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Dentsleeve Technical Note 2 Version 2 - The sleeve sensor

The sleeve sensor

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

  • the focal pressure sensing properties of side holes

  • the narrowness of the region of maximal sphincter pressure

  • the mobility of sphincters relative to a luminal recording assembly (4).

    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.

    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.

    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:

  • respiration-induced sphincter movement (4)

  • changes of manometric assembly position due to changes of head posture or body position

  • 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.


    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.

    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.

    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.


    Tailoring of sleeve design to specific sphincters

    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.

    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).

    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.

    1. Dent. Gastroenterology(1976);71:267-276
    2. Dodds et al. Arch Int Med(1976);136:515-523
    3. Dodds et al. J Clin Invest(1973);52:1-13
    4. Dodds et al. Gastroenterology(1974);67:592-600
    5. Heddle et al. Am J Physio(1988);255:G490-498
    6. Kahrilas et al. Gastroenterology(1988);95:52-62
    7. Willing et al. Gut(1993);34:904-910
    8. Kawahara et al. J Aut Nerv Syst(1994);49:69-80
    9. Omari et al. Gastroenterology(1995);109:1757-1764
    10. Kahrilas et al. Dig Dis Sci(1987);32:121-128
    11. Welch et al. J Clin Invest(1979);63:1036-1041
    12. Heddle et al. Am J Physio(1988);254:G671-679
    13. Sun et al. Gut(1995);37:329-334
    14. Quigley et al. Am J Physiol(1987);252:G585-591
    15. Sivri et al. Gastroenterology(1991);101:962-969
    16. Winans et al. Am J Dig Dis(1977);22:348-354

    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.

    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).

    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


  • Vital information about the care of your Dentsleeve manometric assembly. Dentsleeve Technical Note 1, Version 2, page 63.
  • Cleaning and sterilisation of Dentsleeve assemblies. Dentsleeve Technical Note 3, Version 2, page 68.
  • Procedure for unblocking channels. Dentsleeve Technical Note 4, Version 2 page 69.

    Dentsleeve International Ltd


    Technical Notes