US20220225961A1

US20220225961A1 - Imaging probe adapter

Info

Publication number: US20220225961A1
Application number: US17/716,352
Authority: US
Inventors: Ali Borazjani; Benjamin C. Weed; Jun Liao
Original assignee: Mississippi State University Research and Technology Corp (RTC)
Current assignee: Mississippi State University Research and Technology Corp (RTC)
Priority date: 2013-03-13
Filing date: 2022-04-08
Publication date: 2022-07-21
Also published as: US20170164927A1; US9510766B2; US20140275841A1

Abstract

An imaging probe adapter for measuring the properties of a lumen like the vaginal canal, the rectum, or anal sphincter. The device has an adapter body with a proximal end and a distal end. The distal end of the adapter body may be formed into an insertion tip capable of easy insertion into the appropriate lumenal structure. An inflatable pressure chamber covers the distal end of the adapter body. A baseplate formed on the proximal end of the adapter body incorporates fluid channels for inflating the pressure chamber and a probe channel that receives an ultrasound probe or other suitable imaging probe. The device is used to measure and model lumenal biomechanical properties such as stiffness, compliance, elastic versus viscous contributions to overall stiffness, and total displacement.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

10011 This application claims the benefit of priority as a continuation of U.S. patent application Ser. No. 15/369,638 filed Dec. 5, 2016; which itself claims the benefit of priority as a continuation-in-part of U.S. patent application Ser. No. 14/209,316 filed Mar. 13, 2014, which has issued as U.S. Pat. No. 9,510,766; which itself claims the benefit of priority from U.S. Provisional Patent Application 61/780,198, filed Mar. 13, 2013; the entire disclosures of each being incorporated herein by reference.

FIELD OF THE INVENTION

The field of the invention is the diagnostics and measuring of properties of interior spaces such as lumens of bodies, for example, in the gynecological and intestinal systems.

BACKGROUND OF THE INVENTION

Pelvic floor disorders, such as pelvic organ prolapse (POP) are among the fastest growing health concerns worldwide. POP affects 50% of all women who have given birth, and is a leading indication for surgery among women. Total U.S. societal costs for treating and managing pelvic floor disorders are over $29 billion.
POP is characterized by the loss of structural integrity of the supporting tissues (muscles, ligaments, tendons, etc.) within the female pelvis. As the support tissues weaken, pelvic organs (vagina, bladder, rectum, and bowel) begin to protrude into the vaginal canal and towards the vaginal opening. This leads to numerous complications that may include urinary and fecal incontinence, pain and ulcerations, discomfort, sexual dysfunctions and many psycho-social complications.
The most cited risk factor for POP is pregnancy and childbirth. Women having given birth to 2 or more children are up to 8.4 times more likely than their nulliparous counterparts to be diagnosed with POP and require hospitalization. Explicit tissue damage during vaginal delivery may, in part, be attributable, but there is evidence that suggests C-section is only partially protective in the development of pelvic floor disorders. In a study by Fritel et al., no protective effect was found between C-section and the development of stress urinary incontinence. In contrast, other investigators have shown that compared with C-section, spontaneous vaginal delivery significantly increases the odds for both stress urinary incontinence and POP. Animal studies have shown that C-section delays the development of POP. Similarly, others have found that the association between stress urinary incontinence and parity seems to fade or disappear with increasing age. Nonetheless, it is clear that pregnancy and parturition have pronounced effects on the pelvic connective tissues.
Overall, studies have described a maternal adaptation which functions to allow for less-traumatic delivery of offspring in a manner that accommodates favorable neonatal and maternal outcomes. These adaptations in the pelvic connective tissues such as the vagina may include decreased collagen density, increased elastic fiber density, decreased stiffness, and increased distensibility. Importantly, these adaptations are thought to return to a pre-pregnancy state after delivery and during the postpartum period. It may be the case that in some women adaptations during pregnancy (and/or return to pre-pregnancy state after delivery) of the pelvic tissues to pregnancy and parturition may be deficient, incomplete, or exceeded. This may account for both the high incidence of obstetric trauma and development of POP in parous women. The invention allows for monitoring of these adaptions throughout pregnancy and postpartum in a non-invasive manner.
The underlying phenomenon of the POP pathology, the process that leads to symptomatic POP, and the surgical treatments that correct POP are all inherently mechanical or structural. The ability to evaluate the structure of the organs and tissues involved in POP is crucial to understanding, diagnosing, and treating this pathology. The most common diagnostic method for evaluating POP is a physical exam of the pelvis conducted by a physician or nurse along with the completion of a brief“scoring” system (the Pelvic Organ Prolapse Quantification system or POPQ) which stages the prolapse as grade 1-4. This system is quick and effective, but inherently subjective. Vaginal manometry is another common technique, in which a balloon is inserted into the vagina and inflated while pressure is tracked to assess the patients ability of contracting her pelvic floor muscles. A similar technique to vaginal manometry is employed to evaluate the structural competency of the anus and rectum, called anorectal manometry (ARM). These techniques all seek to evaluate the way lumenal tissues respond to specific loading conditions. These existing systems are limited by their ability to simultaneously track the magnitude of the load and the magnitude of the displacement of the structures they evaluate.
Current in vivo biomechanics methods limit the ability of researchers, and greatly limit the potential for application of biomechanics in day-to-day diagnostics/treatment for practicing clinicians. A tool is needed to allow researchers and clinicians to perform in vivo biomechanics studies of the vagina or rectum (or any other lumenal tissues, as is relevant) in a manner that is not too time-consuming and that produces objective data.

