CA1334487C - Biomedical pressure transducer - Google Patents
Biomedical pressure transducerInfo
- Publication number
- CA1334487C CA1334487C CA000616563A CA616563A CA1334487C CA 1334487 C CA1334487 C CA 1334487C CA 000616563 A CA000616563 A CA 000616563A CA 616563 A CA616563 A CA 616563A CA 1334487 C CA1334487 C CA 1334487C
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- chamber
- contacts
- tissue
- pressure
- flexible
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Abstract
A biomedical transducer which is useful for interposing between a tissue and apparatus or another tissue or organ which is applying pressure to the tissue, in order to estimate the pressure applied to a selected area of the tissue. The biomedical pressure transducer comprises: a first flexible layer carrying at least one electrical contact; a second flexible layer carrying at least one electrical contact and cooperating with the first flexible layer to define a pressurizable chamber wherein the contacts are normally touching when the chamber is not pressurized;
and pressure estimation means for selectably pressurizing the pressurizing chamber so as to move at least one of said flexible layers sufficiently to separate the electrical contacts, and for indicating the lowest selected pressure at which the contacts are separated.
and pressure estimation means for selectably pressurizing the pressurizing chamber so as to move at least one of said flexible layers sufficiently to separate the electrical contacts, and for indicating the lowest selected pressure at which the contacts are separated.
Description
BIOMEE)ICAL PRESSURE TRANSDUCER
The present application is a division of Canadian patent application serial number 556,593 filed January 15, 1988.
Field of the Invention This invention pertains to transducers for estimating the pressure applied to a tissue of a body by an object such as a medical device or body part. The invention particularly pertains to a thin~and flexible transducer useful in health care for interposing at the surface between a tissue and an object, without substantially displacing either the tissue or the object from the surface, to estimate the pressure applied near at least one predetermined tissue location.
- Background of the Invention There are many clinical situations in which it is desirable to have an accurate estimate of the pressure applied to a tissue of a body by a medical device or by a body part such as another tissue or organ. These clinical situations include:
the evaluation of new and existing types of occlusive cuffs for pneumatic tourniquet systems and sphygmomanometers; the evaluation, improvement and standardization of the techniques employed by clinical staff in selecting and snugly applying an occlusive cuff to an extremity having a particular size, shape and tissue composition; the development and evaluation of innovative and potentially less expensive automatic tourniquet systems, including non-pneumatic tourniquet systems; the develop-ment and evaluation of advanced robotic devices and pre-robotic devices for tissue manipulation and limb manipulation in surgery and rehabilitation; the development 1 334~B~
and evaluc.~sn of improved, safe! systems for a common anesthet_c techr.ique (intravenous regional anesthesia) which ~s based on the proper use of a special occlusive cuff; the development, improvement and evaluation of biomechanical models of tissue; the evaluation and fitting o' specia'~ dressings and garments 'or applying pressure within a pressure-tolerance window to the tissue of burn patients in order to enh~nce healing; the diagnosis and treatment of compartmental pressure syndrome in orthopedics; the monitoring and control of sequential limb compression devices for prevention of deep venous thrcmbosis, and medical anti-shoc~ trousers for emergency treatment; and perhaps the investigation and treatment of pressure sores in immobile patients.
Different types of biomedical pressure tr~ns~tc rs known in the prior art may have a n~her of disadvantages when used in clinical situations such as those described above. First, many tr~n~ucers known in the prior art are not sufficiently thin and flexible for interposing between selected b~dy tissues and objects such as medical devices or body parts, e.g. organs, skeletal structures and other tissues, without displacing substantially either the tissue or the object. Tra~sducers which require a rigid substrate for proper operation are not particularly useful for estimating the pressure applied to one soft tissue by an adjacent soft tissue, or for estimating the pressure applied to the tissue by an object havir.g a curved or irregular surface. Many types of transducers known in the prior art are mass-produced in one st~nd~a form using expensive fabrication technologies to ac:~ieve economies af 1 3344~
scale, an~ t;-U5 ~hese t~ansduce_s cannc~ be read~ly adapted. ~dap~_on is impor~ant in many oiomedical situations: ~ ;s frequently desiraDle to nave a transducer ar-ay, or a plurality of t_ansducers, 40r simultaneously es;imatins the pressures at a plurality of predeterm ~ed locations of a tissue beneath a pressure-applying object; and it is often desirable to change the number and area of the pressure transducers at those locations for selected combinations of tissues and obiects.
Similarl~, in many prior art tr~s~cers which are mass-produced in one st~ rd form, the composition and physical ~ nsions of various elements of these transducers cannot be conveniently and economically modified so that the tr~s~-~c~r conforms more closely between a particular tissue and object of interest. Many of the biomedica~
pressure tr~sdt-cers known in the prior art are inherently complex and ~xre~cive~ thus reducing the probability that such tr~nC~uc~rs might be conveniently and econ~ically integrated if desired into medical devices such as 2Q occlusive cuffs, pressure dressings for burn patients, tissue retractors and the patient-applied parts of robatic systems for surgery and rehabilitation. Other tr~nC~lcers known in the prior art have the disadvantage that they cannot be conveniently sterilized by commonly used 2S techni$ues, ar.d this precludes the use ~f such prior-art transducers inside the body, either between adjacent soft tissues (e.g. in the diagnosis and treatment of compartmental pressure syndrome), or in surgery (e.g. between a soft tissue and an abject such as a tissue retractor~. Some transducers known in the prior art re~uire complex and expensive support circuitry, a~d others re~uire ~ifficult 2nd time-consuming calibration p-ocedures. Anothe- disadvantage of some prior-art trAnsdl~cers is that their accuracy and hysteresis cannot be conveniently chec~ed by clinical staff in a health-care environment using readily available apparatus and electronic pressure transducers. A final disadvantage of certain biomedical pressure transducers is that, because of unacceptable inaccuracy, calibration difficulties or unreliability associated with repetitive usage, these transducers cannot be safely incorporated into systems for automatically controlling the pressure applied to a body tissue near a predetermined location.
~he biomedical pressure trAn~ cer of the present invention was developed to overcome many of the disadvantages of prior-art tr~n~ rers fcr clinical situations such as those indicated above. The tranc~llcer ~f the present invention makes advant-geous use of some of the t~ logy developed for, and now commonly employed in, the fabrication of i~yr~ncive and flexible membrane switches in small batches for a wide variety of applications.
