U.S. patent application number 11/790354 was filed with the patent office on 2007-08-23 for method and apparatus for measurement of pressure at a device/body interface.
This patent application is currently assigned to ResMed Limited. Invention is credited to Robert Henry Frater, Patrick John McAuliffe, Milind Chandrakant Raje, Andrew Selim.
Application Number | 20070193339 11/790354 |
Document ID | / |
Family ID | 32298305 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070193339 |
Kind Code |
A1 |
Selim; Andrew ; et
al. |
August 23, 2007 |
Method and apparatus for measurement of pressure at a device/body
interface
Abstract
A system and method for measuring contact pressures between two
surfaces, and especially, between the body and a device resting on
the body, e.g., the skin and a breathable gas mask. A deformable,
resilient probe having a flow passage therein is initially placed
between the two surfaces such that the flow passage is blocked.
Fluid pressure within the probe is then increased until the
pressure in the probe overcomes the contact pressure between the
two surfaces, such that fluid begins to flow through the flow
passage in the probe. The pressure at which the fluid begins to
flow through the flow passage in the probe is recorded as the
contact pressure between the two surfaces. Contact pressure maps
created using this apparatus and method may be used to create
anthropometric models of the face and other body parts.
Inventors: |
Selim; Andrew; (Caringbah,
AU) ; McAuliffe; Patrick John; (Chatswood, AU)
; Raje; Milind Chandrakant; (Wentworthville, AU) ;
Frater; Robert Henry; (Lindfield, AU) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
ResMed Limited
Bella Vista
AU
|
Family ID: |
32298305 |
Appl. No.: |
11/790354 |
Filed: |
April 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11191952 |
Jul 29, 2005 |
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11790354 |
Apr 25, 2007 |
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10720175 |
Nov 25, 2003 |
6941182 |
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11191952 |
Jul 29, 2005 |
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60429066 |
Nov 26, 2002 |
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Current U.S.
Class: |
73/37 |
Current CPC
Class: |
A61M 2016/0661 20130101;
A61M 16/0841 20140204; A61M 16/0858 20140204; G01L 5/00 20130101;
A61M 16/06 20130101; G01L 1/02 20130101; A61B 2090/065
20160201 |
Class at
Publication: |
073/037 |
International
Class: |
G01M 3/02 20060101
G01M003/02 |
Claims
1-21. (canceled)
22. A sensor for measuring contact pressure between a cushion of a
mask and a surface of a patient's face, comprising: at least one
deformable probe having a flow passage therein, the probe being
adapted to be inserted between the cushion and the surface of the
patient's face in use and being adapted for connection to and in
fluid communication with a pressurized conduit, wherein the probe
is deformable from a normally open flow passage configuration to a
substantially closed flow passage configuration by application of a
force urging the cushion against the surface of the patient's face,
the probe adapted for connection to and in fluid communication with
the pressurized conduit such that fluid flow through the probe and
fluid pressure within the probe is measurable to provide a measure
of contact pressure.
23. The sensor of claim 22, wherein the probe is tubular.
24. The sensor of claim 22, wherein the probe is formed of a rubber
material.
25. The sensor of claim 24, wherein the probe is formed of silicone
rubber.
26. The sensor of claim 22, wherein an amount of opening of the
flow passage is a measure of contact pressure.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/429,066, filed Nov. 26, 2002, the contents
of which are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to devices for
measuring contact pressures between two interfacing components, and
more particularly, to measuring pressures between skin and a
component placed thereon.
[0004] 2. Description of Related Art
[0005] Many medical devices, clothing items, and other objects are
designed to rest against the body during operation. For many of
these devices, a proper fit of the device against the body is
desirable for user comfort and/or proper device function.
[0006] For example, breathable gas delivery masks are used in many
types of medical treatments, ranging from simple oxygen therapy to
the treatment of obstructive sleep apnea by application of
continuous or variable positive airway pressure. These masks are
usually designed to rest against the skin adjacent the nose, or in
some cases, the nose and mouth. The portion of the mask that rests
against the skin is usually a soft, conforming cushion or flange. A
good seal between the mask and the skin facilitates delivery of
breathable gas. Gas leaks between the mask and the skin reduce the
volume of gas delivered to the patient, thus reducing the efficacy
of the treatment.