SUMMARY OF THE INVENTION

The present invention eliminates the above difficulties and disadvantages by providing an imaging probe adapter for measuring the properties of a lumen like the vaginal canal, the rectum, or anal sphincter. The imaging probe adapter may be simply constructed, and it may be inexpensively manufactured so that it is disposable after one use. The imaging probe adapter has an adapter body with a proximal end and a distal end. The adapter body may be made of rigid, semi-rigid, or flexible materials that are capable of transmitting ultrasound or other imaging waves.
The distal end of the adapter body may be formed into an insertion tip capable of easy insertion into the appropriate lumenal structure. A pressure chamber covers the distal end of the adapter body. The pressure chamber may be configured as a compliant balloon made capable of stretching when the balloon is inflated or a non-compliant balloon that is larger than the volume of the lumen being assessed.
The proximal end of the adapter body forms a baseplate that is the widest portion of the adapter body. One or more flow channels are formed in the baseplate. The flow channels communicate with the interior of the pressure chamber, and the channels allow fluid (air or liquid) to be pumped into the pressure chamber to inflate the pressure chamber. A syringe pump or other appropriate method may be used to inflate the pressure chamber and monitor the internal pressures in the pressure chamber. The pressure chamber may be inflated with water or other suitable liquid or air.
The interior of the adapter body forms a probe channel that is adapted for receiving an imaging probe. In one embodiment, the imaging probe is an endoanal ultrasound probe, but the probe channel may be configured to accept other types of imaging probes. An imaging probe may be coated with ultrasound gel before it is inserted into the probe channel to aid in the transmission of ultrasound waves.
To use the imaging probe adapter, an imaging probe is inserted into the probe channel. Then the adapter is inserted into the patient to a desired depth, such as the depth of the cervix when the vagina is relaxed and the patient is in a supine position with legs in stirrups.
The balloon is inflated to a desired volume or pressure value, and at a desired speed, and inflation is stopped when the optimum or desired pressure or volume threshold is reached. The pressure of the pressure chamber is continuously recorded, and the imaging probe obtains measurements of the deformation and geometry of the pressure chamber. The measurements are resolved to model a variety of vaginal (or lumenal) biomechanical properties such as, but not limited to, stiffness, compliance, elastic versus viscous contributions to overall stiffness, and total displacement. The balloon is then deflated, and the probe is removed from the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is an elevation view of the exterior of the imaging probe adapter. Dashed lines depict the interior structure of the adapter.

FIG. 2 is a cut-away view of the interior of the imaging probe adapter with an imaging probe installed in the adapter.

