several embodiments of the plastically and elastically deformable sensor holder will now be described in relation to the accompanying drawing which at least assist in illustrating its various pertinent features . for example , fig1 - 5 b show a first embodiment of a sensor holder that is utilized to hold a generally t - shaped pulse oximetry sensor relative to a finger while fig6 and 7 show a second embodiment of a sensor holder for use in holding an l - shaped pulse oximetry sensor relative to an earlobe . however , it is to be expressly understood that other embodiments of the sensor holder may be utilized to accommodate different sensors and / or other patient appendages , such as nasal septums , toes , etc . furthermore , as used herein the term “ plastically deformable ” is understood to represent permanent deformation of a body in any direction without rupture . that is , the plastically deformable material is able to deform permanently under the application of a stress and maintain that deformation after the stress is removed . the term “ elastically deformable ” represents the deformation of a body by an applied stress , wherein the body returns to its original shape after the stress is removed . the terms “ elastic limit ” and “ yield strength ” interchangeably represent the defining line between elastic deformation and plastic deformation for a material . fig1 shows a first embodiment of the sensor holder 40 . the sensor holder 40 contains a deformable backing layer 50 that makes up the outside surface or “ shell ” of the sensor holder 40 . in accordance with the present invention , the deformable backing layer is both plastically deformable to allow the sensor holder to maintain a desired shape and elastically deformable to provide a resilient spring - like holding force , as will be more fully discussed herein . interconnected to the inside surface of the deformable backing layer 50 is a patient interface layer 60 for providing a gentle interface with a patient appendage . the inside ( i . e ., patient side ) surface of the patient interface layer 60 contains a sensor recess 70 that is utilized to selectively receive a sensor and hold the sensor relative to the sensor holder . as shown in fig1 , the sensor holder 40 is formed substantially as an elongate member that is particularly apt for application to a finger ( see fig4 ). referring again to fig1 , it is noted that the sensor holder 40 has a semi - arcuate shape prior to application to the finger , however , it will be appreciated that prior to deformation to a desired shape , the sensor holder 40 may have any configuration ( e . g . a flat elongated strip ). referring to fig1 , it will be noted that in this embodiment the sensor holder 40 is generally defined by first and second and portions 42 , 44 and a central portion 46 interconnecting the first and second portions 42 , 44 . upon application of the sensor holder 40 to the finger , each end portion 42 , 44 will be disposed on opposing surfaces of that finger ( see fig4 ). accordingly , the central portion 46 of the sensor holder 40 plastically deforms to allow the first and second end portions 42 , 44 to be disposed in an opposing relationship . that is , the sensor holder 40 is bent to a generally u - shaped configuration . as shown in fig4 , when the sensor holder 40 is in the u - shaped configuration , the index finger 90 of a patient is disposed between the first and second end portions 42 , 44 as well as being disposed between first and second halves 72 , 74 of the sensor recess 70 , as will be more fully discussed herein . in this present embodiment , the end portions 42 , 44 are each semi - cylindrical in shape to better conform to the finger as well as provide enhanced ambient light - blocking characteristics . the deformable backing layer 50 may be formed of any material that imparts the desired elastic and plastic deformation properties . that is , the material should have an elastic limit or yield strength that allows a medical technician to easily plastically deform the backing layer 50 to a first shape to engage a patient appendage such as a finger 90 . that is , first and second portions 42 , 44 of the sensor holder 40 may be easily bent into an opposing relationship to allow these portions to engage opposing surfaces of a patient appendage ( see fig4 ). furthermore , the deformable material should have an elastic limit that , once conformed to a patient appendage ( i . e . plastically deformed to a desired shape ), provides enough elastic deformation to create a resilient spring - like retaining force to hold the sensor holder 40 on the appendage . that is , the central portion 46 may be elastically deformed to allow the first and second end portions 42 , 44 to slightly spread to allow the finger 90 to be inserted therebetween . once inserted , the resilient retaining force may compress the finger 90 between the first and second end portions 42 , 44 . in order to plastically deform the central section of the sensor holder 40 , the yield strength of the backing layer 50 must be overcome . the overall yield strength of an object will depend on the bending moment of inertia of that object as well as the modules of elasticity ( e ) for the material used to form that object . referring to fig5 a , a cross section of the sensor 40 taken along section lines a - a ( not to scale ) shows the plastically deformable backing layer 50 , the patient interface layer 60 and a portion of the sensor recess 70 . as shown , the backing layer 50 is an isotropic layer having a height ( h ) and a width ( w ). the moment of inertia ( i ) for this rectangular cross section is i = wh 3 / 12 where “ h ” is the height of the rectangle perpendicular to the bending axis and “ w ” is the width of the rectangle parallel with the bending axis . this moment of inertia