve is designed to tolerate a degree of flexion before
its perfusion resistance rises.
However, to prevent signalling of spurious sphincter pressures
as a result of sleeve flexion, all sleeve-bearing segments
of manometric assemblies need to be stiffened selectively.
In some sphincters, there are some special requirements for
the design of stiffening; these are outlined in comments about
particular sleeve types that follow. |
Upper oesophageal
sphincter sleeves
Cross section
Sleeve assemblies for use in the upper oesophageal sphincter
are made with an oval cross section (10).
This cross section ensures that the sleeve radial position
in the sphincter is either anterior or posterior, because
of the slit-like shape of the sphincter when it is contracted.
Consistent orientation to the antero-posterior position is
important, as there is marked asymmetry of the sphincter's
radial pressure profile, with the lateral pressures frequently
being one third of the antero-posterior pressures (11).
Sleeve stiffening
No special features are needed.
Arrangement of side holes around the sleeve sensor
Side holes at either end of the sleeve sensor are useful to
monitor position.
Routine measurements do not require side holes along the sleeve
length.
Lower oesophageal sphincter sleeves
Cross section
This is designed to be as round as possible.
Sleeve stiffening
No special features are needed.
Arrangement of side holes around the sleeve sensor
Side holes at either end of the sleeve sensor are useful to
monitor position.
Routine measurements do not require side holes along the sleeve
length. |
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Pyloric sleeves
Cross section
This is designed to be as round as possible.
Sleeve stiffening
The pylorus presents some special requirements for stiffening.
All pyloric sleeves are made with an especially flexible 3
cm segment immediately distal to the end of the sleeve.
This flexibility is achieved by selective stiffening alone
or handbuilding a flexible segment from individual tubes just
distal to the sleeve (12).
The sleeve stiffener only extends
2-3 mm beyond the tip end of the sleeve so that it does
not interfere with the flexible segment.
The flexible segment just beyond the tip end of the sleeve
allows this part of the assembly to curve around the acute
angle of the proximal duodenum without imposing leverage on
the sleeve in the pylorus.
Early pilot studies in dogs with less focally stiffened pyloric
sleeves showed that leverage produced standing pressures at
the pylorus which did not reflect pyloric motility accurately.
Arrangement of side holes around the sleeve sensor
It is essential that there be a chain of side holes within
the span of the sleeve sensor.
For adults, the side holes in this chain should be no more
than 2 cm apart, and preferably 1.5 cm.
Pyloric sleeve tracings can only be interpreted reliably in
conjunction with the tracings from side holes arranged along
the sleeve (13). |
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Ileocaecal sphincter
sleeves
Cross section
This is designed to be as round as possible.
Sleeve stiffening
There has been little evaluation of the best design.
It would seem desirable to avoid extending stiffening too
far into the caecum because of the angulation of the ileocaecal
sphincter relative to the caecum.
Arrangement of side holes around the sleeve sensor
Motor patterns are a mixture of tonic, localised phasic and
propagated phasic contractions (14).
In principle, these patterns are very similar to the pylorus.
Ileocaecal sleeve recordings are only interpretable when combined
with recordings from a chain of side holes along the span
of the sleeve.
Anal sphincter sleeves
Cross section
This is designed to be as round as possible.
Sleeve stiffening
It is desirable to have a relatively flexible segment immediately
beyond the margin of the tip end of the sleeve sensor, to
accommodate the anorectal angle, without applying leverage
to the sleeve in the sphincter.
Arrangement of side holes around the sleeve sensor
A chain of side holes is useful along the sleeve length for
distinguishing between internal and external sphincter activity.
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Reverse-perfused
sleeves
The sleeve may have difficulty in tracking pressure if the
sphincter moves rapidly away from the point of entry of the
sleeve perfusate.
This can be a problem in the case of the lower oesophageal
sphincter which descends with inspiration.
The use of a reverse-perfused sleeve overcomes this difficulty
(15).