The applicant is aware of the following United States patents which are more or less relevant to the subject matter of the applicant's inventi~n.
4,605,010 8/1986 McEwen 128/686 4,419,494 10~1984 McEwen 128/327 128/682 4,469,099 9/1984 McEwen 128~327 128/682 4,300,029 11/1981 Maser 200/159B
`^` 1334487 4,218,600 8/1980 Klssner 200/159B
4,217,473 8/1980 Parklnson 200/159B
3,095,873 7/1963 Bdmunds 128-2.05 The appllcant 18 also aware of the followlng publlshed references whlch are more or le~s relevant to the sub~ect matter of the appllcant's lnventlon.
J.A. McBwen and R.W. McGraw, "An adaptive tournl~uet for lmproved safety ln surgery. n IEEB Transactlons ln Blomedlcal Bnglneerlng, Vol. BMB-29, February 1982, pp. 122-128.
J.A. ;~cE~en and G.F. A~hlnleck, "Advances in surgical - tour-.i~ue~s.~ J. Assn. opera~ing Room Nurses, Vol.
~6, i382, p~. 889-896.
J.A. Shaw and D.G. Murray, "The relationship between tourniquet pressure and underlying soft-tlssue pressure in tne thigh." The Journal of ~one and Joint Surgery, Vol. 64-A, 1982, FP- 1148 -11;2.
A.C. McLaren and C.H. Rorabeck, "The pressure distribution under tourniquets." ~he Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 433-438.
R.J. Newman and A. Muirhead, "A safe and effective low pressure tourniquet." Journal of Bone and Joint Surgery, Vol. 68-8, 1986, pp. 625-628.
J.A. Shaw, W.W. Demuth, and A.W. Gillespy, "Guidelines for the use of digital tourniquets based on physiological pressure measurements." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 1086-1090 .
S.E. Grice et al., ~Intravenous regional anesthesia:
Evaluation and prevention of leakage under the tourniguet.~ Anesthesiology, Vol. 6;, pp. 316-320, 1986.
Summary ~ the Invention The invention is directed toward a transducer for estimating t:-e pressure app~ied to a body tissue near a predetermined tissue location by a~ object such as a medical device or body part, comprising: a first flexible layer car~ing a first eLectrical contact; a second flexible layer carrying a second electrical contact and cooperating with the first flexible layer to define a flexible pressuri2able chamher for interposing between a tissue and an o~ject wherein the first and second electrical contacts are to~lchi ng near a predeter~ine~
tissue location when the c~amher is not pressurized; and pressure estLmation means for selectably pressurizing the c~mher, and for indicating the lowest selected pressure at which the contacts are separated.
The pressure estimation means may include means for selectably depressurizing the chamber from a level at which the contacts are separated and for indicating the highest selected pressure at which the contacts touch. The chAmher may surround the contacts. The contacts may be located near ~he longit~ AI axis of the ~hamher. The first and second flexible layers may be formed of material that is substantially inextensible.
The c~am~er may be remote from the pressure estimation means and the cooperating first and second flexi~le layers may also define fluid passageway means for coupling the c~Amher surrounding the contacts to the remote pressure estimation means. The pressure estimation means may include e~ectrical circuit means for determining remotely whether the contacts are touching or separated. The electrical circ~it means may include electrically conductive lead means carriee by at least one of the cooperating first and second flexible layers.
In clinical usage of the invention, the tissue and the object may be predetermined and may meet along a predetermined surface when the c~mh~r is not interposed, and the layers defining the ch~mher may have physical sions and flexibility selected sa that interposing ~mher conforms to the surface without displacing substantially the tissue or object from the surface.
The invention is also directed toward a tr~ns~cer for estimating the pressure applied to a body tissue near a plurality of predeterm;ne~ tissue locations ~y an object such as a medical device or body part, comprising: a first flexible layer carrying a plurality of first electrical contacts; a S~CG~ flexible layer carrying a plurality of secon~ electrical contacts and cooperating with the first flexible layer to define a flexible pressurizable chAmher for interposing between a tissue and an object, wherein pairs of first and s~co~d electrical contacts are to~lchj ng near prede~r~1 n~d tissue locations when the chamber is not pressurized; and pressure estimation means for selectably increasing the pressure in the c~mh~r and for indicating the lowest selected pressure at which each pair of contac~s is separated.
The invention is also directed toward a system which uses the transducer for controlling the pressure applied tO
a body tissue near a predeter~;ne~ tissue location comprising: pressure-applying means respansi~e ta a pressure control signal for applying pressure to a tissue near a predetermined location; transducing means comprised of a first flexible layer carrying a first electricàl contact, a second flexible layer carrying a second electrical contact and cooperating with the first flexible layer to define a flexible pressuriza~le chAmh~r interposed between the tissue and the pressure-applying means wherein the first and second electrical contacts are touc~i~g near the predetermined location when the c~mher is not pressurized, and pressure estimation means for selectably pressurizing the ch~her, and for producing an applied pressure signal representative of the lowest pressure at which the first and secon~ electrical contacts are separated; and pressure-regulating means responsive to the applied pressure signal for producing a pressure control signal to maintain the pressure applied to the ~tcsl~e by the pressure-applying means near a predetermined reference pressure.
Brie.DescriPtion of the Drawinqs A specific embodiment of this invention has been chosen for purposes of illustration and description wherein:
FIG. 1 is a schematic diagram depicting the biomedical pressure transducer of this invention.
FIG. 2 is a perspective view of the transducer of FIG.
1.
FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.
FIGS. 4A and 48 are sectionai views taken along line 4-4 of FIG. 2 while the transducer is not pressurized, and while the t:ansducer is pressurized, respectively.
-FIG. ~ is a bloc~ diagram of the transducer con~ted to electrical circuitry and apparatus for controlling the pressure applied by an occlusive band to a predetermined tissue location.
Description of the ~pe~ifi~ Embodiment The specific ~ho~;me~t illustrated is not inte~e~ to be exhaustive or to limit the invention to the precise form disclosed. It is rhos~n and descri~ed in order to explain the principlec of the invention and its application and practical use, and thereby enable others s~itl~ in the art to utilize the invention.