[0007] Anthropometric data on the human face (i.e., normalized
measurements of facial dimensions) can be used to design breathable
gas masks so that they make better seals with the skin. However,
anthropometric data on the human face does not describe the
response of the facial tissues to the mask, and thus, there are
certain circumstances in which pure anthropometric data may be
insufficient. One such circumstance occurs when positive airway
pressure systems are used. These systems deliver breathable gas at
substantial pressures in order to pneumatically splint a patient's
airway. If a breathable gas mask is used with a positive airway
pressure system, the pressures created by the system may cause the
facial tissues to deflect, and at higher pressures, may cause the
mask to lift away from the face. In these circumstances, the
complex response of the facial tissues to the applied pressures
makes it more difficult to design a well-fitting mask.
[0008] Data on the operational contact pressures between a
breathable gas mask and the skin on which it rests can be used in
lieu of or in addition to available anthropometric data in order to
design masks with better fit. However, data on the contact
pressures between a breathable gas mask and skin while the mask is
in use is more difficult to obtain than anthropometric data.
[0009] Similar problems in obtaining good anthropometric data and
predicting the skin's response to applied pressures occur when
attempting to design and fit other objects, such as shoes,
harnesses, orthotics, prosthetics, headgear for securing breathable
gas masks, backpacks, and/or items of clothing, particularly with
elastic properties and/or elements.
SUMMARY OF THE INVENTION
[0010] One aspect of the invention relates to an apparatus for
measuring contact pressures between two surfaces and, particularly,
between a breathable gas mask and the face.
[0011] Another aspect of the invention relates to a method of
measuring a contact pressure/force between two surfaces, e.g.,
curved and/or deformable surfaces, and, particularly, between a
breathable gas mask and the face.
[0012] A further aspect of the invention relates to a method of
dynamically measuring and monitoring contact pressure between a
cushion of a breathable gas mask and a portion of the face.
[0013] Yet another aspect of the invention relates to a method of
designing a breathable gas mask using the measurement methods
described above.
[0014] Another further aspect of the invention relates to a method
for creating an anthropometric model of a face.
[0015] In particular, one embodiment of the apparatus for measuring
contact pressures between two surfaces comprises a deformable,
resilient probe having a flow passage therein. The probe is adapted
to be inserted between the two surfaces such that the flow passage
is substantially blocked in a first operative position of the
probe. The apparatus also includes a fluid flow generator coupled
to the probe, a fluid flow meter coupled between the fluid flow
generator and the probe, and a manometer coupled between the fluid
flow generator and the probe. The apparatus may also include a data
acquisition system coupled to at least the fluid flow generator and
the manometer.
[0016] Additionally, the method for measuring a contact pressure
between two surfaces generally comprises inserting at least one
deformable, resilient probe having a flow passage therein between
the two deformable surfaces such that the flow passage is
substantially blocked in a first operative position. The method
also comprises generating fluid pressure within the probe,
measuring the fluid pressure within the probe, measuring fluid flow
through the probe, and recording the fluid pressure at which the
fluid flow increases above a baseline flow value as the contact
pressure.
[0017] These and other aspects, features, and advantages of the
invention will be described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The present invention will be described with respect to the
following Drawings, in which like numerals represent like features
throughout the several views, and in which:
[0019] FIG. 1 is a schematic diagram of a pressure measurement
system according to an embodiment of the present invention;
[0020] FIG. 2 is a top plan view of the pressure measurement
probe;
[0021] FIG. 3 is a cross-sectional view of the pressure measurement
probe;
[0022] FIG. 4 is a top plan view of the pressure measurement probe
operatively positioned between a breathable gas mask and a
patient's skin;
[0023] FIG. 5A is a sectional view of the compressed, operatively
positioned pressure measurement probe;
[0024] FIG. 5B is a sectional view similar to that of FIG. 5A
showing the pressure measurement probe in a partially compressed
operative position;
[0025] FIG. 5C illustrates a cross section of another embodiment of
the present invention;
[0026] FIG. 6 is a high-level schematic flow diagram of a method of
using the pressure measurement system of FIG. 1;
[0027] FIG. 7 is a schematic waveform illustrating pressure and
flow data that may be generated by the pressure measurement system
of FIG. 1;
[0028] FIG. 8 is a schematic illustration of a pressure measurement
system according to another embodiment of the present invention in
which multiple pressure measurement probes are used simultaneously;
and
[0029] FIG. 9 is a sectional view similar to those of FIGS. 5A and
5B, illustrating the multiple pressure measurement probes of the
pressure measurement system of FIG. 7 installed in operative
positions along an interface.