The reverse-perfused lower oesophageal sphincter sleeve is
perfused from the tip end of the assembly so that the perfusate
vents from the sleeve end into the oesophageal body.
Dentsleeve can supply reverse-perfused
sleeves to order.
Radial asymmetry and the sleeve
Sleeve recordings are influenced by radial asymmetry of the
sphincter pressure profile.
Because the sleeve samples from a larger radial angle than
a side hole, it would be expected to be less susceptible to
asymmetry that is confined to a small segment of the radial
pressure profile (16).
The functional importance of radial asymmetry is likely to
vary for different sphincters, but in general has probably
been overestimated relative to the performance of the sphincter
over time.
Manometric assemblies can be supplied which combine the capacity
for side hole sampling of the radial pressure profile with
the capacity to monitor sphincter pressure with a sleeve. |
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Positioning of
oesophageal and anal sleeve assemblies
In general, the sleeve should be positioned so that the zone
of maximal sphincter pressure is at the midsleeve position.
Upper oesophageal sphincter sleeves are an exception to this,
since the major sphincter movement that occurs from the basal
position is upwards, during swallowing (6). This movement
is best allowed for by positioning the centre of the zone
of maximal sphincter pressure at rest about two thirds down
the sleeve length.
Sleeve position is best determined by passing the assembly
beyond the optimal recording position, and then withdrawing
slowly as pressures are recorded from the side holes at either
end of the sleeve.
Passage of the high pressure zone over these side holes allows
accurate positioning of the sphincter on the sleeve.
During monitoring of sphincter pressure, impending displacement
of the sleeve can be recognised if the pressure tracing from
one of the side holes at either end of the sleeve shows signs
of entering the sphincteric high pressure zone.
Side holes at or only 1 cm beyond the sleeve ends are therefore
an essential component of sleeve assembly design.
Positioning of pyloric and ileocaecal
sleeves
Pyloric and ileocaecal sleeves can be positioned on the basis
of recording of region-specific pressure wave patterns at
either end of the sleeve.
This approach has limitations because of periods of motor
quiescence and the considerable variation of the morphology
and duration of pressure waves on either side of the sphincter.
Positioning is greatly aided by the recording of transmucosal
potential difference at either end of the sleeve (12).
Recording of pressures from a chain of side holes along the
length of the sleeve also aids evaluation of sleeve position
in the pylorus and ileocaecal sphincter (13, 14). |
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Detection
of damage to the sleeve
The sleeve membrane must be thin
in order for the sleeve to have adequate fidelity.
The sleeve membrane is therefore the most delicate part of
the assembly.
Vigorous flushing of the sleeve channel and sharp objects
can perforate the sleeve channel.
| We recommend that
sleeve integrity be tested before each use by occluding
the distal margin of the sleeve with a finger with the
perfusion running, and during recording of the sleeve
channel pressure. |
The recorded pressure should be allowed to ramp up to 100
mmHg.
If it fails to do this the sleeve must be perforated and will
not give valid measurements.
Examination of the sleeve under a dissecting microscope during
gentle flushing with a 10ml syringe will usually reveal the
defect in the sleeve membrane.
We strongly advise against attempts at repair of damaged sleeves
by users, as these may impair fidelity seriously.
Dentsleeve is happy to evaluate
autoclaved assemblies for repair of damage. It is only possible
to repair small defects in sleeve membranes.
Aspects of care of sleeve assemblies
PLEASE REFER TO THE FOLLOWING DENTSLEEVE
TECHNICAL NOTES:
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Vital information about the care
of your Dentsleeve manometric
assembly. Dentsleeve Technical
Note 1, Version 2, page 63.
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Cleaning and sterilisation of Dentsleeve
assemblies. Dentsleeve
Technical Note 3, Version 2, page 68.
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Procedure for unblocking channels.
Dentsleeve Technical Note
4, Version 2 page 69. |
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