The biomedical pressure trAnCAltcer 10 of this invention, as can be seen in FIG. 2, includes upper contact support layer 12 and lower contact suppart layer 14 which have a s~milar, generally rectangular shape and which are made of flexible, inextensi~le transparent polyester known as Mylar (DuPont trademark) that is approximately 5 mils thick.
FIG. 3 shows lower contact support layer 14 which has five circular switch contact areas 16, 1~3, 20, 22 and 24.
In each sw~tc~ contact area on lower contact support layer 14 are adjacent switch contacts 26 formed of a pattern of conductive silver ink (Electrodag 41~5S, manufactured by Acheson Colloids, Port Huron, MI) having a thickness of ~ 1 334487 apprcxi.ma_ely C.' mils and ccnr.ected ;o l_ads of similar thickness -o~-med o. conduct ve silver ink which go through connectlng b oc:~ 28 to elec~rical ccnnec~or 30. On upper contac~ suppor_ layer 12 di-ectly over each of switch contact a_eas io, 18, 20, 22 and 24 of lower contact support layer 1 A is an upper switch contact 32 formed of a pattern of conductive silver ink having a thickness of about 0.4 mils and designed to short and form an electrical connection between adjacent switch cont~cts 26 on lower contact support layer 14 when the two layers are pressed together, as shown in FIG 4A. Thus adjacent switch contacts 26 at each of the five switch contact areas 16 to 24 on lower contact support layer 14, together with the shorting upper switch contact 32 on upper contact support layer 12, form five switches located within switch contact areas 16, 18, 20, 22 and 24 near the longituAinAl axis of layers 12 and 14. ~he five switches formed in this ~nner are normally closed, i.e. upper switch contact 32 is touching and shorting electrically adjacent switch contacts 26, when the upper and lower contact support layers 12 and 14 are pressed together. For the specific ~mho~;ment, upper contact support layer 12, lower contact support layer 14 and elec_rical connector 30 were conveniently obtained by disassembling and modifying components of a commercially available membrane switch (Brady Xymox lxS Membrane switcn Unit manufactured by W.~. Brady Co., Milwaukee, wI).
Upper c..d lower contact suppor~ la-~ers 12 and 14 were sealed toge~her along edges 34 and 36 from approximately 1 cm below electrical connector 30 to distal end 38 by first wrapping flexible, transparent adhesive tape 40 (Yi~hland Trpe "371" Tape manufacslred by t:.e 3M Comp~ny, St. Paul, M~) around the outer surfaces o' urper and lower contact support layers 12 and 14 as shown in FIG. 4A. Care was ta.~en to seal tape 40 thoroughly to itself at distal end 38, and to assure that the entire outer surfaces of upper and lower contact support layers 12 and 14 adhered firmly to tape 40. The taped por.ion of layers 12 and 14 was then repeatedly dipped in a rubber coating liguid (Plasti Dip Flexible Air Dry Rubber Coating manufactured by PDI Inc., St. Paul, MN) which dried in air to form a thin, flexible, transparent sheath 42 which was fluid-tight and which enabled the taped and sheathed portion of tr~nc~llcer 10 to withstand repeated pressurization to more than 600 mmHg without leaking or rupturing.
After sheath 42 was applied, the sheathed layers were positioned in relation to connecting block 28 as shown in FIG. 2. A short length of clear vinyl tubing 44 with male Luer-lock fitting 46 attached at one end was inserted throu~h a side of connecting block 28 and then between upper and lower contact support layers 12 and 14, as shown in FIG. 2. After tubing 44 was inserted, connecting bloc~
28 was filled with a clear epoxy resin which, when it cured, formed a strong, fluid-tight seal at the proximal end of transducer 10, thus establishing a pressurizable ch~mher 48 shawn in FIGS. 4A and 4B. Pressurizable cham~er 48 extends along substantially all of the length of sheathed con~act support layers 12 and 1~ and surrounds a11 switch contact areas 16 to 24 due to the non-zero thickness of the switch contacts and leads, as shown in FIG. 4A, and can be pressurized via the c-nduit means comprised of tubins 44 and Luer-lock f ltting 46.
As shown in FIG. 1, in order to use tr~ns~ucer lO, fitting 46 is first coupled to pressurizing means S0, S depressurizing means 52, ana pressure-indicating means 54.
In the specific ~mhodime~t, pressurizing means 50 was a hand bulb from an aneroid sphygmomA~meter set, depressurizing means 52 was a manual bleed valve attached to the hand ~ulb, and pressure-indicating means 54 was an aneroid pressure gage. Although pressurized air is described in the specific ~mho~ i ment, any pressurized fluid that is non-conductive electrically and non-reactive chemically may be employed. Tran~ er 10 is c~nected via electrical cable 56 to electrical circuitry 58, as lS shown in FIG. 1. Electrical circuitry 58, which includes five similar current-limiting resistors 60, five light-emitting diodes 62, 64, 66, 68 and 70, and battery 72, connects the switch contacts in each of the five switch contact areas 16 through 24 to a corresp~ g li~ht-emitting diode so that light is emitted when thecorrespor~in~ switch contacts are tol~ch i n~, i.e. when the correspon~ switch is in its ~or~lly closed state.
In the simplest typical clinical application illustrated in FIG. 1, trAncd~cer 10 is interposed between the surface of extremity 74 and occlusive band 76 which encircles and applies pressure to extremity 74. Transducer 10 is designed to be sufficientlv thin, narrow and flexible so that it does not displace substantially the tissue o f extremity 74 from its normal location in relation to ccclusive band 76, and is designed to be sufficiently lonq to extend above and below the edges or occLusive band 76 and to have switch contact areas 1~, 18, 20, 22, and 24 positioned at proximal, mid-proximal, middle, mid-distal, and distal locations, respectively, in relation to occlusive band 76. If desired, the relative locations of the switch contact areas 16 to 24 with respect to occlusive band 76 may be fixed temporarily by attaching transducer 10 to the inner surface of ccclusive band 76 with double-sided adhesive tape. While the pressurizable ch~her 48 of tr~n-C~t~ er 10 is not pressurized, all switch contacts are tollchi ng i . e. all switches are in their normally closed state, and all light-emitting diodes 62 to 70 emit light.