can be thought of as the stiffness of the backing layer 50 ( e . g ., a backing layer with a greater thickness “ h ” will be stiffer ). as noted , the plastic deformation of the sensor holder 40 of fig1 is generally isolated to the central section 46 . in order to plastically deform this section 46 , the stress applied ( i . e . bending force ) must exceed the allowable bending stress ( i . e . yield strength ) for this section 46 , which can be thought of as a beam ( see fig5 b ). it will be appreciated that by increasing the length of the central section , the required bending force will be reduced . in this regard , it will be appreciated by varying the physical parameters ( h , w , and / or length ) of the bending section ( i . e . central section 46 ) and / or the material utilized for the deformable backing layer 50 ( e . g ., the modulus of elasticity e ), numerous materials may be utilized to provide a deformable backing layer 50 having a predetermined yield strength . as shown , an isotropic plastic material is utilized as the plastically deformable backing layer 50 . additionally , the plastic is opaque to provide added light blocking characteristics for the sensor holder 40 . the plastic may have any elastic limit that permits the sensor to easily bend while providing sufficient elasticity to provide an adequate holding force . other materials that can be utilized include : metals and / or composite materials such as wires encased in a rubberized matrix material . generally , the patient interface layer 60 will be formed of a compressible material to provide cushioning between the sensor holder 40 and the appendage of the patient . further , an adhesive could be incorporated onto the patient interface layer 60 as well ( not shown ). the compressible material has a compression setting that , upon application of a predetermined pressure , substantially conforms to the surface contacting the compressible material ( e . g ., a patient &# 39 ; s finger ). that is , the compressible material preferably has a plurality of void spaces to permit compression . preferred compressible material is open or closed cell foam , neoprene , rubber , fabric , and composites thereof , with foam being the most preferred . fig2 shows a transmittance type pulse oximetry sensor 80 that may be utilized with the sensor holder 40 as shown in fig1 . in this regard , the pulse oximetry sensor 80 contains a generally t - shaped configuration , corresponding to the t - shaped configuration of the sensor recess 70 of the sensor holder 40 . the pulse oximetry sensor 80 contains an emitting surface 82 that may contain one or more leds , as well as a detecting surface 84 that may contain one or more photodiodes . the emitting surface and detecting surface 84 are separated by a flexible conduit portion 84 of the sensor 80 that allows the light emitting surface 82 and light detecting surface 84 to be disposed on opposing surfaces of a patient appendage when the sensor 80 is utilized . finally , the sensor 80 contains a cable 88 that interconnects the light emitting surface 82 and light detecting surface 84 to appropriately configured monitoring equipment . as will be appreciated , when the transmittance - type pulse oximeter 80 is placed within the recess 70 at least a portion of the finger will be disposed between the light emitting surface 82 , and light detecting surface 84 of the sensor 80 such that an optical path is created through the finger . as noted , the sensor holder 40 contains a recess 70 for use in selectively receiving a sensor . this recess 70 is substantially the same size and shape of the sensor that will be utilized with the sensor holder 40 . as shown , the sensor recess 70 is generally t - shaped for use with the t - shaped sensor shown in fig2 . further , the depth of the recess 70 is such that upon application to a patient appendage , the front surface of a sensor 80 contained within the recess 70 will be substantially level with the front surface of the patient interface layer 60 . in this regard , the light emitting 82 and light detecting 84 surfaces of the sensor 80 may be held in conformal relationship to the finger without applying pressure thereto . this recess 70 is generally formed by removing a portion of the compressible material utilizing , for example , a cutting dye with the same size and shape as the sensor . that is , the patient interface layer 60 ( i . e ., a compressible material layer ) will have the same thickness as the sensor 80 , thereby allowing facilitated formation of the recess 70 . as shown in fig1 and 2 , the recess 70 contains a first half 72 and a second half 74 that are sized and shaped to receive the first and second portions of the sensor 80 . that is , the light emitting surface 82 and light detecting surface 84 . furthermore , the recess 70 contains a lateral portion that extends to the lateral edges of the sensor holder 40 . this lateral portion 76 of the recess 70 provides an access for the sensor cable 88 from beneath the sensor holder 40 when applied to a finger . that is , the cable 88 of the sensor 80 is routed out one side of the lateral recess portion 76 when the sensor holder 40 is applied to the finger . in this regard , the sensor cable 88 is able to exit the sensor holder 40 without applying pressure to the patient &# 39 ; s tissue which may affect sensor readings . fig3 and 4 show application of the sensor holder 40 to a patient appendage ( in this case , the patient &# 39 ; s index finger ). initially , a transmittance type pulse oximetry sensor 80 is seated within the sensor recess 70 of the sensor holder 40 . as shown in fig3 , the plastically deformable backing layer 50 of the sensor holder 40 may be initially deformed such that the sensor holder 40 has an open u - shape . this may entail plastically deforming the