FIG. 3 is a cut-away view of the interior of the imaging probe adapter

FIG. 4A is a perspective views of the exterior of the imaging probe adapter with the balloon inflated.

FIG. 4B is a perspective views of the exterior of the imaging probe adapter with the balloon inflated.

DETAILED DESCRIPTION

The invention is an imaging probe adapter 1 for measuring the properties of a lumenal structure like the vaginal canal, the rectum, or anal sphincter. The exterior of the imaging probe adapter 1 is depicted in FIG. 1. Dashed lines depict the interior structure. The adapter 1 has an adapter body 3 with a proximal end 5 and a distal end 7. The adapter body 3 may be made of rigid, semi-rigid, or flexible materials that are capable of transmitting ultrasound or other imaging waves.
The distal end 7 of the adapter body 3 may be formed into an insertion tip capable of easy insertion into the appropriate lumenal structure. In one embodiment for assessing the female pelvic floor the insertion tip is designed to insert easily and comfortably into the vagina without encouraging dilation of the cervix. The distal end 7 may comprise a piece having two rounded steps, cut so that the first step is narrow enough to easily separate the labia as would be the case with a cone, but is blunt enough to prevent cervical dilation as would be the case with a cone. In another embodiment, the anatomical tip can be cast, molded or formed in one piece.
A pressure chamber 9 may be constructed of a bag like structure that fits over the adapter body 3. The pressure chamber 9 may be configured as a balloon made of compliant materials such that the material stretches to accommodate the volume within the balloon. The balloon may be made of any suitable flexible material with known mechanical properties that is capable of stretching when the balloon is inflated. By knowing the mechanical properties of the material, the pressures resulted from the tensions and loads being placed by the lumen onto the pressure chamber 9 may resolved and mathematically separated from the pressure generated by the tension within the balloon. In another embodiment, the pressure chamber 9 may be configured as a balloon made of non-compliant materials. In this embodiment, the material of the balloon does not stretch but the balloon is constructed such that it can be filled to a volume that can distend the lumen being evaluated, in this embodiment, the minimal tension is generated within the balloon material and therefore the pressures generated within the pressure chamber 9 are due to the tensions and loads being placed by the lumen onto the pressure chamber 9. In one embodiment, the balloon is a durable polyurethane polymer of medical grade material.
One or more balloon attachment points 11 may be incorporated into the adapter body 3. In this embodiment, the balloon attachment points 1 are channels molded into the adapter body 3 that are configured to receive elastic bands or circumferential clamps 13 to hold the balloon in place. The balloon may also be attached to the adapter body 3 by adhesives or other suitable attachment methods.
The proximal end 5 of the adapter body 3 forms a baseplate 15. The baseplate 15 is the widest portion of the adapter body 3. One or more flow channels 17 are formed in the baseplate 15. The flow channels 17 communicate with the interior of the pressure chamber 9, and the channels 17 allow fluid to be pumped into the pressure chamber 9 to inflate the pressure chamber 9. A system (not shown) for inflating the pressure chamber 9 may include a pump for moving fluid into and out of the balloon by means of a tube secured to a flow channel 17. Flow of liquid or air into the pressure chamber 9 may be both controlled and monitored.
In one embodiment, a syringe pump is employed in which the flow rate of around 25-100 mL/min is achieved, and in which the flow is monitored by the position of the syringe plunger. In another embodiment a flow meter is employed. The pump controls the flow of fluid into the pressure chamber 9. The internal pressure of the pressure chamber 9 may be measured with a pressure transducer (not shown) mounted in the pressure chamber 9 or pressure transmission tubing may be attached to one of the flow channels 17 and the pressure may be measured by a pressure transducer external to the adapter 1.
FIG. 2 is a cut-away view of the interior of the imaging probe adapter 1. The interior of the adapter body 3 forms a probe channel 19 that is adapted for receiving an imaging probe 21. In FIG. 2, an imaging probe 21 is inserted into the probe channel 19. In this embodiment, the imaging probe 21 is an endoanal ultrasound probe, but the probe channel 19 may be configured to accept other types of imaging probes 21. An imaging probe 21 may be coated with ultrasound gel before it is inserted into the probe channel 19 to aid in the transmission of ultrasound waves. FIG. 3 is a cut-away view of the imaging probe adapter 1 without an imaging probe 21 inserted into the probe channel 19.
FIG. 4a is a perspective view of the exterior of the imaging probe adapter 1. In this embodiment, the baseplate 15 is in shape of a flattened, circular flange. The baseplate 15 may be configured into different shapes in other embodiments. The bottom of the baseplate 15 is visible in FIG. 4 b. Two flow channels 17 are present in the baseplate 15, but other embodiments may be configured with one or more flow channels 17. One or more of the flow channels 17 may serve as a port to conduct components (such as tubes, wires, or cables) through the baseplate 15 into the interior of the pressure chamber 9.
To use the imaging probe adapter 1, an imaging probe 21 is inserted into the probe channel 19. Then the adapter 1 is inserted into the patient to a desired depth, such as the depth of the cervix when the vagina is relaxed and the patient is in a supine position with legs in stirrups.