Pressurizable ch~mher 48 of tranc~tlcer 10 is then gra~llAlly pressurized by an operator activating pressurizing means 50, who observes the status of light-omitting diodes 62 through 70 and at the same time observes the pressure indicated by pressure-indicating means 54. The lowest pressure at which ea,ch light-emitting diode stops emitting light is recorded: each pressure thus recorded is an estimate of the pressure applied by occlusive band 76 in a normal direction onto the surface of extremity 74 beneath the correspo~ing switch contact area. Once pressurizable c~mher 48 of transducer 10 has been pressurized sufficiently to extinguish all light-emitting diodes, the operator may use depressurizing means 52 to gradually depressurize chamber 48 of trA~c~ er 10 and record the highest p.essure at which each of the light-emit~ing diodes begins emitting light, thus providing a second estimate of the pressure applied in a normal direction beneath the corresponding switch contact area and also providing (by `` 1 334487 comparison with z~e corresponding es~imate obr~ireq previously whilz pressure was increasing) an estimate of any inherent hys~eresis that may exist in tr~n~ cer lO and in the other elements of the pressure estimation system.
The set of pressure estimates obtAine~ by m~nu~lly pressurizing and depressurizing pressurizable ~hAmher 48 of transducer 10 as described above is of intrinsic significance in many clinical applications.
For more complex clinical applications where repetitive pressure estimates are required by a clinical operator, or where it is desired by the operator to automatically maintain the pressure applied to the surface of tissue beneath a selected switch contact area near a predetermi~ reference pressure, tr~nsAucer 10 is attached to automated tr~ c^r controller 78 as shown in FIG. S.
Automated tr~nc~tlc~r controller 78 includes digital processor 80 for selectably pressurizing and depressurizing pressurizable ~hamher 48 of tran-C~l~cDr 10 by controlling pressure generator 82, comprised of an electric pump and electrical pressure-relief valve. Digital proc ssor 80 estimates the pressures applied to the surface of tissue beneath switch contact areas by readinq the level of the signal produced by generated pressure sensor 84 as the switches at switch contact areas 16 to 24, which are monitored via electrical cable 56, change states during predeter~in~ pressurization and depressurization cycles.
Digital processor 80 produces an output signal representative of the pressures applied at the switch contact areas for display to an operator, and if desired for controlling applied pressure regulator 86 in order tO
` I 3344~
maintain the pressure applied to an area of the surface of extremity 7~ beneath a selected switch contact area near a predetermined reference pressure.
An evaluation of the accuracy and hysteresis of s transducer 10 may be performed by an operator whe~ desired by placing trAns~ucer lO on a flat surface, applying a series of known pressures to the upper surface of transducer 10 at selected switch contact areas, pressurizing and depressurizing pressurizable rh~mher 48 of transducer 10, recording the pressures at which the switches change state, and comparing the recorded pressures to the known pressures.
As will be apparent to those skilled in the art, in the light of the foregoing disclosure many alterations and modifications are possible in the practice of this invention without departing from the scope or spirit - thereof. For example, a smaller or larger nl~mher of switch contact areas could be included, and the size, spacing and - patterns of the switch contact areas could be modified for a specific clinLcal application, as could the physical e~cions and type of material used to form the upper and lower switch contact support layers. As other examples:
another method of sealing the upper and lower contact support layers around the edges, such at heat sealing, may be better suited for manufacture than taping, sheathing and potting in epoxy as described; and for some clinical applications it may be pre~erable to couple t_b ng to both ends of the transducer ~h~mh r to permit pressurization from both ends simultaneously, or to couple tubing to the middle of the transducer c~Amh~r to permit pressurization from the midpoint if, for example, the tr~ncdl~cer were to be interposed circumferentially rather than transversely between an occlusive band and an extremity. Accordingly, the scope of the invention is to be construed in accordance S with the substance defined by the following claims.
The present application is a division of Canadian patent application serial number 556,593 filed January 15, 1988.
Field of the Invention This invention pertains to transducers for estimating the pressure applied to a tissue of a body by an object such as a medical device or body part. The invention particularly pertains to a thin~and flexible transducer useful in health care for interposing at the surface between a tissue and an object, without substantially displacing either the tissue or the object from the surface, to estimate the pressure applied near at least one predetermined tissue location.
- Background of the Invention There are many clinical situations in which it is desirable to have an accurate estimate of the pressure applied to a tissue of a body by a medical device or by a body part such as another tissue or organ. These clinical situations include:
the evaluation of new and existing types of occlusive cuffs for pneumatic tourniquet systems and sphygmomanometers; the evaluation, improvement and standardization of the techniques employed by clinical staff in selecting and snugly applying an occlusive cuff to an extremity having a particular size, shape and tissue composition; the development and evaluation of innovative and potentially less expensive automatic tourniquet systems, including non-pneumatic tourniquet systems; the develop-ment and evaluation of advanced robotic devices and pre-robotic devices for tissue manipulation and limb manipulation in surgery and rehabilitation; the development 1 334~B~
and evaluc.~sn of improved, safe! systems for a common anesthet_c techr.ique (intravenous regional anesthesia) which ~s based on the proper use of a special occlusive cuff; the development, improvement and evaluation of biomechanical models of tissue; the evaluation and fitting o' specia'~ dressings and garments 'or applying pressure within a pressure-tolerance window to the tissue of burn patients in order to enh~nce healing; the diagnosis and treatment of compartmental pressure syndrome in orthopedics; the monitoring and control of sequential limb compression devices for prevention of deep venous thrcmbosis, and medical anti-shoc~ trousers for emergency treatment; and perhaps the investigation and treatment of pressure sores in immobile patients.
Different types of biomedical pressure tr~ns~tc rs known in the prior art may have a n~her of disadvantages when used in clinical situations such as those described above. First, many tr~n~ucers known in the prior art are not sufficiently thin and flexible for interposing between selected b~dy tissues and objects such as medical devices or body parts, e.g. organs, skeletal structures and other tissues, without displacing substantially either the tissue or the object. Tra~sducers which require a rigid substrate for proper operation are not particularly useful for estimating the pressure applied to one soft tissue by an adjacent soft tissue, or for estimating the pressure applied to the tissue by an object havir.g a curved or irregular surface. Many types of transducers known in the prior art are mass-produced in one st~nd~a form using expensive fabrication technologies to ac:~ieve economies af 1 3344~
scale, an~ t;-U5 ~hese t~ansduce_s cannc~ be read~ly adapted. ~dap~_on is impor~ant in many oiomedical situations: ~ ;s frequently desiraDle to nave a transducer ar-ay, or a plurality of t_ansducers, 40r simultaneously es;imatins the pressures at a plurality of predeterm ~ed locations of a tissue beneath a pressure-applying object; and it is often desirable to change the number and area of the pressure transducers at those locations for selected combinations of tissues and obiects.