DETAILED DESCRIPTION
[0030] A pressure measurement system 10 according to an embodiment
of the present invention is illustrated in the schematic view of
FIG. 1. In general, the pressure measurement system 10 is
configured and adapted to measure contact pressures between two
surfaces. More particularly, the pressure measurement system 10 is
well suited for measuring contact pressures between two curved
and/or deformable surfaces. This is not possible with conventional
microstrain gauges due to hysterisis calibration issues. Certain
aspects of the pressure measurement system 10 and methods for using
it will be described below with respect to measuring contact
pressures between skin and a breathable gas mask, although the
pressure measurement system 10 may be used to determine contact
pressures between the body and other objects, such as shoes,
harnesses, orthotics, prosthetics, headgear for securing breathable
gas masks, and backpacks.
[0031] The pressure measurement system 10 comprises a deformable
pressure measurement vessel or probe 12 which is connected by a
length of tubing 14 to a flow generator 16. The flow generator 16
may include a control valve. Connected in series with the probe 12
and the flow generator 16 is a flow meter 20. A manometer 18 is
connected to the tubing 14 at a position downstream from the flow
meter 16 to measure the pressure within the tubing 14. The
manometer 18 and flow meter 20 of this embodiment are digital
instruments and are connected to a data acquisition system 22. (The
dotted-line connection between the flow generator 16 and the data
acquisition system 22 in FIG. 1 indicates that the flow generator
may optionally be connected to or in communication with the data
acquisition system 22.) The data acquisition system 22 is, in turn,
connected to a computing unit 24, which may perform further
analysis on the collected data. Each of these components will be
described in more detail below.
[0032] The probe 12 and a section of tubing 14 are shown in more
detail the top plan view of FIG. 2. The probe 12 is a thin
flexible, resilient tubular membrane that is connected to the
tubing 14 on one end and is open to the atmosphere on the other
end. The probe 12 may be connected to the tubing 14 by adhesives or
other conventional type of connection. In general, any connection
that produces an airtight seal between the probe 12 and tubing 14
is suitable. The probe 12 of this embodiment is formed of silicone
rubber by a known process, such as dip molding. The probe 12 may
also be made of a metal foil or composite material. FIG. 3 is a
cross-sectional view of the probe 12 illustrating tubular nature of
the probe 12 and the connection between the tubing 14 and probe
12.
[0033] The tubing 14 may be any sort of flexible tubing that is
compatible with the fluids that are to be used. For example, in
breathable gas mask contact pressure measurement applications,
silicone rubber or flexible PVC tubing is suitable. In general,
those of ordinary skill in the art would be capable of selecting
flexible tubing with appropriate inner and outer diameters,
pressure ratings, and other characteristics. For example, the
tubing 14 may have an inner diameter of 2.6 millimeters and an
outer diameter of 4.0 millimeters, although the particular inner
and outer diameters of the tubing are not critical.
[0034] The tubing 14 is of sufficient length to connect the probe
12 with the flow generator 16 and other components, which may vary
from application to application. (A length of approximately 1.5
meters may be appropriate for most in-laboratory measurements,
although longer or shorter lengths may be used in other settings
and for other applications.) A connector 26 is provided at one end
of the tubing 14 to connect the tubing 14 to the other components
of the apparatus 10. One exemplary type of connector is shown in
FIG. 2, although the actual connector 26 that is used will vary
depending on the characteristics of the component(s) to which it is
attached. The connector 26 should provide an airtight seal between
the tubing 14 and the other components of the apparatus 10. As
shown in FIG. 2, an in-line connector 28 may be used to connect
shorter segments of tubing 14 together, or to connect the segment
of tubing 14 on which the probe 12 is mounted with the rest of the
tubing 14.
[0035] The probe 12 is designed to be positioned between two
contacting surfaces, as in the top plan view of FIG. 4, in which it
is illustrated as positioned between skin 30 and the cushion 32 of
a breathable gas mask 34. (Although a cushion 32 is shown in FIG.