The balloon may be inflated at a desired speed while simultaneously recording pressure, volume, and deformation data. This technique allows for creation of load-versus-displacement curves, or other derivatives thereof, such as stress-versus-strain curves, and load-versus-time curves. This data may be processed to identify specific parameters (i.e. stiffness, extensibility, bulk modulus, novel parameter(s) identified from the described device's data set) of interest to the researcher or clinician. The balloon may also be inflated to a desired volume or pressure value, and at a desired speed, and inflation may be stopped when the pressure or volume threshold is reached. The balloon is held at the above-reached volume for a desired amount of time. This may be from zero seconds up to as much as about an hour or more if stress relaxation behavior is of interest. Alternatively, the balloon may quickly be inflated to a desired pressure, then continually inflated at a very slow inflation rate in order to maintain the desired pressure. This technique would allow the observation of creep phenomenon. The balloon can then be deflated to the original volume.
The endoanal ultrasound probe 21 may be used to obtain balloon geometry at a single plane of interest or it may scan the entire length of the balloon to obtain a 3D volumetric geometry of the balloon as it is being inflated. By means of this invention, detailed vaginal biomechanical properties may be obtained with a resolution high enough to resolve for differences in the biomechanical properties throughout the various locations of the vagina. Data may be output numerically or accompanied by a graphic representation consisting of the 3D shape of the vagina under various pressures overlayed with a map representing various biomechanical properties along the vaginal geometry. The map may be in the form of a heatmap, with different colors representing different values of the mapped biomechanical properties. The biomechanical properties are not limited to but may include stiffness, compliance, elastic versus viscous contributions to overall stiffness, total displacement, etc.
The above-described techniques and procedures may be used in a number of diagnostic, preventative, and therapeutic modes including, without limitation, the following.
1. Diagnosis/characterization of lumenal strength and structural integrity. This information is directly related to the presence and severity of structural disorders of, for example, the pelvic soft tissues such as pelvic organ prolapse or other pelvic floor disorders.
2 Creation of a “baseline” parameter, similar to a patient's normal blood pressure, which is related to lumenal health. This allows the continuous tracking of a patient's progress allowing for a more personalized approach to prenatal care and obstetrics.
3. Diagnosis/identification of patients at high risk for obstetric or other trauma or complications. Structural data is used to evaluate the vagina's ability to accommodate the loading during childbirth, so the clinician can make more informed decisions regarding interventions (C-section, forceps, vacuum suction, for example).
4. Evaluation of surgical interventions which seek to restore structural integrity to the female pelvic floor. These surgeries employ meshes, slings, and major repair and restructure of tissues. Assessment of the structural effects of these procedures allows for better tracking of progress and better understanding of a patient's benefits/complications associated with the surgery.
5. The evaluation of therapy progress, as in physical therapy or fitness training. These therapies seek to strengthen the vaginal tissues through commonly-used methods.
6. Detection or characterization of complications associated with surgery, pelvic injury, and/or radiation which can result in narrowing of the vagina as well as fibrosis.
The terms “comprising,” “including,” and “having,” as used in the claims and the specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms “a,” “an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The term “one” or“single” may be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as “two” may be used when a specific number of things is intended. The terms “preferably.” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.
The following detailed description is presented to enable any person skilled in the art to make and use the invention. For purposes of explanation, specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required to practice the invention. Descriptions of specific applications are provided only as representative examples. Various modifications to the preferred embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. The present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest possible scope consistent with the principles and features disclosed herein.
The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention. It will be apparent to one of ordinary skill in the art that methods, devices, device elements, materials, procedures and techniques other than those specifically described herein can be applied to the practice of the invention as broadly disclosed herein without resort to undue experimentation. All art-known functional equivalents of methods, devices, device elements, materials, procedures and techniques described herein are intended to be encompassed. This invention is not to be limited by the embodiments enclosed, including any shown in the drawings or exemplified in the specification, which are given by way of example and not of limitation.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having, benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