Similarl~, in many prior art tr~s~cers which are mass-produced in one st~ rd form, the composition and physical ~ nsions of various elements of these transducers cannot be conveniently and economically modified so that the tr~s~-~c~r conforms more closely between a particular tissue and object of interest. Many of the biomedica~
pressure tr~sdt-cers known in the prior art are inherently complex and ~xre~cive~ thus reducing the probability that such tr~nC~uc~rs might be conveniently and econ~ically integrated if desired into medical devices such as 2Q occlusive cuffs, pressure dressings for burn patients, tissue retractors and the patient-applied parts of robatic systems for surgery and rehabilitation. Other tr~nC~lcers known in the prior art have the disadvantage that they cannot be conveniently sterilized by commonly used 2S techni$ues, ar.d this precludes the use ~f such prior-art transducers inside the body, either between adjacent soft tissues (e.g. in the diagnosis and treatment of compartmental pressure syndrome), or in surgery (e.g. between a soft tissue and an abject such as a tissue retractor~. Some transducers known in the prior art re~uire complex and expensive support circuitry, a~d others re~uire ~ifficult 2nd time-consuming calibration p-ocedures. Anothe- disadvantage of some prior-art trAnsdl~cers is that their accuracy and hysteresis cannot be conveniently chec~ed by clinical staff in a health-care environment using readily available apparatus and electronic pressure transducers. A final disadvantage of certain biomedical pressure transducers is that, because of unacceptable inaccuracy, calibration difficulties or unreliability associated with repetitive usage, these transducers cannot be safely incorporated into systems for automatically controlling the pressure applied to a body tissue near a predetermined location.
~he biomedical pressure trAn~ cer of the present invention was developed to overcome many of the disadvantages of prior-art tr~n~ rers fcr clinical situations such as those indicated above. The tranc~llcer ~f the present invention makes advant-geous use of some of the t~ logy developed for, and now commonly employed in, the fabrication of i~yr~ncive and flexible membrane switches in small batches for a wide variety of applications.
The applicant is aware of the following United States patents which are more or less relevant to the subject matter of the applicant's inventi~n.
4,605,010 8/1986 McEwen 128/686 4,419,494 10~1984 McEwen 128/327 128/682 4,469,099 9/1984 McEwen 128~327 128/682 4,300,029 11/1981 Maser 200/159B
`^` 1334487 4,218,600 8/1980 Klssner 200/159B
4,217,473 8/1980 Parklnson 200/159B
3,095,873 7/1963 Bdmunds 128-2.05 The appllcant 18 also aware of the followlng publlshed references whlch are more or le~s relevant to the sub~ect matter of the appllcant's lnventlon.
J.A. McBwen and R.W. McGraw, "An adaptive tournl~uet for lmproved safety ln surgery. n IEEB Transactlons ln Blomedlcal Bnglneerlng, Vol. BMB-29, February 1982, pp. 122-128.
J.A. ;~cE~en and G.F. A~hlnleck, "Advances in surgical - tour-.i~ue~s.~ J. Assn. opera~ing Room Nurses, Vol.
~6, i382, p~. 889-896.
J.A. Shaw and D.G. Murray, "The relationship between tourniquet pressure and underlying soft-tlssue pressure in tne thigh." The Journal of ~one and Joint Surgery, Vol. 64-A, 1982, FP- 1148 -11;2.
A.C. McLaren and C.H. Rorabeck, "The pressure distribution under tourniquets." ~he Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 433-438.
R.J. Newman and A. Muirhead, "A safe and effective low pressure tourniquet." Journal of Bone and Joint Surgery, Vol. 68-8, 1986, pp. 625-628.
J.A. Shaw, W.W. Demuth, and A.W. Gillespy, "Guidelines for the use of digital tourniquets based on physiological pressure measurements." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 1086-1090 .
S.E. Grice et al., ~Intravenous regional anesthesia:
Evaluation and prevention of leakage under the tourniguet.~ Anesthesiology, Vol. 6;, pp. 316-320, 1986.
Summary ~ the Invention The invention is directed toward a transducer for estimating t:-e pressure app~ied to a body tissue near a predetermined tissue location by a~ object such as a medical device or body part, comprising: a first flexible layer car~ing a first eLectrical contact; a second flexible layer carrying a second electrical contact and cooperating with the first flexible layer to define a flexible pressuri2able chamher for interposing between a tissue and an o~ject wherein the first and second electrical contacts are to~lchi ng near a predeter~ine~
tissue location when the c~amher is not pressurized; and pressure estLmation means for selectably pressurizing the c~mher, and for indicating the lowest selected pressure at which the contacts are separated.
The pressure estimation means may include means for selectably depressurizing the chamber from a level at which the contacts are separated and for indicating the highest selected pressure at which the contacts touch. The chAmher may surround the contacts. The contacts may be located near ~he longit~ AI axis of the ~hamher. The first and second flexible layers may be formed of material that is substantially inextensible.
The c~am~er may be remote from the pressure estimation means and the cooperating first and second flexi~le layers may also define fluid passageway means for coupling the c~Amher surrounding the contacts to the remote pressure estimation means. The pressure estimation means may include e~ectrical circuit means for determining remotely whether the contacts are touching or separated. The electrical circ~it means may include electrically conductive lead means carriee by at least one of the cooperating first and second flexible layers.
In clinical usage of the invention, the tissue and the object may be predetermined and may meet along a predetermined surface when the c~mh~r is not interposed, and the layers defining the ch~mher may have physical sions and flexibility selected sa that interposing ~mher conforms to the surface without displacing substantially the tissue or object from the surface.