4, breathable gas masks may alternatively use a conforming flange
of soft rubber, such as silicone rubber and/or foam. Masks made
with an inflatable chamber are also contemplated. The term
"cushion," as used herein, is meant to encompass all of these
structures and materials.) The probe 12 is usually positioned such
that the end portion 36 of the probe 12 extends beyond the inner
edge of the cushion 32. For example, the end portion 36 may extend
about 10 mm beyond the inner edge of the cushion 32, towards the
interior of the mask 34. The length of the end portion 34 of the
probe 12 that extends beyond the interface between the two objects
would depend on the width of the two objects and may be arbitrarily
selected.
[0036] The initial contact pressure between the skin 30 and the
cushion of the breathable gas mask 34 causes the probe 12 to be
compressed between the skin 30 and the mask 34, as shown in FIG. 4.
The initial, compressed operative position of the probe 12 between
the skin and mask 34 is also shown in FIG. 5A, a sectional view of
the probe 12, skin 30, and mask cushion 32. Typically, the
compressive forces on the probe 12 cause its open end to be
entirely or almost entirely closed in the initial operative
position. As pressure and flow are generated by the flow generator
16, the pressure within the probe 12 and tubing 14 grows until the
internal pressure within the probe 12 and tubing 14 begins to
overcome the contact pressure between the mask 34 and skin 30. When
the internal pressure of the probe 12 begins to overcome the
contact pressure between the mask 34 and skin 30, the end of the
probe 12 is forced open, as illustrated in the sectional view of
FIG. 5B, allowing flow though the open end of the probe 12. Data on
the contact pressure between the mask 34 and skin 30 can be
obtained by monitoring the pressure in the probe 12 and the flow
through the probe 12. This process will be described in greater
detail below.
[0037] FIG. 5C shows an alternate embodiment of the present
invention. In this embodiment, the probe 12' includes upper and
lower side walls 45, 50 that are joined at each end, e.g., via
glue, stitching, and/or the like.
[0038] As will be obvious from the previous paragraph, the probe 12
is adapted to withstand a defined internal pressure which is at
least equal to the maximum contact pressure expected between the
two objects, e.g., the skin 30 and mask cushion 32. For mask
contact pressure applications, the probe 12 may be designed to
withstand interior pressures up to about 40 cm H.sub.2O. Other
applications may require the probe 12 to operate at higher internal
pressures. In higher-pressure applications, the walls of the probe
12 may have a greater thickness, or may be made of other materials,
such as rubber materials with greater stiffness, metal foils, or
deformable composite-reinforced materials. In general, the tubing
14 may be rated to handle the same pressure as the probe 12, or it
may be rated to handle higher pressures.
[0039] The material from which the probe 12 is made should be
strong enough in tension to contain whatever fluid pressures are
required. However, it is desirable if the material is also
relatively soft and compliant in bending/crushing, such that the
force necessary to deform the probe 12 itself may be considered
negligible. If the force required to deform the probe is negligible
in comparison with the applied pressures, it may be ignored when
taking pressure data with the apparatus 10. In embodiments of the
invention, if the force required to deform the probe 12 is not
negligible, the data acquisition system 22 or computing unit 24 may
be configured or adapted to actively compensate for the force
required to deform the probe 12. Compensation could be performed
by, e.g., modeling the force-deformation response of a particular
probe material and normalizing the acquired pressure data using the
model for that particular probe material. Compensation could also
be performed by using known, measured force-deflection data for a
particular probe material to normalize the acquired pressure
data.
[0040] Fluid flow and pressure within the pressure measurement
system 10 are generated by the flow generator 16. The flow
generator 16 may be a variable or constant pressure compressor
adapted to compress room air, oxygen, or another mix of gases to
desired pressures. (If mask contact pressure measurements are to be
taken on a live subject, the mixture of gases may be either
breathable or, if the patient is supplied with sufficient
breathable gas, physiologically inert.) Preferably, the flow
generator 16 should be able to provide a plurality of pressure
values so that measurements can be made at each pressure value. For
example, the flow generator 16 can be set to ramp up through a
range of pressure values. "Desired pressures" for breathable gas
mask contact pressure applications typically range from about 0 cm
H.sub.2O to about 40 cm H.sub.2O, although other pressures may be
used for other applications. In breathable gas mask contact
pressure applications, a variable positive airway pressure (VPAP)
compressor such as the VPAP II STA (ResMed Ltd., North Ryde, NSW,
Australia) may be used.