central portion 46 of the sensor holder by , for example , grasping the first and second end portions 42 , 44 in each hand and bending the central portion 46 to the desired shape . preferably , the central portion 46 is bent to allow the first and second end portions 42 , 44 to be disposed apart a space slightly less than the outside surface of the appendage to which the sensor holder is applied . the tensile force is then applied between the first and second end portions 42 , 44 to elastically deform ( spring ) the central portion 46 as well as slightly spread the first and second end portions 42 , 44 . the appendage is then inserted into the sensor holder 40 . preferably , the finger is inserted within the sensor holder until it is disposed between the first and second halves 72 , 74 of the sensor recess and thereby the emitting surface 82 and detecting surface 84 of the pulse oximetry sensor 80 . at this point , the tensile force is released allowing the first and second end portions 42 , 44 of the sensor holder with the top and bottom surfaces of the finger 90 . as will be appreciated , this compressive force provides a retaining force to maintain the sensor holder 40 relative to the finger 90 . once the first and second end portions are contacting opposing surfaces of the finger 90 , an additional compressive force may be applied to the end portions and central portion 46 to compress the compressible patient interface layer 60 and provide a secure attachment of the sensor holder 40 to the finger . as will be appreciated , this additional compressive force may further plastically deform the backing layer 50 ( i . e ., crimps the central portion 46 ) which then acts as a spring that resists opening . in any case , it will be appreciated that by utilizing an elastically and plastically deformable backing layer 50 , the sensor holder 40 is able to be applied to the finger without the use of adhesives or other fastening means . this provides a sensor holder that has a reduced part count , is easily manufactured , and is easy for a medical technician to apply and remove . fig6 a and 6 b show a second embodiment of a plastically deformable sensor holder 100 . as in the first embodiment , the second embodiment of the sensor holder 100 contains a deformable backing layer 110 having elastic and plastic characteristics and a compressible patient interface layer 112 . these two layers 110 , 112 may be formed using material as described above . formed into the patient side surface of the patient interface layer 112 is an l - shaped recess 116 for selectively receiving an l - shaped sensor 120 . again , this sensor contains a light emitter 122 and a light detector 124 . as shown in fig5 b , the l - shaped sensor 120 is seated within the l - shaped recess 116 and the deformable backing layer is deformed to dispose first and second portions of the sensor holder 100 in an opposing relationship for receiving a patient appendage . accordingly , the flexible conduit 126 interconnecting the light emitter 122 and light detector 124 of the l - shaped sensor 120 bends to dispose the emitter 122 and the detector 124 in an opposing relationship . fig7 shows the second embodiment of the sensor holder 100 as applied to an earlobe . after insertion of the patient appendage , the deformable backing layer 110 may be crimped to provide a retention force that holds the sensor holder 100 and sensor 120 on the earlobe . fig8 shows a third embodiment of a deformable sensor holder 200 in accordance with the present invention . in this embodiment , the sensor holder 200 contains first and second members 210 , 220 that are substantially rigid in comparison with a deformable interconnecting member 230 . as will be appreciated , in this embodiment , all deformation of the sensor holder 200 is isolated in the interconnecting member 230 . this allows the first and second members to be pre - formed to interface with a particular patient appendage . as shown , the first and second members 210 , 220 are formed to matingly receive a finger and in this regard each contain a finger trough 240 . as will be appreciated , utilizing the finger troughs 240 , the sensor holder 200 is able to better conform to a patient finger and to provide added light blocking characteristics for a sensor that may be inserted within the troughs 240 . the foregoing description of the present invention has been presented for purposes of illustration and description . furthermore , the description is not intended to limit the invention to the form disclosed herein . consequently , variations , adaptations , modifications , and skill and knowledge of the relevant art , are within the scope of the present invention as determined by the claims that follow .
a conformable medical sensor is provided that has particular applicability for positioning a pulse oximeter sensor relative to a patient appendage . in one embodiment , the sensor holder includes a patient engaging member that is plastically deformable to permit the sensor holder to be conformed to the patient appendage , and plastically deformable to provide a retention force relative to the patient appendage . for example , the engaging member may be bent into a first shape that disposes first and second portions of the sensor holder into an opposing relationship the for receiving a patient appendage therebetween . once deformed , the engaging member may be elastically deformed to a second shape to provide a retention force so as to maintain the sensor holder and a sensor interconnected thereto in contact with the patient appendage . in another embodiment , and the sensor holder may include a deformable backing layer that is plastically and elastically deformable , as described above , together with a patient interface layer having a recess located for the receipt of the sensor therein .