The invention is also directed toward a tr~ns~cer for estimating the pressure applied to a body tissue near a plurality of predeterm;ne~ tissue locations ~y an object such as a medical device or body part, comprising: a first flexible layer carrying a plurality of first electrical contacts; a S~CG~ flexible layer carrying a plurality of secon~ electrical contacts and cooperating with the first flexible layer to define a flexible pressurizable chAmher for interposing between a tissue and an object, wherein pairs of first and s~co~d electrical contacts are to~lchj ng near prede~r~1 n~d tissue locations when the chamber is not pressurized; and pressure estimation means for selectably increasing the pressure in the c~mh~r and for indicating the lowest selected pressure at which each pair of contac~s is separated.
The invention is also directed toward a system which uses the transducer for controlling the pressure applied tO
a body tissue near a predeter~;ne~ tissue location comprising: pressure-applying means respansi~e ta a pressure control signal for applying pressure to a tissue near a predetermined location; transducing means comprised of a first flexible layer carrying a first electricàl contact, a second flexible layer carrying a second electrical contact and cooperating with the first flexible layer to define a flexible pressuriza~le chAmh~r interposed between the tissue and the pressure-applying means wherein the first and second electrical contacts are touc~i~g near the predetermined location when the c~mher is not pressurized, and pressure estimation means for selectably pressurizing the ch~her, and for producing an applied pressure signal representative of the lowest pressure at which the first and secon~ electrical contacts are separated; and pressure-regulating means responsive to the applied pressure signal for producing a pressure control signal to maintain the pressure applied to the ~tcsl~e by the pressure-applying means near a predetermined reference pressure.
Brie.DescriPtion of the Drawinqs A specific embodiment of this invention has been chosen for purposes of illustration and description wherein:
FIG. 1 is a schematic diagram depicting the biomedical pressure transducer of this invention.
FIG. 2 is a perspective view of the transducer of FIG.
1.
FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.
FIGS. 4A and 48 are sectionai views taken along line 4-4 of FIG. 2 while the transducer is not pressurized, and while the t:ansducer is pressurized, respectively.
-FIG. ~ is a bloc~ diagram of the transducer con~ted to electrical circuitry and apparatus for controlling the pressure applied by an occlusive band to a predetermined tissue location.
Description of the ~pe~ifi~ Embodiment The specific ~ho~;me~t illustrated is not inte~e~ to be exhaustive or to limit the invention to the precise form disclosed. It is rhos~n and descri~ed in order to explain the principlec of the invention and its application and practical use, and thereby enable others s~itl~ in the art to utilize the invention.
The biomedical pressure trAnCAltcer 10 of this invention, as can be seen in FIG. 2, includes upper contact support layer 12 and lower contact suppart layer 14 which have a s~milar, generally rectangular shape and which are made of flexible, inextensi~le transparent polyester known as Mylar (DuPont trademark) that is approximately 5 mils thick.
FIG. 3 shows lower contact support layer 14 which has five circular switch contact areas 16, 1~3, 20, 22 and 24.
In each sw~tc~ contact area on lower contact support layer 14 are adjacent switch contacts 26 formed of a pattern of conductive silver ink (Electrodag 41~5S, manufactured by Acheson Colloids, Port Huron, MI) having a thickness of ~ 1 334487 apprcxi.ma_ely C.' mils and ccnr.ected ;o l_ads of similar thickness -o~-med o. conduct ve silver ink which go through connectlng b oc:~ 28 to elec~rical ccnnec~or 30. On upper contac~ suppor_ layer 12 di-ectly over each of switch contact a_eas io, 18, 20, 22 and 24 of lower contact support layer 1 A is an upper switch contact 32 formed of a pattern of conductive silver ink having a thickness of about 0.4 mils and designed to short and form an electrical connection between adjacent switch cont~cts 26 on lower contact support layer 14 when the two layers are pressed together, as shown in FIG 4A. Thus adjacent switch contacts 26 at each of the five switch contact areas 16 to 24 on lower contact support layer 14, together with the shorting upper switch contact 32 on upper contact support layer 12, form five switches located within switch contact areas 16, 18, 20, 22 and 24 near the longituAinAl axis of layers 12 and 14. ~he five switches formed in this ~nner are normally closed, i.e. upper switch contact 32 is touching and shorting electrically adjacent switch contacts 26, when the upper and lower contact support layers 12 and 14 are pressed together. For the specific ~mho~;ment, upper contact support layer 12, lower contact support layer 14 and elec_rical connector 30 were conveniently obtained by disassembling and modifying components of a commercially available membrane switch (Brady Xymox lxS Membrane switcn Unit manufactured by W.~. Brady Co., Milwaukee, wI).
Upper c..d lower contact suppor~ la-~ers 12 and 14 were sealed toge~her along edges 34 and 36 from approximately 1 cm below electrical connector 30 to distal end 38 by first wrapping flexible, transparent adhesive tape 40 (Yi~hland Trpe "371" Tape manufacslred by t:.e 3M Comp~ny, St. Paul, M~) around the outer surfaces o' urper and lower contact support layers 12 and 14 as shown in FIG. 4A. Care was ta.~en to seal tape 40 thoroughly to itself at distal end 38, and to assure that the entire outer surfaces of upper and lower contact support layers 12 and 14 adhered firmly to tape 40. The taped por.ion of layers 12 and 14 was then repeatedly dipped in a rubber coating liguid (Plasti Dip Flexible Air Dry Rubber Coating manufactured by PDI Inc., St. Paul, MN) which dried in air to form a thin, flexible, transparent sheath 42 which was fluid-tight and which enabled the taped and sheathed portion of tr~nc~llcer 10 to withstand repeated pressurization to more than 600 mmHg without leaking or rupturing.
After sheath 42 was applied, the sheathed layers were positioned in relation to connecting block 28 as shown in FIG. 2. A short length of clear vinyl tubing 44 with male Luer-lock fitting 46 attached at one end was inserted throu~h a side of connecting block 28 and then between upper and lower contact support layers 12 and 14, as shown in FIG. 2. After tubing 44 was inserted, connecting bloc~
28 was filled with a clear epoxy resin which, when it cured, formed a strong, fluid-tight seal at the proximal end of transducer 10, thus establishing a pressurizable ch~mher 48 shawn in FIGS. 4A and 4B. Pressurizable cham~er 48 extends along substantially all of the length of sheathed con~act support layers 12 and 1~ and surrounds a11 switch contact areas 16 to 24 due to the non-zero thickness of the switch contacts and leads, as shown in FIG. 4A, and can be pressurized via the c-nduit means comprised of tubins 44 and Luer-lock f ltting 46.