What is claimed is:

1. A method of measuring the properties of a lumen, comprising:

providing an imaging probe adapter comprising:

an adapter body with a proximal end and a distal end, where the distal end is adapted for insertion into the lumen and the proximal end forms a baseplate adapted to remain outside the lumen;

a pressure chamber capable of being demountably attached to the adapter body and inflated with a fluid;

a probe channel formed in the adapter body for insertion and removal of an imaging probe having a first open end at the proximal end of the adapter body and a second closed end disposed towards the distal end of the adapter body, and

one or more flow channels formed in the baseplate in communication with the pressure chamber such that the pressure chamber can be inflated and deflated;

inserting the imaging probe adapter into the lumen;

inserting the imaging probe into the probe channel of the adapter body; and

measuring a geometry of the pressure chamber with the imaging probe; wherein

the imaging probe is not mechanically attached to the imaging probe adapter and the imaging probe can be inserted and removed from the imaging probe adapter when the imaging probe adapter is inserted into the lumen.

2. The method according to claim 1, wherein

the pressure chamber comprises:

a body formed from an elastic material within which the adapter body is inserted;

a first sealed end; and

a second open end;

the adapter body further comprises:

a first mounting point disposed towards the proximal end of the adapter body; and

a second mounting point disposed towards at the distal end of the adapter body, and the pressure chamber is assembled with the adapter body by a process comprising:

inserting the adapter body into the second open end of the pressure chamber such that the distal end of the adapter body is proximate the first sealed end and the proximal end of the adapter body is proximate the second open end;

demountably attaching the pressure chamber to the first mounting point of the adapter body with a first demountable attachment; and

demountably attaching the pressure chamber to the second mounting point of the adapter body with a second demountable attachment.

3. The method according to claim 1, wherein

the pressure chamber comprises:

a first end sealed end; and

a second open end;

the adapter body further comprises:

a first mounting point disposed towards the proximal end of the adapter body;

a second mounting point disposed towards at the distal end of the adapter body; and

one or more flow channels formed in the baseplate;

the pressure chamber is assembled with the adapter body by a process comprising:

demountably attaching the pressure chamber to the second mounting point of the adapter body with a second demountable attachment;

the one or more flow channels formed in the baseplate are in fluid communication with an interior portion of the body of the pressure chamber which is sealed against the adapter body by the first demountable attachment and the second demountable attachment; and

the pressure chamber when inflated with the fluid only inflates around that portion of the adapter body between the first mounting point of the adapter body and the second mounting point of the adapter body.

4. The method according to claim 1, wherein

the pressure chamber is assembled over the adapter body and demountably attached to the adapter body at a first location proximate the distal end of the adapter body and a second location proximate the proximal end of the adapter body;

the adapter body further comprises one or more flow channels formed in the baseplate which are in fluid communication with an interior portion of the pressure chamber; and

each flow channel of the one or more flow channels has:

a first opening disposed on a surface of the baseplate disposed away from the distal end of the adapter body; and

a second opening disposed on another surface of the baseplate disposed towards the distal end of the adapter body; and

each second opening of the one or more flow channels is between the first location and the second location.