[0041] Alternatively, depending on the nature of the components,
the gas or mix of gases may comprise noble gases, such as argon or
helium. If the gas or gases are initially provided in high-pressure
compressed gas cylinders, the flow generator 16 may be a gas
pressure regulator configured to provide a gas flow at a desired
pressure (which is typically lower than the gas storage pressure in
the gas cylinder). A pressure regulator may also be used if the
compressor used as the flow generator 16 is a constant pressure
compressor.
[0042] Additionally, liquid fluids such as water may be used to
generate the desired pressures and flow rates, depending on the
nature of the pressure measurement application.
[0043] The internal pressure in the tubing 14 and probe 12, and the
flow through the tubing 14 and out the open end of the probe 12,
are measured by the manometer 18 and flow meter 20, respectively.
The manometer 18 and flow meter 20 may be digital or analog
instruments that are connected to the tubing 14 in series with the
pressure generator 16 by appropriate connectors 26, 28. Examples of
suitable digital instruments include electronic manometer model
number PS 309 available from Validyne Engineering Company
(Northridge, Calif., USA) and electronic flowmeter model number TSI
4040 available from TSI, Inc. (Shoreview, Minn., USA).
[0044] In the embodiment illustrated in FIG. 1, the manometer 18
and flow meter 20 are connected via data connections to the data
acquisition system 22, although those of ordinary skill in the art
will realize that the data acquisition system 22 and computing unit
24 are not required in order to obtain data from the pressure
measurement system 10. Instead, especially if the pressure and flow
rates in the tubing 14 and probe 12 rise slowly, data may be read
directly from the manometer 18 and flow meter 20, e.g.,
manually.
[0045] The term "data acquisition system" is meant to encompass
data acquisition hardware such as signal amplifiers, filters, and
other signal conditioning equipment, as well as the breakout boxes
and other components that make the physical data connection between
the data acquisition system 22 and the manometer 18 and flow meter
20. Depending on the particular installation and available
equipment, the data acquisition system 22 may be a stand alone
unit, or its functions may be integrated into the computing unit
24. If the data acquisition system 22 is a stand alone unit, it may
include sufficient computing and storage ability to acquire and
store data points for later analysis and, thus, may not be
connected to a separate computing unit 24 during data acquisition.
Alternatively, the data acquisition system 22 could provide the
computing unit 24 with data in real time.
[0046] One type of appropriate data acquisition system 22 is the
DAQBOOK.RTM. 260 data acquisition system (IoTech, Inc., Cleveland,
Ohio, USA), in which case the computing unit 24 may be a personal
computer equipped with the DAQVIEW.TM. software (IoTech, Inc.).
Other common data acquisition products and supporting software may
be used, including LabVIEW.RTM.-based data acquisition systems
(National Instruments, Inc., Austin, Tex., USA). Customized data
acquisition software may also be created in a conventional
programming language, such as C++ or Java. Depending on user needs,
the computing unit 24 may also be equipped with more generalized
analysis software, such as spreadsheet software. The data
acquisition software of the computing unit 24 may also be adapted
to provide the acquired pressure and flow data to mechanical
modeling software, such as finite element method software or CAD
software.
[0047] Those of ordinary skill in the art will realize that the
computing unit 24 need not be a personal computer, or even a
multipurpose computer. The computing unit 24 may be any type of
computing device having numerical analysis capabilities
commensurate with user needs. Other types of computing units
include microprocessors or ASICs coupled with appropriate memory
and display devices. Depending on the capabilities of the computing
unit 24, the analysis software may be hard-coded into the computing
unit 24 in a lower-level programming language, such as assembly
code.