As shown in FIG. 1, in order to use tr~ns~ucer lO, fitting 46 is first coupled to pressurizing means S0, S depressurizing means 52, ana pressure-indicating means 54.
In the specific ~mhodime~t, pressurizing means 50 was a hand bulb from an aneroid sphygmomA~meter set, depressurizing means 52 was a manual bleed valve attached to the hand ~ulb, and pressure-indicating means 54 was an aneroid pressure gage. Although pressurized air is described in the specific ~mho~ i ment, any pressurized fluid that is non-conductive electrically and non-reactive chemically may be employed. Tran~ er 10 is c~nected via electrical cable 56 to electrical circuitry 58, as lS shown in FIG. 1. Electrical circuitry 58, which includes five similar current-limiting resistors 60, five light-emitting diodes 62, 64, 66, 68 and 70, and battery 72, connects the switch contacts in each of the five switch contact areas 16 through 24 to a corresp~ g li~ht-emitting diode so that light is emitted when thecorrespor~in~ switch contacts are tol~ch i n~, i.e. when the correspon~ switch is in its ~or~lly closed state.
In the simplest typical clinical application illustrated in FIG. 1, trAncd~cer 10 is interposed between the surface of extremity 74 and occlusive band 76 which encircles and applies pressure to extremity 74. Transducer 10 is designed to be sufficientlv thin, narrow and flexible so that it does not displace substantially the tissue o f extremity 74 from its normal location in relation to ccclusive band 76, and is designed to be sufficiently lonq to extend above and below the edges or occLusive band 76 and to have switch contact areas 1~, 18, 20, 22, and 24 positioned at proximal, mid-proximal, middle, mid-distal, and distal locations, respectively, in relation to occlusive band 76. If desired, the relative locations of the switch contact areas 16 to 24 with respect to occlusive band 76 may be fixed temporarily by attaching transducer 10 to the inner surface of ccclusive band 76 with double-sided adhesive tape. While the pressurizable ch~her 48 of tr~n-C~t~ er 10 is not pressurized, all switch contacts are tollchi ng i . e. all switches are in their normally closed state, and all light-emitting diodes 62 to 70 emit light.
Pressurizable ch~mher 48 of tranc~tlcer 10 is then gra~llAlly pressurized by an operator activating pressurizing means 50, who observes the status of light-omitting diodes 62 through 70 and at the same time observes the pressure indicated by pressure-indicating means 54. The lowest pressure at which ea,ch light-emitting diode stops emitting light is recorded: each pressure thus recorded is an estimate of the pressure applied by occlusive band 76 in a normal direction onto the surface of extremity 74 beneath the correspo~ing switch contact area. Once pressurizable c~mher 48 of transducer 10 has been pressurized sufficiently to extinguish all light-emitting diodes, the operator may use depressurizing means 52 to gradually depressurize chamber 48 of trA~c~ er 10 and record the highest p.essure at which each of the light-emit~ing diodes begins emitting light, thus providing a second estimate of the pressure applied in a normal direction beneath the corresponding switch contact area and also providing (by `` 1 334487 comparison with z~e corresponding es~imate obr~ireq previously whilz pressure was increasing) an estimate of any inherent hys~eresis that may exist in tr~n~ cer lO and in the other elements of the pressure estimation system.
The set of pressure estimates obtAine~ by m~nu~lly pressurizing and depressurizing pressurizable ~hAmher 48 of transducer 10 as described above is of intrinsic significance in many clinical applications.
For more complex clinical applications where repetitive pressure estimates are required by a clinical operator, or where it is desired by the operator to automatically maintain the pressure applied to the surface of tissue beneath a selected switch contact area near a predetermi~ reference pressure, tr~nsAucer 10 is attached to automated tr~ c^r controller 78 as shown in FIG. S.
Automated tr~nc~tlc~r controller 78 includes digital processor 80 for selectably pressurizing and depressurizing pressurizable ~hamher 48 of tran-C~l~cDr 10 by controlling pressure generator 82, comprised of an electric pump and electrical pressure-relief valve. Digital proc ssor 80 estimates the pressures applied to the surface of tissue beneath switch contact areas by readinq the level of the signal produced by generated pressure sensor 84 as the switches at switch contact areas 16 to 24, which are monitored via electrical cable 56, change states during predeter~in~ pressurization and depressurization cycles.
Digital processor 80 produces an output signal representative of the pressures applied at the switch contact areas for display to an operator, and if desired for controlling applied pressure regulator 86 in order tO
` I 3344~
maintain the pressure applied to an area of the surface of extremity 7~ beneath a selected switch contact area near a predetermined reference pressure.
An evaluation of the accuracy and hysteresis of s transducer 10 may be performed by an operator whe~ desired by placing trAns~ucer lO on a flat surface, applying a series of known pressures to the upper surface of transducer 10 at selected switch contact areas, pressurizing and depressurizing pressurizable rh~mher 48 of transducer 10, recording the pressures at which the switches change state, and comparing the recorded pressures to the known pressures.
As will be apparent to those skilled in the art, in the light of the foregoing disclosure many alterations and modifications are possible in the practice of this invention without departing from the scope or spirit - thereof. For example, a smaller or larger nl~mher of switch contact areas could be included, and the size, spacing and - patterns of the switch contact areas could be modified for a specific clinLcal application, as could the physical e~cions and type of material used to form the upper and lower switch contact support layers. As other examples:
another method of sealing the upper and lower contact support layers around the edges, such at heat sealing, may be better suited for manufacture than taping, sheathing and potting in epoxy as described; and for some clinical applications it may be pre~erable to couple t_b ng to both ends of the transducer ~h~mh r to permit pressurization from both ends simultaneously, or to couple tubing to the middle of the transducer c~Amh~r to permit pressurization from the midpoint if, for example, the tr~ncdl~cer were to be interposed circumferentially rather than transversely between an occlusive band and an extremity. Accordingly, the scope of the invention is to be construed in accordance S with the substance defined by the following claims.