5. The method according to claim 1, wherein

the imaging probe is an ultrasonic image probe;

the adapter body is formed from a material transparent to ultrasound signals generated by the ultrasonic imaging probe;

the pressure chamber is formed from or coated with a material reflecting the ultrasound signals generated by the ultrasonic imaging probe; and

the imaging probe is coated with ultrasound gel before it is inserted into the probe channel.

6. The method according to claim 1, wherein

the adapter body is formed from a material transparent to signals generated by the imaging probe;

the pressure chamber is formed from an elastic material; and

either the elastic material or another material coating one of an interior surface of the pressure chamber or an exterior surface of the pressure chamber reflect signals generated by the imaging probe.

7. The method according to claim 1, wherein

the pressure chamber is formed from a non-compliant material; and

either the non-compliant material or another material coating one of an interior surface of the pressure chamber or an exterior surface of the pressure chamber reflect signals generated by the imaging probe.

8. The method according to claim 1, wherein

the pressure chamber is formed from a non-compliant material;

either the non-compliant material or another material coating one of an interior surface of the pressure chamber or an exterior surface of the pressure chamber reflect signals generated by the imaging probe; and

an interior volume of the pressure chamber is larger than the volume of the lumen having its properties measured such that the pressure chamber can be filled to a volume that distends the lumen.

9. The method according to claim 1, wherein

the adapter body further comprises a plurality of flow channels formed in the baseplate;

a first subset of the flow channels are for providing the fluid to an interior volume of the pressure chamber; and

a second subset of the flow channels are ports for conducting components through the baseplate into the interior of the pressure chamber.

10. The method according to claim 1, further comprising

inflating the pressure chamber at a rate; and

establishing pressure, volume and deformation data during inflation of the pressure chamber in dependence upon measurements performed with the imaging probe.

11. The method according to claim 1, further comprising

inflating the pressure chamber at a rate;

establishing pressure, volume and deformation data during inflation of the pressure chamber in dependence upon measurements performed with the imaging probe; and

creating at least one of a load versus displacement curve, a stress versus strain curve, a load versus time curve, a derivative of the load versus displacement curve, a derivative of the stress versus strain curve, and a derivative of the load versus time curve.

12. The method according to claim 1, further comprising

inflating the pressure chamber to a target pressure or target volume; and

when the inflation is to a target volume performing the steps of:

maintaining the pressure chamber at pressure for a predetermined period of time; and

establishing stress relaxation of the lumen in dependence upon measurements performed with the imaging probe; and

when the inflation is to a target pressure performing the steps of:

rapidly inflating the pressure chamber to a target pressure;

continuously maintaining the target pressure; and

establishing creep of the lumen in dependence upon measurements performed with the imaging probe.

13. The method according to claim 1, further comprising

pressuring the pressure chamber; and

inserting the imaging probe to a plurality of positions between the first open end of the probe channel and the second closed end of the probe channel;

measuring the geometry of the pressure chamber with the imaging probe at each position of the plurality of positions; and

establishing a three-dimensional volumetric geometry of the pressure chamber from the geometries of the pressure chamber at a subset of the plurality of positions.

14. A method of measuring the properties of a lumen, comprising:

providing an imaging probe adapter comprising:

inserting the imaging probe adapter into the lumen;

inserting the imaging probe into the probe channel of the adapter body; and

measuring a geometry of the pressure chamber with the imaging probe.

15. The method according to claim 14, wherein

the pressure chamber comprises:

a hollow body;

a first sealed end; and

a second open end into which the adapter body is inserted;

the adapter body further comprises:

a second mounting point disposed towards at the distal end of the adapter body, and

16. The method according to claim 14, wherein

the pressure chamber comprises:

a hollow body;

a first sealed end; and

a second open end into which the adapter body is inserted;

the adapter body further comprises:

a first mounting point disposed towards the proximal end of the adapter body;

one or more flow channels formed in the baseplate;

17. The method according to claim 14, wherein

each flow channel of the one or more flow channels has:

18. The method according to claim 14, wherein

the imaging probe is an ultrasonic image probe;

19. The method according to claim 14, wherein

the pressure chamber is formed from an elastic material or a non-compliant material; and

20. The method according to claim 14, wherein

the pressure chamber is formed from a non-compliant material;