[0048] A method 50 of using the pressure measurement system 10 is
shown in the high-level schematic flow diagram of FIG. 6. Method 50
begins at S52 and continues with S54. At S54, the user places the
probe 12 between the two contacting objects, for example, between
the mask 34 and the skin 30, as in FIG. 4. The probe 12 is inserted
between the mask 34 and skin 30 such that it does not wrinkle or
distort, which might create unwanted flow obstructions. Once the
probe 12 is placed in S54, the user may begin the typical regimen
usually used with the mask 34, for example, variable positive
airway pressure. (Treatment regimens would typically be implemented
using a separate flow generator, not the flow generator 16 used in
the pressure measurement system 10.) Method 50 continues with S56,
at which the user sets the initial pressure of the flow generator
16, and S58, at which the user sets the final pressure of the flow
generator 16. Depending on the type of flow generator 16 and the
data acquisition system 22, the user may simply activate the data
acquisition system 22 at this point and allow it to acquire data
from the manometer 18 and flow meter 20 while the flow generator 22
ramps from the initial to the final pressure. The remaining tasks
illustrated in method 50, and the following description, assume
that the flow generator 16 is controlled by the data acquisition
system 22.
[0049] Method 50 then continues with S60, at which the user sets
the ramp rate of the flow generator 16. Once the ramp rate is set
in S60, the flow generator 16 is activated and the user begins data
acquisition (DAQ) at S62. At S64, the data acquisition system 22
acquires a data point and control passes to S66, at which the data
acquisition system 22 increments the flow generator 16 pressure.
Alternatively, the pressure can be incremented manually. Control
then passes to S68. At S68, the data acquisition system 22 or
computing unit 24 compares the current flow generator 16 pressure
with the desired final pressure. If the current pressure is greater
than or equal to the desired final pressure (S68: YES), control
passes to S70 and the data acquisition terminates. Otherwise (S68:
NO), control returns to S64 and another data point is acquired.
Method 50 terminates and returns at S72.
[0050] FIG. 7 illustrates a schematic waveform 74 of pressure
versus flow data that may be generated by the pressure measurement
system 10 using a method such as method 50. In FIG. 7, exemplary
units and numerical values are shown for a mask/skin contact
pressure measurement application, although those of ordinary skill
will realize that the pressures and flow rates will be different in
different applications, and that the results may be reported in any
convenient units. Initially, the probe 12 is seated between the
mask 34 and skin 30, as in FIG. 4, and is compressed and
substantially sealed by the contact pressure between the two.
During segment A-B of waveform 74, pressurized gas fills the
initially unpressurized tubing 14 and probe 12. During segment B-C,
the pressure in the probe 12 continues to increase, but does not
overcome the contact pressure between the mask 34 and skin 30, and
so the probe 12 stays closed, allowing only a constant,
insubstantial amount of gas to flow out. During segment C-D, the
pressure in the probe 12 exceeds the contact pressure between the
mask 34 and skin 30, causing the probe 12 to begin opening and,
consequently, causing the amount of flow through the tubing 14 and
probe 12 to increase. (The pressure at point C, approximately 16 cm
H.sub.2O, would be taken as the contact pressure between the mask
34 and skin 30.) In segment D-E, pressure in the probe 12 has
caused the mask 34 to lift completely away from the skin 30. In the
illustrated mask/skin application, method 50 may be executed such
that the pressure in the probe 12 ramps from 0 cm H.sub.2O to 36 cm
H.sub.2O in about 15 seconds.
[0051] Method 50 and waveform 74 illustrate the acquisition of a
single contact pressure data point. However, the pressure
measurement system 10 may also be used to gather multiple contact
pressure data points in the same location over time. For example,
instead of increasing pressure substantially beyond the contact
pressure (i.e., as in segment D-E of waveform 74) and terminating
data acquisition, the pressure within the tubing 14 and probe 12
could be reduced quickly to a pressure that is lower than the
contact pressure between the two surfaces. Once pressure within the
tubing 14 and probe 12 is reduced, it could then be increased again
while continuing data acquisition, which would generate another
contact pressure data point. This process could be repeated at
intervals, for example, to generate a contact pressure data point
every few seconds. Data points may be taken at essentially any
desired data acquisition rate, subject only to the frequency
limitations of the data acquisition hardware (including the data
acquisition system 22 and flow meter 20). (Those of skill in the
art will appreciate that at higher frequencies, some materials,
such as skin, respond non-linearly to the application of pressure,
an effect which may or may not be desirable, depending on the
application.) Typically, it is preferable to gather at least two
data points at each particular pressure, and may be more preferable
to gather about ten data points per particular pressure.
[0052] The embodiment described above involves the use of a single
probe 12 to collect contact pressure at one location between two
surfaces. However, in other embodiments, multiple probes 12 may
collect contact pressure data at a plurality of locations
simultaneously.