Claims (18)
1. Apparatus for estimating the pressure applied to a body tissue near a predetermined tissue location by an object such as a medical device or body part, comprising:
a first flexible layer carrying a first electrical contact;
a second flexible layer carrying a second electrical contact and cooperating with the first flexible layer to define a flexible pressurizable chamber for interposing between a tissue and an object wherein the first and second electrical contacts are touching near a predetermined tissue location when the chamber is not pressurized; and pressure estimation means for selectably pressurizing the chamber, and for indicating the lowest selected pressure at which the contacts are separated.
a first flexible layer carrying a first electrical contact;
a second flexible layer carrying a second electrical contact and cooperating with the first flexible layer to define a flexible pressurizable chamber for interposing between a tissue and an object wherein the first and second electrical contacts are touching near a predetermined tissue location when the chamber is not pressurized; and pressure estimation means for selectably pressurizing the chamber, and for indicating the lowest selected pressure at which the contacts are separated.
2. Apparatus as defined in claim 1 wherein the pressure estimation means includes means for selectably depressurizing the chamber from a level at which the contacts are separated and for indicating the highest selected pressure at which the contacts touch.
3. Apparatus as defined in claim 1 wherein the chamber surrounds the contacts.
4. Apparatus as defined in claim 3 wherein the contacts are located near the longitudinal axis of the chamber.
5. Apparatus as defined in claim 1 wherein the first and second flexible layers are formed of material that is substantially inextensible.
6. Apparatus as defined in claim 3 wherein the chamber is remote from the pressure estimation means and wherein the cooperating first and second flexible layers also define fluid passageway means for coupling the chamber surrounding the contacts to the remote pressure estimation means.
7. Apparatus as defined in claim 6 wherein the pressure estimation means includes electrical circuit means for determining remotely whether the contacts are touching or separated.
8. Apparatus as defined in claim 7 wherein the electrical circuit means includes electrically conductive lead means carried by at least one the cooperating first and second flexible layers.
9. Apparatus as defined in claim 1 wherein the tissue and the object are predetermined and meet along a predetermined surface when the chamber is not interposed, and wherein the layers defining the chamber have physical dimensions and flexibility selected so that interposing chamber conforms to the surface without displacing substantially the tissue or object from the surface.
10. Apparatus as defined in claim 9 wherein the object is a pneumatic tourniquet cuff which encircles the extremity of a subject and applies pressure to the extremity, the tissue is the tissue beneath the encircling cuff, and each layer is comprised of a transparent polyester substance available under the trade mark Mylar having a length of 17 cm, a width of 2 cm and a thickness of 5 mils.
11. Apparatus for estimating the pressure applied to a body tissue near a plurality of predetermined tissue locations by an object such as a medical device or body part, comprising:
a first flexible layer carrying a plurality of first electrical contacts;
a second flexible layer carrying a plurality of second electrical contacts and cooperating with the first flexible layer to define a flexible pressurizable chamber for interposing between a tissue and an object, wherein pairs of first and second electrical contacts are touching near predetermined tissue locations when the chamber is not pressurized; and pressure estimation means for selectably increasing the pressure in the chamber and for indicating the lowest selected pressure at which each pair of contacts is separated.
a first flexible layer carrying a plurality of first electrical contacts;
a second flexible layer carrying a plurality of second electrical contacts and cooperating with the first flexible layer to define a flexible pressurizable chamber for interposing between a tissue and an object, wherein pairs of first and second electrical contacts are touching near predetermined tissue locations when the chamber is not pressurized; and pressure estimation means for selectably increasing the pressure in the chamber and for indicating the lowest selected pressure at which each pair of contacts is separated.
12. Appatarus as defined in claim 11 wherein the pressure estimation means for selectably depressurizing the chamber from a level at which all pairs of contacts are separated, and for indicating each of the lowest selected pressures at which corresponding pairs of contacts are touching.
13. Apparatus as defined in claim 11 wherein the chamber surrounds the pairs of contacts.
14. Apparatus as defined in claim 13 wherein the paris of contacts are located near the longitudinal axis of the chamber.
15. Apparatus as defined in claim 14 wherein the chamber is remote from the pressure estimation means and wherein the cooperating first and second flexible layers also define fluid passageway means for coupling the chamber surrounding the contacts to the remote pressure estimation means.
16. Apparatus as defined in claim 15 wherein the pressure estimation means includes electrical circuit means for determining remotely whether the pairs of contacts are touching or separated.
17. Apparatus as defined in claim 16 wherein the electrical circuit means includes electrically conductive lead means carried by at least one of the cooperating first and second flexible layers.
18. Apparatus as defined in claim 11 wherein the tissue and the object are predetermined and meet along a predetermined surface when the chamber is not interposed, and wherein the layers defining the chamber are comprised of material having a degree of flexibility and physical dimensions selected so that the interposing chamber conforms to the surface without displacing substantially the tissue or the object from the surface.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/033,770 | 1987-04-03 | ||
| US07/033,770 US4869265A (en) | 1987-04-03 | 1987-04-03 | Biomedical pressure transducer |
| CA556593 | 1988-01-15 |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000616563A Division CA1334487C (en) | 1987-04-03 | 1993-01-25 | Biomedical pressure transducer |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000616563A Division CA1334487C (en) | 1987-04-03 | 1993-01-25 | Biomedical pressure transducer |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1334487C true CA1334487C (en) | 1995-02-21 |
Family
ID=25671664
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000616563A Expired - Lifetime CA1334487C (en) | 1987-04-03 | 1993-01-25 | Biomedical pressure transducer |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1334487C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007016772A1 (en) * | 2005-08-05 | 2007-02-15 | Western Clinical Engineering Ltd. | Surgical tourniquet cuff for limiting usage to improve safety |
| CN111801042A (en) * | 2018-03-30 | 2020-10-20 | 奥林巴斯株式会社 | Stress estimation system, stress estimation device, and endoscope system |
-
1993
- 1993-01-25 CA CA000616563A patent/CA1334487C/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007016772A1 (en) * | 2005-08-05 | 2007-02-15 | Western Clinical Engineering Ltd. | Surgical tourniquet cuff for limiting usage to improve safety |
| CN111801042A (en) * | 2018-03-30 | 2020-10-20 | 奥林巴斯株式会社 | Stress estimation system, stress estimation device, and endoscope system |
| CN111801042B (en) * | 2018-03-30 | 2023-08-18 | 奥林巴斯株式会社 | Stress estimation system, stress estimation device, endoscope system, and stress estimation method |
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