[0053] A multiple-probe embodiment of a pressure measurement system
100 according to the present invention is illustrated schematically
in FIG. 8. The data acquisition system 22 and computing unit 24 are
not shown in FIG. 8, although they would be connected to the
pressure measurement system 100 in the same way as illustrated in
FIG. 1. In general, only those portions of the pressure measurement
system 100 that differ from those in pressure measurement system 10
are described; the description above will suffice for the other
components.
[0054] In pressure measurement system 100, the flow generator 16 is
connected to a connection block 102. The connection block 102 has a
plurality of outlets (five in FIG. 8) to which individual lengths
of tubing 14 can be connected, such that flow from the flow
generator 16 is divided and flows through the tubing 14 and into a
corresponding plurality of probes 12. The individual probes 12 are
connected in parallel with respect to each other. A flow meter 20
is connected in series with each one of the plurality of probes 12,
and a single manometer 18 is connected to the connection block 102.
A plurality of valves or switches 40 can be selectively activated
to control flow through each of the outlets. Alternatively, a
single flowmeter 20 could be provided, if that flowmeter was
capable of taking individual flow measurements for each of the
probes 12. In yet another alternative, a plurality of manometers
may be provided, one for each outlet.
[0055] Multi-probe pressure measurement system 100 allows a user to
simultaneously gather contact pressure data at several points along
an interface between two surfaces. For example, FIG. 9 is a
sectional view similar to that of FIGS. 5A and 5B, illustrating
several probes 12 operatively positioned between skin 30 and the
cushion 32 of a mask 34. As shown, the contact pressures between
the mask cushion 32 and the skin 30 are different at each point,
thus the individual probes 12 are each compressed to varying
degrees, and consequently, the flow through each probe 12 is
different (ranging from essentially no flow for the probe 12 on the
extreme left of FIG. 9 to considerable flow for the probe 12 on the
extreme right of FIG. 9). Although the probes 12 are shown as
linearly adjacent in FIG. 9 for clarity of illustration, they need
not be linearly adjacent in actual use. Instead, they may be
arranged in any way. Additionally, if only a few of the available
probes 12 are to be used for a particular measurement task, the
connection block 102 could be provided with an individual shut-off
valve for each probe, such that flow from the flow generator 16
would not flow into the unused probe 12. Alternatively, the user
may disconnect the unused probes 12 from the connection block 102
and install appropriate caps to seal the open outlets of the
connection block 102.
[0056] Once contact pressures have been determined over an area of
the interface between two surfaces, a map can be created,
illustrating how the contact pressures vary along the interface. A
contact pressure map such as this may be used to design or custom
fit a breathable gas mask or other device for a better fit. For
example, an existing breathable gas mask may be modified in
accordance with contact pressures determined by using a method such
as method 50. This may be done iteratively. For example, a user
could perform method 50 on an existing mask to create a contact
pressure maps of that mask on a representative group of subjects or
models. Using the pressure maps, the user would then "build up" the
mask where contact pressures are consistently low and "cut down"
the mask where contact pressures are consistently high to obtain
the desired distribution, e.g., a more even pressure distribution.
In another embodiment, the desired pressure/force distribution may
be uneven, to apply less pressure/force on sensitive areas and more
pressure/force or less sensitive areas, preferably while providing
the user with an improved comfort level and/or the appearance of an
even pressure distribution. The new or improved mask design could
then be validated by performing method 50 again.
[0057] Additionally, contact pressure maps may be used to create
accurate models, both computational and physical, of human faces
and other body parts. These model faces and other body parts may be
created using contact pressure maps from several experimental
subjects, and may be made in a range of "standard" sizes. The
"standard" sizes for these models may, for example, represent mean
anthropometric values for desired body parts or facial features,
plus or minus a number of standard deviations. The model faces and
other body parts would then used to design and test breathable gas
masks and other devices.
[0058] Certain components of the apparatus 10 may be built into a
breathable gas mask or other component to be tested, such that a
testing method like method 50 may be employed without providing a
separate probe 12.
[0059] Although the invention has been described with respect to
several exemplary embodiments, those of ordinary skill will realize
that variations and modifications are possible within the scope of
the invention. The embodiments described herein are intended to be
exemplary only and are not to be construed as limiting.
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